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wileyonlinelibrary.com/journal/ina Indoor Air. 2019;29:1040–1049.
© 2019 John Wiley & Sons A/S.
Published by John Wiley & Sons Ltd
1 | INTRODUCTION
Since the thermoregulatory and sleep regulatory systems of human
are interact, thermal environment is one of the primary causes of
sleep disturbance, which has been evidenced by many human sub-
ject studies.1,2 With climate change, higher temperatures during the
daytime are leading to persistently higher temperatures at night.
Toward better insulation of homes, warm bedrooms are more and
more commonly observed even during a cool summer. Two convinc-
ing studies, one review and another a large sample data analysis
found negative effects of higher temperatures on sleep time and
sleep quality, especially among the most vulnerable populations
including the elderly.3,4 Many crippling healthcare systems, such as
heart disease, obesity, diabetes, cancer and critically, Alzheimers, all
have recognized causal links to a lack of sleep.5 However, the elderly
individuals usually fail to connect their deterioration in health with
their deterioration in sleep.
As a consequence of biological aging, many factors related to
thermoregulation are impaired in the elderly.6-8 Studies on awake
subjects found that the elderly have reduced sensory efficiency of
and abilit y to detect cold and warm environments. They have atten-
uated sweating capacity, abilit y to transport heat from body core
to skin, and lower cardiovascular flexibility. All these changes make
the elderly more vulnerable to extreme thermal conditions. During
sleeping period, even mild heat exposure may increase thermal load,
suppress the decrease of rectal temperature, and decrease sleep
Received: 16 July 2019
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Revised: 20 August 2019
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Accepted: 25 August 2019
DOI : 10.1111 /in a.12599
ORIGINAL ARTICLE
Elevated airflow can maintain sleep quality and thermal
comfort of the elderly in a hot environment
Li Lan1 | Lulu Xia1 | Jieyu Tang1 | Xiaojing Zhang2 | Yanbin Lin3 |
Zhentao Wang3
1Depar tment of A rchitecture, S chool of
Design, Shanghai Jiao Tong University,
Shanghai, China
2Key Laboratory of Green B uilt Envir onment
and Energy Efficient Techno logy, Beij ing
University of Technology, Beijing, China
3School of Medicine Affiliated Ninth
People's Hospital, Shanghai Jiao Tong
University, Shanghai, China
Correspondence
Li Lan, Depar tment of Architec ture, School
of Design, Shanghai Jiao Tong University,
Shanghai, China.
Email: lanli2006@sjtu.edu.cn
Funding information
Nationa l Natura l Science Foundation of
China, G rant/Award Number : 51778359;
51478 26 0
Abstract
The effect of elevated air flow on sleep quality was investigated with 18 elderly.
Three airflow conditions were set: ceiling fan/30°C/max.0.8 m/s and mean 0.7 m/s,
task fan/30°C/max.0.8 m/s and mean 0.6 m/s, and thermally neutral /27°C/0.2 m/s.
Sleep quality was evaluated objectively by analysis of electroencephalogram signals
that were continuously monitored during the sleeping period. Urinary cortisol con-
centrations were analyzed to measure the activity of sympathetic nervous system.
No significant difference in sleep quality, thermal comfort, or cortisol concentration
was found between the ceiling fan and the neutral condition. The duration of total
sleep time decreased by 35 minutes, the duration of REM sleep decreased by 15 min-
utes, and the cortisol concentration in the morning increased by 50 ng/mL in the
task fan than the other two conditions. Compared with ceiling fan, less heat load was
removed in the task fan condition, possibly due to the lower air speed. This study
shows that even small heat load led to reduced sleep quality and overactive sympa-
thetic ner vous system of the elderly. By supplying an airflow of 0.8 m/s evenly over
the human body, the elderly could maintain sleep quality and thermal comfort at an
air temperature that was 3 K higher than the neutral temperature.
KEY WORDS
age, airflow, elderly, heat, sleep quality, thermal comfort
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LAN e t AL.
quality of older men.9 Raymann and Van Someren (2008) found that
the elderly people have diminished capability to recognize the opti-
mal temperature for sleep initiation, which may contribute to their
poor sleep.10These evidence suggest that it is extremely important
to provide a thermally comfortable sleeping environment for the el-
derly to maintain their sleep quality and health.
