ArticlePDF Available

Abstract and Figures

The use of personal protective equipment (PPE) increases the risk of heat related maladies. A means to enhance heat dissipation capacity of individuals clad in PPE would be of benefit. The glabrous skin regions of the hands, face, and feet are portals for direct heat transfer between the body core and the external environment. The effects of PPE outerwear and palmar glabrous skin cooling on heat storage were assessed. Subjects engaged in fixed load treadmill exercise in a thermoneutral environment (Ta = 20 – 24ºC) or rested in a hot environment (45 ± 0.5ºC). The use of PPE outerwear increased the rate of core temperature rise by five-fold during vigorous exercise. Palm cooling using a stationary water circulation system attenuated the rate of core temperature rise by 30 – 60% during rest and light, moderate, and vigorous exercise while wearing PPE outerwear. However, the subjects were tethered to the system. A wearable cooling system was devised that allowed free range of motion and unrestricted mobility. The wearable system provided thermal benefits equivalent to the use of the tethering cooling system. With optimization, this wearable cooling technique could neutralize the negative thermoregulatory effects of wearing PPE while engaged in light workload activities such as those encountered by health care professionals working in infectious disease treatment centers. For individuals working at higher workloads, such as firefighters, a wearable glabrous skin based cooling system could extend work bout duration as well as enhance heat loss during episodic recovery periods.
Content may be subject to copyright.
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=uoeh20
Journal of Occupational and Environmental Hygiene
ISSN: 1545-9624 (Print) 1545-9632 (Online) Journal homepage: http://www.tandfonline.com/loi/uoeh20
A method to reduce heat strain while clad in
encapsulating outerwear
Dennis Grahn, Megha Makam & H. Craig Heller
To cite this article: Dennis Grahn, Megha Makam & H. Craig Heller (2018) A method to reduce
heat strain while clad in encapsulating outerwear, Journal of Occupational and Environmental
Hygiene, 15:8, 573-579, DOI: 10.1080/15459624.2018.1470635
To link to this article: https://doi.org/10.1080/15459624.2018.1470635
Accepted author version posted online: 30
Apr 2018.
Published online: 30 Apr 2018.
Submit your article to this journal
Article views: 140
View Crossmark data
A method to reduce heat strain while clad in encapsulating outerwear
Dennis Grahn, Megha Makam, and H. Craig Heller
Department of Biology, Stanford University, Stanford, California
ABSTRACT
The use of personal protective equipment (PPE) increases the risk of heat related maladies.
A means to enhance heat dissipation capacity of individuals clad in PPE would be of benefit.
The glabrous skin regions of the hands, face, and feet are portals for direct heat transfer
between the body core and the external environment. The effects of PPE outerwear and
palmar glabrous skin cooling on heat storage were assessed. Subjects engaged in fixed load
treadmill exercise in a thermoneutral environment (T
a
¼2024C) or rested in a hot environ-
ment (45 ± 0.5C). The use of PPE outerwear increased the rate of core temperature rise by
five-fold during vigorous exercise. Palm cooling using a stationary water circulation system
attenuated the rate of core temperature rise by 3060% during rest and light, moderate,
and vigorous exercise while wearing PPE outerwear. However, the subjects were tethered to
the system. A wearable cooling system was devised that allowed free range of motion and
unrestricted mobility. The wearable system provided thermal benefits equivalent to the use
of the tethering cooling system. With optimization, this wearable cooling technique could
neutralize the negative thermoregulatory effects of wearing PPE while engaged in light
workload activities such as those encountered by healthcare professionals working in infec-
tious disease treatment centers. For individuals working at higher workloads, such as fire-
fighters, a wearable glabrous skin-based cooling system could extend work bout duration as
well as enhance heat loss during episodic recovery periods.
KEYWORDS
Core temperature; heat
illness; hyperthermia;
protective clothing;
temperature; work/
rest cycles
Introduction
Personal protective equipment (PPE) can greatly reduce
or eliminate the risk of exposure to hazardous chemi-
cals, physical hazards, and disease-causing organisms
such as the Ebola virus. However, wearing PPE increases
the risk of developing heat-related illnesses because the
encapsulating ensembles severely compromised convect-
ive, conductive, radiative, and evaporative heat dissipa-
tion modalities.
[1,2]
For example, PPE worn by Health
Care Personnel (HCP) working in the hot zones (patient
care units) of the Ebola Treatment Centers (ETC) in
tropical Western Africa during the 20142015 Ebola
outbreak consisted of overlapping impermeable material
coverings (a surgical cap and gown, impermeable
hooded coveralls, a face shield, a visor, a respirator, two
layers of gloves, a waterproof apron, and rubber
boots).
[3]
The use of PPE in the ETCs severely limited
HCP work times in the hot zones, potentially impaired
mental and physical performance, and increased the
risks of heat related maladies (including heat exhaustion,
heat cramps, heat stroke, and, in extreme cases, death).
The inability to dissipate heat while clad in PPE also
elevated the risk of self-contamination during the post-
work shift PPE removal process by: (1) limiting work
shift duration, thereby, increasing the frequency of PPE
doffing and (2) increasing the likelihood of a misstep
during the doffing process due to heat-related deterior-
ation of mental acuity. A means to facilitate heat dissi-
pation from PPE encapsulated individuals would
improve the safety of workers in situations that require
isolation from the local environment.
Unique radiator like vascular structures underlie the
glabrous skin regions of the bodythe palms of the
hands, the soles of the feet, and regions of the face and
ears. These subcutaneous vascular structures (arterioven-
ous anastomoses and the associated retia venosa) provide
a direct thermal portal between the body core and the
external environment. The application of a heat source or
aheatsinktoglabrousskinsurfacesisaneffectivemeans
for transferring heat into or out of the body core.
[49]
The objective of this current effort was to replicate,
and expand on, previous studies that assessed the
effects of glabrous skin surface cooling on heat
stressed individuals. The hypothesis to be tested was
that a closed-loop water circulating system interfacing
CONTACT Dennis Grahn dagrahn@stanford.edu Department of Biology, 371 Serra Mall, Stanford University, Stanford, CA 94305.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/uoeh.
ß2018 JOEH, LLC
JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HYGIENE
2018, VOL. 15, NO. 8, 573579
https://doi.org/10.1080/15459624.2018.1470635
with the palms of the hands worn inside encapsulating
outerwear would reduce the rate of core temperature
rise during fixed load exercise ranging in intensity from
rest to vigorous. A first step was to determine the effect
of wearing PPE on heat accumulation during fixed load
exercise, followed by a series of trials on palm cooling
of subjects exercising at a variety of workloads. A stand-
alone and wearable cooling system that enabled a free
range of motion and unlimited mobility was developed.
The relative cooling efficacy of the wearable system was
compared with the use of commercially available sta-
tionary water circulation-based systems that tethered the
subjects to the heat sink and limited their mobility.
