1. Estimate how much mechanical work an average heart performs with each heartbe
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Question
1. Estimate how much mechanical work an average heart performs with each heartbeat. Then calculate the energy cost of pumping blood at an average of 72 beats per minute for an entire day. [5] Things you need to know: Diastolic Pressure: 80 mmHg Systolic Pressure: 120 mmHg 1 mmHg- 133 pascals simplifying assumptions we can estimate work in moving a End Diastolic Volume: 120 ml End Systolic Volume: 50 ml . The motion of fluids is very complex but by making some fluid as: Work Pressure x AVolume Assume that the average pressure is midway between systolic and diastolic. Be careful with units, as mL is not an SI unit you can use to calculate Joules. Think units. Work = force x distance, hence Newtons x metres.Explanation / Answer
A normal heart in an average sized person will pump 4 to 5 liters of blood per minute. And the average heart will beat almost 4 million times per year [sic, they probably mean 40 million -- ed.]. It is estimated that the energy required to continuously pump blood at these rates is almost 5 watts of power per hour.
Under normal conditions, the heart beats 75 times per minute, delivering about 5 liters per minute, but its flow can be five times greater under extreme conditions. The peak blood pressure in the heart is about one-sixth of an atmosphere, and the heart develops about two watts of mechanical power.
Mechanical Power = Pmax(C,O)
Chemical Power = Mechanical Power/nth
Systolic Pressure: 16 kN/m2
Cardiac Output: 107 × 10?6 m3/s
nth = 0.2
Answer:
Pmech = (16 kN/m2)(107 × 10?6 m3/s) = 1.71 (Nm)/s [W]
Pchem = 1.71 (Nm)/s = 8.6 (Nm)/s
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