Full air conditioning may be one of the easiest ways to improve
thermal environment. However, due to economic reasons, thermal
preference, or living habits, many elderly people prefer to use fan
instead of air conditioner during night-time sleep period in hot sum-
mer. Elevated air speeds can be used to improve thermal comfort
beyond the maximum temperature limit. ASHRAE Standard 55-2017
specifies the air speeds necessary to compensate for a tempera-
ture increase above the warm-temperature border when people are
awake.11 Increased air flow (1.7m/s) has been shown to reduce the
heat load and wakefulness of young people in the warm humid cli-
mate.12 The higher air velocity increased the convec tive heat loss and
decreased the skin and rectal temperatures and the rate of sweating;
consequently, sleep efficiency was improved in the warm humid cli-
mate. Local cooling applied to large body sections maintained good
sleep and improved thermal comfort of young people in a hot envi-
ronment.13 To age well in place, the elderly should be able to con-
trol their own thermal environment with their preferred strategies.14
However, to our knowledge, no study on the effects of airflow on
sleep quality of elderly people has yet been published. In the present
study, the effects of two levels of airflow supplied by two types of
fans on sleep qualit y and thermal comfort of elderly people were in-
vestigated, aiming to confirm whether the higher air temperature in
sleeping environment could be effectively offset by using of elevated
airflow, compared to the thermally neutral environment.
2 | METHOD
2.1 | Participants
Eighteen elderly people aged over 65 years old (10 males and 8 fe-
males, 71 ± 5 years old, body mass index (BMI): 23.1 ± 2.7 k g/m2), par-
ticipated in this experiment. The participants were non-smokers, free
of chronic diseases, asthma, allergy, and hay fever and were not tak-
ing any medications. The information was obtained from a question-
naire distributed during recruitment; none was examined medically.
They did not suffer sleep disorder, which was verified by using of
Pittsburgh Sleep Quality Index (PSQI) questionnaire, assessed sleep
quality and disturbances over a one-month time interval.15 If the can-
dida te had a PSQ I gl oba l sc or e ≥ 8, whi ch is su gge stive of a sig nif ic ant
sleep disturbance, he/she was excluded. And the participants were
supposed to have a good living abilit y, which was obtained by using
activities of daily living (ADL) scale.16 If the candidate had an ADL
global score ≤ 20, which suggested a bad living ability, he/she was
excluded. On the days of the experiment, the participants were re-
quired to avoid alcohol, c affeine, and intense physical activity. Their
emotional state was investigated with the Profile Of Mood States
Short Form (POMS-SF) on arrival for each experimental session.17
No significant difference in the mood states of each participant was
observed between experimental days. The participants were in-
structed to wear the same short-sleeved nightshir t in all exposure.
At night, they slept on a mattress bed and covered with a sheet of
0.96 mm in thickness, with an estimated insulation level (including
clothing) of 1.64 clo when a 67% of body surface area was covered.
Results from questionnaire survey on the participants and observa-
tion of experiment performers confirmed that the participants used
similar coverage percentage of sheet in all experimental conditions.
All protocols were approved by the university's ethics committee
and conformed to the guidelines contained within the Declaration
of Helsinki Verbal and written informed consent was obtained from
each participant prior to the participation in the experiment.
2.2 | Approach and facility
The experiment was c arried out from July to August, 2018, in
Shanghai in two identical field sleep chambers, which were ar-
ranged and decorated to simulate bedroom. Three experiment al
conditions were investigated, ie, Condition 1: using a task fan
(five blades, 0.25 m in diameter), room temperature was 30°C;
Condition 2: using a ceiling fan (three blades, 0.42 m in diameter,
downward in direction), room temperature was 30°C; Condition 3:
the neutral condition, the room temperature was set to be ther-
mally neutral at 27°C by using air conditioner. With a bed covering
of 1.64 clo, the young people felt thermally neutral when slept
at 26°C, as indicated in our former experiments.18 Considering
that older adults prefer a warmer environment than younger sub-
jects;6 in this experiment, the thermally neutral temperature was
set to be 27°C , ie, 1°C higher than 26°C. In the task fan or ceil-
ing fan condition, the maximum air velocity around human body
was around 0.8 m/s, and the air temperature was maintained to
be 30°C. Previous study shows that the young adult felt hot and
had poorer sleep quality (longer time to fall sleep and shorter deep
sleep time) at 30°C as compared to neutral condition of 26°C .18
Practical Implications
• Since many factors related to thermoregulation are im-
paired with biological ageing, the elderly are more vul-
nerable and thus their sleep quality are more disrupted
by non-neutral thermal conditions. This study also con-
firms that the sleep quality and health of the elderly was
very vulnerable to heat exposure.