Materials and methods
The human subject research was divided into four dis-
crete protocols that assessed the effects on core tempera-
ture of: (1) the use of a PPE ensemble during vigorous
fixed load exercise, (2) palm cooling of PPE clad sub-
jects during light, moderate, and vigorous exercise under
normothermic ambient conditions, (3) palm cooling of
PPE clad subjects during rest under hot ambient condi-
tions, and (4) the use of a lightweight wearable cooling
system compared to the use of a stationary temperature-
controlled water circulation system that tethered the
subjects. The protocols were approved by the Stanford
University Institutional Review Board (IRB), and written
informed consent was obtained from each volunteer
prior to participation in the studies using an instrument
approved by the Stanford University IRB.
Subjects
Twenty-three volunteer subjects recruited from the
Stanford University community participated in these
studies (12 males and 11 females, age 23 ± 3 years,
mean ±SD). All subjects met the inclusion criteria of
being healthy (no illnesses or chronic debilitating condi-
tions),active(regularexerciseofaminimumof6hr/
week), and over 18 years of age. The subjects all partici-
pated in more than one protocol. Eleven subjects (six
male and five female) participated in protocol 1, 13 sub-
jects (six male and seven female) participated in protocol
2, 10 subjects (seven male and three female) participated
in protocol 3, and 12 subjects (six males and six
females) participated in protocol 4.
Clothing
In all trials, the subjects wore a lightweight exercise
clothing base layer (i.e., t-shirts, shorts, undergarments,
ankle height socks, and athletic shoes). An outer-layer
PPE ensemble that simulated the outerwear worn by
HCPs in the ETCs consisted of impermeable protective
coveralls with hood and foot coverings (TyCHEM QC,
Tyvek, DuPont, Wilmington, DE), a polypropylene bala-
clava worn under the PPE hood and covering the head
and face (Tullahoma Industries, Tullahoma, TN), and
plastic bags (Hi-density medical bags 710 gal, Elkay
Plastics Co., Los Angeles, CA) secured with surgical tape
(Transpore, 3M Corporation, St. Paul, MN) to the PPE
shell at the wrists to create a contiguous vapor barrier
around the hands.
Facilities and monitoring
The trials were conducted in either a thermoneutral
environment or a hot environment. The thermoneu-
tral environment consisted of an 8 m x 6 m x 3 m
(width, length, height) laboratory that housed four
treadmills (model SC7000, SciFit, Tulsa, OK). The
temperature and humidity of the room were main-
tained by the buildings central HVAC system
(T
a
¼2024C, RH ¼1535%). The hot environment
consisted of a 2.4 m x 3.3 m x 2.4 m (width, length,
height) temperature-controlled environmental cham-
ber (T
a
¼45 ± 0.5C, RH ¼2035%).
Esophageal temperatures (T
es
)werecontinuously
monitored throughout all trials using general purpose
thermocouple probes (Mon-a-Therm #503-0028,
Mallinckrodt Medical Inc., St. Louis, MO) self-inserted
throughthenoseormouthtoadepthof3839 cm and
held in place with a small piece of surgical tape
(Transpore, 3M Corporation, St. Paul, MN) attached to
the skin surrounding the anterior nares or the cheek.
The probe was connected to a laptop-based thermo-
couple transducer/data collection system (GEC instru-
ments, Gainesville, FL) that recorded temperature data
at 1-sec intervals. The T
es
data streams were uploaded
to a secure server from which they were subsequently
accessed for off-line analysis.
Cooling systems
The cooling systems consisted of water perfused pal-
mar surface heat exchange interfaces and a means for
delivering a continuous stream of temperature-con-
trolled water to the interfaces.
Heat exchange interfaces
The palmar heat exchange interfaces consisted of 13 x
13 cm urethane coated nylon cloth water perfusion
pads (American National Manufacturing, Corona,
574 D. GRAHN ET AL.
CA) held in close apposition to the palmar surfaces
with 4-way stretch fabric (Lycra) mitts sized for the
individual subjects (Figure 1(C)). The interfaces were
designed to provide minimal compromise of fine
motor activity by leaving the thumb and fingers
uncovered and unencumbered. The water perfusion
pads were connected via polyurethane tubing (1/4ID
x 1/16wall laboratory tubing, Tygon) to a tempera-
ture-controlled water circulating system.
Temperature-controlled water circulating systems
For protocols 2 and 3, the heat exchange interfaces were
connected to commercially available temperature-con-
trolled water circulating systems that circulated a 6.0 l/
min stream of 16 ± 0.5C water (either a Meditherm III,
Gaymar Industries, Orchard Park, NY or Blankroll III,
Cincinnati Sub-Zero, Cincinnati, OH).
For protocol 4, a small closed-loop temperature-
controlled circulating system was designed in house
(Figure 1). The system consisted of a pump (3.6 L/min
mini DC brushless submersible water pump, item #
EWP-DC30A1230, Light Objects, Sacramento, CA,
http://www.lightobject.com/), a wax piston-driven
thermostatic mixing valve (custom designed by Rostra
Veratherm, Bristol, CT), a bubble trap/expansion
chamber assembly, a heat sink water perfusion pad,
and the two hand interfaces, connected with plumbing
fittings and laboratory tubing and powered by four
AA (1.5 volt) batteries aligned in series. The path of
the water flow through the system was from pump
outlet to the inlet of a tee fitting. One outlet of the tee
fitting connected to a water perfusion pad (23 x
13 cm) that abutted the heat sink, which in turn was
connected to the cold inlet of the thermostatic mixing
valve. The second outlet of the tee connected directly
to the warm inlet port of the thermostatic mixing valve.
The outlet of the mixing valve fed into the palmar heat
exchange interfaces. The return from the interfaces
flowed through the bubble trap/expansion chamber
complex before returning to the inlet of the circulating
pump. The bubble trap/expansion chamber assembly
consisted of a 250 mL square wide mouth bottle
(Nalgene) plumbed to a bubble capturing manifold. A
hydration backpack (Model Lobo, Camelbak, Petaluma,
CA) was used to house the water circulating system and
heat sink. The heat sink was created by freezing 1 L of
water contained in the hydration pack bladder (the
bladder was lain flat during freezing). The wax in the
thermostatic mixing valve had a melting point of 18C.
This system delivered a 600 mL/min stream of
18C±2
C water to the hand interfaces. The entire sys-
tem weighed <2.25 kg (5 lb), was quiet (<10 decibels
at 10 cm), and fit under PPE outerwear.
Experimental protocols
Prior to participation in the experimental trials each
subjects physical condition was assessed using a
Modified Bruce Test that determined VO
2max
.
[5]
Figure 1. A self-contained cooling system worn inside encapsulating outerwear (See Methodssection for details). (A) Schematic
diagram of the components. Arrowheads indicate direction of water flow. Black outlined forms: core components connected with
rigid tubing (1. pump, 2. mixing valve, 5. bubble trap, and 6. expansion chamber). Shaded forms: peripheral components con-
nected via polyurethane tubing or electrical wire (4. palm interfaces, 3. heat sink interface, and 7. battery). Component 8 is the
external heat sink (e.g., frozen hydration bladder). (B) An individual clad in PPE wearing the cooling system. (C) The palm interface.
(D) The core of the system sitting atop the hydration pack in which it is housed.
JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HYGIENE 575
All trials on individual subjects were conducted at
the same time of day and were separated by a min-
imum of 2 days. Prior to participation in a trial, sub-
jects measured their nude weight, self-inserted the
esophageal probe, attached the HR monitors, donned
the assigned attire (base clothing or base clothing and
PPE ensemble outerwear) and attached the palmar
heat transfer equipment. The orders of the treatments
were randomized. Upon completion of a trial the PPE
outerwear was removed and the subject rested quietly
in a thermoneutral environment for 30 minutes after
which the monitoring devices and heat transfer equip-
ment were removed and nude body weight was meas-
ured. No water was consumed during trials, but each
subject consumed a volume of fluid equivalent to his
or her weight loss prior to leaving the laboratory.
The slopes of the treadmills were adjusted for indi-
vidual subjects to achieve the desired exercise power
outputs based on the formula:
Power output Watts
ðÞ
¼0:11 þfractional grade
ðÞ
speed weight g;
where speed ¼treadmill speed (m/sec), fractional gra-
de ¼treadmill slope, weight ¼body weight (kg), and
g¼gravity (9.8 m/sec
2
).
[10]
The constant 0.11 accounts
for the power required to move the body mass over
level ground. The speeds of the treadmills were fixed
at 1.56 m/sec (3.5 mile/hr). The exercise was stopped
when one of the criteria was met: subjective fatigue,
T
es
¼39C, or an exercise duration of 40 min. The
subjects were encouraged to expectorate excess saliva
into a spittoon during the trials to minimize swallow-
ing artifacts in the T
es
data sets.
Protocol 1
Subjects engaged in vigorous (250 W) fixed load
treadmill exercise in a thermoneutral environment
while clad in the base layer only or in the base layer
and the PPE outerwear.
Protocol 2
Subjects clad in PPE outerwear exercised on the tread-
mill at power output levels simulating vigorous, mod-
erate and light intensity activity (250 W, 180 W,
and 100 W, respectively) in a thermoneutral environ-
ment with and without palm cooling.
Protocol 3
Subjects clad in PPE outerwear rested quietly (power
output ¼0 W) in a hot environment (T
a
¼45 ± 0.5C)
with and without palm cooling.
Protocol 4
Subjects clad in PPE outerwear engaged in light inten-
sity treadmill exercise with or without palm cooling
using the portable water circulating system or the
tethering stationary water-circulating device.
Data analysis
The raw T
es
vs.timedataweregraphedforeachtrial
using Microsoft Excel software and the graphs were
screened for irregularities. Artifactual data points were
expunged from the datasets. The data were then sorted
by 30-sec intervals and subjected to regression analysis
to determine rates of change of T
es
(DT
es
/min). Profiles of
T
es
vs. time during fixed-load exercise are typically bin-
arycharacterized by an initial rapid rise, followed by a
sustained shallower sloped linear rise (e.g., Fig. 2). The T
es
data from the final linear section of the plots (i.e., the last
20 min of the trials) were subjected to the regression ana-
lysis. The slopes from the regression analyses were tabu-
lated and sorted according to protocol, subject, and
treatment. Statistical analyses were performed using
Microsoft Office Excel for Windows data analysis tools.
The sorted data were summarized using descriptive statis-
tics (mean ± SD). The T
es
regression analysis data from
paired trials were analyzed using paired t-tests. Statistical
significance was established at a¼0.01.
Results
Protocol 1
The PPE ensemble compromised heat dissipation cap-
acity of individuals during vigorous fixed workload
treadmill exercise (power output ¼241 ± 53 W)
(Figure 2). The rate of core temperature rise (DT
es
/
Figure 2. The effect of PPE outerwear ensembles on T
es
dur-
ing vigorous fixed load treadmill exercise. Left: data from an
individual subject clad in PPE (gray) and without PPE (black).
Dotted lines represent the regression lines (regression line
equations, and R
2
coefficients are listed). Right: Rates of
changes in T
es
(C/min) during the last 20 min of exercise (as
determined by regression analysis) with and without PPE
(mean ± SD, p<0.001, paired t-test).
576 D. GRAHN ET AL.
min) while wearing PPE was approximately five times
that of DT
es
/min without the PPE ensemble
(0.064 ± 0.018C/min with PPE vs. 0.011 ± 0.005C/
min without PPE, p<0.001).
Protocol 2
Palm cooling reduced the rate of T
es
rise in subjects clad
in PPE during fixed load exercise at three intensity levels
(Figure 3). During vigorous exercise (power output
¼250 ± 73 W), DT
es
/min ¼0.095 ± 0.04C/min without
cooling vs. 0.063 ± 0.019C/min with cooling. During
moderate exercise (181 ± 78 W), DT
es
/min ¼
0.062 ± 0.014C/min without cooling vs. 0.044 ± 0.014C/
min with cooling. During light exercise (108 ± 40 W),
DT
es
/min ¼0.023 ± 0.012C/min without cooling vs.
0.016 ± 0.007C/min with cooling, (p<0.01, at
all workloads).
Protocol 3
Palm cooling reduced heat stress during rest in a hot
environment (T
a
¼45 ± 0.5C) (Figure 4). T
es
of PPE clad
individuals increased at a rate of 0.037 ± 0.008C/min with-
out cooling compared to 0.015 ± 0.005C/min with cool-
ing (p<0.001).
Protocol 4
The effect of palm cooling on T
es
of individuals clad in
PPE during light intensity exercise was independent of
the circulating water source (Figure 5). Both water circu-
lating systems reduced DT
es
/min to a comparable degree
(wearable system: DT
es
¼0.019 ± 0.012C/min without
palm cooling vs. 0.01 ± 0.009C/min with palm cooling,
tethering stationary systems: DT
es
/min ¼0.023 ± 0.01C/
min without palm cooling vs. 0.016 ± 0.007C/min with
palm cooling) (p<0.01 for both comparisons). The
choice of heat sink was not a significant factor (p¼0.09,
t-test assuming equal variance).
Discussion
The conditions in the Kerrytown, Sierra Leone, Ebola
Treatment Center were well documented and provide
a useful framework for the discussion of the portable
cooling system described in this article. The ETC in
Kerrytown, Sierra Leone, was in operation from
November 2014September 2016. During that time
the monthly average day time high temperatures
ranged from 32C (August 2015) to 36C (December
2015) and nighttime lows ranged from 2427C. The
risk of heat stress while wearing PPE in the ETC hot
zones limited work shift durations. Permissible work
periods were based on established guidelines for miti-
gating heat illness.
[11]
The United States Department
of Labor Occupational Health and Safety
Administration (OSHA) recommends an hourly work/
Figure 4. The effect of palm cooling on T
es
of subjects clad in
PPE during rest (power output ¼0 W) in a hot environment
(Ta ¼45 ± 0.5C, n ¼10). Left: T
es
vs. time (mean ± SD, n ¼10).
- significant treatment effect. Right: Rates of changes in T
es
(C/min) during the last 20 min of the trial with (C) and with-
out (N) palm cooling (mean ± SD, p<0.01 paired t-test).
Figure 5. Rates of change in T
es
during the last 20 min of
exercise with and without palm cooling using a wearable sys-
tem vs. the use of a tethering stationary heat sink
(mean ± SD). Treatment effects (cooling vs. no cooling) under
both conditions were significant (p<0.01, paired t-tests). The
type of heat sink did not influence treatment effect
(NS, p¼0.09).
