Pulmonary Blood Flow
Two Circulations in the Lung
Pulmonary Circulation.
Arises from Right Ventricle.
Receives 100% of blood flow.
Bronchial Circulation.
Arises from the aorta.
Part of systemic circulation.
Receives about 2% of left ventricular output.
Pulmonary Circulation
Pulmonary circulation
Right ventricle pulmonary artery right and left pulmonary arteries pulmonary capillaries pulmonary veins left atrium
Pulmonary Circulation
Pulmonary Circulation
In series with the systemic circulation.Receives 100% of cardiac output (3.5L/min/m2).RBC travels through lung in 4-5 seconds.280 billion capillaries, supplying 300 million alveoli.Surface area for gas exchange = 50 – 100 m2
Functional Anatomy of the Pulmonary Circulation
Thin walled vessels at all levels.
Pulmonary arteries have far less smooth muscle in the wall than systemic arteries.
Consequences of this anatomy- the vessels are:
Distensible.
Compressible.
Pulmonary Circulation Pressures
180 mmHg
Feet
50 mmHg
Head
100 mmHg
Aorta
25 mmHg
Base
2 mmHg
Apex
15 mmHg
Main PA
Systemic
Pulmonary
Reasons Why Pressures Are Different in Pulmonary and Systemic Circulations?
Gravity and Distance:
Distance above or below the heart adds to, or subtracts from, both arterial and venous pressure
Distance between Apex and Base
Influences on Pulmonary Vascular Resistance
Pulmonary vessels have:
-Little vascular smooth muscle.
-Low intravascular pressure.
-High distensiblility and compressiblility.
Vessel diameter influenced by extravascular forces:
-Gravity
-Body position
-Lung volume
-Alveolar pressures/intrapleurql pressures
-Intravascular pressures
Gravity, Alveolar Pressure and Blood Flow
Pressure in the pulmonary arterioles depends on both mean pulmonary artery pressure and the vertical position of the vessel in the chest, relative to the heart.Driving pressure (gradient) for perfusion is different in the 3 lung zones:Flow in zone may be absent because there is inadequate pressure to overcome alveolar pressure.Flow in zone 3 is continuous and driven by the pressure in the pulmonary arteriole – pulmonary venous pressure.Flow in zone 2 may be pulsatile and driven by the pressure in the pulmonary arteriole – alveolar pressure (collapsing the capillaries).
Gravity, Alveolar Pressure, and Blood Flow
Hypoxic Pulmonary Vasoconstriction
Alveolar hypoxia causes active vasoconstriction at level of pre-capillary arteriole.
Functions to reduce the mismatching of ventilation and perfusion.
Not a strong response due to limited muscle in pulmonary vasculature.
General hypoxemia (high altitude or hypoventilation) can cause extensive pulmonary artery vasoconstriction.