• Many elderly people prefer to use fan than air condi-
tioner at nighttime in hot summer. This study shows
that if efficient air flow was supplied by fans, the elderly
could maint ain their sleep quality, health and thermal
comfort in a hot as compared to a thermally neutral en-
vironment, thus allowing them to control the thermal
environment with their preferred strategies.
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LAN et AL.
While the authors observed that some elderly still used fans in-
stead of air conditioners when their bedroom air temperatures
were up to 30°C in a field survey in Shanghai [not published]. As
confirmed in a preliminary experiment, the elderly felt neutral at
27°C and did not report discomfort at the higher velocity in ceil-
ing fan or task fan condition. The air velocity was 0. 2 m/s in the
neutral condition. Figure 1 shows the location of task fan and ceil-
ing fan relative to the bed in the room. The air velocities were
measured with an ultrasonic anemometer (Model DA-600, range:
0 m/s-10 m/s, accuracy: ± (2% + 0.03 m/s of absolute value of indi-
cated value)) in the main area of the bed (Figure 2). The maximum
air speed was around 0.8 m/s in the two fan conditions, while the
mean value of air speed at the bed area was around 0.7 m/s in
ceiling fan condition, and around 0.6 m/s in the task fan condition.
The air speed was less evenly distributed, and the averaged value
was lower in the task fan than the ceiling fan condition.
The participants were randomly assigned to three groups, and
each group was exposed to the three experimental conditions in a
Latin-square design, balanced for order of presentation. There was
a 3-day inter val between any two experimental nights. During each
exposure in the chamber, electroencephalogram (EEG) for brain
wave, electrooculogram (EOG) for eye movements and electromyo-
gram (EMG) for chin muscle tension were continuously monitored,
to obtain the basic information required for quantifying sleep qual-
ity. The par ticipants reported sleep qualit y after waking and thermal
comfort both before going to bed and after getting up. Their urine
samples were collected before sleep and after getting up.
The background air temperature and relative humidity were re-
corded at intervals of 1 minute by placing a data logger at each of two
positions: the middle of the bed head and the bed end, both at a height
of 0.4 m above the bed. The data logger (TR-76Ui, T&D corporation)
had a built-in temperature sensor (range: 0°C-55°C, accuracy: ±0.5°C),
FIGURE 1 Layout of the experiment
room
FIGURE 2 Air velocit y measured at different point s of the bed
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LAN e t AL.
a humidity sensor (range: 10%-95%, accuracy: ±5%), and a CO2 sensor
(range: 0-9999 pm, accur acy: ±50 ppm + 5% of reading at 500 0 ppm or
less). The globe temperature was measured in the middle of the room
at interval of 5 minutes (AZ8778, range: 0°C-50°C, accuracy: ±0.8°C).
2.3 | Measurements
2.3.1 | Physiological measurements
Polysomnography (PSG)
EEG (F4-M1, C4-M1, O2-M1, F3-M2, C3-M2, O1-M2), bilateral EOG,
and chin EMG were recorded using a portable polysomnographic
sleep recording system (Somté 32 PSG, Compumedics, Australian).
The EEG, EOG, and EMG of a noc turnal sleep period is characterized
by alternating periods of non-rapid-eye movement (NREM) sleep,
subdivided into three (N1, N2 and N3) st ages, and rapid-eye move-
ment (REM) sleep. Sleep stages were visually scored ever y 30 sec-
onds based on the 2007 AASM Manual for the Scoring of Sleep and
Associated Events.19 The calculated sleep statistics included Total
Sleep Time (TST)—total time scored as sleep (in minutes), Sleep
Efficiency (SE)—percentage of time in bed actually spent sleeping (%),
Number of awakenings (NOA), Wake time after sleep onset (WASO,
in minutes), and Sleep Onset Latency (SOL)—the time between lights
off and the first occurrence of stage N1 sleep (the start of sleep) (in
minutes), Total duration of stage N1, N2, N3, and REM stage (in min-
utes). Lower TST and SE, longer SOL or WASO, lower duration of
N3 or REM stage, and larger NOA are all indicators of poorer sleep
quality.
