Two students, Vineet and Kamlesh were asked to demonstrate in dogs the role of sinus nerve in hypovolemic shock. Vineet severed the sinus nerve when the mean blood pressure (MBP) was 85 mm Hg and Kamlesh cut the sinus nerve when the mean blood pressure was 60 mm Hg. On cutting the sinus nerve

Carotid sinus activation decreases cardiac contractility, heart rate and BP. When the sinus nerve is cut, the control is lost and the mean BP increases. This happens only if the mean BP is above 70mmHg. Normally when mean BP is below 70mmHg, the chemoreceptors get stimulated to cause an increase in BP. At that level of mean BP, baroreceptor discharge is extremely low as BP is already low. So when the sinus nerve is cut at mean BP below 70mmHg, the chemoreceptor activity gets hindered. Hence chemoreceptor mediated vasoconstriction and BP elevation are blocked. This will lead to further fall in mean BP. In the given scenario, Vineet cut the sinus nerve when the mean BP was 85mmHg. So the mean BP after severing the nerve will increase. Kamlesh cut the sinus nerve when the mean BP was 60mmHg. So the mean BP after severing the nerve will decrease.