Respiratory mechanics during ventricular asystole in dogs with complete heart block.

Abstract

Eleven mongrel dogs were studied in which complete heart block had been produced surgically. Ventricular rate was maintained by artificial stimulation until the time of study. Each experiment involved abrupt cessation of stimulation and the monitoring of pulmonary mechanical behavior during the ensuing period of ventricular asystole. These studies have shown that all aspects of the mechanical behavior of the lungs are altered during ventricular asystole in complete heart block. The changes which occur during this short interval of time are basically attributable to the systemic, stagnant hypoxia and the central vascular congestion. The pulmonary changes produced include augmentation of the rate and depth of breathing, reduction of the functional residual capacity, decreased pulmonary compliance, and increased pulmonary airway resistance. The result is that both the inspiratory and expiratory work of breathing are increased, while the efficiency of breathing is decreased. All of these alterations occur within the 20-second period of ventricular asystole and are restored to control levels soon after the re-establishment of a normal ventricular rate. The possible mechanisms involved are discussed.