Question

7B.9 (P, C) There is a pressure drop from the left side to the right side of the heart. (a) What is the magnitude of this pressure drop? (b) As the blood moves through the body, the pressure drops due to vas- cular resistance, or peripheral resistance, which is the friction of the blood along the vessel wall. What is the numerical value of the periph- eral resistance for the body? Report the answer in peripheral resistance units (PRU [mmHg s/cm3]). (c) During exercise, a person's total peripheral resistance (TPR) drops. If a person has a TPR of 0.47 PRU, and his mean arterial pressure is 140 mmHg, what is his cardiac output? (d) Discuss qualitatively and quantitatively (with formulas) how the re- sistance through various organs and parts of the body combines to give the TPR. Is the resistance seen through the kidneys greater or less than the total peripheral resistance? Why?

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Answer 1

B)Peripheral resistance = Mean arterial pressure / Cardiac output

Normal MAP =100 mm Hg

Normal cardiac output = 5 L/min =5000/60 =83.3 ml/second

Resistance = 100 /83.3 =1.2 PRU

C) Mean arterial pressure = cardiac output * TPR

140 = Cardiac output * 0.47

Cardiac output = 300 ml/second = 300*60 =18 L/min

D)The various organs are arranged in series and parallel combinations.

In series ; the blood flow to all the organs is same but the pressure difference is different.The individual resistance gets added up.

Net R = R1 +R2+ R3.....

Blood flow = Delta P /Net R

In parallel ; the pressure difference is same but blood flow is different to different organs depending on the resistance.

1/R = 1/R1 + 1/R2 ....

Blood flow = delta P/R

Resistance through the kidneys is more than the total peripheral resistance because it is in parallel with systekic circulation and receives a part of cardiac output.