Round 1

Reviewer 1 Report

 

In the introduction the reasonableness of the study the sleep quality is justified with the accumulation of disasters. However, it seems very questionable whether in the case of disasters the effect on the calculation performance on the following day is really of interest. It also does not seem adequate to base the daytime functionality on the calculation performance alone.

The used method with portable two-channel EEG and EOG was presented as established. However, when the references were checked, considerable doubts arose about the scientific establishment of the method.

Only one of the first author's own paper was cited as a reference for the device. The co-authors of reference 11 are also all co-authors of the present paper.

11. Ogata, H.; Kayaba, M.; Kaneko, M.; Ogawa, K.; Kiyono, K. Evaluation of sleep quality in a disaster evacuee environment. Int J Environ Res Public Health. 2020, 17, 4252.

The same device was used in this paper and the same references were cited as in the present paper, which are, however, all judged to be insufficient (see below).

References of Refernce 11:

19. American Academy of Sleep Medicine. The AASM Manual for the Scoring of Sleep and Associated Events Summary of Updates in Version 2.6. Available online: https://j2vjt3dnbra3ps7ll1clb4q2-wpengine.netdna-ssl. com/wp-content/uploads/2020/01/Summary-of-Updates-in-v2.6-1.pdf (accessed on 23 December 2019).

20. Nonoue, S.; Mashita, M.; Haraki, S.; Mikami, A.; Adachi, H.; Yatani, H.; Yoshida, A.; Taniike, M.; Kato, T. Inter-scorer reliability of sleep assessment using EEG and EOG recording system in comparison to polysomnography. Sleep Biol. Rhythms 2017, 15, 39–48. [CrossRef]

21. Kanemura, T.; Kadotani, H.; Matsuo, M.; Masuda, F.; Fujiwara, K.; Ohira, M.; Yamada, N. Evaluation of a portable two-channel electroencephalogram monitoring system to analyze sleep stages. J. Oral Sleep Med. 2016, 2, 101–108

The following references were cited in the methods section of the current paper, but all are estimated to be insufficient.

Reference 18.: American Academy of Sleep Medicine. The AASM Manual for the Scoring of Sleep and Associated Events Summary of Updates in version 2.6. https://j2vjt3dnbra3ps7ll1clb4q2-wpengine.netdna-ssl.com/wp-content/uploads/2020/01/Summary-of-Updates-in-v2.6.pdf. (accessed on 2 February 2020)

The cited AASM reference could not be found

Screenshot (see file)

Reference 19: According to the abstract the number of participants was 14. This number is far too low to make reliable statements about inter-rater reliability

Abstract There are increasing needs for self-applicable

methods assessing sleep in clinical and non-clinical settings.

This study aimed to investigate the inter-scorer

reliability for the sleep stage scoring and for the sleep

variable assessments in the portable electroencephalography

(EEG) and electro-oculography (EOG) recording system.

Sleep recordings were performed simultaneously with

polysomnography (PSG) and portable EEG/EOG recordings

in 14 healthy adults. The inter-scorer concordance of

the sleep stage scoring was assessed in the two recording

methods. Sleep variables were compared between the two

methods using the Bland–Altman plots in each scorer. The

overall inter-scorer concordance rate of sleep stage scoring

for the EEG/EOG data was 85.5 %, and the Cohen’s j was

0.80 (p\0.001), being equivalent to those for the PSG

data (89.2 %, 0.85, p\0.001) while that for StageN1 was

relatively low (EEG/EOG 60.1 %, PSG 71.7 %). In both scorers,

Bland–Altman plots showed that the mean difference

between sleep variables obtained from the two systems

was within the acceptable range although the interclass

correlations between the two systems were lower for

StageN2 or StageR in either scorer. Although the results

suggest that the sufficient inter-scorer reliability can be

obtained with the EEG/EOG recording system based on

manual sleep stage scoring in healthy young adults, the

nature of the EEG/EOG recording system can influence the

precisions in manually assessing sleep architectures in

comparison to PSG.

