Cardiac Physiology 3

Question 1

Equation for flow

Answer 1

Q=V/t (Flow=volume/time)

Question 2

Equation relating velocity and flow

Answer 2

Velocity=flow/area, v=Q/A

Question 3

Units of flow

Answer 3

mL/min or L/min

Question 4

Formula for hydrostatic pressure

Answer 4

P=pxgxh (Where P=pressure in mmHg, p=density, g=gravitational constant, h=height)

Question 5

What is the potential energy of a fluid?

Answer 5

Hydrostatic

Question 6

What is the kinetic energy of a fluid?

Answer 6

Hydrodynamic

Question 7

How does the pressure change in a smaller vessel compared to a larger vessel?

Answer 7

Total pressure remains the same but hydrostatic pressure decreases in the smaller vessel. Velocity is proportional to dynamic pressure.

Question 8

Poiseuille’s Law equation for flow

Answer 8

Q= (Pi-P0)r^4/8nl where Pi-Po is the pressure difference, n=viscosity, l=length, r=radius

Question 9

What is the equation for the sum of resistance in series?

Answer 9

Rt=R1+R2+R3…

Question 10

What is the equation for the sum of resistance in parallel?

Answer 10

1/Rt=1/R1+1/R2+1/R3…

Question 11

What happens to the resistance against blood between aorta to arterioles?

Answer 11

It rises because the radius drops and the subdivisions are not enough to increase the cross-sectional area.

Question 12

What happens to the resistance against blood between arterioles and the capillaries?

Answer 12

It drops because the subdivision into so many capillaries to increase the total cross-sectional area overwhelms the decrease in radius.

Question 13

Equation for Reynold’s number

Answer 13

Nr=pDv/μ where Nr=Reynold’s number, p=density, D=diameter, v=velocity, μ or n=viscosity

Question 14

What is the value of Reynold’s number for laminar flow?

Answer 14

2000 or less

Question 15

Definition of laminar fluid flow

Answer 15

Velocity of flow near the surface of the cylinder is zero and maximal in the center of the cylinder. Most effective and requires least energy and less work required to move the fluid vs turbulent flow.

Question 16

How does anemia affect the viscosity and flow of the blood?

Answer 16

Reduces viscosity which increases turbulence. May create a murmur if passing through narrowed vessel or valve.

Question 17

What ar Korotkoff sounds?

Answer 17

Pulse heard during BP measurement. Due to turbulent flow in brachial artery from artificial narrowing of the BP cuff.

Question 18

What is the difference between a compliant and rigid aorta in systole and diastole?

Answer 18

Aorta stretches in systole and accommodates more volume with less changes in pressure in a compliant system and shrinks in diastole. In a rigid system it doesn’t move. A compliant system allows more continuous blood flow.

Question 19

How does rigidity of the aorta affect O2 consumption?

Answer 19

More rigidity means more O2 consumption, directly proportional to stroke volume.

Question 20

Pressure volume relationship in the aorta compared at different ages (graph)

Answer 20

Young aortas are capable of accommodating larger volumes with smaller increments in perssure and are more compliant. dV/dP is the compliance of the vessel and decreases with age.

Question 21

Equation for elastic modulus/elastance

Answer 21

Ep=ΔP/(Da/Db) where Ep=elastic modulus, Da=max change in aortic diameter, Db=mean aortic diameter. Da/Db=ΔV

Question 22

How does elastance relate to compliance?

Answer 22

They are reciprocals.

Question 23

Elastic modulus definition

Answer 23

Measure of rigidity, measured by change in pressure vs fractional change in aortic diameter or another compliant vessel. Another way of looking at distensibility in a vessel.

Question 24

Ohm’s law equation

Answer 24

Q=P/R, Qh=cardiac output, Qr=peripheral outflow, R=peripheral resistance.

Question 25

Equation relating Mean Arterial Pressure (MAP) to compliance

Answer 25

Pa=(Qh-Qr)/Ca, Qh=inflow (CO), Qr=outflow, Ca=compliance, Pa=MAP

Question 26

How does MAP relate to the cardiac output and compliance?

Answer 26

MAP is directly proportional to the difference between inflow into the arterial system or Qh (given by CO) minus outflow from the arterial system or Qr (given by peripheral resistance) and indirectly proportional to compliance. If we consider that at any given age range compliance will remain rather constant, then the major factors regulating MAP will be the cardiac output (CO) and the peripheral resistance (R).

Question 27

What is the main regulator of peripheral resistance?

Answer 27

Arterioles, can be changed neurally. Compliance cannot because it is dependent on age.

Question 28

Definition of arterial pulse pressure

Answer 28

Difference between systolic and diastolic blood pressures. Also a function of SV and arterial compliance.

Question 29

How does compliance relate to pulse pressure?

Answer 29

In higher compliance, there is larger changes in pulse pressure with increased TPR because the vessels accommodate more to differences in systole when filling.

Question 30

How does the central venous pressure (CVP) relate to cardiac output?

Answer 30

In the vascular function curve CO increases as CVP decreases. At normal CO (5L/min) CVP=2mmHg.

Question 31

Where is the CVP measured?

Answer 31

Pressure in the right atrium.

Question 32

What is the mean circulatory pressure (Pmc) in cardiac arrest?

Answer 32

Pressure gradient between arteries and veins pushes at first but then equilibrates to 7mmHg. Arteries drop from over 100 and veins rise about 5mmHg.

Question 33

How do changes in total blood volume impact the vascular function curve?

Answer 33

Shifts to the right (increase/transfusion) or left (decrease/hemorrhage).

Question 34

What is the effect of increasing or decreasing venomotor tone on the vascular function curve?

Answer 34

Contracting veins will more curve to the right (like a transfusion, higher cardiac output), a decrease sill produce a hemorrhage-like effect.

Question 35

Cardiac function curve and Vascular function curve intersection graph

Answer 35

Cardiac Output and CVP will equilize at cardiovascular steady state through Frank-Starling. In sympathetic stimulation the CVP lowers and equilibrates at a higher cardiac output.

Question 36

Changes in blood volume and peripheral resistance in the cardiac function curve (graphs)

Answer 36

Increase in volume changes the vascular function curve but not the cardiac function curve so equilibrium is at a higher CVP and CO. Increased resistance lowers the cardiac and vascular function curve so CVP doesn’t change but CO decreases.

Question 37

Cardiac and vascular function curve in heart failure

Answer 37

In moderate HF, Cardiac function curve drops on the same vascular function curve, lowering the CO and increasing CVP. Further lowers in severe HF. However, the hypervolemia caused by HF increases the CO so it remains the same while CVP increases.

Question 38

What does Qh represent?

Answer 38

Inflow to the arterial system, 5L/min at normal.

Question 39

What does Qr represent?

Answer 39

Outflow at level of arterioles. Regulated by arterial system. Usually equivalent to inflow (5L/min)

Question 40

What is the Mean arterial Pressure at normal inflow?

Answer 40

100mmHg

Question 41

What is more compliant, veins or arteries?

Answer 41

Veins about 19x more than arteries.

Question 42

What is the arterial and venous pressure as the heart starts pumping again at a flow of 1L/min?

Answer 42

MAP rises slowly to 26 as CVP lowers to 6.