To the Editor:—
Boyce and Peters 1describe the interesting case of complete vasomotor collapse during resection of a recurrent right carotid body tumor involving the right carotid bifurcation requiring excision and autologous vein grafting. The authors suggest mechanical or electrical stimulation of the right carotid sinus nerve as the initiating event leading to vasomotor collapse. Rarely, however, does a significant increase in afferent activity from a single baroreceptor site result in the described persistent profound hypotension because of compensation from other baroreceptor sites, even in the absence of a right vagus nerve.
Alternatively, if in this patient the tumor had infiltrated the right carotid sinus wall such that no deformation (strain) of the baroreceptors could take place as can occur in severe carotid atherosclerosis, 2then there would be no afferent neural input to the hindbrain from this site. Under these circumstances, the vasomotor integration centers in the hindbrain would not recognize zero input from the right carotid sinus as a legitimate null signal, particularly in the presence of normal afferent signals from other baroreceptor sites. 3Subsequently, sudden significant afferent activity in the right carotid sinus nerve, either from exogenous deformation of the sinus wall or direct stimulation, would probably be interpreted as a very significant signal by the hindbrain because of the neural history from this site, resulting in the reported dramatic decrease in blood pressure. A similar phenomenon is occasionally seen during carotid endarterectomy when severe atherosclerotic plaque is suddenly removed from the carotid sinus area. 4,5