CARDIOVASCULAR - 6 BLOOD PRESSURE

Arterial Blood Pressure Blood Pressure – force the blood exerts against the inner walls of the blood vessels Arterial Blood Pressure rises when ventricles contract falls when ventricles relax systolic pressure – maximum pressure diastolic pressure – minimum pressure

What factors affect Blood Pressure? Affected by blood volume/stroke volume, total peripheral resistance (e.g. vasoconstriction), and cardiac rate Increase in any of these will increase blood pressure. Arterial blood = cardiac x total peripheral pressure output resistance Vasoconstriction of arterioles raises blood pressure upstream in the arteries.

Blood Pressure versus total x-sectional area of vessels Blood pressure is related to the total cross-sectional area of blood vessels Capillary blood pressure is low because of large total cross-sectional area. Artery blood pressure is high because of small total cross-sectional area

Blood Pressure Regulation Kidneys - control blood volume and thus stroke volume. Sympathoadrenal system stimulates vasoconstriction of arterioles (raising total peripheral resistance) and increased cardiac output. Baroreceptor reflex – occurs when changes in blood pressure are detected by baroreceptors (stretch resulting from pressure) in aortic arch and carotid sinuses  action potentials to vasomotor and cardiac control center in medulla  vasoconstriction or dilation AND control of heart rate

Structures involved in the Baroreceptor Reflex

Atrial Stretch Reflexes Activated by increased venous return to: Stimulate reflex tachycardia Inhibit ADH release; results in excretion of more urine Stimulate secretion of atrial natriuretic peptide; results in excretion of more salts and water in urine  lowers b.p.

Blood Pressure Measurement Measured in mmHg by sphygmomanometer. A cuff is wrapped around upper arm and inflated to beyond systolic b.p. to pinch off brachial artery. As pressure is released, first sound is heard at systole  take reading. The last Korotkoff sound is heard when pressure in cuff reaches diastolic pressure  take 2nd reading. AVG. b.p. = 120/80.

Five Phases of Blood Pressure Measurement KOROTKOFF SOUNDS VIDEO

Pulse Pressure “Taking the pulse” is a measure of heart rate. What the health professional feels is increased blood pressure in that artery at systole. The difference between blood pressure at systole and at diastole is the pulse pressure. If your blood pressure is 120/80, your pulse pressure is 40 mmHg. Pulse pressure is a reflection of stroke volume

Mean Arterial Pressure The average pressure in the arteries during one cardiac cycle is the mean arterial pressure. This is significant because it is the difference between mean arterial pressure and venous pressure that drives the blood into the capillaries. Calculated as: diastolic pressure + 1/3 pulse pressure

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