Caitlin-Physio

Question 1

What is the main measure of cardiac function?

Answer 1

Cardiac output (L/min): volume of blood that is pumped into the aorta per unit time

Question 2

What is the normal resting value for cardiac output?

Answer 2

5 L/min

Can increase 6x during exercise

Question 3

What is cardiac index, and what is the normal value range?

Answer 3

Cardiac output adjusted for differences in body surface area (L/min/m^2)

Normal: 2.5-4.0 L/min/m^2

Question 4

What is the normal range for ejection fraction? What is the significance of an abnormally high or abormally low measure?

Answer 4

55-70%: normal

40-55%: indicates damage (e.g., previous heart attack)

Under 40%: may be evidence of current heart failure or cardiomyopathy; at risk for complications

Over 75%: may indicate hypertrophy cardiomyopathy

Generally, reduced –> systolic heart failure; preserved: diastolic heart failure

Question 5

What are the 3 factors that affect contractility?

Answer 5

1. number of acting/myosin crossbriges
2. speed of forming crossbridges
3. availability/sensitivity to Ca^2+

Question 6

What is the index of contractility

Answer 6

dP/dt (change in pressure over change in time)

Question 7

Define stroke work. What are its components (3)?

Answer 7

Amt of energy that the heart converts to to work during one contraction cycle.

Components: almost all external work (incl 1. pressure work and 2. volume work) and 3. increase blood velocity

Question 8

What is the most important determinant of myocardial consumption?

Answer 8

Wall tension (impt because it can be affected by disease states)

Question 9

What is the normal efficiency of cardiac contraction?

Answer 9

20-25%

Question 10

Describe the phases of the pressure/volume relationship of the left ventricle during the contraction cycle.

Answer 10

• Phase I: gradual increase in pressure as heart fills with blood (Pre-load)
• Phase II: pressure rises rapidly with no change in volume just before the valve opens (isovolumic contraction)
• Phase III: pressure drops slightly as volume drops sharply while ventricle contracts (Afterload)
• Phase IV: pressure drops as volume stays constant (maximally contracted), before valve closes (isovolumic relaxation)

Question 11

Name the 2 methods of intrinsic regulation of cardiac function.

Answer 11

1. Frank-Starling Mechanism: greater force of contraction with increased stretch during filling (lengthen heart fibers to optimal, increased sensitivity to Ca^2+)
2. Right Atrial Stretch (SA node): affects discharge frequency

Question 12

Generally, what affects end diastolic volume? (3)

Answer 12

• effective filling pressure (pre-load)
• filling time
• wall distensibilty or compliance

Question 13

What are the major factors affecting pre-load (effective filling pressure)? (7)

Answer 13

ALL STRETCH MYOCARDIUM:

• total blood volume (e.g., hemorrhage)
• intrathoracic pressure (respiration)
• peripheral venous tone (e.g., vasodilation)
• pumping action of skeletal muscle (e.g., exercise)
• impaired inflow (e.g., mitral and tricuspid valve stenosis)
• atrial contribution to ventricular filling (e.g., atrial arrhythmias)
• body position (e.g., gravity)

Question 14

How does increased heart rate affect filling time?

Answer 14

It reduces both diastolic period and filling time

Question 15

What is the main mechanism of extrinsic regulation of the heart?

Answer 15

innervation (sympathetic and parasympathetic)

Question 16

What’s the simple way to calculate maximal heart rate?

Answer 16

220-age

Question 17

What can increase intracellular Ca^2+ in the heart?

Answer 17

sympathetic stimulation (phosphorylation of L-type channels and phopholamban)

Question 18

What is the mechanism for the effects of parasympathetic stimulation of the heart?

Answer 18

Vagal nerve releases Ach –> binds muscarinic receptors, inhibition of adenyl cyclase, decreased intracellular AMP

• slowed heart rate
• strong vagal stimulation: cessation of atrial contraction