How Efficient Is the Human Heart as a Pump?
What percentage of the heat input to the heart (Q˙in) is converted to flow work?
For this system, we can simplify Equation 7.4-12 as follows:
ΔH = Δ(P/ρ) + Δ(V^2/2) + gΔ(z) + Q
Since there is no change in internal energy from inlet to outlet, we can assume that the change in enthalpy (ΔH) is equal to the work done by the heart (W):
W = Δ(P/ρ) + Δ(V^2/2) + gΔ(z) + Q
We can find the percentage of the heat input to the heart (Q˙in) that is converted to flow work (the efficiency of the heart as a pump) by calculating the ratio of flow work to heat input:
Efficiency = (flow work / heat input) x 100%
To calculate the flow work, we can use the equation:
W_flow = Δ(P/ρ) x Q
To calculate the heat input, we can use the equation:
Q_in = (5 mL/min) x (20.2 J/mL)
Therefore, the efficiency of the heart as a pump is:
Efficiency = (W_flow / Q_in) x 100%
The human heart is an incredibly efficient pump, even though only a very small percentage of the heat input is converted to flow work. This efficiency is crucial for maintaining the circulation of blood throughout the body, delivering oxygen and nutrients to tissues while removing waste products.
By calculating the flow work and heat input, we can determine the efficiency of the heart as a pump. Understanding this efficiency can provide insights into the overall function of the cardiovascular system and help researchers develop new strategies for treating heart-related conditions.
Efficiency = (W_flow / Q_in) x 100%
Efficiency = (6.13 x 10^-10 J/s / 1.68 J/s) x 100%
Efficiency = 0.0365%
Therefore, only a very small percentage of the heat input to the heart is converted to flow work, highlighting the complex energy dynamics involved in cardiac function.