Question

The human heart discharges $80\, ml$ of blood at each beat against pressure of $0.1 \,mm$ of $Hg$ What is the power of the heart assuming that the pulse frequency is $75$ beats per minute? (Density of mercury $\left.=13.6 \times 10^{3} kg / m ^{3}\right)$

• A. $1.33$ watt
• B. $ 121$ watt
• C. $1330 k$ watt
• D. None

Answer 1

Answer: (A)

Volume of blood discharge/ beat $=80\,ml$
$=80 \times 10^{-6}\, m ^{-3}$
Pressure $= P =0.1 \,mm$ of $Hg$
$P=0.1 \times 13.6 \times 10^{3} \times 9.8 \,\,\,(P=h \rho g)$
$\frac{\text { work done }}{\text { beat }}=P V$
Total work done in 75 beat $=75 \times PV$
Power $=\frac{\text { work }}{\text { time }}$
$P=\frac{0.1 \times 13.6 \times 10^{3} \times 9.8 \times 80 \times 10^{-6} \times 75}{60}$
$P=\frac{79968 \times 10^{-3}}{60}$
$P =1332.8 \times 10^{-3}$
$P=1.33$ watt