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quiz1_solutions

quiz1_solutions - Harvard-MIT Division of Health Sciences...

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Harvard-MIT Division of Health Sciences and Technology HST.542 J : 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 QUIZ 1 SOLUTIONS
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Problem 1 A. Draw normal P ( t ) waveforms for the left ventricle, left atrium, and aorta. Show two com- plete cardiac cycles, and use typical normal values for the pressures. Use the time axis provided in Figure 1.1a, and assume a heart rate of 60 bpm. C.O. = ˙ V O 2 C A O 2 C V O 2 = 363 ml O 2 /min ( 200 14 . 5 ) ml O 2 /liter blood = 363 55 = 6 . 6 L/min So SV = 6 . 6 L/min 60 beat/min = 110 cc/beat (See Figure.) B. The cardiac output was measured using the Fick method. Oxygen uptake 363 ml O 2 per minute Arterial oxygen content 200 ml O 2 per liter of blood Mixed venous oxygen content 145 ml O 2 per liter of blood Using this data together with your P ( t ) waveforms, draw the corresponding P-V loop for the LV. Assume an end-diastolic LV volume of 170 cc., and a LV “dead” volume of 15 cc for both systole and diastole. Draw linear systolic and diastolic P-V curves, and use the axes provided. See Figure. C. Correlate the following landmarks on the P-V loop with the appropriate points on the P ( t ) curves using the numeric labels below: a: begin LV contraction b: peak LV pressure c: begin LV filling d: end ejection e: begin LV ejection See Figure. D. “Ejection fraction” (EF) is defined as the percentage of the end-diastolic volume that is ejected during systole. What is the EF in this case? (Normal > 55%.) 110 EF = = 64 . 7% 170 6.022j—2004: Solutions to Quiz 1 2
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E. A papillary muscle in the LV ruptures. (Assume that there are no functioning controls, and that the system has reached a new steady state.) The new arterial BP (systolic, diastolic, and mean) drops to 60% of its original value. New BP: 120 × 0 . 6 = 72 80 × 0 . 6 = 48 110 × 0 . 6 = 66 (i) Sketch two cardiac cycles showing the new P ( t ) waveforms, using the axes supplied in Figure 1.1b. Pay particular attention to the new amplitudes of the LV and LA pressures. Assume no change in the left ventricular end-diastolic pressure and volume.
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