Figure 3. The effects of palm cooling on rates of changes in
T
es
(C/min) during the last 20 min of light, moderate, and vig-
orous fixed load treadmill exercise by individuals clad in PPE
ensembles (mean ± SD, p<0.01, paired t-tests at all work-
loads). Open bars: no palm cooling. Closed bars: palm cooling.
JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HYGIENE 577
rest schedule of 40 min of work and 20 min of rest for
individuals clad in chemical resistance suits engaged
in light work in a no-sun 33C environment. In con-
trast, there are no such work/rest schedule recommen-
dations for individuals clad in normal work clothes
under those environmental conditions. HCPs at the
Kerrytown, Sierra Leone ETC typically occupied the
hot zone for a maximum of 70 min during the daily
thermal peak periods.
[3]
Sufficient time for thermal
recovery (a minimum of 30 min) was enforced
between the doffing of the used PPE ensemble and
subsequent donning of a fresh PPE ensemble. The
adoption of wearable devices that enhance heat dissi-
pation capacity would reduce the need for limiting
work time of individuals clad in PPE and would also
decrease the number of PPE ensemble replace-
ments required.
The impetus for this project was to develop a prac-
tical solution to mitigate the heat stress problems
experienced by HCPs working at infectious disease
treatment centers such as the Kerrytown ETC during
the 20142015 Ebola virus outbreak in western Africa.
While the 20142015 Ebola outbreak has waned, a
wearable cooling system would be a valuable tool for
field applications in hostile work environments that
require the use of encapsulating protective outerwear.
If properly developed, future iterations of this wear-
able technology could dramatically impact the logistics
of the workforce in environments that require the use
of PPE.
The glabrous skin regions of the distal extremities
and face are the primary heat exchange surfaces of the
body. The direct arterial input from the heart and dir-
ect venous return to the vena cava creates an efficient
thermal conduit for transferring heat directly between
the body core and the external environment. Under
heat stress conditions, heat transfer from a single
hand to cool water can exceed 100 W.
[12,13]
Immersion of distal appendages in cool water has
been shown to be effective in reducing heat stress sub-
jects clad in military-style protective outerwear.
[1421]
Heat transfer across the skin surface is dependent on
subcutaneous blood flow. The only regions of the dis-
tal appendages that contain vascular structures capable
of accommodating large subcutaneous blood flows are
the anatomically distinct glabrous skin regions. Thus,
the bulk of the heat transfer across the surface of the
distal appendages is via the glabrous skin regions. The
portable heat dissipation system described here utilizes
the glabrous skin thermoregulatory effector vascular
structures to maximize the thermal impact of treat-
ment on critical core regions of the body.
The results presented here demonstrate that a
wearable cooling system is a viable means for reduc-
ing the thermal load despite encapsulating outerwear.
However, a demonstration of feasibility in a controlled
laboratory setting is a far cry from a field ready piece
of equipment. Optimization of efficiency and utility
are critical for the transition into a field useful tool. A
short list of required design modifications includes:
optimizing heat sink temperatures, improving the
ergonomics of the interfaces, incorporating the system
into garments, potentially utilizing additional glabrous
skin regions, and reducing the size of the system. The
heat sink temperature is critical for optimizing the
system. The greater the differential temperature gradi-
ent across the heat exchange surface (i.e., the lower
the temperature of the circulating water heat sink) the
more efficient the heat transfer.
[17]
However, below a
critical temperature a local feedback response causes
vasoconstriction of the arteriovenous anastomoses that
supply blood to the subcutaneous radiator structures
and, as a result, effectively shuts down the heat trans-
fer. Also, a heat sink maintained at a temperature
below the vasoconstrictive threshold will, over time,
become uncomfortable and could compromise fine
motor function. We anticipate that circulating water
temperatures near 10C will prove to be optimal for
individuals clad in encapsulating outerwear conduct-
ing light to moderate workload activities.
Conclusions
Glabrous skin region cooling as an effective means for
extending fixed workload exercise in individuals clad
in encapsulating outerwear. A self-contained tempera-
ture-controlled water circulation system worn beneath
the encapsulating outerwear is a solution for tempera-
ture management in field applications.
Acknowledgments
The authors acknowledge and appreciate the support of
Vinh Cao and Patricia Seawell for the execution of the pro-
tocols as well as the undergraduate students who partici-
pated in the studies. Our thanks to DuPont and Camelbak
Products for generously supplying the PPE overalls and the
hydration packs (respectively). No external funding sup-
ported these studies.
References
[1] U.S. Centers for Disease Control and Prevention:
Interim guidance for healthcare workers providing
care in West African countries affected by the Ebola
outbreak: Limiting heat burden while wearing
578 D. GRAHN ET AL.
personal protective equipment (PPE). In CDC 24/7:
Saving Lives, Protecting People. Available at: https://
www.cdc.gov/vhf/ebola/hcp/limiting-heat-burden.html
(accessed January 11, 2018).
[2] McLellan, T.M., H.A.M. Daanen, and S.S. Cheung:
Encapsulated environment. Compr. Physiol.
3:13631391 (2013).
[3] Maynard, S.L., R. Kao, and D. Craig: Impact of
personal protective equipment on clinical output and
perceived exertion. J. R. Army Medical Corps.
162:180183 (2016).
[4] Grahn, D., J.G. Brock-Utne, D. Watenpaugh, and
H.C. Heller: Rewarming from mild hypothermia can
be accelerated by mechanically distending blood ves-
sels in the hand. J. Appl. Physiol.85:16431648
(1999).
[5] Grahn, D.A., V.H. Cao, and H.C. Heller: Heat
extraction through the palm of one hand improves
aerobic exercise endurance in a hot environment. J.
Appl. Physiol.99:972978 (2005).
[6] Grahn, D.A., J.L. Dillon, and H.C. Heller:
Enhancing heat loss through the glabrous skin surfa-
ces of heavily insulated individuals. J. Biomech. Eng.
131(7):17(2009).
[7] Grahn, D.A., J.V.L.S. Murry, and H.C. Heller:
Cooling via one hand improves physical performance
in heat-sensitive individuals with Multiple Sclerosis:
A preliminary study. BMC Neurol.8:14 (2008).
[8] Heller, H.C., and D.A. Grahn: Enhancing thermal
exchange in humans and practical applications. J.
Disrupt. Sci. and Technol.1:1119. (2012)
[9] Zhang, Y., P.A. Bishop, C. Casaru, and J.K. Davis:
A new hand-cooling device to enhance firefighter
heat strain recovery. J. Occup. Environ. Hyg.
6:283288 (2009).
[10] Glass, S., and B. Gregory:ACSMs Metabolic
Calculations Handbook. Baltimore, MD: Lippincott
Williams & Wilkins, 2007. pp. 2574.
[11] U.S. Dept. of Health and Human Services, Public
Health Service, Centers for Disease Control and
Prevention, National Institute for Occupational
Safety and Health, DHHS (NIOSH):Occupational
Exposure to Heat and Hot Environments.B.
Jacklitsch, W.J. Williams, K. Musolin, A. Coca, J.-H.
Kim, and N. Turner (eds.). NIOSH Publication
2016-106, February 2016.
