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BME 501 FINAL EXAM STUDY GUIDE v1

BME 501 FINAL EXAM STUDY GUIDE v1 - Chapter 16 Mechanical...

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Chapter 16 Mechanical Aspects of Cardiac Performance How is the PCW (pulmonary capillary wage) pressure measured (Hint: refer to figure 20 on page 215)? The Pulmonary capillary wedge pressure (abbreviated PCWP), as measured by a Swan- Ganz catheter , is the pressure measured in a pulmonary artery after occlusion of that artery. Because of the large compliance of the pulmonary circulation , it provides an indirect measure of the left atrial pressure. PCWP is measured by inserting balloon-tipped, multi-lumen catheter ( Swan-Ganz catheter ) into a peripheral vein, then advancing the catheter into the right atrium, right ventricle, pulmonary artery, and then into a branch of the pulmonary artery. Just behind the tip of the catheter is a small balloon that can be inflated with air (~1 cc). The catheter has one opening (port) at the tip (distal to the balloon) and a second port several centimeters proximal to the balloon. These ports are connected to pressure transducers. When properly positioned in a branch of the pulmonary artery, the distal port measures pulmonary artery pressure (~ 25/10 mmHg) and the proximal port measures right atrial pressure (~ 0-3 mmHg). The balloon is then inflated, which occludes the branch of the pulmonary artery. When this occurs, the pressure in the distal port rapidly falls, and after several seconds, reaches a stable lower value that is very similar to left atrial pressure (normally about 8-10 mmHg). The balloon is then deflated. The same catheter can be used to measure cardiac output by the thermodilution technique. The pressure recorded during balloon inflation is similar to left atrial pressure because the occluded vessel, along with its distal branches that eventually form the
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pulmonary veins, acts as a long catheter that measures the blood pressures within the pulmonary veins and left atrium. PCW is used as a surrogate for preload. What is the reading for PCW? Pulmonary capillary wedge pressure (PCWP) provides an indirect estimate of left atrial pressure (LAP). Although left ventricular pressure can be directly measured by placing a catheter into the left ventricle by feeding it through a peripheral artery, into the aorta, and then into the ventricle, it is not feasible to advance this catheter back into the left atrium. LAP can be measured by placing a special catheter into the right atrium then punching through the interatrial septum; however, for obvious reasons, this is not usually performed because of damage to the septum and potential harm to the patient. Draw a pressure volume loop (P-V loop) and label 1, 2, 3, and 4. Which numbers correspond to preload and afterload, respectively?
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Label the diastolic pressure-volume curve? When there is a decrease in compliance during diastole, is the slope shifting upward or downward? Ans: Upward Active = End-systolic and isovolumic pressure-volume curve Passive= Diastolic pressure-volume curve Refer to figure 6 in your textbook, is it possible for digitalis to increase contractility on the pressure-volume loop while maintaining preload and afterload?
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