The HICS Physiology blog

  CE R EBRAL OXYGENATION AND ITS MARKERS                                                                   Contributed by Jyothi Reshma S, Calicut Physiology of Cerebral Oxygenation The brain receives a high metabolic demand for oxygen via tightly regulated blood flow. Under normal conditions CBF is ~50 mL/100g/min and remains constant (autoregulated) over a wide perfusion range (CPP ~60–160 mmHg). Within this autoregulatory range, reductions in CPP lead to compensatory vasodilation and increased oxygen extraction to preserve CMRO₂. Only when CPP falls below the lower limit does CBF fall linearly and tissue hypoxia ensues, since extraction can no longer meet demand...

  CEREBRAL AUTOREGULATION Contributed by Lt Col Purushotham G   DEFINITION Cerebral autoregulation (CA) is a homeostatic process defined as the intrinsic ability of brain to maintain a steady cerebral perfusion matched to cerebral metabolic demand across a range of blood pressures. It is a protective mechanism critical to preserving brain function at extremes of arterial blood pressure as brain is sensitive to both under and over perfusion and prevents damage from hyperemia , or ischemia .  Cerebral autoregulation (CA) is achieved by reflex vasoconstriction or vasodilation of the cerebral arterioles in response to changes in perfusion pressure. IMPORTANCE OF CA The cerebral autoregulation curve also known as the “Lassen curve”, first described by Lassen in 1959 is a graphical representation of the relationship between Cerebral blood flow (CBF) and Cerebral perfusion pressures (CPP). It represents the autoregulatory capacity of the cerebral vasculature over ...

  PERFUSION PRESSURES Contributed by Srinivas Samavedam What is it? Perfusion pressure is a term commonly used in the description of cardiovascular physiology, referring to the force that drives blood flow through the circulatory system to reach tissues and organs. This pressure is essential for ensuring that tissues receive an adequate supply of oxygen and metabolic requirements while also facilitating the elimination of the products and by-products of tissue energy utilisation.   Proper regulation of perfusion pressure is vital for maintaining homeostasis and overall functioning of organs What is its importance? Perfusion pressure is defined as the difference in pressure across a vascular bed. This difference in pressure creates the driving force that enables blood to flow from arteries, through capillaries, and into veins. Adequacy of perfusion of tissues and tissue oxygen delivery is determined by an effective perfusion pressure. How is it calculated? ...