USMLE Step 1 Physiology Review 55 02 Hemodynamics (3_3)

USMLE Step 1 Physiology Review 55 02 Hemodynamics (3_3)

 

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Begin 55 02 Hemodynamics (3_3) Transcription

Now for some questions about arteriole blood volume. What is arteriole blood volume?

  • It is the amount of blood in the arteriole vessels.

What percentage of the total blood volume is the arteriole blood volume?

  • Ten to fifteen percent

How does the arteriole blood volume determine arteriole pressure?

  • Blood in the artery stretches the wall of the blood vessel which then recoils generating pressure.

What is the term for this recoil force?

  • Elastance.

Elastance is the reciprocal of what other blood vessel characteristics?

  • Compliance, Compliance is the ability of a blood vessel to become distended with increased blood volume.

Student doctor please pause the tape and summarize the information on arteriole blood volume.

  • Arteriole blood volume is the amount of blood in the arteriole vessels. Ten to fifteen percent of the total blood volume is the arteriole blood volume. Blood in the artery stretches the wall of the blood vessels which tend recoils generating pressure. This recoil force is called Elastance. Elastance is the reciprocal of compliance. Compliance is the ability of the blood vessels to become distended with increased blood volume.

Ok now for some questions about arteriole blood pressure. What are the four factors that increase blood pressure?

  •  First, increased heart rate; Second, increased peripheral resistance; Third, increased stroke volume; Fourth, increased elastic constant.

Why does increasing heart rate increase arteriole volume and pressure?

  • There are two reasons, first there is less time for blood to leave the arteriole tree. Second, cardiac output usually increases.

When does peripheral resistance increase?

  • It increases when contraction of the smooth muscle in the walls of the arterioles narrows the lumina.

Why does increased stroke volume raise arteriole pressure?

  •  Because increased stroke volume increases cardiac output and therefore flow rate.

What does the elastic constant refer to?

  •  It refers to the stiffness of the arteriole system. The elastic constant increases progressively from birth till the time of death.

Aside from the decreases in heart rate, peripheral resistance stroke volume, or elastic constant, what two other conditions or factors could decrease arteriole pressure?

  •  Hemorrhage and blood pooling.

Student doctor, please pause the tape and summarize the information on arteriole blood pressure.

  •  The following four factors increase arteriole blood pressure; increased heart rate, increased peripheral resistance, increased stroke volume, and increased elastic constant. Increasing heart rate increases arteriole volume and pressure because there is less time for blood to leave the arteriole tree and cardiac output usually increases. Peripheral resistance increases when contraction of the smooth muscle in the walls of the arterioles narrows the lumina. Increased stroke volume raises arteriole pressure because it increases cardiac output and therefore flow rate. The elastic constant which increase progressive from birth till the time of death, refers to the stiffness of the arteriole system. Aside from the decreases in heart rate, peripheral resistance, stroke volume, or elastic constant; two other conditions or factors could decrease arteriole pressure, they are hemorrhage and blood pooling.

Now for some questions about pulse pressure. How does blood flow through the capillaries continuously or in pulses?

  • Continuously, although the heart ejects blood intermittently, blood flows in the capillaries continuously.

When does systolic pressure occur?

  • During ventricular ejection. Systolic pressure is the highest pressure in the arteriole system.

What is the value for normal arteriole systolic pressure?

  • 120mmHg

When does diastolic pressure occur?

  •   It occurs just prior to ventricular ejection. Diastolic pressure is the lowest pressure in the arteriole system.

What is the approximate value for normal diastolic pressure?

  • 80mmHg

What is pulse pressure?

  • It is the arithmetic difference between the systolic and diastolic pressures.

Since normal systolic pressure is 120mmHg and normal diastolic pressure is 80mmHg, what would normal pulse pressure be?

  •  It would be 40mmHg, 120 minus 80.

Pulse pressure depends on three factors, list them alphabetically:

  •  First, age; second arteriole elastic constant; third, stroke volume.

Either increased heart rate or increased peripheral resistance can increase overall blood pressure, both systolic and diastolic pressures. What effect does increased heart rate and increased peripheral resistance have on pulse pressure?

  • As heart rate and peripheral resistance increases, pulse pressure decreases.

Student doctor, please pause the tape and summarize the information on pulse pressure.

  • Although the heart ejects blood into the arteries intermittently, blood flows though the capillaries continuously. Systolic pressure occurs during ventricular ejection. Systolic pressure is the highest pressure in the arteriole system with a normal approximate value of 120mmHg. Diastolic pressure occurs just prior to ventricular ejection and it is the lowest pressure in the arteriole system with an approximate normal value of 80mmHg. Pulse pressure is the arithmetic difference between systolic and diastolic pressures. Normal pulse pressure is 40mmHg. Pulse pressure depends on age, elastic constant and stroke volume. Either increased heart rate or increased peripheral resistance can increase overall blood pressure but increased heart rate and peripheral resistance decrease pulse pressure.

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