What is blood pressure?
The force exerted by blood upon the walls of blood vessels or the chambers of the heart.
What is systolic pressure?
The peak arterial pressure resulting from ventricular contraction.
What is diastolic pressure?
The arterial pressure during ventricular relaxation.
How is pulse pressure calculated?
Pulse pressure = Systolic pressure − Diastolic pressure.
What is considered a low (narrow) pulse pressure?
A pulse pressure <25% of systolic pressure.
What is mean arterial pressure (MAP)?
The average pressure of blood in the arteries over a cardiac cycle.
How can MAP be estimated?
MAP ≈ Diastolic pressure + 1/3 Pulse pressure OR 1/3 Systolic + 2/3 Diastolic.
What factors determine blood pressure?
Cardiac output, compliance, blood volume, blood viscosity, and vessel length/diameter.
How does cardiac output affect BP?
Increased CO raises BP; decreased CO lowers BP.
What is compliance?
The ability of a vessel to expand to accommodate increased blood volume.
What happens when arteries stiffen?
Compliance decreases and resistance increases, raising BP.
How does blood volume affect BP?
↓ volume (>20%) lowers BP; ↑ volume (water/sodium retention) increases BP.
How does viscosity affect BP?
Higher viscosity increases resistance and decreases flow.
How does vessel length affect resistance?
Longer vessels increase resistance; shorter vessels decrease resistance.
How does vessel radius affect resistance?
Resistance is inversely proportional to radius^4 (Poiseuille’s Law).
What is venous return?
Blood flow back to the heart, driven by a pressure gradient where venous pressure > atrial pressure.
What helps maintain venous return?
Low atrial pressure during diastole and two pumps: skeletal muscle pump and respiratory pump.
How does the skeletal muscle pump work?
Muscle contractions compress veins, pushing blood upward; valves prevent backflow.
How does the respiratory pump work?
Inhalation reduces thoracic pressure, drawing blood into thoracic veins; exhalation increases flow into the heart.
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