title: Time of day affects the frequency and duration of breathing events and the critical closing pressure during NREM sleep in participants with sleep apnea.
abstract: We investigated if the number and duration of breathing events coupled to upper airway collapsibility were affected by the time of day. Male participants with obstructive sleep apnea completed a constant routine protocol that consisted of sleep sessions in the evening (10 PM to 1 AM), morning (6 AM to 9 AM), and afternoon (2 PM to 5 PM). On one occasion the number and duration of breathing events was ascertained for each sleep session. On a second occasion the critical closing pressure that demarcated upper airway collapsibility was determined. The duration of breathing events was consistently greater in the morning compared with the evening and afternoon during N1 and N2, while an increase in event frequency was evident during N1. The critical closing pressure was increased in the morning (2.68 ± 0.98 cmH2O) compared with the evening (1.29 ± 0.91 cmH2O; P ≤ 0.02) and afternoon (1.25 ± 0.79; P ≤ 0.01). The increase in the critical closing pressure was correlated to the decrease in the baseline partial pressure of carbon dioxide in the morning compared with the afternoon and evening (r = -0.73, P ≤ 0.005). Our findings indicate that time of day affects the duration and frequency of events, coupled with alterations in upper airway collapsibility. We propose that increases in airway collapsibility in the morning may be linked to an endogenous modulation of baseline carbon dioxide levels and chemoreflex sensitivity (12), which are independent of the consequences of sleep apnea.
authors.affiliation: John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan; Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan;
authors.forename: Mohamad
authors.initials: M
authors.lastname: El-Chami
authors.affiliation: John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan; Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan;
authors.forename: David
authors.initials: D
authors.lastname: Shaheen
authors.affiliation: John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan; Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan;
authors.forename: Blake
authors.initials: B
authors.lastname: Ivers
authors.affiliation: John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan; Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan;
authors.forename: Ziauddin
authors.initials: Z
authors.lastname: Syed
authors.affiliation: John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan; Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan; Department of Biomedical Engineering, Wayne State University Detroit, Michigan.
authors.forename: M Safwan
authors.initials: MS
authors.lastname: Badr
authors.affiliation: John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan; Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan; Department of Otolaryngology-Head and Neck Surgery, Wayne State University School of Medicine and Karmanos Cancer Institute, Detroit, Michigan; and.
authors.forename: Ho-Sheng
authors.initials: HS
authors.lastname: Lin
authors.affiliation: John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan; Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan; Department of Internal Medicine, Wayne State University School of Medicine, Detroit, Michigan; jmateika@med.wayne.edu.
authors.forename: Jason H
authors.initials: JH
authors.lastname: Mateika
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000378:metabolism; D006801:Humans; D008297:Male; D011312:Pressure; D012119:Respiration; D012137:Respiratory System / Q000378:metabolism / Q000503:physiopathology*; D012890:Sleep / Q000502:physiology*; D020181:Sleep Apnea, Obstructive / Q000378:metabolism / Q000503:physiopathology*; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide
keywords: breathing event duration and frequency; circadian rhythm; passive and active critical closing pressure; upper airway muscle activity