L2: Pulmonary Circ

What is the relationship between pulmonary artery pressure and pulmonary blood resistance?

Pulmonary circulation has low pressure and low resistance compared to systemic circulation. ​

During exercise, pulmonary arterial pressure increases, but resistance decreases due to vessel distension and recruitment, allowing increased blood flow without a large rise in pressure.

What are the effects of distension and recruitment on pulmonary blood pressure?

Distension and recruitment of pulmonary capillaries decrease vascular resistance, allowing increased blood flow. ​ During exercise, non-perfused or poorly perfused vessels open, and existing vessels dilate, accommodating higher cardiac output without significant increases in pulmonary arterial pressure

How does gravity affect pulmonary blood flow?

Gravity increases hydrostatic pressure in lower lung vessels, causing them to distend and reducing resistance to blood flow. ​ This results in more blood flow in the lower parts of the lungs compared to the upper parts. ​ The lung is divided into three zones:

• Zone 1: No blood flow at rest due to low capillary pressure. ​

• Zone 2: Intermittent blood flow during systole. ​

• Zone 3: Continuous blood flow throughout the cardiac cycle.

What are the effects of exercise on pulmonary blood flow?

Exercise increases pulmonary blood flow due to:

1. Opening more capillaries (recruitment). ​

2. Distending capillaries to increase flow rate. ​

3. Increasing pulmonary arterial pressure → Resistance decreases, allowing an 8x increase in blood flow without a large rise in pressure. ​ Blood flow increases significantly in all lung zones, converting intermittent flow in Zone 2 to continuous flow.

How does hypoxia affect pulmonary blood flow?

Hypoxia causes vasoconstriction in pulmonary blood vessels, increasing vascular resistance. ​

-unique: low oxygen levels elsewhere in the body cause vasodilation. ​ Vasoconstriction ensures blood is directed to well-oxygenated alveoli, optimizing gas exchange

-vasoconstrictor substance may be released by alveolar epithelial cells under low oxygen conditions