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Factors affecting arterial blood pressures

Odai Abdelraheem Khlaif ID: 1302

Blood pressure

Blood pressure is the pressure of circulating blood against the walls of blood vessels. Most of this pressure
results from the heart pumping blood through the circulatory system. When used without qualification, the term
"blood pressure" refers to the pressure in the large arteries.

What does a blood pressure reading look like?

When you have your blood pressure measured, you will be given two numbers, a top number and a bottom
number.

o Systolic blood pressure. This is the first, or top, number. This is the highest level your blood pressure
reaches when your heart beats, forcing blood around your body.
o Diastolic blood pressure. The second number, or bottom number, is the lowest level your blood
pressure reaches as your heart relaxes between beats.

Blood pressure is measured in millimetres of mercury (mmHg). If the first number is 120 and the second
number is 80, this would be written as 120/80mmHg, and you’d call it ‘120 over 80’.

Factors That Influence Arterial Blood Pressure

1. Cardiac output
2. Peripheral vascular resistance
3. Volume of circulating blood
4. Viscosity of blood
5. Elasticity of vessels walls

Blood pressure increases with increased cardiac output, peripheral vascular resistance, volume of blood,
viscosity of blood and rigidity of vessel walls.

Blood pressure decreases with decreased cardiac output, peripheral vascular resistance, volume of blood,
viscosity of blood and elasticity of vessel walls.

Cardiac Output

Cardiac output is the volume of blood flow from the heart through the ventricles, and is usually measured in
litres per minute (L/min). Cardiac output can be calculated by the stroke volume multiplied by the heart rate.
Any factor that causes cardiac output to increase, by elevating heart rate or stroke volume or both, will elevate
blood pressure and promote blood flow. These factors include sympathetic stimulation, the catecholamines
epinephrine and norepinephrine, thyroid hormones, and increased calcium ion levels. Conversely, any factor
that decreases cardiac output, by decreasing heart rate or stroke volume or both, will decrease arterial pressure
and blood flow. These factors include parasympathetic stimulation, elevated or decreased potassium ion levels,
decreased calcium levels, anoxia, and acidosis.
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