[Regulation of breathing in conditions of changed gas density and with resistance loading].

In anesthetized cats, an additional resistance for breathing entailed an increase in the work of respiratory muscles and some deceleration of respiratory cycles, particularly during hyperpnoe caused by hypercapnia. Inhalation of a mixture of increased density (SF6-O2) exerted a similar effect. The compensatory increase in the work of respiratory muscles persisted after bilateral vagotomy whereas the response to inhalation of the mixture disappeared. This suggests that extravagal reflexes take part in optimization of breathing in conditions of external resistance whereas the effect of high density of inhaled gas developes, mainly, through the afferent system of the lungs.