Skin temperature
Skin temperature and relative humidity (RH) at seven sites (forehead,
chest, arm, hand, thigh, leg, and foot) were measured at 30s intervals
using PyroButtons (Pyrobutton-TH; Dallas, TX , USA). Temperature:
−20°C to +85°C, ±0.3°C accuracy, ±0.0625°C resolution; Humidity:
3.4% to 97.3%, ±2% RH accuracy, and ±0.04% RH resolution. The
sensor side, with a protruding edge, of the PyroBut ton was fixed
onto the skin with adhesive tape. Mean skin temperature (MST ) was
calculated as the mean of local skin temperatures multiplied by their
respective weight factors.20 Mean relative humidity (MRH) was cal-
culated using the same weight factors as MST.
Biomarkers in urine
Interactions between human sleep structure and the concentra-
tion of a stress hormone called cortisol, which is triggered by the
overactive sympathetic nervous system, have been observed;
cortisol concentrations tend to increase in periods with increased
occurrence of light sleep or wakefulness.21 In sleep-deprived peo-
ple, a chronic increase has been found in cortisol. In the present
study, the cor tisol concentration in urine sample was measured.
Participants were required to collect a urine sample before and
after each sleep period. The urine samples were centrifuged for
25min at 40 00 r/min and frozen and stored in a freezer at −20°C
before being sent for analysis. The analysis was performed by
an external specialized laboratory using a competitive inhibition
enzyme immunoassay technique to determine the concentration
of urinar y cortisol. The minimum detectable does is 5.15 ng/mL,
with an intra-assay variation <10% and an inter-assay variation of
<12% .
2.3.2 | Subjective questionnaires
Subjective sleep quality
The participants repor ted their subjective perception of sleep
quality on seven scales including the calmness of sleep, ease of fall‐
ing asleep, ease of awakening, freshness after awakening, satisfaction
with sleep, night‐time awakening frequency, and sufficient sleep; higher
score indicates higher sleep quality.18
Perception of thermal environment
A 7-point scale (-3-cold, -2-cool, -1-slightly cool, 0-neutral, 1-
slightly warm, 2-warm, and 3-hot) was used to report thermal sen-
sation. Overall thermal comfort was reported on a 6-point scale
(-2-very uncomfortable, -1-uncomfortable, -0.01-just uncomfort-
able, 0.01-just comfortable, 1-comfortable, and 2-very comfort-
able).Perceived airflow was reported on a 6-point scale (-2-clearly
unacceptable, -1-unacceptable, -0.01-just unacceptable, 0.01-just
acceptable, 1-acceptable, and 2-clearly acceptable). The percep-
tion of humidity was assessed with a 3-point scale (-1-slightly
humid, 0-neutral, and 1-slightly dry). The participants assessed
the sleep environment as pleasurable (+1), neutral (0), or unpleas-
urable (−1).
FIGURE 3 Experimental procedures for an all-night sleep
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LAN et AL.
2.4 | Experimental procedures
The expe rimental pr ocedures for a n all-night sleep a re shown in Figur e 3.
The participants arrived at the waiting room (which was adjacent to
their sleeping chambers and was maintained at 26°C) at 20:30, rested
for 30 minu tes in order to adapt thermally, wearing shor t-sleeved night-
shirts (the estimated clothing value was 0.5 clo), filled out the POMS
questionnaire (Q1) for 10 minutes, and collected their urine samples for
10 minutes. Then they entered their sleeping chamber, filled out ther-
mal environment perception questionnaires (Q2) for 10 minutes after a
30 minutes adaptation, and have the physiological parameter sensors
attached, which lasted 30 minutes. At 22:30, the participants lay on
the bed and started sleep period when the lights were turned off. The
physiological parameters were continuously measured throughout the
night until the participants were woken up promptly at 6:30 in the next
morning. After get ting up, the participants filled out the thermal envi-
ronment perception and sleep quality questionnaires (Q2, Q3) in their
sleeping chamber. In addition to their perception of thermal comfort
at that moment, they were also asked to recall their thermal sensation
during the night. Finally, they collected their urine samples again.
