ps2_solutions

ps2_solutions - Harvard-MIT Division of Health Sciences and...

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Unformatted text preview: Harvard-MIT Division of Health Sciences and Technology HST.542J: Quantitative Physiology: Organ Transport Systems Instructors: Roger Mark and Jose Venegas MASSACHUSETTS INSTITUTE OF TECHNOLOGY Departments of Electrical Engineering, Mechanical Engineering, and the Harvard-MIT Division of Health Sciences and Technology 6.022J/2.792J/BEH.371J/HST542J: Quantitative Physiology: Organ Transport Systems PROBLEM SET 2 SOLUTIONS February 19, 2004 Problem 1 A twenty-year-old student was involved in an automobile accident and sustained a chest injury. Upon admission to the hospital he had a rapid, weak pulse, feeble heart sounds, and a low blood pressure. Because of the suspicion of heart damage, he was evaluated in the cardiac catheterization laboratory. A left-sided cath study was performed, complete with bi-plane cine ventriculograms (X-ray movies of the ventricle obtained in orthogonal projections following injection of radio- opaque dye into the ventricle). It was discovered that the patient had a significant amount of blood in the pericardial cavity (between the heart and the pericardial sac). Three hundred milliliters of blood were removed and the patient improved considerably. As part of the evaluation procedure, diastolic pressure-volume curves for the left ventricle were measured both before and after the pericardial tap (removal of the pericardial blood). (This was done by simultaneous measurement of LV volume from the cine data, and of the LV pressure from and intracardiac pressure transducer.) These curves are presented in Figure 1. Figure 2A shows the LV and aortic pressures recorded prior to removal of the pericardial blood. Figure 2B shows these pressures after removal when the cardiovascular system had reached steady state. At the time indicated by the arrow, a balloon was suddenly inflated in the ascending aorta (see Figure 3), which presented an increased afterload to the left ventricle. Note that the aortic pressure was measured proximal to (on the heart side of) the balloon. The added pressure load was sudden, and compensatory mechanisms did not have time to act for several beats. Thus, the heart’s contractile state may be considered constant for 10-15 seconds, and this period certainly includes beats numbered 3, 4, and 5 in the figure. Additional data gathered during the work-up included: A. Fick data during steady state before the pericardium was drained: O 2 uptake 300 cc/min. Arterial O 2 content 180 cc/liter Mixed venous O 2 content 80 cc/liter B. Individual stroke volumes during the balloon test are indicated in Figure 2B. The steady state stroke volume was 75 cc. before balloon inflation. 6.022j—2004: Solutions to Problem Set 2 2 Questions: A. From the raw data supplied, complete the table below....
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This note was uploaded on 11/11/2011 for the course BIO 2.797j taught by Professor Matthewlang during the Fall '06 term at MIT.

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ps2_solutions - Harvard-MIT Division of Health Sciences and...

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