Perfusion

Perfusion is the process of delivering blood to a capillary bed in biological tissue, ensuring the delivery of oxygen and nutrients and the removal of metabolic wastes. It describes the flow of blood to specific tissues and depends on arterial supply, microvascular resistance, and the tissue’s metabolic demand. Perfusion is distinct from whole-body circulation in that it focuses on the adequacy of flow to individual tissues or organs.

Physiologically, tissue perfusion is governed by perfusion pressure and vascular resistance. Autoregulation adjusts arteriolar tone to maintain relatively stable flow across a range of blood pressures. Local factors such as endothelial signaling, hypoxia, and metabolic activity influence vasodilation or vasoconstriction. Regional perfusion varies by organ, with the brain, heart, and kidneys typically requiring higher perfusion to meet metabolic needs.

Assessment methods range from invasive measurements of blood flow to noninvasive imaging. Doppler ultrasound evaluates flow in large vessels, while CT and MR perfusion imaging map regional tissue blood flow. PET can combine perfusion data with metabolic activity. Bedside estimates of tissue perfusion can be obtained with near-infrared spectroscopy or fluorescence techniques using agents such as indocyanine green.

Clinically, inadequate perfusion (hypoperfusion) leads to ischemia and organ dysfunction, as seen in stroke, myocardial infarction, acute kidney injury, and septic shock. Perfusion is also a key concern in organ transplantation, where ex vivo machine perfusion preserves organs before implantation and can improve outcomes.

Research and clinical practice continue to explore perfusion dynamics to understand microcirculation, guide therapy, and optimize tissue viability.