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Yoshiro Toyama, MD; Tomoko Wakamura, PhD; Kazuo Chin, MD, PhD
Author and Funding Information

From the Graduate School of Medicine, Kyoto University.

Correspondence to: Kazuo Chin, MD, PhD, Department of Respiratory Care and Sleep Control Medicine, Kyoto University Graduate School of Medicine, Shogoin 54, Kawahara-cho, Sakyo-Ku, Kyoto, 606-8507, Japan; e-mail: chink@kuhp.kyoto-u.ac.jp


Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2014;145(1):183-184. doi:10.1378/chest.13-1932
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To the Editor:

We thank Dr Kawada for his thoughtful comments regarding our study.1 Dr Kawada expressed concern about our use of actigraphy to measure sleep duration. In our previous study of male employees of an urban wholesale company in Japan2 (cited as reference 30 in the study), we had more completely described the method of calculation of sleep duration. In that report, we stated,

Sleep duration was estimated from analysis of the wrist actigraph tracing in conjunction with a sleep diary. The times at which the participant went to bed and got out of bed were obtained from the diary. Sleep onset was estimated by noting sustained cessation of wrist movement on the actigraphy tracing. The time of awakening was noted by the appearance of wrist movements on the actigraphy tracing. Sleep durations were the estimated length of time between the sleep onset and the final awakening.

In addition, the determinants of sleep at onset and the final awakening by actigraph were visually inspected by two researchers who were accustomed to the actigraph.3 We know that combined with a validated method of monitoring respiratory events, the use of actigraphy may improve accuracy in assessing the severity of OSA compared with only using time spent in bed.4 However, the accuracy of actigraphy, as evaluated by Bland-Altman methods, declined in patients with more severe sleep apnea.5 Therefore, in these studies, we used the actigraph only to determine sleep onset and the time of awakening by visual inspection in addition to referring to the sleep diary1,2 because some of the study participants had severe OSA. Although we cited reference 30 (cited here as reference 2) under Subjects in the Materials and Methods section, it might have been better to also cite it under Estimation of Sleep Duration in the Materials and Methods section. Altogether, we believed that the use of the actigraph along with the diary for the purpose of the two studies would be superior to the use of only a sleep diary.

As Dr Kawada mentioned, sleep duration was a key factor in this study,1 and the participants wore the actigraph for 7 days so we could measure the mean daily sleep duration. An actigraph (Actiwatch AW-Light; Mini Mitter or Koninklijke Philips Electronics NV) has been used in many reports. We believed that the use of the actigraph as described here was suitable for this study.

We appreciate the comments of Dr Kawada. They enabled us to provide details of our method for calculating sleep duration that were only briefly provided in our article.1

References

Toyama Y, Chin K, Chihara Y, et al. Association between sleep apnea, sleep duration, and serum lipid profile in an urban, male, working population in Japan. Chest. 2013;143(3):720-728. [PubMed]
 
Nakayama-Ashida Y, Takegami M, Chin K, et al. Sleep-disordered breathing in the usual lifestyle setting as detected with home monitoring in a population of working men in Japan. Sleep. 2008;31(3):419-425. [PubMed]
 
Wakamura T, Tokura H. Influence of bright light during daytime on sleep parameters in hospitalized elderly patients. J Physiol Anthropol Appl Human Sci. 2001;20(6):345-351. [CrossRef] [PubMed]
 
Gagnadoux F, Nguyen XL, Rakotonanahary D, Vidal S, Fleury B. Wrist-actigraphic estimation of sleep time under nCPAP treatment in sleep apnoea patients. Eur Respir J. 2004;23(6):891-895. [CrossRef] [PubMed]
 
Morgenthaler T, Alessi C, Friedman L, et al; Standards of Practice Committee; American Academy of Sleep Medicine. Practice parameters for the use of actigraphy in the assessment of sleep and sleep disorders: an update for 2007. Sleep. 2007;30(4):519-529. [PubMed]
 

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References

Toyama Y, Chin K, Chihara Y, et al. Association between sleep apnea, sleep duration, and serum lipid profile in an urban, male, working population in Japan. Chest. 2013;143(3):720-728. [PubMed]
 
Nakayama-Ashida Y, Takegami M, Chin K, et al. Sleep-disordered breathing in the usual lifestyle setting as detected with home monitoring in a population of working men in Japan. Sleep. 2008;31(3):419-425. [PubMed]
 
Wakamura T, Tokura H. Influence of bright light during daytime on sleep parameters in hospitalized elderly patients. J Physiol Anthropol Appl Human Sci. 2001;20(6):345-351. [CrossRef] [PubMed]
 
Gagnadoux F, Nguyen XL, Rakotonanahary D, Vidal S, Fleury B. Wrist-actigraphic estimation of sleep time under nCPAP treatment in sleep apnoea patients. Eur Respir J. 2004;23(6):891-895. [CrossRef] [PubMed]
 
Morgenthaler T, Alessi C, Friedman L, et al; Standards of Practice Committee; American Academy of Sleep Medicine. Practice parameters for the use of actigraphy in the assessment of sleep and sleep disorders: an update for 2007. Sleep. 2007;30(4):519-529. [PubMed]
 
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