Effect of SO2 on control of breathing in anesthetized cats

In seven anesthetized tracheotomized cats we studied the acute respiratory effects of SO2 inhalation at different steady-state levels of arterial CO2 tension (Paco2). During room air breathing, SO2 (0.05%) addition caused a progressive reduction in tidal volume (VT) and increases in both respiratory frequency (f) and pulmonary resistance (RL). Atropine sulfate abolished the bronchoconstriction response to SO2 and thus permitted the study of the influence of SO2 on VT and f in the absence of constricted airways. Despite marked reductions in the VT VS. PaCO2 relationships with SO2 exposure after atropine, the relationship between pulmonary ventilation (VE) and PaCO2 was not signifcantly altered. This was the case since SO2 caused solely a reduction in inspiratory duration (Ti), affecting neither the mean rate of rise of inspiratory activity (i.e., VT/Ti) nor the relationship between Ti and breath duration. Thus, airways irritation with SO2 produced rapid, shallow breathing characterized by a shortening of inspiratory and total respiratory cycle times with no change in the rate of development of inspiratory activity. The findings suggest an influence exclusively concerned with the timing of inspiration. Perhaps premature onset of inspiratory activity accounts for the observed effects.