Blood pressure is a measure of tension exerted by blood against the walls of the arteries. It denotes the force of ventricular contraction, the resistance within the arterioles and the capillaries and the volume and viscosity of blood. Accurate measurement of blood pressure in the presence of findings in the history and physical examination of a patient can bring to light a diagnosis that may pertain to any of the above factors. This is why measurement of blood pressure is an integral part of general as well as cardiovascular examination. There are several processes that control the blood pressure. The two most important mechanisms are a baroreceptor mechanism and a rennin-angiotensin-aldosterone system. The baroreceptor mechanism works through stretch receptors present within the carotid sinus. A fall in arterial pressure causes a fall in the stretch on the walls of the carotid sinus leading to a fall in the firing rate of carotid sinus nerve, Hering’s nerve and CN IX (Klabunde 2007), which carries information to the brain. In the brain, the set point for mean arterial pressure is 100mmHg and a pressure of less than that triggers responses that include increased sympathetic outflow to the heart and blood vessels and decreased parasympathetic outflow to the heart. As a result, there is an increase in the heart rate, contractility end stroke volume, vasoconstriction of arterioles and vasoconstriction of veins leading to an overall increase in total peripheral resistance and an increase
in blood pressure to the set point.