A major determinant of preload is distribution of blood volume between which compartments?

A major determinant of preload is distribution of blood volume between which compartments?

• A. Intra-thoracic compartments
• B. Intra and extra thoracic compartments
• C. Systemic and pulmonary circulations
• D. Arterial and venous blood compartments

Answer: (B)

Preload is about how much blood returns to and fills the ventricles before they pump. The main factor that governs this filling is where the blood volume sits in the venous system. If most blood is in the intrathoracic (central) compartment, central venous pressure rises and more blood flows into the heart, increasing preload. If more blood pools in the extrathoracic (peripheral) compartments, central venous pressure falls and preload decreases. Things like standing (which promotes venous pooling in the legs) or abdominal pressure changes can shift this distribution and markedly alter preload. So, the distribution of blood volume between intra-thoracic (central) and extra-thoracic (peripheral) compartments is the key determinant.

Preload is about how much blood returns to and fills the ventricles before they pump. The main factor that governs this filling is where the blood volume sits in the venous system. If most blood is in the intrathoracic (central) compartment, central venous pressure rises and more blood flows into the heart, increasing preload. If more blood pools in the extrathoracic (peripheral) compartments, central venous pressure falls and preload decreases. Things like standing (which promotes venous pooling in the legs) or abdominal pressure changes can shift this distribution and markedly alter preload. So, the distribution of blood volume between intra-thoracic (central) and extra-thoracic (peripheral) compartments is the key determinant.