Cardio - Physio (Cardiac Output & related concepts)

Question 1

What is the equation that defines cardiac output?

Answer 1

CO = stroke volume (SV) x heart rate (HR)

Question 2

What is the equation for the fick principle?

Answer 2

CO = rate of O2 consumption / (arterial O2 content - venous O2 content)

Question 3

What is the equation that defines mean arterial pressure? How does MAP relate to diastolic and systolic pressures?

Answer 3

MAP = CO x total peripheral resistance; MAP = 2/3(diastolic pressure) x 1/3(systolic pressure);

Question 4

What is the equation that defines the pulse pressure? What is pulse pressure’s relationship to stroke volume versus arterial compliance?

Answer 4

Pulse pressure = systolic pressure - diastolic pressure; Pulse pressure is directly proportional to stroke volume (i.e., as one goes one way, the other follows in the same direction), inversely proportional to arterial compliance

Question 5

What is/are the equation(s) that define stroke volume?

Answer 5

SV = EDV - ESV (also, SV = CO/HR)

Question 6

Characterize the early and late stages of exercise in terms of changes to heart physiology.

Answer 6

During the early stages of exercise, CO is maintained by the increased HR and increased SV; During the late stages of exercise, CO is maintained by increased HR only (SV plateaus)

Question 7

What happens in heart physiology if HR is too high? Give an example of a clinical condition that exemplifies this.

Answer 7

Diastole is preferentially shortened with high HR; less filling time –> decreased CO (e.g., ventricular tachycardia)

Question 8

What approximates preload versus afterload?

Answer 8

Preload = ventricular EDV; Afterload = mean arterial pressure (proportional to peripheral resistance)

Question 9

What general effect do venodilators have? What is an example of a venodilator? What is a good way to remember this?

Answer 9

vEnodilators decrease prEload; e.g., nitroglycErinE; (see E mnemonic in answer)

Question 10

What general effect do vasodilators have? What is an example of a vasodilator?What is a good way to remember this?

Answer 10

vAsodilators decrease Afterload (Arterial); e.g., hydAlAzine; (see A mnemonic in answer)

Question 11

Again, what approximates preload? What are three things that can increase preload?

Answer 11

ventricular EDV; (1) Exercise (slightly) (2) Increased blood volume (e.g., overtransfusion) (3) Excitement (increased sympathetic activity)

Question 12

What 3 key factors affect stroke volume (and thus affect cardiac output)? What changes in these factors leads to an increase in stroke volume (and thus increase in cardiac output)?

Answer 12

(1) Contractility - increased (2) Afterload - decreased (3) Preload - increased

Question 13

What are 4 examples (including names and mechanisms) of increased contractility? Again, what effect do these have on SV and CO?

Answer 13

(1) Catecholamines (increased activity of Ca2+ in sarcoplasmic reticulum) (2) Increased intracellular Ca2+ (3) Decreased extracellular Na+ (decreased activity of Na+/Ca2+ exchanger) (4) Digitalis (blocks Na+/K+ pump –> increase intracellular Na+ –> decrease Na+/Ca2+ exchanger activity –> increase intracellular Ca2+) ; Increase

Question 14

What effect does digitalis have on contractility, and to which factor impacting contractility does this relate? What is the mechanism behind this effect?

Answer 14

Increase, because increased intracellular Ca2+ by following mechanism: block Na+/K+ pump –> Increase intracellular Na+ –> decrease Na+/Ca2+ exchanger (normally puts calcium out and brings sodium in) activity –> Increase intracellular Ca2+

Question 15

What are 5 examples (including names and mechanisms) of decreased contractility? Again, what effect do these have on SV and CO?

Answer 15

(1) Beta1-blockade (decreased cAMP) (2) Heart Failure (systolic dysfunction) (3) Acidosis (4) Hypoxia/Hypercapnea (decreased PO2/increased PCO2) (5) Non-dihydropyridine Ca2+ channel blockers ; DECREASE

Question 16

In what (non-pathologic) situations might a patient’s SV increase?

Answer 16

(1) Anxiety (2) Exercise (3) Pregnancy

Question 17

What effect does a failing heart have on SV, and why?

Answer 17

A failing heart has decreased SV (both systolic and diastolic dysfunction)

Question 18

What increases myocardial O2 demand?

Answer 18

(1) Increased afterload (directly proportional to arterial pressure) (2) Increased contractility (3) Increased heart rate (4) Increased heart size (increased wall tension)

Question 19

To what is the force of contraction proportional?

Answer 19

End-diastolic length of cardiac muscle fiber (preload)

Question 20

What 3 factors/conditions increase contractility?

Answer 20

(1) Sympathetic stimulation (2) Catecholamines (3) Digoxin;

Question 21

What 4 factors/conditions decrease contractility?

Answer 21

(1) Loss of myocardium (MI) (2) Beta-blockers (3) Calcium channel blockers (4) Dilated cardiomyopathy

Question 22

Draw the Starling graph/curve, labeling its axes and creating curves for the following scenarios: (1) Exercise (2) Normal (3) CHF+digoxin (4) CHF.

Answer 22

Axes: y = CO or stroke volume, x = Ventricular EDV (preload); See FA p. 254 for Starling curve visual

Question 23

What is/are the equation(s) that characterizes/defines ejection fraction?

Answer 23

EF = SV / EDV = (EDV - ESV) / EDV

Question 24

Of what is left ventricular ejection fraction an index?

Answer 24

Ventricular contractility

Question 25

What is a normal EF?

Answer 25

Greater than or equal to 55%

Question 26

What effects do systolic versus diastolic heart failure have on EF?

Answer 26

EF decreases in systolic heart failure; EF is normal in diastolic heart failure

Question 27

Name 5 conditions in which there is high pulse pressure.

Answer 27

High pulse pressure in (1) hyperthyroidism (2) aortic regurgitation (3) arteriosclerosis (4) obstructive sleep apnea (increased sympathetic tone) (5) exercise (transient)

Question 28

Name 4 conditions in which there is low pulse pressure.

Answer 28

Low pulse pressure in (1) aortic stenosis (2) cardiogenic shock (3) cardiac tamponade (4) advanced heart failure

Question 29

On what 2 factors does preload depend?

Answer 29

Depends on venous tone and circulating blood volume

Question 30

What does Laplace’s law tell us about afterload? Give the equation. Relate this equation to LV compensation for increased afterload.

Answer 30

Relation of LV size and afterload –> Laplace’s law; Wall tension = (pressure x radius) / (2 x wall thickness); LV compensates for increased afterload by thickening (hypertrophy) to decrease wall tension

Question 31

What effect do ACE inhibitors have on preload and/or afterload? What other substance has this same effect?

Answer 31

ACE inhibitors and ARBs decrease both preload and afterload

Question 32

What physiological change occurs with chronic hypertension? What effect does this have on the heart?

Answer 32

Chronic hypertension (increased MAP) –> LV hypertrophy