[12] Cabanac M., B. Massonnet, and R. Belaiche:
Preferred temperature as a function of internal and
mean skin temperature. J. Appl. Physiol.33:699703
(1972).
[13] Cabanac, M., and B. Massonnet: Thermoregulatory
behavior as a function of core temperature in
humans. J. Physiol.265:587596 (1977).
[14] Allsopp, A.J., and K.A. Poole: The effect of hand
immersion on body temperature when wearing imper-
meable clothing. J. R. Nav Med. Serv.77:4147 (1991).
[15] Giesbrecht, G.G., C. Jamieson, and F. Cahill:
Cooling hyperthermic firefighters by immersing fore-
arms and hands in 10C and 20C water. Aviat.
Space Environ. Med.78:561567 (2007).
[16] House, J.R.: Extremity cooling as a method for
reducing heat strain. Defense Sci. J.3:108114 (1998).
[17] House J.R., C. Holmes, and A.J. Allsopp:
Prevention of heat strain by immersing the hands
and forearms in water. J. R. Nav. Med. Serv.
83:2630 (1997).
[18] Livingstone, S.D., R.W. Nolan, and S.W. Cattroll:
Heat loss caused by immersing the hands in water.
Aviat. Space Environ. Med.60:11661171 (1989).
[19] Livingstone, S.D., R.W. Nolan, and A.A. Keefe:
Heat loss caused by cooling the feet. Aviat. Space
Environ. Med.66:232237 (1995).
[20] Selkirk, G.A., T.M. McLellan, and J. Wong: Active
versus passive cooling during work in warm environ-
ments while wearing firefighting protective clothing.
J. Occup. Environ. Hyg.1:521531 (2004).
[21] Tipton, M. J., A. Allsopp, P.J. Balmi, and J.R.
House: Hand immersion as a method of cooling and
rewarming: A short review. J. R. Nav. Med. Serv.
79:125131 (1993).
JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HYGIENE 579
... Our study demonstrated that healthcare workers not only reported heat strain symptoms that relate to health (i.e., discomfort, headache, thirst, nausea), but also symptoms that relate to the execution of their work activities (i.e., reduced work speed, less accurate work, loss of coordination). This is alarming, as these symptoms could increase the risk of work-related injuries (i.e., health, recovery or overall outcome) in both healthcare workers and their patients [17,[23][24][25]. Furthermore, it has been suggested that heat strain might increase the risk of self-contamination by healthcare workers during the post-work shift PPE removal process [23]. ...
... This is alarming, as these symptoms could increase the risk of work-related injuries (i.e., health, recovery or overall outcome) in both healthcare workers and their patients [17,[23][24][25]. Furthermore, it has been suggested that heat strain might increase the risk of self-contamination by healthcare workers during the post-work shift PPE removal process [23]. This could be explained by (1) the limiting work shift duration, and thereby increased frequency of PPE removal and (2) greater chance of a misstep during the removal process due to a decreased cognitive function [23]. ...
... Furthermore, it has been suggested that heat strain might increase the risk of self-contamination by healthcare workers during the post-work shift PPE removal process [23]. This could be explained by (1) the limiting work shift duration, and thereby increased frequency of PPE removal and (2) greater chance of a misstep during the removal process due to a decreased cognitive function [23]. During an already intensive and stressful crisis like the current COVID-19 pandemic, comfortable working conditions are of utmost importance, and therefore, healthcare workers and their managers need to apply heat mitigation measures to reduce the prevalence of heat strain symptoms and lower injury risk. ...
Article
Full-text available
The combination of an exacerbated workload and impermeable nature of the personal protective equipment (PPE) worn by COVID-19 healthcare workers increases heat strain. We aimed to compare the prevalence of heat strain symptoms before (routine care without PPE) versus during the COVID-19 pandemic (COVID-19 care with PPE), identify risk factors associated with experiencing heat strain, and evaluate the access to and use of heat mitigation strategies. Dutch healthcare workers (n = 791) working at COVID-19 wards for ≥1 week, completed an online questionnaire to assess personal characteristics, heat strain symptoms before and during the COVID-19 pandemic, and the access to and use of heat mitigation strategies. Healthcare workers experienced ~25× more often heat strain symptoms during medical duties with PPE (93% of healthcare workers) compared to without PPE (30% of healthcare workers; OR = 25.57 (95% CI = 18.17–35.98)). Female healthcare workers and those with an age <40 years were most affected by heat strain, whereas exposure time and sports activity level were not significantly associated with heat strain prevalence. Cold drinks and ice slurry ingestion were the most frequently used heat mitigation strategies and were available in 63.5% and 30.1% of participants, respectively. Our findings indicate that heat strain is a major challenge for COVID-19 healthcare workers, and heat mitigations strategies are often used to counteract heat strain.
... Khomenok et al. showed that 10 °C hand immersion between two 50-min exercise bouts while subjects wore nuclear, biological, or chemical (NBC) suits was able to decrease T core, T sk, and HR during the second bout (Khomenok et al. 2008). Additionally, a novel approach has recently utilized a custom temperature controlled (~ 16 °C) circulating water system to cool the hands during activity to maximize convective heat losses (Grahn et al. 2018), which mitigated esophageal temperature elevations during low intensity work in the heat with encapsulating outerwear. The same group also demonstrated effectiveness in heavily insulated individuals with the addition of sub-atmospheric pressure gradients to create a "heat sink" (Grahn et al. 2009), showing T core differences of > 1 °C vs controls 1 h post-exercise. ...
... These traditional cooling methods should be modified if attempting to optimally attenuate the rise in core temperature while thermally resistive clothing remains on, which could preclude the drop in skin temperature necessary to widen the core-skin temperature gradient. Colder water temperatures and/or the addition of circulating water to maximize convective heat loss (Grahn et al. 2018) with or without sub-atmospheric pressure (Grahn et al. 2009) have shown promise in cooling capability when worn during exercise with PPE and should be explored in future work in military and occupational populations during intermittent activity. Additionally, future work is encouraged that investigates the biophysical properties of different modalities and the associated heat loss in Joules that is required to reach a desired T core . ...
Article
Full-text available
IntroductionPersonal protective equipment (PPE) inhibits heat dissipation and elevates heat strain. Impaired cooling with PPE warrants investigation into practical strategies to improve work capacity and mitigate exertional heat illness.PurposeExamine physiological and subjective effects of forearm immersion (FC), fan mist (MC), and passive cooling (PC) following three intermittent treadmill bouts while wearing PPE.Methods Twelve males (27 ± 6 years; 57.6 ± 6.2 ml/kg/min; 78.3 ± 8.1 kg; 183.1 ± 7.2 cm) performed three 50-min (10 min of 40%, 70%, 40%, 60%, 50% vVO2max) treadmill bouts in the heat (36 °C, 30% relative humidity). Thirty minutes of cooling followed each bout, using one of the three strategies per trial. Rectal temperature (Tcore), skin temperature (Tsk), heart rate (HR), heart rate recovery (HRR), rating of perceived exertion (RPE), thirst, thermal sensation (TS), and fatigue were obtained. Repeated-measures analysis of variance (condition x time) detected differences between interventions.ResultsFinal Tcore was similar between trials (P > .05). Cooling rates were larger in FC and MC vs PC following bout one (P < .05). HRR was greatest in FC following bouts two (P = .013) and three (P < .001). Tsk, fluid consumption, and sweat rate were similar between all trials (P > .05). TS and fatigue during bout three were lower in MC, despite similar Tcore and HR.Conclusion Utilizing FC and MC during intermittent work in the heat with PPE yields some thermoregulatory and cardiovascular benefit, but military health and safety personnel should explore new and novel strategies to mitigate risk and maximize performance under hot conditions while wearing PPE.
