Influence of cardiac action on gas mixing in closed-chest dogs. Zhang, Shaoping, Alan R. Saltzman, Robert A. Klocke. Departments of Medicine and Physiology, State University of New York at Buffalo, Buffalo, New York 14214
APStracts 2:0117A, 1995.
We performed single-breath tests (SBT) in closed-chest, paralyzed, anesthetized dogs (six with bilateral vagotomy and six with intact vagi) with the heart beating and during cardiac arrest. Repeated cardiac arrest was achieved by ventricular fibrillation and subsequent defibrillation. Twenty-four SBT's per dog were performed in combinations of three inspiratory volumes (VI) (0.2, 0.5 and 0.8 l) and four post-inspiratory pauses (0, 5, 10 and 30 s), either with or without cardiac arrest. The test gas contained four inert, relatively insoluble gases (helium, neon, argon and sulfur hexafluoride) with a six fold range in diffusivity. Series dead space (VD) decreased with increasing post-inspiratory pause, with increasing gas diffusivity or with decreasing VI. In vagotomized animals VD was smaller with the heart beating than during cardiac arrest, but this relationship was reversed in animals with intact vagi. The decrease in VD due to cardiogenic mixing accounted for only 10.8% of the total decrease in VD occurring during a 30 s post -inspiratory pause. The slope of phase III decreased with increasing post-inspiratory pause except at VI of 0.2 l. No significant differences were noted in the slope of phase III between experiments performed with the heart beating or arrested. Tracer gas retained in the residual volume following expiration increased with increasing inspiratory pause. Gas retention was greater for helium than SF6 but was not affected by cardiac action. These findings indicate that cardiac action mainly affects the interface between inspired and alveolar gas, and has little effect on mixing in the alveolar compartment. 

Received 10 May 1994; accepted in final form 10 March 1995.
APS Manuscript Number A448-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 March 1995.