Reference 20: The original article is only available in Japanese and is not listed in PubMed.

According to the abstract in English the participants were in total 16 participants (see below). This number is much too low for the establishment and validation of a method

The fact that the article was not published in English and not in an internationally recognized journal listed at Pubmed indicates that the study is not of sufficient scientific quality.

Objective: All-night polysomnography （PSG） is a useful tool for evaluating sleep quality. However, it requires subjects to sleep in an unfamiliar environment, which can influence sleep quality. Moreover, PSG is labor-intensive, timeconsuming, and expensive. We evaluated a portable two-channel electroencephalogram （EEG） monitoring system and compared the signals obtained from the device with those of simultaneously recorded full PSG. Accordingly, it is not a sufficiently well-studied and established method.

Methods: Signals obtained from two-channel EEG were comparing with simultaneously recorded full PSG signals. Sleep stages were scored using the American Academy of Sleep Medicine Manual for Scoring Sleep 2007. The epochby-epoch percent agreement and Cohen’s kappa coefficient were used for agreement evaluation of sleep stage in both devices.

Results: The participants were healthy Japanese volunteers （mean （standard deviation）: age: 20.9 （1.8） years; seven women and nine men）. In epoch-by-epoch comparison, the average agreement and kappa value of sleep stages between two-channel EEG and PSG were 0.83 （0.04） and 0.75 （0.05）, respectively. Kappa coefficients showed strong agreement for stage R （REM: rapid eye movement）, stage W （wake）, stage N3 （non-REM: NREM 3）, and stage N2 （NREM 2）（0.86（0.09）, 0.76（0.12）, 0.74（0.15） and 0.73（0.06）, respectively） and weak agreement for stage N1（NREM 1）（0.44（0.13））.

Conclusion: These results demonstrate that two-channel EEG facilitates home sleep monitoring and exhibits acceptable agreement with PSG. Therefore, this tool may be suitable for use in epidemiological and intervention studies.

See Screenshot (File)

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Dear Editor and Authors

This is a well organized study trying to objectively and subjectively investigate the effect of different front seat angles (45^o and 60^o) during overnight stays in a car on sleep quality. The findings are the same with those that the authors already published in ‘Ogata, H.; Kayaba, M.; Kaneko, M.; Ogawa, K.; Kiyono, K. Evaluation of sleep quality in a disaster evacuee environment. Int J 399 Environ Res Public Health. 2020, 17, 4252’. However, as the authors made a different experimental project they added more specific and detailed results.

The authors attempted to assess the impact of different front seat angles overnight stays in a car on calculation performance the following day. They found significant difference in this performance between sleeping in their cars versus sleeping at home.

Major revision

Line 90. The authors wrote that the participants “slept for 8 hours”. Please specify the total sleep time (TST) based on polysomnography.Is it possible for each of these participants to sleep for an 8-hour-period in these 3 trials?

Line 104. The authors wrote that “all three trials were conducted with the participants wearing the same clothes”. Please report on why the participants did not use their usual pajamas dresses at home as this is the control/base measurement. Please, make a comment.

Line 262. Calculation performance

The authors presented that “the difference in the numbers of responses for each trial after waking up were significantly lower than that of before sleep in the intervention trials”. This is the primary target of the study. However, they did not provide any correlation between these performance findings and the objective and subjective questionnaires that they used. Please provide such data even if they did not reach statistical significance.

Line 296-300. While the participants did not show a significant difference in the three trials on the number of “stage shifts”, the authors explained that this happened because they succeeded at a high PSQI score. The “ceiling effect” is a limitation of the study and must be referred as it is.

