Warm Steam Inhalation before Bedtime Improved Sleep Quality in Adult Men

Abstract

In humans, the inhalation of warm steam has been reported to decrease the respiratory rate. However, the effects of warm steam inhalation on sleep have not been studied closely. This study aimed to examine the effects of warm steam inhalation before bedtime on subsequent sleep quality. The participants included 17 adult men with mild sleep difficulties and anxiety. All experiments were conducted in the participants’ homes. The participants were instructed to wear a warm steam-generating mask or sham mask over the nose and mouth for 15 minutes immediately before habitual bedtime and were then allowed to sleep until their habitual waking time. The functional mask provided approximately 600 mg of steam for 10 minutes and maintained an interior temperature of 38–40°C for 15 minutes. We evaluated the participants’ electrocardiograms and subjective moods while wearing the mask. During sleep, electroencephalograms (EEGs) were recorded using a single-channel portable device. In the morning, each participant was instructed to report their sleep details subjectively using a visual analog scale. At bedtime, the subjects’ subjective apprehension of the next day was reduced significantly under steam inhalation, compared with the sham condition. Compared to the sham condition, steam inhalation before bedtime was associated with a higher EEG delta power density during the first third of sleep episodes and better subjective sleep quality in the morning. These results suggest that safe and easy inhalation of warm steam via a steam-generating mask improves psychological relaxation and sleep.

Full text

Research Article
Warm Steam Inhalation before Bedtime Improved Sleep
Quality in Adult Men
Tomohisa Ichiba ,
1
,
2
Kenta Kakiuchi,
1
Masahiro Suzuki,
2
and Makoto Uchiyama
2
1
Personal Health Care Laboratory, Kao Corporation, Tokyo, Japan
2
Department of Psychiatry, Nihon University School of Medicine, Tokyo, Japan
Correspondence should be addressed to Tomohisa Ichiba; ichiba.tomohisa@kao.com
Received 8 April 2019; Revised 31 July 2019; Accepted 13 August 2019; Published 25 August 2019
Academic Editor: Arroyo-Morales Manuel
Copyright ©2019 Tomohisa Ichiba et al. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
In humans, the inhalation of warm steam has been reported to decrease the respiratory rate. However, the effects of warm steam
inhalation on sleep have not been studied closely. is study aimed to examine the effects of warm steam inhalation before
bedtime on subsequent sleep quality. e participants included 17 adult men with mild sleep difficulties and anxiety. All ex-
periments were conducted in the participants’ homes. e participants were instructed to wear a warm steam-generating mask or
sham mask over the nose and mouth for 15 minutes immediately before habitual bedtime and were then allowed to sleep until
their habitual waking time. e functional mask provided approximately 600 mg of steam for 10 minutes and maintained an
interior temperature of 38–40°C for 15 minutes. We evaluated the participants’ electrocardiograms and subjective moods while
wearing the mask. During sleep, electroencephalograms (EEGs) were recorded using a single-channel portable device. In the
morning, each participant was instructed to report their sleep details subjectively using a visual analog scale. At bedtime, the
subjects’ subjective apprehension of the next day was reduced significantly under steam inhalation, compared with the sham
condition. Compared to the sham condition, steam inhalation before bedtime was associated with a higher EEG delta power
density during the first third of sleep episodes and better subjective sleep quality in the morning. ese results suggest that safe and
easy inhalation of warm steam via a steam-generating mask improves psychological relaxation and sleep.
1. Introduction
Pharmacotherapy for insomnia has been widely employed.
However, the associated side effects and dependencies
present challenges to the long-term use of hypnotic drugs
[1]. Nonpharmacological treatments, such as relaxation
techniques or cognitive behavior therapy for insomnia
(CBT-I), are recommended as complementary and alter-
native therapies [2]. Various relaxation techniques are used
to reduce somatic tension and treat insomnia (e.g., pro-
gressive muscle relaxation and diaphragmatic breathing) [3].
