Blood pressure

Hydrostatic pressure

Pressure of a fluid against the walls of a closed container is called hydrostatic pressure

Blood pressure is a form of hydrostatic pressure

• It is the pressure applied against blood vessel walls when we temporarily occlude it with a sphygmomanometer and its inflatable cuff

Hydraulic blood pressure can also be measured as blood is in motion

• A more invasive procedures when a canula is inserted into an artery

• Usually reserved for lengthy surgeries and intensive care units

• Allows for blood pressure to be monitored continuously

Factor #1 that affect blood pressure

Total Blood Volume

Since we are studying the normal, adult cardiovascular system, we can consider the volume of the cardiovascular system as constant

Therefore,

• As blood volume increases, the pressure inside the network will increase

• As blood volume decreases, the pressure inside the network will decrease

Can the volume of blood change?

Yes, the volume of blood in your body can absolutely change, and it is constantly being regulated to meet your body's demands. While an average adult has about 5 liters of blood, this volume fluctuates based on factors like hydration, physical activity, and medical conditions.

Total blood volume is managed by the _____ (organ) and the volume of urine they produce

kidneys

Factor #2 that affect blood pressure

Total Peripheral Resistance

Total Peripheral Resistance

is the opposition to the flow of blood through vessels due to friction

• Blood cells lose kinetic energy when they rub against each other and vessel walls

Total Peripheral Resistance is directly related to pressure in a blood vessel

as TPR increases, blood pressure increases, and as TPR decreases, blood pressure decreases

Subfactors that affect Total Peripheral Resistance

• Vessel diameter

• Blood viscosity

• Vessel length

Vessel diameter, vasoconstriction, and vasodilation

Vessel diameter

• diameter or radius of the lumen that blood has to pass through

Vasoconstriction

• decreases the diameter of the lumen, increases resistance, and decreases blood flow to subsequent vessels and tissues

Vasodilation

• increases the diameter of the lumen, decreases resistance, and increases blood flow to subsequent vessels and tissues

Blood viscosity

Thickness of blood

• increased thickness leads to increased resistance

• more water/plasma, decreases thickness and decreases resistance

Vessel length

• The longer the vessel, the greater the resistance

How long would it take for each of these factors to change?

• Which can change immediately with the correct stimulus?

• Which can change within many minutes to less than an house?

• Which would require days or weeks to show changes?

Factor #3 that affects blood pressure

Cardiac output

Cardiac output

is the total amount of blood pumped by the left ventricle in one minute

• Two sub factors affect this….

→ heart rate (HR): the number of heart beats (cardiac cycles) per minute

→ stroke volume (SV): the volume of blood pumped by one ventricle during a contraction

→ Cardiac output: HR x SV