The pumping power of the human heart is approximately 2W (assuming a normal cardiac output of 5 liters/min). Like any pump, however, the heart is not 100% efficient, and, therefore, the power that is supplied to the heart muscle will actually exceed 2W. In this question we will estimate the heart’s pumping efficiency η by calculating how much energy is supplied to the heart muscle from the blood.(Note that the heart muscle has its own vasculature, called the coronarycirculation.) (a) When we calculated the pumping power of the heart, we only considered the head gain across the heart from the pressure increase. In general, there could also be changes in elevation (very small) and in kineticenergy. Estimate the ratio of kinetic energy head to pressure head at peaksystole, when pressure is 120 mmHg and blood velocity is 100 cm/s.Can we safely neglect kinetic energy gains in calculating pumpingpower?(b) At rest, the coronary blood flow is 225 ml/min, and 65% of the O2 isremoved from the blood as it passes through the coronary vasculature.The oxygen capacity of blood is 19.4 ml O2/100 ml blood, and in anormal diet 4.83 kcal of food energy is released for every liter of O2consumed. From this data, estimate η for the heart. State assumptions.(c) The basal metabolic rate of a normal individual is 72 kcal/h. What fraction of this is consumed by the heart?
The pumping power of the human heart is approximately 2W (assuming a normal cardiac output of 5 liters/min). Like any pump, however, the heart is not 100% efficient, and, therefore, the power that is supplied to the heart muscle will actually exceed 2W. In this question we will estimate the heart’s pumping efficiency η by calculating how much energy is supplied to the heart muscle from the blood.
(Note that the heart muscle has its own vasculature, called the coronary
circulation.)
(a) When we calculated the pumping power of the heart, we only considered the head gain across the heart from the pressure increase. In general, there could also be changes in elevation (very small) and in kinetic
energy. Estimate the ratio of kinetic energy head to pressure head at peak
systole, when pressure is 120 mmHg and blood velocity is 100 cm/s.
Can we safely neglect kinetic energy gains in calculating pumping
power?
(b) At rest, the coronary blood flow is 225 ml/min, and 65% of the O2 is
removed from the blood as it passes through the coronary vasculature.
The oxygen capacity of blood is 19.4 ml O2/100 ml blood, and in a
normal diet 4.83 kcal of food energy is released for every liter of O2
consumed. From this data, estimate η for the heart. State assumptions.
(c) The basal metabolic rate of a normal individual is 72 kcal/h. What fraction of this is consumed by the heart?
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