Physiological impact of the N95 filtering facepiece respirator on healthcare workers

Abstract

To assess the physiological impact of the N95 filtering facepiece respirator (FFR) on healthcare workers.
Ten healthcare workers each conducted multiple 1-hour treadmill walking sessions, at 1.7 miles/h, and at 2.5 miles/h, while wearing FFR with exhalation valve, FFR without exhalation valve, and without FFR (control session). We monitored heart rate, respiratory rate, tidal volume, minute volume, blood oxygen saturation, and transcutaneously measured P(CO2). We also measured user comfort and exertion, FFR moisture retention, and the carbon dioxide and oxygen concentrations in the FFR's dead space.
There were no significant differences between FFR and control in the physiological variables, exertion scores, or comfort scores. There was no significant difference in moisture retention between FFR with and without exhalation valve. Two subjects had peak P(CO2) > or = 50 mm Hg. The FFR with exhalation valve offered no benefit in physiological burden over the FFR without valve. The FFR dead-space oxygen and carbon dioxide levels did not meet the Occupational Safety and Health Administration's ambient workplace standards.
In healthy healthcare workers, FFR did not impose any important physiological burden during 1 hour of use, at realistic clinical work rates, but the FFR dead-space carbon dioxide and oxygen levels were significantly above and below, respectively, the ambient workplace standards, and elevated P(CO2) is a possibility. Exhalation valve did not significantly ameliorate the FFR's P(CO2) impact.

Full text

Physiological Impact of the N95 Filtering Facepiece Respirator
on Healthcare Workers
Raymond J Roberge MD MPH, Aitor Coca PhD, W Jon Williams PhD,
Jeffrey B Powell MSc, and Andrew J Palmiero
OBJECTIVE: To assess the physiological impact of the N95 filtering facepiece respirator (FFR) on
healthcare workers. METHODS: Ten healthcare workers each conducted multiple 1-hour treadmill
walking sessions, at 1.7 miles/h, and at 2.5 miles/h, while wearing FFR with exhalation valve, FFR
without exhalation valve, and without FFR (control session). We monitored heart rate, respiratory rate,
tidal volume, minute volume, blood oxygen saturation, and transcutaneously measured P
CO
2
. We also
measured user comfort and exertion, FFR moisture retention, and the carbon dioxide and oxygen
concentrations in the FFR’s dead space. RESULTS: There were no significant differences between FFR
and control in the physiological variables, exertion scores, or comfort scores. There was no significant
difference in moisture retention between FFR with and without exhalation valve. Two subjects had peak
P
CO
2
> 50 mm Hg. The FFR with exhalation valve offered no benefit in physiological burden over the
FFR without valve. The FFR dead-space oxygen and carbon dioxide levels did not meet the Occupa-
tional Safety and Health Administration’s ambient workplace standards. CONCLUSIONS: In healthy
healthcare workers, FFR did not impose any important physiological burden during 1 hour of use, at
realistic clinical work rates, but the FFR dead-space carbon dioxide and oxygen levels were significantly
above and below, respectively, the ambient workplace standards, and elevated P
CO
2
is a possibility.
Exhalation valve did not significantly ameliorate the FFR’s P
CO
2
impact. Key words: N95 filtering
facepiece; respirator; physiological; healthcare workers; comfort; exertion; Occupational Safety and Health
Administration; workplace. [Respir Care 2010;55(5):569 –577]
Introduction
Concerns over emerging airborne infectious diseases
have highlighted the importance of respiratory protection
for healthcare workers.
1
Respiratory protection in health-
care settings is generally accomplished by engineering and
administrative controls and the use of respiratory protec-
tive equipment such as filtering facepiece respirators
(FFRs), of which the most commonly recommended and
used are N95 FFRs
2
(frequently incorrectly referred to as
N95 masks). Despite widespread use, few published data
exist regarding the physiological impact of FFRs on health-
care workers. We assessed the physiological impact upon
healthcare workers of an N95 FFR with and without an
exhalation valve, and measured the oxygen and carbon
dioxide levels in the FFR’s dead space (FFR V
D
).
Methods
Subjects
We recruited 10 healthy healthcare workers (7 women,
3 men, ages 20 – 45 y) who were experienced with wearing
FFR (Table 1). Exclusion criteria included pregnancy, smok-
ing, cardiopulmonary disorder, musculoskeletal disorder that
prevented exercise, and inability to be adequately fit-tested
Raymond J Roberge MD MPH, Aitor Coca PhD, W Jon Williams PhD,
Jeffrey B Powell MSc, and Andrew J Palmiero are affiliated with the Tech-
nology Research Branch, National Personal Protective Technology Labora-
tory, National Institute for Occupational Safety and Health, Centers for Dis-
ease Control and Prevention, Pittsburgh, Pennsylvania.
The authors have disclosed no conflicts of interest.
The findings and conclusions in this report are those of the authors and
do not necessarily represent the views of the National Institute for Oc-
cupational Safety and Health.
Correspondence: Raymond J Roberge MD MPH, Technology Research
Branch, National Personal Protective Technology Laboratory, National In-
stitute for Occupational Safety and Health, Centers for Disease Control and
Prevention, 626 Cochrans Mill Road, Pittsburgh PA 15236. E-mail:
dtn0@cdc.gov.
RESPIRATORY CARE • MAY 2010 VOL 55 NO 5 569

with the FFR. Nine of the subjects had never smoked, and
one had not smoked in ⬎ 1 y (20 pack-year history). The
study was approved by the National Institute for Occupa-
tional Safety and Health (NIOSH) human subjects review
board, and all subjects provided oral and written informed
consent.