2.5 | Statistical analysis
The data were first tested for normalit y using Shapiro-Wilk's W
test. Normally distributed data were subjected to analysis of vari-
ance with General Linear Model (GLM) in a repeated measures de-
sign and a Paired Samples T test. Not-normally distributed data were
analyzed using Friedman's One-Way analysis of variance and the
Wilcoxon Matched-Pairs Signed-Ranks test. The significance level
was set to be .05 (P < .05). The ef fect size (ES), the dif ference be-
tween the true value, and the value specified by the null hypothesis,
was derived as an indicator of whether the dif ference was of practi-
cal importance.22
3 | RESULTS
3.1 | Physical environment parameters
Table 1 shows the measured air temperature, relative humidit y, and
CO2 concentration of the sleeping chamber in the three conditions.
The air temperatur e did not deviate system atically from the designed
level and varied within a narrow range. No difference in relative hu-
midity or CO2 concentration was found among the conditions. The
measurement results of air velocity were shown in Figure 2.
3.2 | Thermal comfort
Compared with the air conditioning room, the participants felt
warmer when slept at the task fan or ceiling fan condition; but most
of them felt thermally neutral (−0.5 < thermal sensation vote < +0. 5)
in the three conditions (Figure 4). Most of them felt thermally com-
fortable and reported high acceptability of airflow in the three
conditions; no significant dif ference was found in thermal comfort,
humidity, or acceptability of air flow among the three conditions. The
participants assessed the room to be more pleasant in the neutral
than the task fan condition; no significant difference in pleasure was
found bet ween other conditions (Figure 5).
3.3 | Sleep quality
EEG, EOG, and EMG recordings show that the total sleep time (TST)
and duration of REM sleep were significantly lower in the t ask fan
condition than the other two conditions ( TST: 307 ± 46 minutes in
the task fan, 341 ± 47 minutes in the ceiling fan, and 315 ± 49 min-
utes in the neutral condition; REM sleep: 51 ± 20 minutes in the
task fan, 65 ± 25 minutes in the ceiling fan, and 66 ± 31 minutes in
the neutral condition); no significant difference in these two sleep
quality indicators was found between the ceiling fan and the neutral
condition (Figure 6). Table 2 summarizes the results of other objec-
tive sleep quality indicators as calculated from the EEG, EOG, and
EMG recordings. No significant difference was found in these sleep
quality indicators among the three conditions.
Table 3 shows the results of subjective sleep quality assess-
ment. No significant difference was found in subjective sleep qualit y
among the three conditions; the participants rated that they had rel-
atively good sleep quality in all the three conditions.
3.4 | Skin temperature
Figure 7 shows the variation of mean skin temperature and mean
skin relative humidity throughout the sleeping period; higher skin
temperature and skin relative humidity were observed in the task
Conditions
Task fan, at 30 °C
Ceiling f an, at
30°C
Air condi-
tioner, at 27°C
Parameters
Air temperature (oC) 29.7 ± 0.2 29.8 ± 0.2 26.7 ± 0.2
Mean radiant tempera-
ture (oC)
29.5 ± 0.3 29.7 ± 0.4 26.9 ± 0.3
Relative humidity (%) 55 ± 7 56 ± 6 61 ± 5
CO2 (ppm) 1399 ± 204 1405 ± 272 1402 ± 192
TABLE 1 physical environment
measured at the three conditions
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LAN e t AL.
fan or ceiling fan condition, compared to the 27°C condition. Similar
variation trends in skin temperature and skin relative humidity were
observed in the three conditions. The skin temperature increased
after lights off and then decreased gradually and began to fluctuate
with small variations. High-skin relative humidity was obser ved in
the three conditions; it increased gradually after lights off and lev-
eled off at about 95%.
Figure 8 illustrates the averaged skin temperature and skin rela-
tive humidity at the seven body positions. The skin temperatures of
the seven body positions and the MST were higher in the task fan
than the neutral condition; they were also slightly higher compared
to the ceiling fan condition. The skin temperatures of forehead, thigh
and leg, and the MST were higher in the ceiling fan than the neutral
condition. As to the skin relative humidity, less significant increases
were obser ved; the skin relative humidity of the chest, thigh, and leg
area were higher in the task fan or the ceiling fan condition, com-
pared to the reference condition.
