Chapter 8- Pulmonary Hemodynamics

What is blood pressure (BP)?

BP is the force of blood pushing against blood vessel walls as blood moves through the body

What factors affect BP?

CO, vascular resistance (VR), cardiac pump strength, blood volume, and blood viscosity.

What is systolic blood pressure?

Maximum pressure during the pumping phase of the heart (systole). Units = mmHg

What is diastolic blood pressure?

Minimum pressure during heart relaxation (diastole). Units = mmHg

What is Mean Arterial Pressure (MAP)?

The average pressure pushing blood through circulation.
MAP = (2 × DBP + SBP) / 3.

Why is MAP clinically important?

Indicates tissue perfusion—too low = poor perfusion; too high = increased cardiac workload.

Formula for blood pressure?

BP = CO × VR

What is cardiac output (CO)?

Volume of blood the heart pumps per minute; normal = 4–8 L/min.
CO = HR × SV

What is systemic vascular resistance (SVR)?

Resistance systemic vessels pose to blood flow. Normal = 900–1400 dyn·s·cm⁻⁵.

 What is pulmonary vascular resistance (PVR)?

Resistance pulmonary vessels pose to blood flow. Normal = <250 dyn·s·cm⁻

Why is systemic BP higher than pulmonary BP?

Systemic circulation must deliver oxygen and nutrients to tissues; pulmonary circulation focuses on gas exchange.

Typical systemic BP?

Approximately 120/80 mmHg

Typical pulmonary artery pressures?

20–30 / 6–15 mmHg.

Why must pulmonary pressure remain low?

To protect delicate alveoli and support efficient gas exchange.

What is the pulmonary capillary pressure range?

What is the pulmonary capillary pressure range?

Why is low pressure crucial in capillaries?

Prevents damage to alveoli and allows effective oxygen and CO₂ diffusion.

How does gravity affect pulmonary blood flow?

Blood pools in the lowest lung regions (bases when upright), increasing perfusion there.

What is hydrostatic pressure in the lungs?

Pressure exerted by the blood column that increases from apex → base.

What are lung zones?

Functional regions showing how perfusion and ventilation vary with hydrostatic pressure. Not anatomical.

What happens in Lung Zone 1?

PA > Pa > Pv.
No blood flow; does not occur normally. Seen in hemorrhage or positive pressure ventilation.

What happens in Lung Zone 2?

What happens in Lung Zone 2?
A: Pa > PA > Pv.
Pulsatile flow; occurs near apex depending on arterial pressure.

What happens in Lung Zone 3?

Pa > Pv > PA.
Continuous blood flow; occurs at the lung bases.

Where is ventilation greatest?

Lung bases (alveoli expand more during inspiration).

Where is perfusion greatest?

Lung bases due to gravity.

Why do bases have best gas exchange?

They receive both the most ventilation and the most blood flow (optimal V/Q

What happens to alveolar vessels at high lung volumes?

They compress → increasing PVR.

What happens to extra-alveolar vessels at high lung volumes?

They dilate → decreasing PVR.

At which lung volume is total PVR lowest?

FRC (Functional Residual Capacity).

What is recruitment?

Opening previously closed or non-perfused capillaries to increase surface area.

What is distension?

Already-perfused capillaries widen to handle increased blood flow

Why are recruitment and distension important during exercise?

Allow increased pulmonary blood flow without increasing PVR.

Effect of hypoxia on pulmonary vessels?

Low PAO₂ causes vasoconstriction → increases PVR. (Opposite effect in systemic vessels.)

Effect of hypercapnia on pulmonary vessels?

Causes vasoconstriction, though less potent than hypoxia; may be triggered by low pH.

What does nitric oxide (NO) do in the lungs?

Potent vasodilator that decreases PVR.

Why is inhaled NO used clinically?

Selectively dilates pulmonary vessels without affecting systemic resistance; useful in pulmonary hypertension.