Physiological Monitoring Equipment
We used the LifeShirt System (VivoMetrics, Ventura, Cal-
ifornia), a lightweight spandex vest that incorporates physi-
ological sensors and circumferential respiratory-inductive-
plethysmography bands, to monitor heart rate, respiratory rate,
and tidal volume (V
T
). We calculated minute volume (V
˙
E
)as
the product of respiratory rate and V
T
. We calibrated the
LifeShirt against a fixed volume before each use.
Timed CO
2
and O
2
averages were obtained via a gas
analyzer (CO
2
sensor model p61-B, O
2
analyzer model
S3-A/I, AEI Technologies, Naperville, Illinois) that con-
tinuously sampled the FFR V
D
gas at 18 samples/s (total
sampling volume 500 mL/min) via a 2-mm inner-diameter
sampling line attached to a port in the FFR that was equi-
distant between the nares and mouth. The gas analyzer was
calibrated daily with a protocol that uses standards trace-
able to the National Institute of Standards and Technology.
We continuously transcutaneously measured CO
2
(P
tcCO
2
) and O
2
saturation (S
pO
2
) (Tosca 500 monitor, Ra
-
diometer, Copenhagen, Denmark, which uses a heated,
earlobe-mounted, combination pulse oximeter and Sever-
inghaus-type heated sensor that potentiometrically mea-
sures the partial pressure of CO
2
by determining the pH of
an electrolyte layer separated from the skin by a highly
permeable membrane: a pH change is proportional to the
logarithm of P
CO
2
change).
3
We calibrated the unit over a
10-min period prior to each use.
Filtering Facepiece Respirator Model Selection
The 2 N95 FFR models (from 2 manufacturers) we studied
are representative of supplies in the National Strategic Stock-
pile, which is a federal-government-maintained repository of
medical supplies likely to be the first distributed to healthcare
workers in a large-scale medical emergency.
4
The National
Strategic Stockpile does not include FFRs with exhalation
valves, so we chose 2 exhalation-valved FFRs that were sim-
ilar in shape and size to the National Strategic Stockpile
FFRs, and made by the same manufacturers. All the FFRs we
tested were cup-shaped, and we used a new FFR for each
study session. We weighed each FFR before and after the
session to measure moisture retention.
Filtering Facepiece Respirator Fit Testing
To determine the FFR size that provided the best seal on
the face, we quantitatively evaluated FFR fit. We quantified
fit factor (ratio of ambient-air particle concentration to inside-
the-FFR particle concentration) with a respirator-fit test de-
vice (PortaCount Plus, TSI, Shoreview, Minnesota), which
measures optical density with condensation-nucleus-counting
technology, to calculate leakage into the FFR while the sub-
ject performed a series of 8 exercises.
5
We fit tested the
subjects with each FFR and FFR-with-valve model, and all
subjects attained an overall fit factor of ⱖ 100, which indi-
cates leakage of ⱕ 1%, the level required by the Occupa-
tional Safety and Health Administration.
5,6
Eight subjects
passed fit testing with the medium/large (ie, standard) FFR,
and 2 subjects required the small FFR.
Test Procedures
Control Studies. Subjects donned the LifeShirt, and were
tested in athletic shorts, tee-shirt and athletic shoes. The
Tosca 500 sensor was attached to the left earlobe, and we
Table 1. Subject Demographics
Subject Professional Category
Age
(y)
Weight
(kg)
Height
(cm)
Body Mass
Index (kg/m
2
)
Sex
1 Nurse 42 75.3 155 31.3 Female
2 Nurse 22 47.6 165 17.4 Female
3 Physical therapy technician 24 64.5 162 24.4 Female
4 Physical therapy technician 23 126.4 162 47.7 Female
5 Patient-care assistant 20 105.4 183 31.5 Male
6 Patient-care assistant 34 55.4 157 22.3 Female
7 Patient-care assistant 20 68.8 188 19.4 Male
9 Nursing student 21 56.8 165 20.8 Female
9 Nursing student 22 69.5 170 23.9 Female
10 Physical therapy student 23 85.8 183 25.5 Male
Mean 25 76.0 169 26.4
PHYSIOLOGICAL IMPACT OF THE N95 FILTERING FACEPIECE RESPIRATOR ON HEALTHCARE WORKERS
570 RESPIRATORY CARE • MAY 2010 VOL 55 NO 5

obtained control physiologic data for each subject contin-
uously over 15 min at 2 treadmill speeds that represent
realistic healthcare worker activity levels and that have
been used in other FFR studies
7-9
: treadmill speed
1.7 miles/h, incline 0°, which equates to stationary work
(eg, writing nursing notes, answering phones); and tread-
mill speed 2.5 miles/h, incline 0°, which equates to bed-
side nursing patient-care activities. The control 15-min
exercise interval was selected because, at relatively low-
intensity steady-state exercise, steady-state respiratory vari-
ables are achieved in 3– 6 min in healthy subjects.
10,11
The
treadmill was calibrated prior to the study.
Filtering Facepiece Respirator Studies. Subjects were
clothed and instrumented as in the control studies, donned, in
randomly-assigned order, and according to the manufactur-
er’s instructions, the FFR or FFR-with-valve, performed pos-
itive and negative face-seal checks (with the gas-sampling
line pinched off), and treadmill-walked for 1 hour (mean
nurse FFR wear time per shift
12
), in the randomly-assigned
order for work rate, while physiological variables were con-
tinuously monitored. Every 5 min we queried the subjects
with the modified Borg Perceived Exertion Scale
13
and the
modified Perceived Comfort Scale.
