CHANGES IN THE BALANCE OF RESPIRATORY DRIVES RESULTING FROM OPEN PNEUMOTHORAX

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Abstract
Bilateral open pneumothorax in the anesthetized dog produced a systematic progression of changes in breathing. The first effect was a marked intensification and prolongation of inspiratory activity associated with a relatively weak expiratory activity. The 2d effect was a slowly increasing intensity of both inspiratory and expiratory activity in which the increase of expiratory activity predominated. This led to a shortening of the inspiratory phase and to an acceleration of breathing. Acceleration of breathing continued up to an equalization of inspiratory and expiratory activity. Passing that point expiratory activity predominated, leading to a marked prolongation of the expiratory phase and to a diminution in the respiratory rhythm. The marked intensification and prolongation of the inspiratory act at the beginning of pneumothorax was attributed to a combined change in vagal proprioeeptive drives[long dash]a powerful inspiratory excitatory pulmonary deflation reflex replaces a predominantly expiratory excitatory stretch reflex. The acceleration of the frequency of breathing was attributed to a disproportionately increasing intensity of expiratory activity. This increasing expiratory activity was thought to originate in the increasing asphyxial chemical drive operating more powerfully on the expiratory half center and in a progressive synaptic summation of expiratory drives originating in excessive deformation of proprioeeptive endings in the respiratory muscles and their attachments and joints. The final slowing of respiratory rhythm is attributed to an intensified reciprocal inhibition of the inspiratory half center associated with the increasing predominance of expiratory activity.

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