3.5 | Cortisol
Figure 9 shows the results of cortisol concentration measured be-
fore and after sleep. No significant difference in cortisol concentra-
tion of urine samples collected before sleep was found among the
three conditions. While after getting up, the cortisol concentration
was significantly higher in the task fan (195 ± 128 ng/mL) than the
neutral condition (142 ± 90 ng/mL). No significant difference in cor-
tisol concentration measured after getting up was found between
the ceiling fan and the neutral condition.
4 | DISCUSSION
Both objective sleep quality measurement and subjective assess-
ment show that the elderly maintained thermal comfort and con-
ventional sleep quality at a high air temperature of 30 °C, when a
ceiling fan was used. Their thermal sensation was close to thermally
neutral, and they felt thermally comfortable in the ceiling fan condi-
tion (Figure 3). No significant difference in sleep quality, perceived
pleasure, or cortisol concentration was found bet ween the neutral
condition and the ceiling fan condition (Figures 5 and 6, Table 2).
It has been observed that the stress hormone (cortisol) was more
sensitive than sleep quality indictors to changes in thermal environ-
ment, in which a pronounced increase in secretion occurred without
changes in polygraphic EEG criteria.23 The above results suggest
that, by using of ceiling fan, the heat load was removed effectively,
thus allowing the elderly maintained a normal sympathetic nervous
FIGURE 4 Thermal sensation and
thermal comfort votes assessed before,
during and after getting up in the three
conditions (Error bars represent the
standard deviation of mean, ES-effect
size)
FIGURE 5 Assessment of pleasure in the three conditions (Error
bars represent the standard deviation of mean, ES-effect size)
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LAN et AL.
system and a conventional sleep at an air temperature of 30°C. This
claim is par tly supported by the results of mean skin temperature,
which was 34.6 ± 0.4°C in the ceiling fan condition, and 34.3 ± 0.4°C
in the neutral condition (Figure 8). Although the mean skin tempera-
tures were higher in the ceiling fan conditions, they are similar to
the mean skin temperature observed in thermally neutral environ-
ments24 and lower than 35°C, which was observed in young adults
at an air temperature of 30°C without air flow18 and in older adults at
an air temperature of 32°C9 when their sleep quality were impaired.
These results may suggest that thermoregulation of the elderly in
the ceiling fan condition was within the tolerable range and had no
negative impact on sleep quality. Airflow usually should be con-
trolled in air conditioning room to avoided downdraft, but in warm
environment it can be higher to offset temperatures above warm-
temperature boundaries. In the latest updated A SHRAE Standard
55, if occupant s do not have control over the local air speed, the
upper limit to average air speed is 0.8 m/s for temperatures above
25.5°C.11 For sleeping people, about one-third part of their body is in
contact with bed and other two thirds not.24 Therefore, it is possible
to increase convective heat loss by increase of airflow. A high air
velocity of 1.7 m/s was shown to reduce the duration of wakefulness
of young adult in a warm humid condition.12 However, considering
that people, especially the older adults, are more vulnerable to their
thermal environment during the long-time sleep period, in the pre-
sent study, the maximum air velocit y was set to be 0.8m/s, which is
the upper limit stipulated in ASHRAE Standard 55. This velocity was
confirmed to be acceptable and pleasurable by the elderly for sleep
(Figure 5).
However, poorer sleep quality (shor ter total sleep time and du-
ration of REM sleep), higher urinar y cortisol concentration (which in-
dicates overactive sympathetic ner vous system) in the morning, and
lower pleasure were observed in the task fan condition, compared
FIGURE 6 The total sleep time (TST) and duration of REM
sleep are significantly lower at the task fan condition (Error bars
represent the standard deviation of mean, ES-ef fect size)
Parametersa
Conditions
PESTask fan, at 30 °C
Ceiling f an, at
30°C
Air conditioner,
at 27°C
SE (%) 65.3 ± 11.2 69.1 ± 7.6 66.5 ± 11.7 .32 0.33
SOL (min) 14.2 ± 12.9 12.4 ± 7.2 17.7 ± 16.2 .43 0.26
SRL (min) 84.5 ± 45.6 108.9 ± 67.8 80.0 ± 39.7 .23 0.36
WASO (min) 145.6 ± 60.5 137.4 ± 33.9 137.5 ± 54.0 .71 0.17
NOA 27.3 ± 10.4 24.8 ± 8.6 24.8 ± 8.6 .26 0.36
Total duration of (min)
Stage N1 57.7 ± 55.4 63.9 ± 38.2 52.3 ± 41.7 .43 0.27
Stage N2 133.0 ± 37.7 140.7 ± 40.2 128.1 ± 35.3 .58 0.22
Stage N3 70.7 ± 31.3 77.2 ± 29.3 75.6 ± 29.6 .43 0.28
aNotation of the parameters are explained in 2. 3.1.
