Anaes · Applied cardiovascular & respiratory physiology

Coronary & cerebral circulation

Also known as Coronary blood flow · Cerebral blood flow · Cerebral autoregulation · Coronary perfusion pressure · CO2 reactivity · Special circulations

The coronary and cerebral circulations are the two most vital special circulations, and each is defended by its own tightly-regulated autoregulation. The framework rests on five exam-critical ideas: the coronary circulation is unusual in that flow occurs predominantly in DIASTOLE, because the contracting myocardium in systole compresses the intramural vessels, so coronary perfusion pressure is diastolic blood pressure minus the left-ventricular end-diastolic pressure; coronary flow is matched to myocardial oxygen demand chiefly by metabolic vasodilation (the heart extracts oxygen near-maximally at rest, so increased demand must be met by increased flow); the cerebral circulation autoregulates, holding cerebral blood flow constant across a cerebral perfusion pressure range of roughly 50 to 150 mmHg, with the curve shifted right in chronic hypertension; cerebral blood flow is exquisitely sensitive to arterial carbon dioxide (hypercarbia increases, hypocarbia decreases it); and cerebral perfusion pressure equals mean arterial pressure minus intracranial pressure, so raised intracranial pressure threatens cerebral perfusion. Built on the cerebrovascular-autoregulation study (Soule 2026), the cerebrovascular-function MRI study (Walsh 2026), the intraoperative cerebral zero-flow-pressure study (Murakami 2026), the flow-mediated epicardial-vasodilation study (Tribhuvan 2026), the perioperative LVAD study (Bottiroli 2026), and the coronary-flow-interventions study (Shah 2026).