title: Time of day affects chemoreflex sensitivity and the carbon dioxide reserve during NREM sleep in participants with sleep apnea.
abstract: Our investigation was designed to determine whether the time of day affects the carbon dioxide reserve and chemoreflex sensitivity during non-rapid eye movement (NREM) sleep. Ten healthy men 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). Between sleep sessions, the participants were awake. During each sleep session, core body temperature, baseline levels of carbon dioxide (PET(CO2)) and minute ventilation, as well as the PET(CO2) that demarcated the apneic threshold and hypocapnic ventilatory response, were measured. The nadir of core body temperature during sleep occurred in the morning and was accompanied by reductions in minute ventilation and PetCO2 compared with the evening and afternoon (minute ventilation: 5.3 ± 0.3 vs. 6.2 ± 0.2 vs. 6.1 ± 0.2 l/min, P < 0.02; PET(CO2): 39.7 ± 0.4 vs. 41.4 ± 0.6 vs. 40.4 ± 0.6 Torr, P < 0.02). The carbon dioxide reserve was reduced, and the hypocapnic ventilatory response increased in the morning compared with the evening and afternoon (carbon dioxide reserve: 2.1 ± 0.3 vs. 3.6 ± 0.5 vs. 3.5 ± 0.3 Torr, P < 0.002; hypocapnic ventilatory response: 2.3 ± 0.3 vs. 1.6 ± 0.2 vs. 1.8 ± 0.2 l·min(-1)·mmHg(-1), P < 0.001). We conclude that time of day affects chemoreflex properties during sleep, which may contribute to increases in breathing instability in the morning compared with other periods throughout the day/night cycle in individuals with 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 & 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: D056044:Actigraphy; D000204:Activity Cycles; D000328:Adult; D001833:Body Temperature Regulation; D002245:Carbon Dioxide / Q000378:metabolism*; D002628:Chemoreceptor Cells / Q000378:metabolism*; D002940:Circadian Rhythm; D006801:Humans; D008168:Lung / Q000294:innervation*; D008297:Male; D017286:Polysomnography; D012123:Pulmonary Ventilation; D012018:Reflex; D015656:Respiratory Mechanics; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis / Q000378:metabolism* / Q000503:physiopathology; D012894:Sleep Stages; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide
keywords: circadian rhythm; inherent characteristics; intermittent hypoxia; minute ventilation