However, these relaxation techniques require training and
practice to be effective and may be difficult for those with a
limited range of motion. erefore, nonpharmacological
treatments are not widely used in adults with insomnia or
mild sleep difficulties. erefore, safe and easy relaxation
techniques are needed to treat the large population of in-
dividuals experiencing insomnia and other sleep difficulties.
Breathing plays an important role in both physiological
and psychological states and influences emotions such as
anxiety, fear, sadness, and happiness [4, 5]. Moreover,
therapeutic breathing techniques (e.g., biofeedback and
autogenic training) have been associated with relaxation
[6, 7]. We recently developed a novel breathing technique
based on a disposable heat-and-steam generator (HSG) sheet
to enable safe and easy inhalation of warm steam. is
practice has been reported to induce psychological re-
laxation and decrease respiratory frequency in healthy men
[8, 9] and in patients with chronic obstructive pulmonary
disease (COPD) [10].
We previously reported that periocular skin warming
induced psychological and physiological relaxation [11] and
Hindawi
Evidence-Based Complementary and Alternative Medicine
Volume 2019, Article ID 2453483, 7 pages
https://doi.org/10.1155/2019/2453483

improved the subjective and objective quality of sleep
[12, 13]. Possibly, warm steam inhalation may have similar
beneficial effects on sleep quality through psychological
relaxation. However, the sleep-related effects of warm steam
inhalation have not been studied in detail.
In this study, we investigated whether warm steam in-
halation before bedtime would improve the sleep quality in
individuals with mild sleep difficulties and anxiety by
promoting psychological relaxation. We monitored the
electrocardiogram (ECG) results and changes in subjective
status at bedtime while the participants inhaled warm steam
via a mask fitted with an HSG sheet, as described in previous
studies [8–10]. We then evaluated the participants’ sub-
sequent sleep quality using electroencephalograms (EEGs)
and a visual analog scale (VAS).
2. Materials and Methods
2.1. Participants. We recruited, through a clinical research
organization, 25 adult men with mild sleep difficulties
(Pittsburgh Sleep Questionnaire Index (PSQI) [14] scores of
6–9) and anxiety (State-Trait Anxiety Inventory (STAI) [15]
scores of 33–53). None of the participants had taken hyp-
notic medicines in the previous month, and none had
previous or current physical or psychological disorders.
ose who had engaged in shift work or who had a ha-
bitually short nocturnal sleep duration (<5 hours) were
excluded. All participants were nonsmokers, and none ha-
bitually consumed alcohol before bedtime. Written in-
formed consent was obtained from all study participants
after they had received a detailed explanation of the ex-
periment. Ethical approval was obtained from the Ethics
Committee of Nihon University (approval number: 28–10).
e study protocol was registered in the University Hospital
Medical Information Network Clinical Trials Registry
(UMIN-CTR registry ID: UMIN000025298) on December
16, 2016. e study itself was conducted in January and
February 2017.
One participant dropped out of the because of a business
trip during the study period, five participants were unable to
adhere to their daily habitual sleep-wake schedule or limit
alcohol consumption, and two participants misunderstood
the experimental procedure. Finally, the data of 17 partic-
ipants (mean ±standard deviation (SD) age: 41.2 ±5.0 years,
PSQI: 6.4 ±0.6, Trait-STAI: 39.5 ±6.5) were included in the
analysis.
2.2. Experimental Design. A single-blind, placebo-con-
trolled, randomized cross-over design was used. All ex-
periments were performed in the participant’s homes.
Figure 1 depicts the experimental protocol. First, all par-
ticipants were instructed to maintain their habitual sleep-
wake schedule for 7 days (observational period). After this
period, participants were assigned to two experimental
sessions separated by a 3-day interval. One experimental
session involved the “steam-inhalation condition,” and the
other involved the “sham condition.” In the steam-in-
halation condition, participants used a disposable steam-
generating mask (SG-mask) that covered the nose and
mouth and inhaled warm steam via this mask before bed-
time. In the sham condition, participants wore a non-steam
sham mask (NS-mask). Each experimental session com-
prised 4 consecutive nights. e first 2 nights were used for
adaptation, and the last 2 nights were used for analysis. e
participants were required to maintain their habitual daily
sleep-wake schedule throughout the experimental period
and were prohibited from consuming alcohol or ingesting
foods or beverages containing caffeine after dinner. ey
were also instructed to finish bathing or showering 1 hour
before bedtime.
