Vasodilation (or vasodilatation) is the widening of blood vessels due to relaxation of vascular smooth muscle, increasing blood flow and decreasing vascular resistance.
Physiological Triggers
- Metabolic demand (exercise, hypoxia) – local metabolites (adenosine, K⁺, H⁺, CO₂).
- Endothelial factors – nitric oxide (NO), prostacyclin (PGI₂), EDHF.
- Neural – withdrawal of sympathetic tone, cholinergic vasodilator fibers.
- Thermoregulation – cutaneous vasodilation for heat dissipation.
Pharmacologic Vasodilators
- Arterial: Hydralazine, minoxidil, CCBs, nitrates – reduce afterload (HTN, HF).
- Venous: Nitrates – reduce preload (angina, acute HF).
- Mixed: ACEi, ARBs, nitroprusside.
Clinical Relevance
- Essential for matching perfusion to metabolic needs.
- Therapeutic target in hypertension, heart failure, angina, pulmonary hypertension, Raynaud’s.
- Excessive/inappropriate vasodilation → hypotension, shock (septic, anaphylactic, neurogenic).