Line 344. Conclusions

The authors stated in an excellent way the differences between objective vs subjective findings between intervention trials and sleet at home. However, they concluded nothing on the calculation performance of their participants, even though this is one of the primary targets of this study.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

 

Everybody knows that sleeping in seating position is uncomfortable. Sleep in this position is expected to reduce sleep and to decrease the next day neurocognitive performance. However, it remains mostly undocumented in experimental research whether sleep in seating position can significantly reduce objective sleep quality and the evaluations of next day performance. On the example of the effect of sleep when seating in a car chair, the authors studied the impact of seat angle during sleeping in a car on sleep architecture and the evaluation of the following day performance. Fifteen healthy males participated in three trials (sleeping home and under laboratory condition - in a car with the front seat angled at either 45° or 60°). The effect of seat angle on sleep was confirmed objectively rather than subjectively (increased wake stage after sleep onset and decreased amount of slow-wave sleep were observed in one, the 60°, trial). Subjective sleep quality and calculation performance in the 45° and 60° trials were poorer than those observed in the home trial. The authors concluded that a large seat angle, that is, near-vertical, might cause further sleep impairment while staying in a car overnight. 

Abstract

“that is, near-vertical,” might be moved in one of the previous sentences.

Introduction.

The first paragraph of Introduction describes one of road travel conditions forcing the drivers to sleep in car chairs overnight. Some of many other typical conditions might be mentioned.

Was this a hypothesis-deriving study?

Methods.

“Sleep stages, WASO, rapid eye movement, and non-rapid eye movement (NREM 1,  NREM 2, and slow-wave sleep (SWS)) were manually scored according to the standard criteria” Sleep stages include the stages of NREM sleep.

Results

General. Given that only two trials were conducted in the same setting, it is necessary to repeat all analyses with data on only these two (45° and 60°) trials.

Notes of significant difference (e.g., “Significant difference observed between the home and 60° trials”) can be replaced by additional columns in the body of tables with more information on statistics (was this a result on F-ratio or on Bonferroni pairwise comparison.

SSS scores (e.g., “the scores after waking were worse in the 45° and 60° trials than in the home trials”), VAS scores, etc., would be wiser additionally analyze as pre-post differences in a score in three conditions.  Might be with repeated measure ANOVAs.

Discussion

“Because passenger cars are frequently chosen as emergency and evacuation places to stay during disasters and disaster recovery, it is necessary to evaluate the physical effects of overnight stays in cars to study disaster countermeasures.” See the comment to Introduction.

It is necessary to add, at least, one sentence the limitation paragraph in the end of discussion. For instance, the applicability of results to real life situations is limited due to selection of people with good sleep and health to the present experiments.  

 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Unfortunately, the method used is still not considered to be sufficiently scientifically established. The additional articles mentioned are all papers that use the device but do not investigate the validity and reliability of the method. Thus, the fundamental concerns already expressed in the first report remain.

After correcting the internet address, I was able to access the website. The manual of the AASM refers to the standardized evaluation of polysomnography. However, this method was not used in the present work, which is why it is not considered an adequate reference.

Overall, there is a lack of sufficient scientific evidence to support the establishment of the device.

Author Response

Comments and Suggestions for Authors

Unfortunately, the method used is still not considered to be sufficiently scientifically established. The additional articles mentioned are all papers that use the device but do not investigate the validity and reliability of the method. Thus, the fundamental concerns already expressed in the first report remain.

→Thank you for your comment. The validity and reliability of the device are written in the Measurements (Lines 127-131). We added the sentence in the limitation section (Lines 361-363).

After correcting the internet address, I was able to access the website. The manual of the AASM refers to the standardized evaluation of polysomnography. However, this method was not used in the present work, which is why it is not considered an adequate reference.

Overall, there is a lack of sufficient scientific evidence to support the establishment of the device.

→Thank you for your comment. This word was modified (Lines 125-126). Although the EEG is a little less accurate than PSG, the AASM guidelines were applied since this device measured the EEG.

 

For example:

When characteristic waves such as Spindle, K-Complex, etc. appear: Judged as "NREM 2".

When a slow wave of 75 µV or more appears: Judged as "NREM 3".

When the power of EEG and EMG is low and fast eye movement appears: Judged as "REM".

When fast eye movement appears do not appear, but appears before and after the eye movement: Judged as "REM".

Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors 

I found the correction in the right way. Everything is ok.

Author Response

Thank you for your helpful comments.