During each experimental session, the participants were
instructed to prepare for ECG and EEG measurements
before their habitual bedtime and to maintain a resting state
on our provided recumbent chair for 4 minutes during ECG
measurements. e participants were then asked to wear the
SG- or NS-mask for 15 minutes while maintaining the same
posture. During each treatment session, the participants
were instructed to manage their time using an electronic
timer with an alarm function. Once the 15 minutes had
passed, each participant removed the mask, completed the
VAS questionnaire, and laid down to sleep with a portable
EEG device.
2.3. Mask. e SG-mask used in the present study was made
of nonwoven fabric shaped in three dimensions. HSG sheets
were inserted into each mask [8–10]. e mask was sealed in
an aluminum package before use. Warm steam was gen-
erated through a chemical reaction of iron, water, and ox-
ygen when the package was opened. is warm steam was
applied to the skin and inhaled safely once the mask covered
the nose and mouth. Our previous study showed that the
mask provided approximately 600 mg of warm steam during
a 10-minute period, which maintained the skin temperature
underneath the mask at 38–40°C for approximately
15 minutes [8–10]. e NS-mask was composed of the same
nonwoven fabric and was indistinguishable from the SG-
mask. e NS-mask did not provide steam when the package
was opened because the HSG sheets were inactivated. Each
mask covered the nose and mouth to ensure that all
breathing occurred within the mask. e masks were a
prototype produced for the present study by Kao Corpo-
ration (Tokyo, Japan).
2.4. Evaluation of Subjective Status. In each treatment ses-
sion, the subjective status was assessed before bedtime using
a 100 mm VAS comprising the following seven items [16]:
“How do you think the next day will be?” (an apprehension
measure: 0, very pleasant; 100, very difficult), “Uneasiness”
(0, very calm; 100, very uneasy), “Tension” (0, very relaxed;
100, very tense), “Nervousness” (0, not nervous at all; 100,
very nervous), “Stress” (0, not stressed at all; 100, very
stressed), “How do you think it will be to wake up in the
morning?” (measure of difficulty in waking: 0, very easy; 100,
very difficult), and “Fatigue” (0, not at all tired; 100, ex-
tremely tired). Each participant was instructed to complete
the subjective status questionnaire before and after the 15-
2Evidence-Based Complementary and Alternative Medicine

minute treatment session in accordance with how they felt at
that moment. To compare subjective changes between the
sham and steam-inhalation conditions, all subjective sta-
tuses were expressed relative to the subjective status ob-
tained before the treatment.
e subjective sleep status during the sleep session was
assessed using a 100 mm VAS after the final waking in the
morning. e following items were used: “Sleep initiation”
(0, very difficult; 100, very easy), “Sleep quality” (0, very poor
sleep; 100, very good sleep), and “Feeling of being refreshed
in the morning” (0, not at all; 100, extremely refreshed)
[12, 13].
2.5. Measurement and Analysis of ECG and EEG. ECG and
EEG data were recorded in the participants’ homes using a
single-channel portable EEG device (Brainwave Sensor ZA®;
Proasist Co., Osaka, Japan) at a sampling rate of 128 Hz
[17–19]. Before bedtime, participants were instructed to
place the disposable Ag/AgCl surface electrodes for ECG on
their chests and those for EEG in the median-frontal region
in reference to the right mastoid. e raw signals were stored
on an SD card and later analyzed off-line.
