Variability of carotid occlusion response as affected by vagotomy and open pneumothorax

¹ Department of Pharmacology, Toxicology, and Experimental Therapeutics, University of California School of Medicine, Los Angeles, California

The carotid occlusion response has been measured in the anesthetized, intact cat at different durations of occlusion. It is difficult to use this reflex for quantitative studies as variations of response to a constant duration of occlusion is considerable and the relationship between response and duration of occlusion is complex. A cat with a bilateral vagotomy and open pneumothorax has been shown to have distinct advantages over other preparations studied, which included bilateral vagotomy alone, open pneumothorax alone and the intact preparation. The response is increased in height, the variation in response to a constant occlusion is reduced at durations of occlusion greater than 7.5 seconds, the relationship between the duration of occlusion and the magnitude of the response is simple, and the median effective duration shows very little variation between animals. The increase in amplitude of the response and the change from a complex to a simple relationship between duration and magnitude is most likely due to the removal of the active baroreceptor buffering mechanism on vagotomy. The variation in response is probably reduced because this procedure removes some of the factors that contribute to the total variation in the intact animal.