Cardiac Hemodynamic Phys

Question 1

What is Cardiac Output and Venus return, and which side of the heart does more of what?

Answer 1

Cardiac output is the amount of blood pumped out by the ventricles, and venous return is the amount of blood that enters the atria. Both ventricles and both atria have equal cardiac output and venus return, respectively.
Alternatively, cardiac output should equal venus return in a steady state.

Question 2

What kinds of receptors are found on Arterioles? What are these receptors? What is “tonically active?”

Answer 2

Alpha 1 and Beta 2 receptors, these are sympathetic receptors and arterioles are always tonically active, meaning always slightly contracted.

Question 3

What do the alpha 1 receptors on arterioles do and where are they found generally?

Answer 3

They are found in vascular beds of skin and splanchic vasculature, their job is to cause contraction or constriction of vascular smooth muscles.

Question 4

What is the function of Beta 2 receptors? Where are they found?

Answer 4

Beta 2 are found in the arterioles of smooth muscles, their job is to cause dilation of vascular smooth muscles.

Question 5

What is the physiologic function/benefit of arterioles?

Answer 5

They contain a lot of smooth muscles, thus having the ability to alter resistance of blood by constricting or relaxing. They are the greatest site of pressure control.

Question 6

How do lipid and water soluble contents differ in their passing through capillary walls?

Answer 6

Lipid soluble compounds dissolve through the endothelial walls whereas water soluble contents diffuse out via fenestrations or gaps in the capillary walls.

Question 7

What is “capacitance” in terms of blood vessels, and do veins or arteries have greater capacitance?

Answer 7

In terms of blood vessels, capacitance is the ability to hold amounts of blood, and veins have a greater capacity to hold blood than arteries.

Question 8

How is the capicatance of veins altered?

Answer 8

Veins are also innervated by sympathetic nerve fibers, thus contractions of veins as induced by sympathetic stimulus will decrease capacitance of veins.

Question 9

How is velocity, flow and cross sectional area related?

Answer 9

Velocity (V) = Flow (Q) / Cross Sectional Area (A), V=Q/A.

Question 10

Define “velocity” and “flow.” (In terms of blood)

Answer 10

Velocity is defined as displacement of blood per unit time (cm/sec), whereas flow is a measure of volume, i.e., rate of how much volume of blood moves per unit time (measured in ml/sec)

Question 11

How is flow and velocity, cross sectional area, related?

Answer 11

Flow is always constant, but as the velocity increases the diameter decreases (inversely proportional).

Question 12

How does velocity of blood relate between aorta and capillaries?

Answer 12

Total cross sectional area of aorta is tiny relative to capillaries and since flow is constant, velocity through the aorta is very fast compared to velocity of blood in capillaries, which is much slower.

Question 13

What determines the direction of blood flow between vessels?

Answer 13

Pressure gradient.

Question 14

How does Ohm’s law of V=IR related to hemodynamics?

Answer 14

Voltage = pressure gradient Delta P, Current = Blood Flow (Q) and Resistance is the same. Thus, V=IR is the same as P=QR.

Question 15

How can flow be regulated?

Answer 15

By regulating the resistance applied by the arterioles.

Question 16

What is a consequence of the series and parallel arrangements of blood vessels?

Answer 16

In a series, Flow is constant, but resistance increases as vessels get smaller resulting in increased pressure. In a parallel circuit, the pressure stays constant instead because the resistance decreases in a parallel circuit (1/R1 + 1/R2, etc).

Question 17

How does the compliance of arteries in the elderly compare with the young and what is the consequence?

Answer 17

Older arteries are less compliant so they hold less volume of blood, thus there needs to be increased pressure to in the arteries to hold as much volume as it used to.

Question 18

What drives the blood flow throughout the CV system?

Answer 18

Pressure from the aorta –> arteries –> capillares –> veinules –> continue to decrease progressively, and thus the pressure gradiant allows for a net flow of blood from arteries to veins.

Question 19

What is “dicrotic notch” or “incisura”?

Answer 19

It’s a notch in the pressure curve of arterioles representing the closure of the aortic valve, at this time there is a slight backflow of blood to the valve so a minor dip in pressure of arterioles. The blood bounces off the valve and back towards the aorta, increasing the pressure again.

Question 20

What is “stroke volume?” How is it calculated?

Answer 20

This is the amount of blood ejected from left ventricle in a single beat, and it can be measured by the difference between the systolic pressure and diastolic pressure (of the aorta?), using the formula compliance (C) = V/P, assuming C is constant.

Question 21

Majority of the cardiac cycle is spent in what phase?

Answer 21

The Diastolic phase, systolic phase is about 1/3 of diastolic phase in terms of time.