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(Chest. 2007;131:122-129.)
© 2007 American College of Chest Physicians

Lung Aeration During Sleep*

Jonas Appelberg, PhD; Tatjana Pavlenko, PhD; Henrik Bergman, MD; Hans Ulrich Rothen, MD, PhD and Göran Hedenstierna, MD, PhD

* From the Department of Clinical Physiology (Dr. Appelberg), Sundsvall Hospital, Sundsvall, Sweden; Department of Medical Sciences (Dr. Hedenstierna), Clinical Physiology, University Hospital, Uppsala, Sweden; Research and Development Centre (Dr. Pavlenko), Västernorrland County Council, Sundsvall, Sweden; Department of Radiology (Dr. Bergman), Sundsvall Hospital, Sundsvall, Sweden; and Department of Anaesthesia (Dr. Rothen), University Hospital, Bern, Switzerland.

Correspondence to: Göran Hedenstierna, MD, PhD, Department of Medical Sciences, Clinical Physiology, University Hospital, SE-751 85, Uppsala, Sweden; e-mail goran.hedenstierna{at}medsci.uu.se

Abstract

Background: During sleep, ventilation and functional residual capacity (FRC) decrease slightly. This study addresses regional lung aeration during wakefulness and sleep.

Methods: Ten healthy subjects underwent spirometry awake and with polysomnography, including pulse oximetry, and also CT when awake and during sleep. Lung aeration in different lung regions was analyzed. Another three subjects were studied awake to develop a protocol for dynamic CT scanning during breathing.

Results: Aeration in the dorsal, dependent lung region decreased from a mean of 1.14 ± 0.34 mL (± SD) of gas per gram of lung tissue during wakefulness to 1.04 ± 0.29 mL/g during non-rapid eye movement (NREM) sleep (– 9%) [p = 0.034]. In contrast, aeration increased in the most ventral, nondependent lung region, from 3.52 ± 0.77 to 3.73 ± 0.83 mL/g (+ 6%) [p = 0.007]. In one subject studied during rapid eye movement (REM) sleep, aeration decreased from 0.84 to 0.65 mL/g (– 23%). The fall in dorsal lung aeration during sleep correlated to awake FRC (R2 = 0.60; p = 0.008). Airway closure, measured awake, occurred near and sometimes above the FRC level. Ventilation tended to be larger in dependent, dorsal lung regions, both awake and during sleep (upper region vs lower region, 3.8% vs 4.9% awake, p = 0.16, and 4.5% vs 5.5% asleep, p = 0.09, respectively).

Conclusions: Aeration is reduced in dependent lung regions and increased in ventral regions during NREM and REM sleep. Ventilation was more uniformly distributed between upper and lower lung regions than has previously been reported in awake, upright subjects. Reduced respiratory muscle tone and airway closure are likely causative factors.

Key Words: airway closure • anesthesia • CT • lung aeration • lung volume • sleep • ventilation






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