Vẽ và ghi nhãn các trục như thể hiện. Đánh dấu hai điểm quan trọng trên trục x (50 và 150 mmHg). Giữa những điểm này, đánh dấu một đường ngang tại giá trị ay là 50 . Nhãn phân khúc này "phạm vi autoregulatory '. Trên phạm | Intracranial pressure relationships Autoregulation The ability of an organ to regulate its blood flow despite changes in its perfusion pressure. Autoregulation of cerebral blood flow Mean arterial pressure mmHg Draw and label the axes as shown. Mark the two key points on the x axis 50 and 150 mmHg . Between these points mark a horizontal line at a y value of 50 . Label this segment the autoregulatory range . Above this range cerebral blood flow CBF will increase as mean arterial pressure MAP increases. There will however be a maximum flow at some MAP where no further increase is possible. Below 50 mmHg CBF falls with MAP however the line does not pass through the origin as neither MAP nor flow can be zero in live patients. Demonstrate the response to chronic hypertension by drawing an identical curve displaced to the right to show how the autoregulatory range resets itself under these conditions. Cerebral perfusion pressure CPP MAP - ICP CVP where CPP is cerebral perfusion pressure and CVP is central venous pressure. Intracranial pressure relationships 195 Often CVP is left out of this equation as it is normally negligible. In order to maintain cerebral perfusion when ICP is raised the MAP must also be elevated. Effects of Paco2 on cerebral blood flow Paco2 kPa Draw and label the axes. Normal Mark a point at the intersection of a normal PaCO2 and cerebral blood flow as shown. As CBF will approximately double with a doubling of the PaCO2 extend a line from this point up to a PaCO2 of around 10 kPa. At the extremes of PaCO2 there arise minimum and maximum flows that depend on maximal and minimal vasodilatation respectively. The line should therefore become horizontal as shown at these extremes. Chronic hypercapnoea The curve is identical but shifted to the right of the normal curve as buffering acts to reset the autoregulatory range. 196 Section 9 Neurophysiology Effects of Pao2 on cerebral blood flow Draw and label the axes. Plot a point at a normal .