e R-R interval (RRI), defined as the interval between
the onset times of consecutive R waves, was detected from
the ECG signals, and commercial software were used to
calculate a spectral analysis of the heart-rate variability
(HRV) based on the RRI for each 3-minute epoch according
to the maximum-entropy method (MemCalc/Win ver.2.0;
GMS Co., Ltd., Tokyo, Japan). e values for the HRV bands
were analyzed as follows: low frequency (LF) at 0.04–0.15Hz
and high frequency (HF) at 0.15–0.4 Hz. e ratio of LF to
HF (LF/HF) was also estimated. e heart rate (HR) was
calculated as 1/(RRI ∗60). e LF/HF ratio has been re-
ported as a reflection primarily of the sympathetic nervous
function, while the HF reflects parasympathetic nervous
function. To compare changes in the HR and HRV between
the sham and steam-inhalation conditions, the ratios of
values from the first and second halves of the treatment
session were calculated with reference to the baseline values.
According to the previously described original criteria
[17–19], the sleep EEG record was divided into 30-second
epochs and classified into the following sleep stages: awake,
rapid-eye-movement (REM) sleep (stage N1), light non-
REM (NREM) sleep (stage N2), or deep NREM sleep (stage
N3). Sleep latency, sleep efficiency, and wake after sleep
onset were calculated based on the sleep-stage analysis.
Spectral analyses of the EEG data were performed using a
fast Fourier transform algorithm and specialized software
(SleepSign-Light; KISSEI COMTEC Co., Ltd., Nagano, Ja-
pan). Power values were obtained in the following bands:
delta (1.0–4.0 Hz), theta (4.0–8.0 Hz), alpha (8.0–12.0 Hz),
and beta (16.0–35.0 Hz). e mean spectral power density
and standard deviation (SD) were computed for the indi-
vidual bands. e spectral power data for each epoch that
exceeded the mean spectral power +3 SD and determined
the awake stage were deemed artifacts and excluded from
analysis. Next, the power values in each band were nor-
malized to the mean power values in each band across the
total sleep period. A NREM-REM cycle was defined as a
NREM episode of at least 15 minutes and successive REM
episode of at least 5 minutes [20]. us, the normalized EEG
power was averaged during each NREM-REM cycle [19].
2.6. Statistical Analyses. General values are expressed as
means ±SDs. Participant data were analyzed using non-
parametric statistical tests. Statistical comparisons of con-
ditions were performed using the Wilcoxon signed-rank test.
All statistical analyses were performed using IBM SPSS
Statistics 20 (IBM Corp., Armonk, NY, USA). Probability
values of <0.05 were considered statistically significant.
3. Results
3.1. Subjective and Heart-Rate Changes. Table 1 presents the
results of statistical comparisons and changes in seven
subjective measures after treatments under the sham and
steam-inhalation conditions. A significant reduction in the
change in (Δ) apprehension was observed in the steam-
Observational
period
Experimental
period
Day 1
Day 8 Day 9 Day 10 Day 11 Day 12 Day 13 Day 14 Day 15 Day 16 Day 17 Day 18
Day 2 Day 3 Day 4 Day 5 Day 6 Day 7
Experimental session 1 Experimental session 2Wash ou t
Adaptation Adaptation
Treatment session Sleep session
(habitual sleep)
Baseline
4min
Wearing the mask
15min
Preparing
for bed Sleep Sleep
Sitting position
VAS
(Awake)
VAS
(Post)
VAS
(Pre)
Figure 1: Experimental protocol. After an observational period, the experimental period comprised experimental sessions 1 and 2,
separated by a 3-day interval. In each experimental session, participants performed the study according to their habitual bedtime. e first
half of the experimental session was used as an adaptation period, and the second half was used for analysis.
Evidence-Based Complementary and Alternative Medicine 3

inhalation condition relative to that in the sham condition
(Table 1). Other items related to the subjective status did not
differ significantly between the two conditions (Table 1).
Neither the ΔHR nor the ΔHRV differed significantly be-
tween the sham and steam-inhalation conditions, although
the ΔHR at first treatment and HF at the second treatment
were nearly significant (Table 2).
3.2. EEG and Subjective Sleep Measures. Tables 3 and 4
summarize the EEG and subjective sleep measure data
obtained during the sham and steam-inhalation conditions.
e period of deep NREM latency was significantly shorter
in the steam-inhalation condition than in the sham con-
dition (Table 3). e subjective sleep quality reported upon
waking was significantly better in the steam-inhalation
condition than in the sham condition (Table 4).