TABLE 2 Sleep quality parameters
derived from EEG, EOG, and EMG
recordings
Parameters
Conditions
PES
Task fan, at
30°C
Ceiling fan,
at 30°C
Air condi-
tioner, at 27°C
Calmness of sleep 3.76 ± 0.83 3.88 ± 1.05 3.94 ± 0.66 .67 0.15
Ease of fallin g asleep 3.35 ± 0.86 3.47 ± 1.07 3.71 ± 0.85 .30 0.28
Ease of awakening 4.06 ± 0.56 3.94 ± 0.83 3.94 ± 0.75 .71 0.15
Freshness after awakening 3.59 ± 0.71 3.82 ± 0.88 3.65 ± 0.86 .42 0.23
Satisfaction about sleep 3.53 ± 0.72 3.53 ± 1.01 3.82 ± 0. 81 .64 0.31
Night‐time awakening frequency 2.71 ± 0 .92 2.82 ± 0.73 2.88 ± 0.78 .67 0.17
TABLE 3 Assessment of subjective
sleep quality in the three conditions
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LAN e t AL.
to the ceiling fan and the neutral condition (Figures 5, 6, and 9). The
decrease of REM sleep due to heat exposure is consistent with previ-
ous studies. The sensitivity of the thermoregulatory system in REM
sleep is lower than in slow wave sleep (SWS), so REM sleep was more
disturbed by thermal transients than SWS.25 Okamoto-Mizuno et al
(2004) also observed a decrease of REM sleep in the elderly when
they were exposed to mild heat (at an air temperature of 32°C).9
Compared with the ceiling fan condition, the increased skin tem-
perature (Figure 8) suggest that the less evenly distributed and thus
lower mean airflow(Figure 2) in the task fan condition did not remove
enough heat load from human body and consequently leading to
poorer sleep quality and overactive sympathetic nervous system. The
difference in cooling effec ts bet ween task fan and ceiling fan can be
explained by the distribution of airflow over the bed area(Figure 2);
the maximum air velocity in these two conditions are similar, about
0.8 m/s, but the air velocit y was more evenly distributed over the bed
area and the average air speed was higher in the ceiling fan condition;
for the task fan condition, with the increase of distance to the fan, the
FIGURE 7 Variation of mean skin
temperature and mean relative humidity
throughout the sleep period (Error bars
represent the standard deviation of mean)
FIGURE 8 Whole night-averaged skin
temperature and skin relative humidity in
the three conditions (Error bars represent
the standard deviation of mean)
1048
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LAN et AL.
air velocity gradually decreased to 0.49 m/s in the inner side of the
bed. Thus, in the task fan condition, a part of the human body could
not loss as much heat as in the ceiling fan condition. The difference
in air speed distribution on bed between the task fan and the ceiling
fan may attribute to several influencing factors, including the fan size,
blade shape and number, airflow direction, and air turbulence etc.26-
28 Compared with Okamoto-Mizuno et al’ s study, which observed
decreased sleep quality of the elderly at an air temperature of 32°C,9
a lower air temperature and a higher air velocit y was set in the task
fan condition in the present study. The above analysis suggests that
sleep quality of the elderly is very susceptible to heat and that 30°C
is close to the upper limit air temperature in which the elderly can
maintain thermal comfort and sleep quality with the help of elevated
airflow. As shown in Figure 9, the cortisol concentration in the morn-
ing was found to be significantly higher accompanying a poorer sleep
quality in the task fan than the neutral condition. One undesirable
consequence of the sustained deluge of cortisol is the constriction
of those blood vessels, triggering an even greater increase in blood
pressure. So the present study confirms that poor sleep quality may
lead to health problems of elderly people.
