Lung aeration during sleep.
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 (R(2) = 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.
Appelberg
Jonas
J
Department of Clinical Physiology, Sundsvall Hospital, Sundsvall, Sweden.
Pavlenko
Tatjana
T
Bergman
Henrik
H
Rothen
Hans Ulrich
HU
Hedenstierna
Göran
G
D000328:Adult; D005260:Female; D005652:Functional Residual Capacity / Q000502:physiology*; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000502:physiology*; D008297:Male; D010092:Oximetry; D017286:Polysomnography; D012129:Respiratory Function Tests; D012890:Sleep / Q000502:physiology*; D016683:Supine Position; D036542:Tomography, Spiral Computed