Cardiac Physiology

Question 1

What is the mean arterial pressure?

Answer 1

average pressure for circulation (about 2/3 of systolic pressure). Indicator of adequate tissue perfusion

Question 2

What two factors determine blood pressure?

Answer 2

cardiac output and systemic vascular resistance

Question 3

What can you use to assess perfusion at the bedside?

Answer 3

temperature of extremities and urine output

Question 4

What is the stroke volume?

Answer 4

volume of blood expelled from each ventricle during contraction (EDV-ESV)

Question 5

What is the ejection fraction?

Answer 5

fraction of blood volume that is expelled during contraction (stroke volume/EDV)

Question 6

What factors influence EDV?

Answer 6

total blood volume, atrial filling (afib), ventricular compliance, venous tone (gravity/respirations)

Question 7

What parameters can a PA catheter measure?

Answer 7

CVP, PA Occlusion Pressure (Wedge), PA pressure, systemic and pulmonary vascular resistance, CO, mixed venous saturation

Question 8

What factors affect stroke volume?

Answer 8

preload, inotropic state (degree of contractility of the myocardium), afterload

Question 9

What is afterload?

Answer 9

the tension the myocardium is required to develop during contraction OR the resistance the heart muscle must overcome to eject the blood into the arteries (SVR)

Question 10

What factors affect SVR?

Answer 10

radius of arterioles, blood volume, BP

Question 11

What increases contractility?

Answer 11

cardiac glycosides (positive inotropes), adrenergic agonists (epi), Ca+, increased HR

Question 12

What is the Frank Starling Law of the heart?

Answer 12

The more cardiac muscle is stretched within physiological limits, the more forcibly it will contract. Increasing volumes of blood in ventricles increase the stretch & thus the force of contraction.
Greater stretch means more blood volume is pumped out

Question 13

Describe the depolarization phase of cardiac cycle in relation to membrane potential

Answer 13

Cardiac cell resting membrane potential is -90mv

excitation spreads through gap junctions and fast Na+ channels open for rapid depolarization

Question 14

Describe the plateau phase of the cardiac cycle in relation to membrane potential

Answer 14

slow Ca2+ channels open, let Ca2+ enter from outside cell and from storage in sarcoplasmic reticulum, while K+ channels close, Ca2+ binds to troponin to allow for actin-myosin cross-bridge formation & tension development

Question 15

Describe the repolarization phase of the cardiac cycle in relation to membrane potential

Answer 15

Ca2+ channels close and K+ channels open & -90mv is restored as potassium leaves the cell

Question 16

How does calcium affect contractility?

Answer 16

Increased Ca2+ promotes more cross bridge binding (actin and myosin) and enhances ventricular contractility

Question 17

How does hypocalcemia affect the heart?

Answer 17

reduced Ca2+ blood levels depress the heart

Question 18

How does hypercalcemia affect the heart?

Answer 18

Prolong the plateau phase of action potential. Dramatically increase heart irritability. Lead to spastic heart contractions that permit little rest

Question 19

How does hypernatremia affect the heart?

Answer 19

Inhibits transport of Ca2+ into the cardiac cells, thus blocking heart contraction

Question 20

How does hyperkalemia affect the heart?

Answer 20

Interferes with depolarization by lowering the resting potential, and may lead to heart block and cardiac arrest

Question 21

How does hypokalemia affect the heart?

Answer 21

life threatening, heart beats feebly and arrhythmically

Question 22

What is the most common way to change cardiac output?

Answer 22

increasing or decreasing the heart rate. the stroke volume usually remains relatively constant due to the Frank Starling Law

Question 23

Describe the sympathetic cardioaccelatory center effects on the heart

Answer 23

projects to motor neurons in the T1-T5 level of the spinal cord. Innervate with the SA and AV nodes, heart muscle, and the coronary arteries. Stimulates heart rate (enhances calcium entry into contractile cells)

Question 24

Describe the parasympathetic cardioinhibitory center effects on the heart

Answer 24

sends impulses to the dorsal vagus nucleus in the medulla, which in turn sends inhibitory impulses to the heart via branches of the vagus nerves. Project most heavily to the SA and AV nodes. Slows heart rate

Question 25

What is the Bainbridge reflex?

Answer 25

Acceleration of heart rate by increased right atrial pressure due to stimulation of atrial receptors (ex- when you take a deep breath you get splitting of second heart sound).

Question 26

What can cause systolic dysfunction?

Answer 26

Coronary artery disease is a common cause of systolic dysfunction. It can impair large areas of heart muscle because it can reduce blood flow to large areas of heart muscle.

Question 27

What is the most common cause of diastolic dysfunction?

Answer 27

Inadequately treated high blood pressure. HTN stresses the heart because the heart must pump blood more forcefully than normal to force blood into the arteries against the higher pressure. Eventually, the heart’s walls thicken (hypertrophy), then stiffen.

Question 28

Describe systolic dysfunction

Answer 28

the heart contracts less forcefully and cannot pump out as much of the blood that is returned to it. As a result, more blood remains in the ventricles

Question 29

Describe diastolic dysfunction

Answer 29

the heart is stiff and does not relax normally. it may be able to pump a normal amount of blood out of the ventricles, but does not allow as much blood to enter its chambers. the blood returning to the heart then accumulates in the veins.