3.3. Quantitative Sleep EEG Analyses. Figure 2 presents the
sleep EEG profiles of a representative participant. Notably,
the deep non-REM sleep stage and delta power in the first
NREM-REM cycle were more marked under the steam-
inhalation condition than under the sham condition. In the
first NREM-REM cycle, the delta and theta powers were
enhanced significantly in the steam-inhalation condition,
compared to the sham condition (Table 5). In the second and
third NREM-REM cycles, none of the variables differed
between the sham and steam-inhalation conditions.
4. Discussion
Our findings revealed that warm steam inhalation reduced
the participants’ apprehension before bedtime, shortened
deep NREM sleep latency, and increased the sleep EEG theta
and delta powers in the first third of sleep episodes. Steam
inhalation also improved the subjective sleep quality upon
waking when compared with the sham treatment.
Many studies have indicated that the respiratory or
breathing rate is influenced by the emotional status. For
example, nervousness or anxiety can cause shallow breathing
and an increased respiration rate [5]. Some behavioral
regimens intended to optimize breathing rate reportedly
confer psychological relaxation and are widely utilized in the
field of psychosomatic medicine. Previous studies have
demonstrated that the use of various techniques (e.g., paced
breathing [21], HRV biofeedback [22], and Zen medication
[23]) to reduce the respiratory rate also enhanced the
subjectively reported psychological relaxation. In the present
study, psychological relaxation was achieved after using a
SG-mask, although autonomic respiratory variables were
not measured. Recently, properly controlled warm steam
inhalation has been reported to reduce nasal resistance and
alter the breathing pattern from rapid shallow breathing to
slow deep breathing while achieving psychological re-
laxation [8–10]. ese findings suggest that psychological
changes might be at least partly associated with a reduction
of nasal resistance and/or achievement of slow deep
breathing in the present study. e sensory mechanism
mediating such responses remains unclear, although the
sensory branches of the trigeminal nerve might be involved.
Furthermore, we observed that the HR and HRV in-
dicated changes associated with psychological relaxation,
although the small number of participants and consequent
lack of power precluded the comparison from reaching
statistical significance. As warm steam inhalation may have
had both physiological and psychological effects in this
study, a higher mechanism associated with physiological
changes may have been involved in the observed signs of
psychological relaxation, such as the reduction in appre-
hension at bedtime.
In this study, we found that in addition to reducing
subjective apprehension at bedtime, warm steam inhalation
shortened the deep NREM latency and increased the EEG
delta power in the first third of sleep episodes compared with
the sham condition. As the participants were instructed to
remove the NS- or SG-mask immediately after the 15-
minute treatment, fill out the questions on subjective states,
and then retire, the reduction in subjective apprehension
associated with the steam-inhalation condition might have
influenced the subsequent sleep status. Anxiety at bedtime
has been associated negatively with the amount of slow wave
sleep [16]. Furthermore, we have recently reported that
warming of the periocular skin region to approximately 40°C
before bedtime was associated with an increase in relaxed
feelings at bedtime and an increase in EEG delta power value
in the early hours of subsequent sleep [13]. Together with
those previous findings, our present results support the
notion that psychological relaxation after warm steam in-
halation might contribute to a propensity to sleep and the
amount of slow wave sleep in subjects with mild sleep
difficulties.
In the present study, the subjective sleep quality at the
time of waking was also improved by warm steam inhalation
before bedtime. However, the direct effects of this treatment
on sleep were limited to the early hours of sleep. Huber et al.
have reported that slow wave activity in early sleep was
associated with the recovery of brain function [24]. Recently,
we found that psychological and physiological relaxation via
local skin warming in the periocular area and back of the
neck increased delta power early in the sleep episode and
improved the subjective sleep quality upon waking [13]. e
present finding that an increase in delta sleep in the early
sleep episode after bedtime steam inhalation improved the
subjective sleep quality upon waking may be comparable to
the findings of previous studies [13]. us, enhanced deep
Table 1: Subjective changes during sham and steam-inhalation
conditions.