... In the study conducted at the University of Connecticut (Laxminarayan et al., 2023), participants were instructed to wear either a t-shirt and shorts or their active combat uniform to simulate military training and combat scenarios. The addition of PPE during physical activity has been shown to increase the heat and physiological strain on the body due to its inability to dissipate an individual's body heat adequately coupled with the added weight of the gear (Barker et al., 2022;Grahn, Makam, & Craig Heller, 2018;Petruzzello, Gapin, Snook, & Smith, 2009;Xu, Gonzalez, Santee, Blanchard, & Hoyt, 2016). ...
Article
Full-text available
Core temperature information is important for guiding prevention and treatment measures. Developing new physiological monitoring tools that provide reliable core temperature information is critical for heat injury prevention. The ThriveHRI sensor system is being developed as an efficient core monitoring tool in a smartwatch platform. The current study compared the ThriveHRI sensor/smartwatch to an Equivital LifeMonitor and a rectal thermistor. This study aimed to determine if the ThriveHRI sensor system provides an accurate and precise estimate of core temperature at rest and during physical activity, representing strenuous occupational tasks at elevated temperatures in healthy adults. Twenty-five healthy, physically active adults (N = 14 males; N = 11 females) between the ages of 19–45 years volunteered. Participants completed multiple rounds of deadlifting and treadmill walking in an environmental chamber set to 43.3°C and 50% relative humidity. Participants alternated between performing deadlifts and walking on the treadmill for 35 minutes. Core temperature was monitored continuously via a Datatherm rectal thermometer, Equivital Eq02+LifeMonitor, and a ThriveHRI heat watch. A significant difference in bias between devices was found for easy walking (t(21) = 5.55, p < 0.001, g = 1.01), deadlift (t(19) = 3.60, p = 0.002, g = 0.73), and treadmill (t(16) = 2.42, p = 0.028, g = 0.60). A significant difference in precision between devices was found for easy walking (t(21) = 4.23, p < 0.001, g = 1.21), but no significant difference in precision between devices was found for deadlift or treadmill (ps ≥ 0.067). This study demonstrates the agreeability between the Equivital EQ02+ LifeMonitor, ThriveHRI sensor, and the rectal thermometer remains consistent as core temperature increases and exposure to a heated environment is sustained.
... In addition, when the chiller temperature is low, the cooled water may cause constriction of the arteries near the skin surface. The ideal body area for cooling is the palm 18 ; however, it is difficult to perform work while cooling the hands. One study investigated different areas of the body to be cooled, 19 but the results were inconclusive because of the small sample size. ...
Article
Full-text available
Objectives: To evaluate the efficacy of water-cooled clothing that continuously cools restricted body areas to suppress body temperature increase as an anti-heatstroke measure for workers in hot environments that exceed body temperature. Methods: Ten healthy men were placed in Room A (air temperature: 25°C, relative humidity: 50%) for 15 min. They were then transferred to Room B (air temperature: 40°C, relative humidity: 50%), where they rested for 10 min, then put on cooling clothing, and again rested for 15 min (the control group rested for 25 min). They then performed intense ergometer exercise for 40 min at 40% maximal oxygen consumption after which they rested for 10 min. The three trial conditions were CON (long-sleeved summer work clothes), VEST (cooling vest), and P-VEST (partial cooling vest). In VEST and P-VEST, water-cooled clothing continuously recirculated with 10°C water was used to cool the upper body. In P-VEST, only the neck, axillae, and heart areas were in contact with the cooled clothing. The measured indices were the rectal, esophageal, and external auditory canal temperatures; heart rate; estimated sweat volume; and subjective evaluations. Results: Compared with the CON condition, the rectal, esophageal, and external auditory canal temperatures and the heart rate were significantly lower and the subjective indices were decreased in the VEST and P-VEST conditions. Conclusions: Partial cooling showed a body cooling effect similar to that of whole upper body cooling. Partial body cooling promoted the heat dissipation, suggesting that partial cooling is efficient for maintaining body cooling in hot environments.
Article
Background: Heat strain and dehydration can affect an individual's physical and mental performance. The purpose of this review was to examine the literature for the impact of heat strain on healthcare workers (HCWs) who care for patients with high-consequence infectious diseases (HCIDs) while wearing personal protective equipment (PPE), discuss risks of impaired safety caused by heat strain and dehydration in HCID environments, identify attempts to combat PPE-related heat strain, recognize limitations, and provide suggestions for further research. Materials and methods: A literature search was performed in PubMed/MEDLINE and Google Scholar. Authors screened abstracts for inclusion criteria and reviewed articles if abstracts were considered to include information relevant to the aim. Results: The search terms yielded 30 articles that were sorted based on environment setting, physiological impact, and interventions. Discussion: Safety of HCWs and patients can be enhanced through development and usage of cooler, more comfortable PPE and PPE ensembles to help slow the rate of dehydration and support regulation of core body temperature. Conclusions: Heat strain caused by wearing PPE is an occupational health concern for HCWs in the high-risk environment that is HCID care. Future studies are needed to develop innovative PPE ensembles that can reduce heat strain and improve well-being.
Article
Background: Personal protective equipment (PPE) are essential for medical personnel responding to hazardous materials (HAZMAT) incidents. However, their impermeable design causes increased physiological strain and reduced thermoregulation, limiting work times and causing heat-related illnesses (HRI). Use of wearable cooling devices slow heat accumulation and have been shown to reduce thermal and cardiovascular strain in such situations. Methods: This was a prospective clinical evaluation to determine the tolerability and effectiveness of the CarbonCool cooling system - a half-body cooling vest - in participants undergoing a HAZMAT decontamination recertification. Physiological measurements (heart rate [HR], weight, temperature, and blood pressure) and participant feedback were obtained. The main outcome of interest was participants' tolerability of the cooling vest. Results: A total of 23 healthy participants were recruited, with 10 randomized to the intervention group and 13 in the control group. Mean age in the control and intervention group was 35.5 years old (SD = 7.8) and 30.0 years old (SD = 6.2), respectively. Qualitative feedback obtained from participants regarding safety, mobility, and cooling efficacy was largely positive. Difference of before-after temperature and HR was 0.3°C (SD = 0.8) and 11.5bpm (SD = 13.6) in the control group compared to 0.0°C (SD = 0.5) and 0.0bpm (SD = 6.4) for the intervention group. Conclusion: This clinical evaluation showed that the CarbonCool cooling vest is safe and tolerable in participants wearing PPE. Further trials with sample size powered to detect physiological outcomes are needed to assess the effect of the cooling vest on a subject's endurance to heat stress.