14
Talking was permitted
ad lib during the testing, to mimic healthcare workers com-
municating while wearing the FFR. Upon completing the
exercise session, the subjects filled out questionnaires relat-
ing to complaints commonly referable to FFR use (eg, heat,
sweating, itching, and lightheadedness) and were allowed to
add personal comments related to any subjective sensations
they experienced or FFR design features that caused discom-
fort. The study sessions were generally limited to 2 per day,
with a minimum 30-min break between the sessions. Each
subject conducted 4 exercise sessions (one with each FFR
and FFR-with-valve) and one control session at each work
rate. The study laboratory temperature was maintained at
22°C, and relative humidity averaged 54% (range 39 –70%).
Statistical Analysis
We used statistics software (SPSS 16.0, SPSS, Chicago,
Illinois) for the statistical analyses. We report the physiolog-
ical data and FFR V
D
CO
2
and O
2
data as mean ⫾ SD. The
sessions were 1 hour, and the data variables are summarized
at 1, 15, 30, 45, and 60 min. We performed 2 ⫻ 2 ⫻ 5 (FFR
type ⫻ work rate ⫻ time) analysis of variance (ANOVA) to
assess the differences between FFR and FFR-with-valve at
the 2 exercise intensities. To determine differences in the
physiological variables, we performed 2 ⫻ 2 ⫻ 5 (FFR type ⫻
work rate ⫻ time) repeated-measures ANOVA for S
pO
2
,P
tcCO
2
,
respiratory rate, V
T
,V
˙
E
, and heart rate, using the values from
the control session (no FFR) as a covariate. We performed
2 ⫻ 2 ⫻ 5 (FFR type ⫻ work rate ⫻ time) repeated-measures
ANOVA to examine the FFR V
D
O
2
and CO
2
responses to
the FFR and FFR-with-valve at the 2 exercise intensities. We
further analyzed significant interactions with 1-way ANOVA
and paired t tests with Bonferroni corrections, with the alpha
level set at P ⬍ .05. We analyzed the exertion scores, comfort
scores, and FFR weights with paired t tests. The null hypoth-
esis was that there would be no significant differences (P ⬍ .05)
in the studied physiological variables between the controls
(no respirator) and the FFR and FFR-with-valve.
Results
Physiological Variables
There were no significant differences in the physiolog-
ical variables at either work rate over 1 hour, when com-
paring controls to all FFR models. Similarly, when com-
paring FFR to FFR-with-valve, only respiratory rate was
significantly lower with FFR, at the 1.7 miles/h work rate
(P ⫽ .02). Between FFR and FFR-with-valve there were
no significant differences in FFR V
D
mean mixed inhala
-
tion/exhalation O
2
(16.6% vs 16.7%, P ⫽ .30) or CO
2
(2.9% vs 2.9%, P ⫽ .47), at both work rates (see Tables
2–7). Over 1 hour, the moisture retention in the FFR and
the FFR-with-valve was 0.11 ⫾ 0.15 g and 0.13 ⫾ 0.09 g,
respectively (P ⫽ .46). Tables 8 –10 show the comfort
scores, exertion scores, and subjective complaints.
Discussion
The protection afforded by respiratory protective equip-
ment is partly counterbalanced by the physiological and
psychological burden the equipment imposes on the us-
er.
15
The current study found no significant differences in
heart rate, respiratory rate, V
T
,V
˙
E
,S
pO
2
,orP
tcCO
2
between
control and FFR or FFR-with-valve while exercising over
1 hour at realistic work rates.
The impact of FFR on ventilatory variables was modest.
This was manifested as nonsignificant increases in V
T
(range
38 –148 mL), with concomitant nonsignificant, mild decre-
ments in respiratory rate at both work rates over 1 hour (see
Tables 3–7). This quantifies the mild added effort required to
overcome the filter-media resistance of the relatively low-
resistance FFRs we used (the NIOSH maximum certification
initial exhalation and inhalation resistances are 35 mm H
2
O
and 25 mm H
2
O column height pressure, respectively
5
) and
the FFR V
D
effects at the study work rates.
2,16
Our finding of no significant difference in respiratory
rate between control and FFR or FFR-with-valve is at
variance with a previous investigation that included
8 healthcare workers and 2 industrial workers who tread-
mill exercised with an FFR, in whom there were statisti-
cally significant increases in respiratory rate at rest and
during 5-min exercise periods with mild, moderate, and
heavy work rates.
16
Unfortunately, V
˙
E
was not measured
in that study,
16
and other study differences included FFR
PHYSIOLOGICAL IMPACT OF THE N95 FILTERING FACEPIECE RESPIRATOR ON HEALTHCARE WORKERS
RESPIRATORY CARE • MAY 2010 VOL 55 NO 5 571

features (eg, absence of exhalation valve), dissimilar work
intensities and exercise duration, and different respiratory-
rate measurement techniques and measurement times. FFR
use during a sedentary activity (ie,4hofhemodialysis)
increased respiratory rate by only 2 breaths/min.
17
In the
current study we found a significantly higher respiratory
rate with the FFR-with-valve than with the FFR without
valve at 1.7 miles/h (see Table 2). That finding is some-
what counterintuitive, given that the exhalation valve is
designed to diminish exhalation resistance and, thus, the
work of breathing. However, the exhalation valve’s func-
tion depends on breathing-resistance-related development
of streamline air flows that allow egress of exhaled gas
through the valve, and these air flows may not be gener-
ated at a lower work rate in a low-resistance FFR-with-
valve.
18
We observed no grossly visible exhalation-valve
movement during multiple random checks, though it is
possible that subtle valve movements occurred.
In terms of cardiac impact, the nonsignificant difference
in heart rate between control and FFR and FFR-with-valve
in the current study is congruent with other studies up to
1 hour of FFR use.
