VPB 121: Veterinary Physiology - II (2+1)

PULMONARY VASCULAR RESISTANCE

• Although pulmonary vascular resistance is very low at rest, it can decrease further, as in exercise, during which blood flow increases. Neural : Sympathetic nerves to larger vessels - NE released.
• Effects somewhat controversial - most likely increases pulmonary vascular resistance and decreases distensibility of larger vessels. Parasympathetic - Ach decreases PVR if tone elevated.
• Humoral : Increase PVR: Norepinephrine, alpha adrenergic agonists, serotonin, prostaglandins F₂ and E₂, angiotensin, endothelin, alveolar hypoxia (hypoxic pulmonary vasoconstriction), alveolar hypercapnia, low pH of mixed venous blood.
• Histamine constricts pulmonary veins. Decrease PVR: Acetylcholine, beta adrenergic agonists, bradykinin, prostaglandin E₁ and I₂ (prostacyclin), nitric oxide.