Article
Full-text available
This study examined the effectiveness of a field-type liquid cooling vest (LCV) worn underneath an impermeable protective suit on heat strain during walking. Eight men walked for 60 min at a moderate speed (3.0 km/h) wearing the suit in a warm environment (33 °C, 60% relative humidity) without (control, CON) or with the LCV. A smaller increase in rectal temperature was recorded in participants in the LCV than in the CON condition (37.6 ± 0.1 °C vs. 37.9 ± 0.1°C, p<0.05). Walking while wearing the LCV reduced the level of physiological heat strain, as measured by the mean skin temperature (35.5 ± 0.1°C vs. 36.3 ± 0.1°C), chest sweat rate (13.5 ± 3.0 mg/cm²/h vs. 16.6 ± 3.8 mg/cm²/h), chest cutaneous vascular conductance (349 ± 88% vs. 463 ± 122%), body weight loss (0.72 ± 0.05% vs. 0.93 ± 0.06%), and heart rate (101 ± 6 beats/min vs. 111 ± 7 beats/min) (p<0.05, for all comparisons). These changes were accompanied by a decrease in thermal sensation and discomfort. These results suggest that a field-type LCV attenuates exertional heat strain while wearing impermeable protective clothing.
Article
Full-text available
Background and aim: Safe clinical care within Ebola Virus Disease Treatment Units (EVDTUs) mandate the use of personal protective equipment (PPE), comprising a fluid impermeable hooded suit, visor, gloves and rubber boots. The aim of this study was to assess the impact of this PPE on clinical personnel's performance in the EVDTU, Kerry Town, Sierra Leone. Methods: An anonymous questionnaire was administered to healthcare professionals (HCPs) entering the EVDTU ward area (Red Zone (RZ)), during a 2-week period to assess perceived exertion using the Borg Rating of Perceived Exertion Scale. Results: A total of 62 clinical episodes undertaken by 20 HCPs were analysed. There were no episodes of heat illness during the study. HCPs spent a median of 74 (IQR 55-95) minutes within the RZ. Median durations of RZ activity were similar throughout the 24 h period (p=0.22), but Borg scores were significantly higher between 11:00 and 14:59 compared with RZ entry between 15:00 and 10:59, respectively (12 (6-15), n=13; 8 (6-9), n=48; p=0.022). Rates of weight loss per minute spent within the RZ were significantly greater between 11:00 and 14:59 compared with 15:00-10:59, respectively (0.014 (0.009-0.023) kg/min, n=6; 0.007 (0.004-0.013) kg/min, n=37; p=0.037). Conclusions: Despite acclimatisation and proactive clinical tasking, HCPs in the EVDTU experienced significantly greater rates of weight loss and perceived exertion scores during the hottest times of the day. These findings should be considered by those planning healthcare facilities for future humanitarian missions where HCPs will provide clinical care in full PPE.
Article
Full-text available
Normal human core body temperature is regulated within a narrow range. Deviations from this range can have serious consequences in both health and disease. However, it is difficult to efficiently manipulate body heat con-tent because of the high heat capacity of the body and the low thermal conductance of the body surface. Mammals have evolved vascular adaptations of the nonhairy skin to enable enhanced heat loss. These include arteriovenous anastomoses that bypass the nutritive capillary beds to shunt the blood into retia venosa which serve as radiators. We have quantified the area-specific heat loss from glabrous skin (palms and face) and nonglabrous skin (upper arm, back, thigh, and abdomen). Results show that the heat loss from the nonglabrous skin does not change ap-preciably over the course of exercise in the heat, whereas the heat loss from the glabrous skin rises to values more than five times that of the nonglabrous skin. The application of a mild vacuum increases the heat loss from the glabrous skin by an additional 33%. The effect of cooling of these different skin areas on the heart-rate response to a fixed exercise load was significantly greater for the glabrous than the nonglabrous skin. The intermittent ap-plication of vacuum cooling to the palms of individuals exercising in a hot environment had the effects of lower-ing the rate of rise of core temperature and enhancing performance. The vacuum-enhanced heat exchange via the glabrous skin is a disruptive technology for several reasons. It forces re-formulation of the models of human ther-moregulation that are used to design thermal protective gear. It offers an effective means of treating heat and cold stress. It provides an insight into controversies about the effects of temperature on human athletic performance, and offers a means of enhancing strength and work volume training responses that are more effective than per-formance-enhancing supplements such as anabolic steroids. There are many potential applications of vacuum-enhanced cooling of the glabrous skin in medicine, occupational health and safety, and sport.
Article
Full-text available
Insulation reduces heat exchange between a body and the environment. Glabrous (nonhairy) skin surfaces (palms of the hands, soles of the feet, face, and ears) constitute a small percentage of total body surface area but contain specialized vascular structures that facilitate heat loss. We have previously reported that cooling the glabrous skin surfaces is effective in alleviating heat stress and that the application of local subatmospheric pressure enhances the effect. In this paper, we compare the effects of cooling multiple glabrous skin surfaces with and without vacuum on thermal recovery in heavily insulated heat-stressed individuals. Esophageal temperatures (T(es)) and heart rates were monitored throughout the trials. Water loss was determined from pre- and post-trial nude weights. Treadmill exercise (5.6 km/h, 9-16% slope, and 25-45 min duration) in a hot environment (41.5 degrees C, 20-30% relative humidity) while wearing insulating pants and jackets was used to induce heat stress (T(es)>or=39 degrees C). For postexercise recovery, the subjects donned additional insulation (a balaclava, winter gloves, and impermeable boot covers) and rested in the hot environment for 60 min. Postexercise cooling treatments included control (no cooling) or the application of a 10 degrees C closed water circulating system to (a) the hand(s) with or without application of a local subatmospheric pressure, (b) the face, (c) the feet, or (d) multiple glabrous skin regions. Following exercise induction of heat stress in heavily insulated subjects, the rate of recovery of T(es) was 0.4+/-0.2 degrees C/h(n=12), but with application of cooling to one hand, the rate was 0.8+/-0.3 degrees C/h(n=12), and with one hand cooling with subatmospheric pressure, the rate was 1.0+/-0.2 degrees C/h(n=12). Cooling alone yielded two responses, one resembling that of cooling with subatmospheric pressure (n=8) and one resembling that of no cooling (n=4). The effect of treating multiple surfaces was additive (no cooling, DeltaT(es)=-0.4+/-0.2 degrees C; one hand, -0.9+/-0.3 degrees C; face, -1.0+/-0.3 degrees C; two hands, -1.3+/-0.1 degrees C; two feet, -1.3+/-0.3 degrees C; and face, feet, and hands, -1.6+/-0.2 degrees C). Cooling treatments had a similar effect on water loss and final resting heart rate. In heat-stressed resting subjects, cooling the glabrous skin regions was effective in lowering T(es). Under this protocol, the application of local subatmospheric pressure did not significantly increase heat transfer per se but, presumably, increased the likelihood of an effect.