8,16,19
One study reported a mild de-
crease in heart rate with FFR during 4 hours of sedentary
activity.
17
FFR-associated increased heart rate relates to
breathing resistance, work level, physical fitness, FFR-
associated anxiety, and increased retention of CO
2
.
16,20
The present study’s low work rates, the subjects’ prior
FFR experience, associated normal P
tcCO
2
levels, and our
use of low-resistance FFRs underscore why heart rate was
not significantly higher than control.
The similar S
pO
2
values between the controls and all the
FFR models in the current study mirror a previous report
Table 2. P Values for Differences in Physiological Variables: Control Versus Filtering Facepiece Respirator
P Value for Difference Between After One Hour
Respiratory
Rate
Heart
Rate
Tidal
Volume
Minute
Volume
S
pO
2
P
tcCO
2
Control vs FFR
At 1.7 miles/h .48 .21 .59 .44 .95 .72
At 2.5 miles/h .12 .15 .52 .30 .95 .57
FFR With vs Without Exhalation Valve
At 1.7 miles/h .02 .32 .61 .92 .54 .71
At 2.5 miles/h .37 .47 .12 .07 .71 .55
FFR ⫽ filtering facepiece respirator
S
PO
2
⫽ blood oxygen saturation measured via pulse oximetry
P
tcCO
2
⫽ transcutaneously measured partial pressure of carbon dioxide
Table 3. Physiological Variables After 1 Min of Filtering Facepiece Respirator
At Treadmill Speed 1.7 miles/h At Treadmill Speed 2.5 miles/h
Control
*
FFR With
Valve
FFR Without
Valve
Control
FFR With
Valve
FFR Without
Valve
FFR Dead-Space Gases
O
2
(%)
NA 17.2 ⫾ 0.4 17.0 ⫾ 0.5 NA 17.2 ⫾ 1.0 17.0 ⫾ 0.8
CO
2
(%)
NA 3.0 ⫾ 0.4 3.0 ⫾ 0.2 NA 3.1 ⫾ 0.4 3.0 ⫾ 0.5
S
pO
2
(%)
98.5 ⫾ 0.8 98.4 ⫾ 0.5 98.1 ⫾ 0.9 98.5 ⫾ 0.8 98.1 ⫾ 1.2 98.1 ⫾ 0.9
P
tcCO
2
(mm Hg)
40.7 ⫾ 3.5 40.1 ⫾ 2.7 39.9 ⫾ 2.8 40.8 ⫾ 3.2 39.7 ⫾ 2.6 40.8 ⫾ 2.9
f (breaths/min) 27.7 ⫾ 7.1 25.2 ⫾ 6.9 21.7 ⫾ 6.3 27.7 ⫾ 8.6 22.4 ⫾ 7.0 23.9 ⫾ 9.0
V
T
(mL)
793 ⫾ 215 944 ⫾ 297 932 ⫾ 253 864 ⫾ 205 937 ⫾ 277 1,013 ⫾ 309
V
˙
E
(L/min)
20.9 ⫾ 8.2 22.4 ⫾ 4.6 19.6 ⫾ 6.1 23.0 ⫾ 6.5 20.4 ⫾ 6.3 23.0 ⫾ 7.2
Heart rate (beats/min) 92.3 ⫾ 8.2 92.8 ⫾ 11.2 94.8 ⫾ 10.3 101.3 ⫾ 11.8 98.7 ⫾ 11.0 101.3 ⫾ 9.4
* Control test was 15 min of physiological monitoring while not wearing a filtering facepiece respirator (FFR).
NA ⫽ not applicable
S
PO
2
⫽ blood oxygen saturation measured via pulse oximetry
P
tcCO
2
⫽ transcutaneously measured partial pressure of carbon dioxide
f ⫽ frequency (respiratory rate)
V
T
⫽ tidal volume
V
˙
E
⫽ minute ventilation
PHYSIOLOGICAL IMPACT OF THE N95 FILTERING FACEPIECE RESPIRATOR ON HEALTHCARE WORKERS
572 RESPIRATORY CARE • MAY 2010 VOL 55 NO 5

of a ⬍ 1% difference between controls and subjects wear-
ing N95 FFRs during qualitative respirator-fit testing.
19
A
recent study of the impact of a surgical mask on S
pO
2
in
surgeons during surgery found significant S
pO
2
decreases
only during procedures longer than 60 min.
21
Kao et al
17
found a net P
aO
2
decline of 9 ⫾ 18.5 mm Hg
from baseline in approximately 70% of 39 patients wear-
ing N95 FFR after 4 hours of hemodialysis.
That limited prior experience
19,21
and the current study
data suggest that S
pO
2
decrements are possible with N95
FFR or N95 FFR-with-valve, but are likely to be minor for
FFR use of ⱕ 1 hour during low energy expenditure, and
may not be clinically important.
Compared to control, P
tcCO
2
did not differ significantly
by work rate or FFR model. There were modest absolute
increases in mean P
tcCO
2
over 1 hour, compared to base
-
line, with the FFR-with-valve at 1.7 miles/h (P
tcCO
2
0.5 mm Hg higher) and 2.5 miles/h (P
tcCO
2
1.3 mm Hg
higher), and with FFR at 2.5 miles/h (P
tcCO
2
1.2 mm Hg
higher). These values are similar to those in a study that
reported an average P
aCO
2
of 1 ⫾ 4.1 mm Hg after 4 hours
of N95 FFR use during sedentary activity.