Sham Steam inhalation p
Δapprehension 0.0 ±7.2 –5.7 ±7.3 0.026
Δuneasiness –1.4 ±8.2 –2.3 ±6.9 0.507
Δtension –2.4 ±11.9 –3.7 ±8.7 0.981
Δnervousness –3.5 ±13.1 –6.3 ±12.0 0.407
Δstress –3.7 ±11.3 –3.5 ±12.0 0.408
Δdifficulty waking up –2.3 ±11.3 –3.1 ±6.7 0.756
Δfatigue –5.2 ±8.8 –5.5 ±9.6 0.740
Values are expressed as means ±standard deviations. Comparisons are
relative to the sham condition (Wilcoxon signed-rank test).
4Evidence-Based Complementary and Alternative Medicine

sleep in the early sleep episode may play a key role in im-
proving the subjective sleep quality at waking, as suggested
in previous basic studies [24].
is study had several limitations in the present study.
First, the HR and HRV did not reach statistical significance.
ese results may be attributable to a lack of power caused by
Table 2: HR and HRV during sham and steam-inhalation conditions.
First treatment Second treatment
Sham Steam inhalation pSham Steam inhalation p
HR (bpm) –2.4 ±3.8 –4.0 ±3.2 0.075 –3.7 ±3.8 –4.0 ±5.6 0.600
HF (%) 129 ±48 162 ±76 0.263 125 ±47 184 ±99 0.087
LF/HF (%) 112 ±46 132 ±110 0.972 131 ±97 193 ±152 0.552
Values are expressed as means ±standard deviations. Comparisons are relative to the sham condition (Wilcoxon signed-rank test). HR: heart rate; HF: high
frequency; LF: low frequency; LF/HF: ratio of LF to HF.
Table 3: Comparison of sleep parameters in the two conditions.
Sham Steam inhalation p
Bedtime (h : min) 0 : 46 ±0 : 51 0 : 45 ±0 : 54 0.807
Wake time (h : min) 7 : 02 ±0 : 38 6 : 59 ±0 : 26 0.221
SPT (min) 380.1 ±60.7 370.5 ±63.5 0.221
TST (min) 348.0 ±71.3 342.8 ±66.9 0.311
Sleep latency (min) 20.2 ±25.9 14.1 ±22.5 0.600
WASO (min) 11.9 ±10.7 13.6 ±23.8 0.861
Sleep efficiency (%) 91.2 ±8.5 92.4 ±7.8 0.807
Deep NREM (%) 20.2 ±6.4 22.2 ±10.1 0.753
Deep NREM latency (min) 23.8 ±16.9 17.7 ±12.1 0.045
REM latency (min) 48.6 ±22.8 67.2 ±34.2 0.196
Values are expressed as means ±standard deviations. Comparisons are relative to the sham condition (Wilcoxon signed-rank test). SPT: sleep period time;
TST: total sleep time; WASO: wake after sleep onset; REM: rapid eye movement; NREM: non-REM.
Table 4: Subjective sleep scores in the morning.
Sham Steam inhalation p
Sleep initiation (mm) (0: poor, 100: good) 58.6 ±21.1 66.0 ±16.9 0.058
Sleep quality (mm) (0: low, 100: good) 49.4 ±13.3 59.5 ±16.0 0.005
Feeling of being refreshed (mm) (0: poor, 100: good) 50.2 ±12.1 52.7 ±21.3 0.569
Values are expressed as means ±standard deviations. Comparisons are relative to the control session (Wilcoxon signed-rank test).
Wake
REM
N1
N2
N3
800
600
400
200
0
Delta power (μV2)
0 60 120 180 240 300
Time (min)
(a)
Wake
REM
N1
N2
N3
800
600
400
200
0
Delta power (μV2)
0 60 120 180 240 300
Time (min)
(b)
Figure 2: Hypnogram (upper) and delta power (lower) profiles from a representative participant. (a) Sham condition. (b) Steam-inhalation
condition. W, wake; REM: rapid eye movement; N1: non-REM sleep stage N1; N2: non-REM sleep stage N2; N3: non-REM sleep stage N3.
