Bronchial Circulation

Pulmonary Circulation

Changes in Pulmonary Blood Flow Recruitment Distention

Active Causes
Cause Effect on Resistance Explanation
Increased Sympathetic Activationincreasesa-adrenergic receptors in vascular tissue
Increased Parasympathetic Tonedecreases muscarinic receptors in pulmonary arteries
PGF2a, PGE2IncreasePulmonary Vasoconstricor
AngiotensinIncreasePulmonary Vasoconstrictor
HistamineIncreasePulmonary venoconstrictor
Alveolar HypoxiaIncrease
Alveolar HypercapniaIncrease
Low pH of venous bloodIncrease
PGE1DecreasePulmonary vasodilator
Prostacyclin (PGI2)DecreasePulmonary vasodilator
Nitric OxideDecreaseNO receptors in vascular smooth muscle
Passive Causes
Cause Effect on Resistance Explanation
Increased Lung VolumeincreasesPressure compresses alveolar vessels
Increased Pulmonary Blood PressureDecreasesRecruitment and distention
GravityDecreases in low areas, Increases in higher areaslocal Recruitment and Distention
Increased Blood viscosityincreasesviscosity makes blood harder to pump (Navier-Stokes Equation, anyone?)

Regional Distribution of Pulmonary Bloodflow

Hypoxic Pulmonary Vasoconstriction

Pulmonary Edema