title: How absolute EIT reflects the dependence of unilateral lung aeration on hyper-gravity and weightlessness?
abstract: We studied the influence of three gravity levels (0, 1 and 1.8 g) on unilateral lung aeration in a left lateral position by the application of absolute electrical impedance tomography. The electrical resistivity of the lung tissue was considered to be a meaningful indicator for lung aeration since changes in resistivity have already been validated in other studies to be proportional to changes in lung volume. Twenty-two healthy volunteers were studied during parabolic flights with three phases of different gravity, each lasting ∼20-22 s. Spontaneous breathing at normal tidal volume VT and at increased VT was performed. During transition to hyper-gravity mean expiratory resistivities (±SD in Ωm) increased at normal VT in the upper (right) lung from 7.6 ± 1.5 to 8.0 ± 1.7 and decreased from 5.8 ± 1.2 to 5.7 ± 1.2 in the lower (left) lung. Inspiratory resistivity values are 8.3 ± 1.6 to 8.8 ± 1.8 (right) and 6.3 ± 1.3 to 6.0 ± 1.3 (left). At increased VT, the changes in resistivities at end-expiration were 7.7 ± 1.5 to 8.0 ± 1.7 (right) and 5.8 ± 1.2 to 5.7 ± 1.2 (left). Corresponding end-inspiratory values are 9.9 ± 1.9 to 10.0 ± 2.0 (right) and 8.6 ± 2.1 to 7.9 ± 2.0 (left). During weightlessness, the distortion in the lungs disappeared and both lungs showed a nearly identical aeration, which was between the levels displayed at normal gravity. The small increase in resistivity for the upper lung during transition to hyper-gravity from 1 to 1.8 g at increased VT suggests that the degressive part of the pressure-volume curve has already been reached at end-inspiration. The results for a left lateral position are in agreement with West's lung model which has been introduced for cranio-caudal gravity dependence in the lungs.
authors: Department of Anaesthesiology, Emergency and Intensive Care Medicine, University Medical Centre Göttingen, University of Göttingen, Robert-Koch-Str. 40, D-37075 Göttingen, Germany. ghahn@gwdg.de
authors: G
authors: G
authors: Hahn
authors: A
authors: A
authors: Just
authors: G
authors: G
authors: Hellige
authors: J
authors: J
authors: Dittmar
authors: M
authors: M
authors: Quintel
mesh_terms: D000328:Adult; D017097:Electric Impedance; D005260:Female; D006801:Humans; D018471:Hypergravity; D008168:Lung / Q000166:cytology / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D012123:Pulmonary Ventilation; D012119:Respiration; D012129:Respiratory Function Tests; D014054:Tomography; D014893:Weightlessness; D055815:Young Adult