Article
Full-text available
1. Six healthy humans were immersed sequentially in baths maintained at a steady temperature of either 28 +/- 1 or 38-8 +/- 1 degree C. 2. Metabolic heat production was calculated by respiratory gas analysis. A ventilated capsule was placed on the forehead and sweat secretion was calculated from psychrometric recordings. Convective heat loss from one hand to water-perfused glove provided a continuous measurement of vasomotor response. 3. Heat production, sweating, and vasomotor heat loss were proportional to core temperature. 4. Sweating and vasomotor response were parallel. Vasoconstriction was complete, before the onset of shivering. 5. The thresholds for heat loss and heat production were superimposed, without a 'dead band' core temperature.
Article
The effectiveness of hand immersion in water at l0°C, 20°C and 30°C as a technique for reducing heat strain in Royal Navy (RN) personnel has been investigated at the Institute of Naval Medicine (INM). Four subjects exercised at a moderate work rate, whilst wearing fire fi ghting clothing in an environmental chamber at 40°C. The subjects reached heat strain safety limits within 45 minutes of commencing work at which point they rested in the heat for 30 minutes whilst they underwent one of four experimental conditions: without intervention (control); or with their hands immersed in water at 10°C, 20°C or 30°C. The experiment was repeated on a further three days so that the subjects undertook each experimental condition in a balanced randomised order. During the control condition without hand immersion the subjects were unable to cool. Immersion of the hands in water (at l0°C, 20°C or 30°C) significantly ( P <0.05) lowered body core (auditory canal) temperature within ten minutes. Assessing the effectiveness of this technique by the initial rates of core temperature reduction, revealed that immersion of the hands was more effective the colder the water. Following 20 minutes of hand immersion mean core temperature had dropped from 38.SC to: 36.9(standard deviation 0.19)°C, 37.3 (0.18)°C, and 37.8(0. 10)°C, in l0°C, 20°C and 30°C water respectivel y. Cooling powers estimated from changes in mean body temperature were 334, 307 and 113 watts using 10°C, 20°C and 30°C water respectively. These results indicate that hand immersion in water at a temperature of between 10°C and 30°C is an efficient means of cooling heat stressed personnel who have been exercising. This simple and effective technique may be applied to many industrial and military tasks to reduce heat strain, lower the risk of heat injury, and increase safe total work times in the heat. For the RN, hand immersion could be used in fire fighting, damage control and NBC operations where personnel alternately work and rest.
Book
This handbook provides a step-by-step approach to using metabolic equations, from basic math principles to applying the equations to an exercise plan. Chapters focus separately on each equation, provide an easy-to-follow process of solving, and demonstrate the varied uses of the equation in clinical as well as fitness settings. Each chapter includes a set of problems that focus on real-world applications of the equation. Step-by-step problem solution explanations are provided at the end of each chapter. A comprehensive exam at the end of the book tests the reader's skill in using the equations. © 2007 American College of Sports Medicine. All rights reserved.
Article
In many occupational settings, clothing must be worn to protect individuals from hazards in their work environment. However, personal protective clothing (PPC) restricts heat exchange with the environment due to high thermal resistance and low water vapor permeability. As a consequence, individuals who wear PPC often work in uncompensable heat stress conditions where body heat storage continues to rise and the risk of heat injury is greatly enhanced. Tolerance time while wearing PPC is influenced by three factors: (i) initial core temperature (Tc), affected by heat acclimation, precooling, hydration, aerobic fitness, circadian rhythm, and menstrual cycle (ii) Tc tolerated at exhaustion, influenced by state of encapsulation, hydration, and aerobic fitness; and (iii) the rate of increase in Tc from beginning to end of the heat-stress exposure, which is dependent on the clothing characteristics, thermal environment, work rate, and individual factors like body composition and economy of movement. Methods to reduce heat strain in PPC include increasing clothing permeability for air, adjusting pacing strategy, including work/rest schedules, physical training, and cooling interventions, although the additional weight and bulk of some personal cooling systems offset their intended advantage. Individuals with low body fatness who perform regular aerobic exercise have tolerance times in PPC that exceed those of their sedentary counterparts by as much as 100% due to lower resting Tc, the higher Tc tolerated at exhaustion and a slower increase in Tc during exercise. However, questions remain about the importance of activity levels, exercise intensity, cold water ingestion, and plasma volume expansion for thermotolerance. Published 2013. Compr Physiol 3:1363-1391, 2013.
Article
This study tested a new portable cooling device for fire fighting recovery. Participants (N = 8) walked and did arm curls (time-weighted VO(2): 1.6 L x min(-1) on a treadmill for 40 min in a heated chamber (wet bulb globe temperature: 33.7 degrees C; relative humidity: 40-45%) while wearing firefighter turn-out gear and self-contained breathing apparatus (SCBA). Immediately on finishing exercise, participants recovered for 40 min with either a hand-cooling device or seated passive recovery at an ambient temperature of 22 degrees C, 35% RH in a repeated-measures counterbalanced design. The cooling device had little impact on recovery during the first 30 min; however, compared with passive cooling, the cooling device resulted in significantly lower rectal temperature (T(re)) during the last 10 min. Relative to starting T(re) of the recovery period, Delta T(re) at 35 min had fallen 0.51 +/- 0.19 degrees C (passive) and 0.76 +/- 0.30 degrees C (active) (p = 0.03); and at 40 min Delta T(re) had fallen 0.63 +/- 0.17 degrees C (passive) and 0.88 +/- 0.31 degrees C (active) (p = 0.03). Cooling capacity of the device calculated from Delta T(re) over the whole recovery period averaged about 144% of passive. Reductions in heat storage enhance worker safety and performance in hot environments.
Article
The effects of hand immersion on body temperature have been investigated in men wearing impermeable NBC clothing. Six men worked continuously at a rate of approximately 490 J.sec ⁻¹ in an environmental temperature of 30°C. Each subject was permitted to rest for a period of 20 minutes when their aural temperature reached 37.5°C, and again on reaching 38°C, and for a third time on reaching 38.5°C (three rest periods in total). Each subject completed three experimental conditions whereby, during the rest periods they either: a. Did not immerse their hands (control). b. Immersed both hands in a water bath set at 25°c. c. Immersed both hands in water at 10°C. Physiological measures of core temperature, skin temperature and heart rate were recorded at intervals throughout the experiment. Measures of mean aural temperature and mean skin temperature were significantly (P<0.05) reduced if hands were immersed during these rest periods, compared to non immersion. As a result, the total work time of subjects was extended when in the immersed conditions by some 10–20 minutes within the confines of the protocol. It is concluded that this technique of simple hand immersion may be effective in reducing heat stress where normal routes to heat loss are compromised.
Article
The effect of immersing the hands up to the wrist in cold water to alleviate heat strain was examined in volunteers wearing chemical protective clothing and gloves. Each subject, who was monitored with skin and rectal thermistors, was observed while walking on a treadmill at two different work rates (283 +/- 47 and 455 +/- 58 watts) at 23 degrees C and at a resting state at 35 degrees C. After 20 min of work at 23 degrees C or after 120 min in the hot room, the hands were immersed in water at temperatures of 10, 15, 20, 25, and 30 degrees C. The amount of heat lost via the hands ranged between 124 +/- 14 and 31 +/- 4 watts (W) and was greater, the colder the water and harder the work. In most cases, this amount of cooling was sufficient to decrease skin temperature and lower the rate of increase of core temperature. We concluded that this method may be used to decrease resting time when working in the heat.