Compared with younger adults,1,12,13,18 the present study found
that the older adult s have decreased sleep efficiency, shorter dura-
tion of slow wave, and longer wakefulness (Figure 6, Table 2). Three
key changes in sleep of the elderly have been confirmed in previous
studies, including reduced deep sleep quantit y and quality, reduced
sleep efficiency, and sleep fragmentation.5 The middle-frontal re-
gions of the brain, which suffer the most dramatic deterioration
with aging are, unfortunately, the very same deep sleep generating
regions.29 The impaired sensory and thermoregulation systems,
the diminished capability to recognize the optimal temperature for
sleep initiation all leading to poorer sleep quality in the elderly.6-8 ,10
However, scientific findings support the fact that older adults still
need a full night of sleep, just like young adults.29 Since sleep qual-
ity is a critical determinant of health, such conflic t between abilit y
and need requires scientist s, clinical doctors and engineers to work
together to provide a bedroom that help to facilitate the sleep pro-
cess of the elderly. As to the thermal environment, ensuring that
the bedrooms are reasonabl comfortable without heavily relying
on heating and cooling is critical, through the use of smart home
technologies and energy-efficient equipment. In a recent survey of
a sample of older people conducted in South Australia, most par-
ticipant s (78%) avoided using cooling and heating, as they were not
able, or not wanting, to spend the money to pay for the electric-
ity and gas bills from using heating and cooling equipment.30 This
study indicates that reduced income is also one of the factors that
affect the bedroom thermal environment of the elderly. Compared
with air conditioner, the ceiling fan consumes much less energy,
and thus providing an af fordable method to the elderly to maintain
thermal comfort, although more studies are needed to confirm the
required airflow characteristics and to improve the performance
of the fans.
To exclude the effects of indoor air quality on sleep quality, the
windows were closed at the three conditions. Whereas, in real life,
the elderly usually open their window and let the bedroom natu-
rally ventilated if they use fans. A field study examined how bed-
room air quality affect sleep and showed that the sleep quality and
next-day work performance were improved when the CO2 level in
the bedroom during sleeping period was lower.31 Further studies
are needed to confirm the possible benefits of reduced CO2 level in
the naturally ventilated room accompanying with the use of fans.32
5 | CONCLUSIONS
This study found that the sleep quality and health of the elderly was
very vulnerable to heat exposure, even small heat load leading to
reduced sleep quality (the duration of total sleep time decreased by
35 minutes and the duration of REM sleep decreased by 15 minutes)
and overactive sympathetic nervous system (the concentration of
urinary cortisol increased by 50 ng/mL). By supplying an air flow
of 0.8 m/s evenly over the human body, the heat load could be re-
moved, and the elderly could maintain sleep quality and thermal
comfort at an air temperature that are 3 K higher than the neutral
temperature.
The results of this study suggest that it is possible to control
the sleeping thermal environment of the elderly with their pre-
ferred strategies and provide basis for development of fans for
them. The ceiling fan is an affordable and convenient solution to
improve the sleeping thermal environment for the elderly in hot
summer, although more studies are needed to confirm this effect,
and to improve its design and operation. In this study, mainly the
difference in air speed distribution at bed was compared bet ween
the task fan and the ceiling fan, without exploring the reasons
that result in such difference. Full scale laboratory measurements
of different type of fans and arrangement of fans should be per-
formed, and the influence factors of fans should be investigated
in future study.
FIGURE 9 Concentration of urinary cor tisol measured before
and after sleep in the three conditions (Error bars represent the
standard deviation of mean)
|
1049
LAN e t AL.
ACKNOWLEDGEMENT
This work wa s supported by th e National Natur al Science Foundat ion
of China (No. 51778359 and 51478260).
CONFLICT OF INTEREST
This was not an industry supported study. The authors have indi-
cated no financial conflicts of interest.
ORCID
Li Lan https://orcid.org/0000-0003-3431-9266
Xiaojing Zhang https://orcid.org/0000-0003-4529-7867
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How to cite this article: Lan L, Xia L, Tang J, Zhang X , Lin Y,
Wang Z. Elevated airflow can maintain sleep quality and
thermal comfort of the elderly in a hot environment. Indoor
Air. 2019;29:1040–1049. https ://doi .org/10.1111/ina.1 2599
