Study of heart rate and blood pressure changes under distension of right and left atrial appendages in dogs.

Fifteen healthy stray dogs of both sexes were employed in the present study. The effect of distension of right and left atrial appendages with normal saline was observed on heart rate and blood pressure under different situations. It has been found that distension of either appendages separately or simultaneously invariably evoked tachycardia without any appreciable change in blood pressure. Increase in heart rate was found to be of a same magnitude with 5 ml normal saline in both the atrial appendages. However, a higher response was obtained with 10 ml normal saline distension in case of right atrial appendage as compared to left one. Increase in the extent of distension causes more significant response, the receptors of which are stimulated and may be allied to stretch receptors. It is contended that tachycardia could be a reflex effect which is abolished by vagotomy. It is further contended that either afferent, efferent or both pathways exist in the vagi.