17
At 1.7 miles/h,
the mean P
tcCO
2
with FFR was modestly lower than control
(⫺0.7 mm Hg). The lack of (expected) lower P
tcCO
2
with
the FFR-with-valve suggests that the exhalation valve may
not decrease CO
2
at a low work rate, possibly because the
Table 5. Physiological Variables After 30 Min of Filtering Facepiece Respirator
At Treadmill Speed 1.7 miles/h At Treadmill Speed 2.5 miles/h
Control*
FFR With
Valve
FFR Without
Valve
Control
FFR With
Valve
FFR Without
Valve
FFR Dead-Space Gases
O
2
(%)
NA 17.3 ⫾ 0.6 17.3 ⫾ 0.4 NA 17.6 ⫾ 0.9 17.3 ⫾ 0.7
CO
2
(%)
NA 3.1 ⫾ 0.3 3.0 ⫾ 0.2 NA 3.0 ⫾ 0.5 3.1 ⫾ 0.5
S
pO
2
(%)
98.5 ⫾ 0.8 98.4 ⫾ 0.8 98.3 ⫾ 0.7 98.5 ⫾ 0.8 98.6 ⫾ 1.2 98.0 ⫾ 0.9
P
tcCO
2
(mm Hg)
40.7 ⫾ 3.5 41.3 ⫾ 4.2 40.3 ⫾ 5.2 40.8 ⫾ 3.2 42.4 ⫾ 5.1 42.1 ⫾ 4.7
f (breaths/min) 27.7 ⫾ 7.1 25.4 ⫾ 6.3 24.1 ⫾ 5.0 27.7 ⫾ 8.6 25.6 ⫾ 5.9 26.7 ⫾ 9.0
V
T
(mL)
793 ⫾ 215 915 ⫾ 282 942 ⫾ 339 864 ⫾ 205 972 ⫾ 339 1,001 ⫾ 308
V
˙
E
(L/min)
20.9 ⫾ 8.2 22.1 ⫾ 4.3 22.0 ⫾ 6.3 23.0 ⫾ 6.5 24.0 ⫾ 6.9 25.4 ⫾ 7.0
Heart rate (beats/min) 92.3 ⫾ 8.2 94.9 ⫾ 10.5 99.9 ⫾ 8.8 101.3 ⫾ 11.8 103.9 ⫾ 9.7 105.7 ⫾ 8.9
* Control test was 15 min of physiological monitoring while not wearing a filtering facepiece respirator (FFR).
NA ⫽ not applicable
S
PO
2
⫽ blood oxygen saturation measured via pulse oximetry
P
tcCO
2
⫽ transcutaneously measured partial pressure of carbon dioxide
f ⫽ frequency (respiratory rate)
V
T
⫽ tidal volume
V
˙
E
⫽ minute ventilation
Table 4. Physiological Variables After 15 Min of Filtering Facepiece Respirator
At Treadmill Speed 1.7 miles/h At Treadmill Speed 2.5 miles/h
Control*
FFR With
Valve
FFR Without
Valve
Control
FFR With
Valve
FFR Without
Valve
FFR Dead-Space Gases
O
2
(%)
NA 17.4 ⫾ 0.6 17.3 ⫾ 0.4 NA 17.6 ⫾ 0.9 17.3 ⫾ 0.7
CO
2
(%)
NA 3.0 ⫾ 0.3 3.1 ⫾ 0.2 NA 3.0 ⫾ 0.3 3.2 ⫾ 0.5
S
pO
2
(%)
98.5 ⫾ 0.8 98.3 ⫾ 0.7 98.3 ⫾ 0.8 98.5 ⫾ 0.8 98.5 ⫾ 0.8 98.0 ⫾ 0.7
P
tcCO
2
(mm Hg)
40.7 ⫾ 3.5 41.9 ⫾ 3.7 40.3 ⫾ 4.2 40.8 ⫾ 3.2 43.1 ⫾ 5.0 42.6 ⫾ 4.8
f (breaths/min) 27.7 ⫾ 7.1 24.7 ⫾ 6.6 23.8 ⫾ 4.8 27.7 ⫾ 8.6 25.4 ⫾ 6.3 25.5 ⫾ 9.0
V
T
(mL)
793 ⫾ 215 967 ⫾ 328 972 ⫾ 321 864 ⫾ 205 938 ⫾ 337 1,027 ⫾ 302
V
˙
E
(L/min)
20.9 ⫾ 8.2 22.8 ⫾ 5.6 22.2 ⫾ 4.5 23.0 ⫾ 6.5 23.0 ⫾ 7.4 25.0 ⫾ 7.4
Heart rate (beats/min) 92.3 ⫾ 8.2 96.6 ⫾ 10.6 97.9 ⫾ 8.3 101.3 ⫾ 11.8 103.5 ⫾ 9.1 105.9 ⫾ 9.6
* Control test was 15 min of physiological monitoring while not wearing a filtering facepiece respirator (FFR).
NA ⫽ not applicable
S
PO
2
⫽ blood oxygen saturation measured via pulse oximetry
P
tcCO
2
⫽ transcutaneously measured partial pressure of carbon dioxide
f ⫽ frequency (respiratory rate)
V
T
⫽ tidal volume
V
˙
E
⫽ minute ventilation
PHYSIOLOGICAL IMPACT OF THE N95 FILTERING FACEPIECE RESPIRATOR ON HEALTHCARE WORKERS
RESPIRATORY CARE • MAY 2010 VOL 55 NO 5 573

exhalation pressure is not sufficient to activate the exha-
lation valve, or because of the loss of FFR surface area for
gas exchange if the valve is not activated. The potential for
substantial CO
2
retention with N95 FFR or N95 FFR-
with-valve was highlighted by 2 non-obese subjects, an
otherwise healthy 42-year-old female ex-smoker (peak 60-
min P
tcCO
2
50 mm Hg), and a 21-year-old man with no
noteworthy medical history (peak 60-min P
tcCO
2
52 mm Hg), although both were asymptomatic. Pulmonary
function testing was not carried out in the subjects, but the
normal control values obtained when not wearing an FFR
suggest that the FFR’s effect on CO
2
retention is of some
concern. It is possible that the ex-smoker subject may have
had some degree of pulmonary impairment related to past
tobacco use; however, the other subject had no known risk
factors.
