BREATHING STRATEGY

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The respiratory pump is a robust multi-muscle pump. The actions of various respiratory muscles are highly redundant and provide the means to maintain ventilation under a wide range of conditions. In quadrupeds, quiet breathing is accomplished by the coordinated activation of various respiratory muscles, including those classically considered as being silent, the expiratory muscles. Coordination of the different respiratory muscles is crucial in producing effective and efficient displacements of chest wall structures. In anesthetized animals, conditions producing reductions in the mechanical efficiency of the diaphragm are associated with increases in the active nature of the expiratory phase of breathing. Under these conditions, the expiratory muscles are critical in maintaining ventilation. The active nature of expiration is also present during quiet breathing in awake prone animals, although their response to reduction in inspiratory muscle efficiency have not been addressed. The goal of studies outlined in the proposal is to determine the use, coordination, and mechanical coupling of respiratory muscles in awake animals and to investigate the strategies employed in maintaining ventilation in various physiological and pathophysiological conditions of reduced diaphragm efficiency. We hypothesize that inspiratory and expiratory muscles in awake quadrupeds function synergistically in the maintenance of tidal volume. More specifically, we hypothesize that in states of reduced inspiratory muscle efficiency, ventilation and adequate gas exchange are maintained in awake animals through an augmented role exerted by the expiratory musculature. Reduced inspiratory muscle efficiency will be produced acutely following changes in posture (Specific Aim A) and chronically following papain- induced emphysema (Specific Aim B). To test the above hypothesis, we will 1) assess the activation and coordination of various respiratory pump muscles in awake spontaneously breathing dogs, 2) assess the active and passive mechanical consequences of the activation and coordination between the various muscles, 3) assess the functional role of the inspiratory/expiratory phase of breathing in the generation of tidal volume, and 4) assess the operational lengths of the respiratory pump muscles in awake animals indexed to their optimal force producing length. Descriptions of activation events (EMG and blood flows) and mechanical events (change in muscle length, volume displacements) are viewed as complimentary in developing an analysis of respiratory muscle function and coordination. Because the effects of muscle interactions are still largely unknown, the studies outlined in this proposal should provide new information on the functional organization of the respiratory pump muscles and on their integration in health and in disease.