Regulation of Mean Arterial Pressure

Key Concepts

Mean Arterial Pressure (MAP): A vital measure of blood flow, organ perfusion, and cardiovascular health.
Involves the regulation of:
- Cardiac output
- Systemic vascular resistance
- Venous return

Definition: Blood returning to the heart from the veins.
Significance:
- Determines end diastolic volume (EDV).
- Influences stroke volume via the Frank Starling mechanism.
Veins:
- Capacitance vessels serving as volume reservoirs.
- Surrounded by smooth muscle; contraction (vasoconstriction) stiffens veins.
- Innervated by sympathetic nerves acting on alpha receptors.
- Sympathetic Stimulation: Causes smooth muscle contraction, reducing compliance and capacitance, pushing blood back to heart — increases venous return.
Skeletal Muscle Pump:
- Function: During exercise, skeletal muscles compress veins, reducing volume and pushing blood to the heart.
Respiratory Pump:
- Mechanism: Thoracic cavity volume increases during inspiration, reducing pressure per Boyle's Law, enhancing venous return.

Definition: Resistance left ventricle must overcome to pump blood.
Primary Site: Arterioles (resistance vessels).
Influenced by:
- Arterioles changes
- Outflow tract valves (e.g., Aortic valve issues like stenosis increase resistance).

Using Ohm's Law:
- Pressure = Flow x Resistance
- In Blood Terms:
  - Pressure = Cardiac Output x Systemic Vascular Resistance
  - Cardiac Output: Stroke Volume x Heart Rate
Regulation:
- Adjustments in stroke volume, heart rate, and SVR can regulate MAP.

Heart Rate:
- Increase leads to increased flow, higher blood pressure.
Systemic Vascular Resistance:
- Vasoconstriction raises resistance, increases arterial pressure.

Preload:
- Amount of blood filling ventricles before contraction, related to venous return, affects stroke volume.
Afterload:
- Refers to systemic vascular resistance.