The FFR V
D
is a repository for exhaled gas, which sub
-
sequently mixes with the air that enters through the FFR and
is re-breathed during successive inhalations.
22
Technically,
this can increase the CO
2
and decrease the O
2
entering the
lungs.
23
Quantification of inspired CO
2
level is a criterion for
evaluating FFR performance by governmental agencies in
Table 6. Physiological Variables After 45 Min of Filtering Facepiece Respirator
At Treadmill Speed 1.7 miles/h At Treadmill Speed 2.5 miles/h
Control*
FFR With
Valve
FFR Without
Valve
Control
FFR With
Valve
FFR Without
Valve
FFR Dead-Space Gases
O
2
(%)
NA 16.8 ⫾ 0.7 16.8 ⫾ 0.8 NA 17.3 ⫾ 1.1 16.9 ⫾ 0.4
CO
2
(%)
NA 2.9 ⫾ 0.3 3.0 ⫾ 0.3 NA 3.0 ⫾ 0.4 3.0 ⫾ 0.4
S
pO
2
(%)
98.5 ⫾ 0.8 98.2 ⫾ 1.1 98.2 ⫾ 0.9 98.5 ⫾ 0.8 97.9 ⫾ 1.1 98.4 ⫾ 1.1
P
tcCO
2
(mm Hg)
40.7 ⫾ 3.5 41.4 ⫾ 4.1 39.7 ⫾ 5.2 40.8 ⫾ 3.2 42.5 ⫾ 5.5 42.6 ⫾ 5.7
f (breaths/min) 27.7 ⫾ 7.1 24.8 ⫾ 7.2 25.7 ⫾ 5.1 27.7 ⫾ 8.6 25.5 ⫾ 6.0 26.6 ⫾ 9.7
V
T
(mL)
793 ⫾ 215 915 ⫾ 314 948 ⫾ 343 864 ⫾ 205 962 ⫾ 318 994 ⫾ 313
V
˙
E
(L/min)
20.9 ⫾ 8.2 21.5 ⫾ 4.9 23.5 ⫾ 6.8 23.0 ⫾ 6.5 23.9 ⫾ 7.2 25.0 ⫾ 7.4
Heart rate (beats/min) 92.3 ⫾ 8.2 95.6 ⫾ 8.8 98.5 ⫾ 8.0 101.3 ⫾ 11.8 107.3 ⫾ 8.7 107.4 ⫾ 9.7
* Control test was 15 min of physiological monitoring while not wearing a filtering facepiece respirator (FFR).
NA ⫽ not applicable
S
PO
2
⫽ blood oxygen saturation measured via pulse oximetry
P
tcCO
2
⫽ transcutaneously measured partial pressure of carbon dioxide
f ⫽ frequency (respiratory rate)
V
T
⫽ tidal volume
V
˙
E
⫽ minute ventilation
Table 7. Physiological Variables After 60 Min of Filtering Facepiece Respirator
At Treadmill Speed 1.7 miles/h At Treadmill Speed 2.5 miles/h
Control*
FFR With
Valve
FFR Without
Valve
Control
FFR With
Valve
FFR Without
Valve
FFR Dead-Space Gases
O
2
(%)
NA 16.5 ⫾ 0.6 16.6 ⫾ 0.6 NA 17.2 ⫾ 1.1 16.6 ⫾ 0.6
CO
2
(%)
NA 2.9 ⫾ 0.4 2.9 ⫾ 0.2 NA 3.0 ⫾ 0.5 2.8 ⫾ 0.4
S
pO
2
(%)
98.5 ⫾ 0.8 98.4 ⫾ 1.0 98.1 ⫾ 0.9 98.5 ⫾ 0.8 98.2 ⫾ 1.0 98.4 ⫾ 0.7
P
tcCO
2
(mm Hg)
40.7 ⫾ 3.5 41.5 ⫾ 4.9 39.7 ⫾ 6.0 40.8 ⫾ 3.2 42.6 ⫾ 6.2 42.0 ⫾ 5.6
f (breaths/min) 27.7 ⫾ 7.1 25.2 ⫾ 6.1 25.2 ⫾ 4.0 27.7 ⫾ 8.6 25.5 ⫾ 5.7 26.6 ⫾ 6.8
V
T
(mL)
793 ⫾ 215 878 ⫾ 253 950 ⫾ 358 864 ⫾ 205 932 ⫾ 297 945 ⫾ 241
V
˙
E
(L/min)
20.9 ⫾ 8.2 21.2 ⫾ 4.5 23.4 ⫾ 6.7 23.0 ⫾ 6.5 23.0 ⫾ 5.9 24.4 ⫾ 6.0
Heart rate (beats/min) 92.3 ⫾ 8.2 95.1 ⫾ 9.7 98.1 ⫾ 8.5 101.3 ⫾ 11.8 106.4 ⫾ 9.3 106.4 ⫾ 9.2
* Control test was 15 min of physiological monitoring while not wearing a filtering facepiece respirator (FFR).