Evidence-Based Complementary and Alternative Medicine 5

the small number of participants. Further studies with a
large number of participants are required to clarify the
relationship between physiological relaxation and steam
inhalation. Second, the experimental studies were conducted
in the participants’ homes as described in a previous study
[13]. Although participants in this study were instructed to
maintain their habitual sleep-wake schedule and sleep en-
vironment, potential confounding factors such as the room
temperature and/or humidity, illumination, and noise levels
might have influenced physiological changes such as the HR
and HRV and sleep. Further investigation is needed to clarify
the effects of steam inhalation on the physiological state and
sleep quality in an environment minimized these potential
confounding effects. ird, although participants could not
distinguish the SG- and NS-masks by appearance alone, they
could feel the difference between the masks during use.
Accordingly, the results may have been confounded by the
sensations experienced when wearing the mask. Fourth, the
effect of the respiratory rate on steam inhalation was not
investigated in the present study. Future studies are needed
to clarify the relationship between changes in respiratory
rates and sleep.
5. Conclusion
According to the study findings, warm steam inhalation
before bedtime induced psychological relaxation and in-
creased deep sleep in the early sleep episode, leading to an
improved subjective sleep quality in participants with mild
sleep difficulties and anxiety. ese results suggest that safe
and easy inhalation of warm steam via a steam-generating
mask may have favorable effects on relaxation and sleep.
Data Availability
All data used to support the findings of this study are
available from the corresponding author upon request.
Disclosure
e funders had no role in the study design, data collection
and analysis, decision to publish, or preparation of the
manuscript.
Conflicts of Interest
Dr. M. Uchiyama has received research support from
Astellas Pharma, Eisai, Meiji Seika Pharma, MSD, Taisho
Pharmaceutical, Kao Corporation, and Takeda Pharma-
ceutical, and has consulted for Kao Corporation, Taisho
Pharmaceutical, and Takeda Pharmaceutical. He has also
received honoraria for giving lectures and/or contributing
text from Eisai, Meiji Seika Pharma, MSD, and Takeda
Pharmaceutical. T. Ichiba and K. Kakiuchi are employees of
Kao Corporation. Dr. M. Suzuki declares no potential
conflicts of interest.
Acknowledgments
is study was founded by Kao Corporation. e authors
thank M. Igaki, H. Oda, S. Tsuchiya, and Y. Saita of Kao
Corporation for their support. is study was financially
supported by Kao Corporation. e authors would like to
thank Editage (http://www.editage.jp) for English language
editing.
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Table 5: Courses of sleep EEG power in the delta, theta, alpha, and beta bands in the sham and steam-inhalation conditions.
Normalized EEG First NREM-REM cycle Second NREM-REM cycle ird NREM-REM cycle
Sham Steam pSham Steam pSham Steam p
Delta (%) (1–4 Hz) 89.6 ±36.0 121.0 ±45.1 0.039 105.7 ±34.5 103.5 ±31.3 0.972 101.3 ±45.9 93.2 ±22.6 0.552
eta (%) (4–8 Hz) 90.9 ±40.1 125.1 ±58.0 0.028 145.0 ±44.2 135.9 ±87.2 0.421 150.2 ±71.6 187.8 ±95.7 0.422
Alpha (%) (8–12 Hz) 73.8 ±32.6 98.2 ±44.4 0.064 104.8 ±33.9 104.5 ±36.0 0.917 95.2 ±42.0 94.2 ±23.1 0.807
Beta (%) (16–35 Hz) 70.7 ±36.1 94.7 ±61.2 0.075 95.7 ±34.9 98.6 ±39.5 0.861 106.3 ±46.8 101.2 ±32.3 0.753
Values are expressed as means ±standard deviations. Comparisons are relative to the sham condition (Wilcoxon signed-rank test).
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