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factors affecting blood pressure

Updated on February 9, 2015

F actors that affect blood pressure include:

a) Elasticity of blood vessels.

b) The total blood volume.

c) Cardiac output

d) Peripheral Resistance


a) Elasticity of blood vessels.

Healthy blood vessels are usually elastic. This enables them to absorb the shock of systolic pressure. Inelastic blood vessels either as a result of arteriosclerosis, do not absorb systolic pressure; this pressure is thus maintained in blood resulting into a case of high blood pressure. Such a case can result in weakening of blood vessels.

b) The total blood volume.

Total blood volume refers to the percentage of blood in the body in relation to body weight, usually about 8% of the body weight. A high blood volume results in more fluid acting on the walls of blood vessels, thus a high blood pressure. The reverse is also applicable whereby the blood volume is low (e.g. excessive sweating).

c) Cardiac Output

A high cardiac output, means that more pressure is acting on the walls blood vessels resulting into high blood pressure, this is applicable for instance when a person takes caffeine, the heart beat rises leading to a higher cardiac output. A low cardiac output results in low blood pressure, for instance as a result of taking depressants.

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d) Peripheral Resistance

This refers to the resistance generated as a result of blood acting upon blood vessels as it flows. This resistance is normally affected by three factors:

i. Length of blood vessel.

ii. Blood viscosity (Hematocrit).

iii. Diameter of blood vessel.


i. Length of blood vessel.

Target cells located away from the body also require an efficient blood supply. The longer the blood vessel, the higher the resistance, the higher the blood pressure since blood has to reach the target cells in time.

ii. Blood Viscosity.

Also hematocrit, this refers to the percentage of red blood cells in blood. The higher the hematocrit, the higher the resistance, the higher the blood pressure in order to replenish blood cells in time. The reverse is applicable when the hematocrit is low.

iii. Diameter of blood vessel.

A small blood vessel diameter means that more blood is in contact with the walls of blood vessels thus more resistance, blood pressure increases to catch up. The reverse is true, whereby the blood vessels have a larger diameter. We also have a case of vasoconstriction and vasodilation. Blood vessels undergo vasoconstriction to increase blood pressure, for instance in low temperatures to warm the body since the rate of respiration rises. Vasodilation on the other hand occurs to reduce blood pressure, for instance under high temperatures to help calm the body.

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