NA ⫽ not applicable
S
PO
2
⫽ blood oxygen saturation measured via pulse oximetry
P
tcCO
2
⫽ transcutaneously measured partial pressure of carbon dioxide
f ⫽ frequency (respiratory rate)
V
T
⫽ tidal volume
V
˙
E
⫽ minute ventilation
PHYSIOLOGICAL IMPACT OF THE N95 FILTERING FACEPIECE RESPIRATOR ON HEALTHCARE WORKERS
574 RESPIRATORY CARE • MAY 2010 VOL 55 NO 5

some countries (eg, Japan), but not for NIOSH-certified FFRs.
We measured time-averaged FFR V
D
CO
2
and O
2
concen
-
trations. Although that method is not as robust as volume-
weighted averages for determining inhaled gas concentra-
tions, time averages offer a view of the FFR microenvironment
that is useful for comparisons with ambient gas concentra-
tions. The timed mean mixed inhalation/exhalation FFR V
D
CO
2
and O
2
values, respectively, over 1 hour, for the FFR
(2.9%, 16.6%) and the FFR-with-valve (2.9%, 16.7%) did
not differ significantly by work rate or FFR model, and are
comparable to other studies.
18,24
Although the FFR V
D
O
2
level was lower than the Occupational Safety and Health
Administration’s workplace standard (⬍ 19.5% O
2
is con
-
sidered deficient) and the FFR V
D
CO
2
level was higher
(⬍ 0.5% CO
2
as an 8-h time-weighted average, is normal),
these standards apply to the ambient workplace atmosphere,
not to the FFR V
D
. Nonetheless, breathing-environment CO
2
⬎ 3% has been associated with detrimental physiological
effects,
25
and prolonged breathing of CO
2
at greater than the
atmospheric level can cause symptoms (eg, headache, anxi-
ety, and confusion) and the additional physiological stress of
compensatory mechanisms. Interestingly, we found no sig-
nificant FFR V
D
CO
2
differences between the FFR and the
FFR-with-valve, despite that the exhalation valve ostensibly
prevents CO
2
buildup by allowing beneficial flow-streams
that decrease FFR V
D
.
17
However, the exhalation valve is
activated only at a certain breathing-pressure threshold that
may not have been attained under our study conditions. Irre-
spective of level of function, the exhalation valve may not
dramatically impact FFR V
D
CO
2
because, despite allowing
a smaller proportion of the exhaled breath to be retained in
the FFR V
D
, the retained fraction is the terminal portion of
Table 8. Comfort Scores
Comfort Score* (mean ⫾ SD) P
Control at 1.7 miles/h vs control at 2.5 miles/h 1.10 ⫾ 0.32 vs 1.30 ⫾ 0.67 .34
Control vs FFR without valve, at 1.7 miles/h 1.10 ⫾ 0.32 vs 1.15 ⫾ 0.36 .77
Control vs FFR with valve, at 1.7 miles/h 1.10 ⫾ 0.32 vs 1.44 ⫾ 0.67 .13
Control vs FFR without valve, at 2.5 miles/h 1.30 ⫾ 0.67 vs 1.67 ⫾ 0.53 .07
Control vs FFR with valve, at 2.5 miles/h 1.30 ⫾ 0.67 vs 1.43 ⫾ 0.45 .47
FFR with valve vs FFR without valve, at 1.7 miles/h 1.44 ⫾ 0.67 vs 1.15 ⫾ 0.36 .20
FFR with valve vs FFR without valve, at 2.5 miles/h 1.43 ⫾ 0.45 vs 1.67 ⫾ 0.53 .02
* Comfort score on 1–5 scale, from most comfortable to least comfortable.
FFR ⫽ filtering facepiece respirator
Table 9. Exertion Scores
Exertion Score* (mean ⫾ SD) P
Control at 1.7 miles/h vs control at 2.5 miles/h 0.50 ⫾ 0.85 vs 1.05 ⫾ 1.16 .01
Control vs FFR without valve, at 1.7 miles/h 0.50 ⫾ 0.85 vs 0.83 ⫾ 1.30 .13
Control vs FFR with valve, at 1.7 miles/h 0.50 ⫾ 0.85 vs 0.88 ⫾ 1.26 .07
Control vs FFR without valve, at 2.5 miles/h 1.05 ⫾ 1.16 vs 1.11 ⫾ 1.30 .78
Control vs FFR with valve, at 2.5 miles/h 1.05 ⫾ 1.16 vs 0.93 ⫾ 0.91 .63
FFR with valve vs FFR without valve, at 1.7 miles/h 0.88 ⫾ 1.26 vs 0.83 ⫾ 1.30 .65
FFR with valve vs FFR without valve, at 2.5 miles/h 0.93 ⫾ 0.91 vs 1.11 ⫾ 1.30 .38
* Exertion score on 1–5 scale, from no exertion to maximum exertion.
FFR ⫽ filtering facepiece respirator
Table 10. Study Subjects’ Complaints About Wearing Filtering
Facepiece Respirator*
At Treadmill Speed
1.7 miles/h
At Treadmill Speed
2.5 miles/h
FFR
With
Valve
FFR
Without
Valve
FFR
With
Valve
FFR
Without
Valve
Breathing difficulty 1101
Dizziness 2001
Lightheadedness 0001
Facial warmth 4366
Facial sweating 0001
Facial itching 2101
Facial irritation 1011
Facial pinching 0120
* Subjects could register multiple complaints.
FFR ⫽ filtering facepiece respirator
PHYSIOLOGICAL IMPACT OF THE N95 FILTERING FACEPIECE RESPIRATOR ON HEALTHCARE WORKERS
RESPIRATORY CARE • MAY 2010 VOL 55 NO 5 575

the exhalation, which has the highest CO
2
concentration
(nearly equal to that of arterial blood).
25
Moisture retention in the FFR occurs with prolonged
use and may increase the breathing resistance.
