Essential Cardiovascular Calculations This problem set is designed to take you t

Question

Essential Cardiovascular Calculations

This problem set is designed to take you through important basic calculations involving the cardiovascular system. Use the information provided in Table 1-1 to answer the questions. Part of the challenge in answering these questions will be in deciding which information you need in order to perform each calculation.

Good luck!

Table 1-1 Cardiovascular Values
Parameter       Value

Systolic pressure (aorta)     124 mmHg
Diastolic pressure (aorta)     82 mmHg
R-R interval       800 msec
Left ventricular end-diastolic volume (EDV)  140 ml
Left ventricular end-systolic volume (ESV)  70 ml
Mean pulmonary artery pressure    15 mmHg
Right atrial pressure      2 mmHg
Left atrial pressure      5 mmHg

1. Mean arterial pressure is not the simple average of systolic and diastolic pressures. Why not? How is mean arterial pressure estimated? From the information given in Table 1-1, calculate the mean arterial pressure (MAP) in this case. (To calculate MAP, please see lecture 9, slide 28.) How is this changed during exercise?

2. Calculate the stroke volume (SV), cardiac output (CO), and ejection fraction (EF) of the left ventricle. Ejection fraction is the fraction of blood that is ejected from the left ventricle in relation to the total volume of blood delivered to the left ventricle before ejection. (EF = ?/?, and HR = beats/min)

3.What is the definition of total peripheral resistance (TPR)? What equation describes the relationship between TPR, arterial pressure, and cardiac output? What is the value of TPR in this case?

4. How is pulmonary vascular resistance calculated? What is the value of pulmonary vascular resistance in this case? Compare the calculated values for pulmonary vascular resistance and TPR, and explain any differences in the two values.

5. What is the total blood flow (in mL/min) through all of the pulmonary capillaries?

6. What is the total blood flow (in mL/min) through all of the systemic arteries?

7. What information, in addition to that provided in Table 1-1, is needed to calculate the resistance of the renal vasculature?

8. If the diameter of the aorta is 20 mm, what is the velocity of aortic blood flow? Would you expect the velocity of blood flow in systemic capillaries to be higher, lower, or the same as the velocity of blood flow in the aorta? (A = r2)

Explanation / Answer

1.

Mean arterial pressure is the average pressure in a patient’s arteries during one cardiac cycle. It can be calculated using the below formula.

During static exercise, the mean arterial pressure increases due to an increase in heart rate.

2.

Stroke volume (SV) = end-diastolic volume (EDV) - end-systolic volume (ESV) = 140 – 70 = 70.

Cardiac output (CO) can be calculated as follows:

CO = HR x SV

Where, HR = heart rate

In this case, let suppose the heart rate is 72 beats/min. Then, the CO will be 72 x 70 = 5040 ml/min

Ejection fraction is the fraction of blood ejected from the heart relative to its end-diastolic volume (EDV). It can be calculated as follows:

EF = (SV/EDV) x 100 = (70/140) x 100 = 0.5 x 100 = 50

3.

Total peripheral resistance is the total resistance to the flow of blood in the systemic circulation.

Arterial pressure = Cardiac output (CO) x Total peripheral resistance (TPR)

Total peripheral resistance (TPR) = Arterial pressure/ Cardiac output (CO)

                                                          = 96/5040 = 0.019

4.

PVR = 80 x ( MeanPulmonaryArteryPressure - LeftAtrialPressure) / PulmonaryFlow

     = 80 x (15 – 5)/ Pulmonary Flow

(*the value for Pulmonary Flow is not given here)

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