Cardiac Physiology 3 Flashcards by Maayan Melamed

Equation for flow

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

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Equation relating velocity and flow

Velocity=flow/area, v=Q/A

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Units of flow

mL/min or L/min

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Formula for hydrostatic pressure

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

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What is the potential energy of a fluid?

Hydrostatic

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What is the kinetic energy of a fluid?

Hydrodynamic

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

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

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Poiseuille’s Law equation for flow

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

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

Rt=R1+R2+R3…

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

1/Rt=1/R1+1/R2+1/R3…

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

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

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

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

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Equation for Reynold’s number

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

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

2000 or less

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Definition of laminar fluid flow

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.

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

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

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What ar Korotkoff sounds?

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

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

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.

How does rigidity of the aorta affect O2 consumption?

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

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

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.

Equation for elastic modulus/elastance

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

How does elastance relate to compliance?

They are reciprocals.

Elastic modulus definition

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.

Ohm’s law equation

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

Equation relating Mean Arterial Pressure (MAP) to compliance

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

How does MAP relate to the cardiac output and compliance?

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).

What is the main regulator of peripheral resistance?

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

Definition of arterial pulse pressure

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

How does compliance relate to pulse pressure?

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

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

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

Where is the CVP measured?

Pressure in the right atrium.

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

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

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

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

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

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

Cardiac function curve and Vascular function curve intersection graph

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.

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

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.

Cardiac and vascular function curve in heart failure

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.

What does Qh represent?

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

What does Qr represent?

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

What is the Mean arterial Pressure at normal inflow?

100mmHg

What is more compliant, veins or arteries?

Veins about 19x more than arteries.

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

MAP rises slowly to 26 as CVP lowers to 6.