26
In the
current study the average moisture gain over 1 hour was
0.11 g with the FFR and 0.13 g with the FFR-with-valve
(P ⫽ .46). This small amount of retained moisture is re-
lated to low exertion, the hydrophobicity of the studied
FFRs, and the short duration of use. With an FFR model
we used in the current study, other researchers found a
water-vapor permeability (ie, rate of water vapor diffusion
through the respirator) of 0.06 g/24 h/cm
2
.
27
Although the
exhalation valve is partly designed to decrease moisture
buildup in the FFR, this effect may become manifest only
at higher work rates than we used in the current study.
Despite significant differences in the exertion scores
between controls at the 2 work rates (P ⫽ .01), there were
no significant differences between FFR and FFR-with-
valve compared to control, or for FFR compared to FFR-
with-valve (see Table 9). A recent study reported that an
N95 FFR-with-valve was associated with greater wear tol-
erability by healthcare workers than was an N95 FFR with-
out valve during extended wear (7.7 h vs 5.8 h).
28
It may
be that any benefit from an exhalation valve in the health-
care setting might come only at higher work rates (eg, as
might be expected in a surge situation) or during lengthy
use (eg, continuous wear for several hours).
Comfort is an important factor in healthcare worker ad-
herence to FFR use.
28
Although the comfort scores were not
significantly different when comparing control and FFR at
either work rate in the current study, FFR-with-valve was
rated more comfortable than FFR-without-valve at 2.5 miles/h
(P ⫽ .02) (see Table 8). In the current study we found several
comfort-related issues, including warmth, sweating, itching,
and irritation (see Table 10), and similar complaints were
reported with both types of FFR, despite the fact that the
exhalation valve should presumably enhance comfort by elim-
inating heat and humidity from the FFR microenvironment.
However, a recent healthcare worker study also reported no
differences in absolute numbers between the users of FFR
with and without exhalation valve who complained of heat,
28
which suggests that heat dissipation through the exhalation
valve may only be realized at work rates above those nor-
mally experienced by healthcare workers. The number of
complaints from subjects, in the present study and another
study,
28
is an important issue because comfort significantly
impacts the use of respiratory protective equipment.
The present study was conducted to develop baseline data
on the physiological impact of FFR and FFR-with-valve on
healthcare workers. Our data indicate that FFR and FFR-
with-valve for 1 hour at 2 low-intensity work rates resulted in
minimal additional physiological burden. This finding is sup-
ported by a recent study that found FFR tolerance among
subjects with respiratory diseases.
29
Further, the lack of sig-
nificant effect on S
pO
2
and P
tcCO
2
suggests that specific sub
-
populations of healthcare workers (eg, pregnant, well-con-
trolled asthma) who are considered to be potentially adversely
affected by respiratory protective equipment,
18
might safely
wear FFR or FFR-with-valve for up to 1 hour at low energy
expenditure, though the possibility of CO
2
retention requires
further study. Our data also suggest that, at low work rates up
to 1 hour, FFR-with-valve may offer no physiological advan-
tages over FFR-without-valve, so the higher cost of FFR-
with-valve may not be warranted in a low-work-rate scenario.
Further human studies are required to determine the physio-
logical burden of FFR over longer periods (eg, surge situa-
tions during respiratory infectious outbreaks) and the impact
of different styles of FFR (eg, duck bill, flat fold, or cup-
shaped).
Limitations
Our sample included only 10 subjects, who were young
(mean age 25 y). The average age of a registered nurse in the
year 2000 was 45 years; only 9.1% were ⬍ 30 years of age.
30
We examined only a few FFR models, and the study
was conducted in a laboratory setting, rather than in a
health-care facility. However, laboratory studies may ac-
tually represent the upper-boundary response rather than
the typical responses in field studies.
29
Our use of respi-
ratory inductive plethysmography for V
T
is not as accurate
as other laboratory methods (eg, pneumotachograph, spi-
rometer), but such equipment is not readily amenable for
use with FFR. Recent investigations that compared respi-
ratory inductive plethysmography to pneumotachogra-
phy
31-33
found good to excellent correlation (r
2
0.60 – 0.97)
for V
T
. Some variability (overestimation of P
CO
2
) has been
noted in P
tcCO
2
measurements, compared to arterial CO
2
measurements, which might have been due to differences
in the patient populations tested, sensor temperature, and
inter-subject differences.
34
However, the Tosca 500 mon-
itor allows for noninvasive constant monitoring of P
tcCO
2
,
and studies have demonstrated good correlation between
P
tcCO
2
and arterial CO
2
during exercise testing.
35-38
Conclusions
Healthcare worker use of FFR and FFR-with-valve for
1 hour at clinically realistic low work rates had only mild
physiological impact. At a low work rate, for up to 1 hour,
FFR-with-valve may offer no physiological advantage over
FFR-without-valve. The mixed inhalation/exhalation O
2
and
CO
2
levels in the FFR V
D
microenvironment did not meet the
Occupational Safety and Health Administration’s standards
for workplace ambient O
2
and CO
2
concentrations. FFR com
-
fort issues need to be addressed further to maximize health-
care worker adherence to FFR use.
28
Future studies will also
need to address the possibility of CO
2
retention in susceptible
PHYSIOLOGICAL IMPACT OF THE N95 FILTERING FACEPIECE RESPIRATOR ON HEALTHCARE WORKERS
576 RESPIRATORY CARE • MAY 2010 VOL 55 NO 5

individuals and the physiological impact of FFR (with and
without exhalation valve) worn for longer periods.
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RESPIRATORY CARE • MAY 2010 VOL 55 NO 5 577