Effect of body position on lung emptying in recumbent anesthetized dogs

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Abstract
Closing volume (CV) was determined in the prone, supine and left lateral positions in 14 anesthetized dogs using the single-breath O2 test. N2 concentration, transpulmonary pressure, airway pressure, expiratory flow rate and volume changes were recorded simultaneously during expiration from total lung capacity to residual volume (RV). Closing capacity (CC = CV + RV) was significantly greater in the supine than in either the prone or the left lateral position. The greater CC in the supine posture may be related to lower lung recoil or to the volume and distribution of intrathoracic blood. CC was significantly less than functional residual capacity in all positions. Phase III slope was lowest in the prone position. In 4 awake dogs, FRC exceeding CC and similar effects of body position on CC and phase III slope were observed. Lung volume at the inflection point of the quasi-static deflation pressure-volume curve (VIP) was obtained as described by Glaister. In all postures, absolute VIP was significantly higher than CC and there was no significant difference in absolute VIP between positions. An effect of expiratory flow rate below 1 l/s on CC or CV in 6 supine dogs was not demonstrated.

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