final_exam_solutions

# final_exam_solutions - BENG 100b: Frontiers in Biomedical...

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0 BENG 100b: Frontiers in Biomedical Engineering Spring 2008 FINAL EXAMINATION May 7, 2008 INSTRUCTIONS: You have three hours to complete this exam. This is a closed book exam. You may use a calculator. Only work shown in the space provided will be graded. Partial credit will be given when warranted. The exam is worth a total of 100 points. Instructor: Mark Saltzman Department of Biomedical Engineering Yale University

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1 Question 1. (20 points) Cardiovascular physiology As you know from our section meeting, blood pressure is measured using an inflatable cuff and a stethoscope. Describe how this blood pressure measurement works by answering the following questions: a) What happens in your arm as the inflatable cuff is pressurized? Why is it usually inflated to ~200 mmHg? The pressure cuff is inflated 200 mmHg, to insure that the pressure is higher than the highest pressure generated by the heart (which is usually near 120 mmHg). At this high cuff pressure, the superficial arteries of the arm are collapsed, halting blood flow. b) Blood pressure is recorded as (systolic pressure)/(diastolic pressure), with a typical value of 120/80 (in mmHg). These pressures are determined by listening with a stethoscope as the pressure in the cuff is decreased. What physical process creates the sounds? The sounds are created by the opening and closing of the arteries in the arm. When the pressure in the artery is higher than the cuff pressure, the artery opens; when the pressure in the artery is lower, the artery is closed. If the blood pressure is 120/80: cuff pressure > 120 no sound 120 > cuff pressure > 80 sounds are heard cuff pressure < 80 no sound c) How are pressures measured in the arm related to pressures in the heart? The key assumption is that the pressure of fluid flowing in the arteries of the arm is equal to the pressure of fluid in the left ventricle. As we discussed in class, the resistance to flow of the large vessels (aorta and first braches) is low, and therefore there is little pressure drop from the ventricle to the large arteries of the arm. This fact makes it reasonable to measure ventricular pressures in the arm
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## This note was uploaded on 02/06/2012 for the course BENG 100 taught by Professor Marksaltzman during the Spring '08 term at Yale.

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final_exam_solutions - BENG 100b: Frontiers in Biomedical...

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