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Cardiology > 03: Cardiovascular Physiology > Flashcards

03: Cardiovascular Physiology Flashcards

1
Q

How do you calculate vessel wall tension/ventricular wall stress?

A

Law of Laplace

τ = Pr/2H

τ = tension in vessel wall (dyne/cm2)
P = transmural (internal) pressure (dyne/cm2)
r = radius of vessel (cm)
H = wall thickness (cm)

NB: Utilized to explain adaptation of myocardium to stress (i.e., high BP –> LV thickening –> decreased wall stress).

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2
Q

What is cardiac output (CO)?

A

Rate at which blood is pumped from either ventricle.

In steady state, LV CO = RV CO.

Rate at which blood is returned to RA = venous return.

In steady state, blood flow to left heart = venous return to right heart.

In steady state, left heart CO = venous return to right heart.

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3
Q

Which vessels have the highest resistance?

A

Arterioles

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4
Q

Compare and contrast arteries & veins.

A

Arteries:

  • Thick-walled
  • Carry oxygenated blood to tissues
  • Blood volume under high pressure
  • Branch into arterioles
  • Arterioles contain highest resistance in CV system
  • Arteriolar resistance regulated by** α1** and β2 receptors

Veins

  • Thin-walled w/ valves
  • Carry deoxygenated blood to heart
  • Blood volume under low pressure
  • Vessels coalesce into larger veins
  • Contain highest proportion of blood volume in CV
  • Veno-resistance regulated by α1 receptors
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5
Q

Describe the capillary bed.

A
  • Thin walled, with single layer of endothelial cells surrounded by basal lamina
  • Exchange of diffusable substances between tissue and blood
  • Highest cross-sectional surface area in CV system
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6
Q

What is the stressed volume? The unstressed volume?

A

Stressed volume: small blood volume held in aorta, arteries, arterioles and capillaries.

Unstressed volume: greatest volume of blood, located in the veins and venules.

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7
Q

What factors influence blood flow?

A

Cardiac output
Vessel diameter
Vascular resistance
Circulating volume
Blood viscosity

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8
Q

How do you calculate velocity of blood flow?

A

v = Q/A

v = velocity in cm/sec
Q = CO (flow) in mL/min (or cm3/min)
A = cross-sectional area of vessel

Greatest velocity in aorta, slowest in capillary beds.

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9
Q

How do you calculate the amount of blood ejected from the heart every minute?

A

Ohm’s Law

Q = ΔP/R

Q = CO (flow) in mL/min
ΔP = pressure gradient in mmHg
R = resistance or total peripheral resistance in mmHg/mL/min

NB: Vascular resistance increases with increasing muscularity of the vessel wall.
NB2: For constant blood flow, as resistance increases, downstream pressure must decrease –> increase in ΔP.

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10
Q

How do you calculate resistance to flow?

A

Poiseuille’s Equation: resistance to flow depends on dimenstion of the tube and characteristic of fluid.

R = (8ηl)/(πr4)

η = viscosity of blood
l = length of blood vessel

NB: Principal determinant of resistance is caliber (radius of vessel).

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11
Q

What is laminar flow?

A

All elements in the blood move in streamlines that are parallel to the axis of the vessel.

Blood flow in normal vessels is laminar.

Versus turbulent flow, where blood moves axially and raidally and requires more energy to drive flow.

Turbulent blood flow can be audible with a stethoscope as a murmur.

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12
Q

How do we predict the blood flow profile?

A

Reynold’s Number

NR = ρdv/η

NR = Reynold’s number
ρ = density of blood
d = diameter of vessel
v = velocity of blood
η = viscosity of blood

NR < 2000 = laminar
NR > 3000 = turbulent

Large vessel diameters, high velocities and low viscosity predispose to turbulence.

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13
Q

What is capacitance and how is it calculated?

A

Capacitance is compliance; it describes the volume of blood a vessel can hold at a given pressure.

C = V/P

C = capacitance
V = volume in mL
P = pressure in mmHg

Capacitance greater for veins than arteries.

Arterial capacitance decreases with age.

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14
Q

What is the normal level of cardiac output?

A

5000 mL/min

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15
Q

Describe cardiophysiology of exercising.

A
  • Necessity for increased blood flow to exercising skeletal muscle
  • CO increases via increased HR, myocardial contractility and stroke volume
  • Arteriolar vascular resistance drops in skeletal muscle (promoting preferential flow)
  • Arteriolar resistance increases in non-exercising vascular beds
  • Venous return increases because of venoconstriction and increased skeletal muscle tone
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16
Q

How is cardiac output commonly calculated in the clinic?

A

CO = (MAP-RAP)/TPR

MAP = mean arterial pressure
RAP = right atrial pressure
TPR = total peripheral resistance

MAP = (SBP+2DBP)/3

NB: RAP = CVP (central venous pressure)
NB2: TPR = SVR (systemic vascular resistance)

17
Q

What is the Fick Equation?

A

Calculation of cardiac output based on the conservation of oxygen utilized by the body.

CO = (O2 consumption)/ ([O2]PV - [O2]PA)

O2 Consumption = O2 use by body in mL O2/min (typically 250 mL/min)
[O2]PV = O2 content in pulmonary vein
[O2]PA = O2 content in pulmonary artery

NB: [O2]PV can be estimated via aortic O2 content.

18
Q

How do you convert mmHg min/L (Wood units) to dyne sec/cm5?

A

To convert mmHg to dyne, multiply by 80

19
Q

How do you calculate pulmonary vascular resistance (PVR)?

A

PVR = (MPAP-PCWP)/CO

MPAP = Mean pulmonary arterial pressure
PCWP = pulmonary capillary wedge pressure

Note: PVR should be reported in dyne sec/cm5; if the above values are reported in Wood units, multiply by 80.

20
Q

How is steady blood flow maintained in the capillary beds of the body when cardiac output from the heart is intermittent?

A

Blood flow in the aorta and larger arteries is pulsatile.

Blood flow in the capillaries is non-pulsatile.

Pulsatile blood flow is dampened by the distensibility of the larger arteries and the resistance of the arterioles.

When blood is pumped out of the heart, a substantial fraction is stored in the stretched arterial walls during systole.

During ventricular diastole, previously stretched arteries recoil and volume of blood displaced by vascular recoil provides continuous capillary flow.

21
Q

What is pulse pressure?

A

The difference between systolic and diastolic blood pressure.

Reflects the volume of blood ejected with each heart beat (stroke volume).

22
Q

What is mean arterial pressure and how is it calculated?

A

The driving force for blood flow in the arteries.

Influenced more by diastolic blood pressure than systolic blood pressure.

MAP = (SBP + 2DBP)/3

MAP = DBP + (1/3) PP

23
Q

How does arterial pressure change in arteriosclerosis? Aortic stenosis?

A

MAP rises in arteriosclerosis.

MAP declines in aortic stenosis.

Cardiology (13 decks)

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