title: Lung aeration during sleep.
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 (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.
authors.affiliation: Department of Clinical Physiology, Sundsvall Hospital, Sundsvall, Sweden.
authors.forename: Jonas
authors.initials: J
authors.lastname: Appelberg
authors.forename: Tatjana
authors.initials: T
authors.lastname: Pavlenko
authors.forename: Henrik
authors.initials: H
authors.lastname: Bergman
authors.forename: Hans Ulrich
authors.initials: HU
authors.lastname: Rothen
authors.forename: Göran
authors.initials: G
authors.lastname: Hedenstierna
mesh_terms: 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