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George Washington UniversityECE 3820unit_5_ps2_cardiac_work_answer_key

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5.PS2.3 PROBLEM SET 5.2 CARDIAC WORK AND OXYGEN CONSUMPTION ANSW ER KEY 1. The work done by the heart in each beat contains at least two components. The first is the amount of work done to generate and m aintain the pressure in the ventricle above that in the arterial outlet port. This is defined as pressure-volume work. As blood is ejected, it acquires a velocity. Hence there is kinetic work done to propel the blood forward. 2 consum ption as a m easure of energy input. O2 consum ption at rest (which is the situation in Problem #1) is 0.09 mL O2 per g of tissue per min. Assume a left ventricular weight of 250 g. The average metabolic energy derived from oxidation of substrates by oxygen is 20.3 joule per mL of O2. 4. The radius of the aorta in a test subject determined by MRI is 1.2 cm . At rest, his end diastolic volume is 140 mL and his end systolic volume is 55 mL. His diastolic pressure is 70 mm Hg and his systolic pressure is 115 mm Hg. If we start the cardiac cycle at the opening of the mitral valve, the aortic valve in this person opens at 0.55 seconds and closes at 0.9 seconds. The entire cycle lasts 1.1 seconds in this person. The density of blood is 1.055 g mL-1 and its viscosity is 3.0 x 10-3 Pa s. 5. For the test person is problem #4, the total oxygen content of blood at the root of the aorta where the coronary arteries come off is 20 mL% , or 20 mL of O2 per dL of whole blood. Most of this is carried by hemoglobin inside erythrocytes and a sm all amount is dissolved. Cardiac venous blood contains 10 mL% of O2. His heart weighed 250 g and blood flow at rest is 275 m L m in-1. Assume that 2/3 of the heart m ass form s the left ventricle. 7. Injection of KCl raises its concentration in the plasma to 20 mM. What happens to EK? W hat do you expect would happen to the heart? 8. At the top of the R wave lead I reads 0.35 mV and lead III reads 0.75 mV. W hat is the electrical axis of the heart? 9. The end diastolic volume in a patient was estimated by echocardiography to be 170 mL and the end systolic volum e was 120 m L . Calculate the ejection fraction. Is this normal? 10. During exercise, an athlete consumed 1.0 L of O2 min-1. Arterial content of O2 was 20.5 mL% and mixed venous blood had 12.5 mL %. What is the athlete’s cardiac output during exercise? 11. Estimate the distance from the AV node to the apex of the heart. Compare the time it would take for conduction of an action potential from the AV node to the apex if it were conducted only by nodal cells, atrial cells, ventricular cells, or Purkinje fibers. 13. At steady state A, blood flow through a muscle is 0.025 m L m in-1 g-1. Arteriolar O2 content is 20 mL% and venous O 2 content is 14 mL% . This question deals with the relationship between perfusion and extracellular concentration of O 2. A. W hat is the rate of O 2 consumption of the muscle? 14. The end-diastolic volume of a heart is 140 mL. Assume that it is a sphere. At end diastole, the intraventicular pressure is 7 mm Hg. The wall thickness at this time is 1.1 cm. At the end of isovolumetric contraction, the intraventricular pressure is 80 mm Hg.

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