Blood Pressure

Factors that control blood pressure

• Blood pressure (BP) = Cardiac output (CO) x Peripheral vascular resistance (PVR)
• And CO = Stroke volume (SV) x Heart rate (HR)
• Therefore BP = CO x PVR = SV x HR x PVR

Any hemodynamic factors affecting stroke volume (volume status, cardiac contractility), heart rate, or peripheral arterial resistance (vascular tone) will affect blood pressure.

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Factors affecting organ flow

Blood flow = perfusion pressure / vascular resistance

Perfusion pressure = mean arterial pressure – mean venous pressure

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Role of baroreceptors (carotid/aortic arch) in BP control

Baroreceptors are stretch receptors in the carotid sinus and aortic arch (vessel walls) that maintain BP within a normal range and respond to changes in BP to normalize it.

Increase in BP results in an inhibition of the sympathetic outflow from the vasomotor center and increase in vagal tone causing vasodilation as well as a decrease in HR and contractility, which collectively reduce BP.

A reduction in BP has the opposite effects.

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Role of atrial volume receptors

Cardiopulmonary (stretch) receptors: These receptors located in the left atrium, right atrium, pulmonary arteries, and ventricular endocardium, are activated by increased volume. They send signals to the brain to inhibit sympathetic outflow and increase vagal activity to reduce arterial vasomotor tone and decrease BP.