Muscle Physics & Heart as a Pump (complete)

Question 1

Define cardiac output

Answer 1

Volume of blood pumped per minute by left ventricle

Question 2

What is the equation used for cardiac output?

Answer 2

CO = HR x SV

HR: heart rate
SV: stroke volume

Question 3

Describe the changes in pressure through the cardiac cycle as a function of time

Answer 3

• After diastole & passive filling of LA, atrial contraction => increased atrial pressure => increased ventricular pressure (while mitral valve is open)
• When mitral valve closes, ventricular contraction starts => ventricular pressure ^ rapidly until it exceeds that in aorta => aortic valve opens
• Results in slow decrease in ventricular pressure => then faster drop in pressure once it’s below aortic pressure
• Ventricle continues to relax with both valves closed => pressure falls rapidly

Question 4

Describe the changes in volume through the cardiac cycle as a function of time

Answer 4

• Ventricle passively fills => Atrium contract towards the end of diastole
• During isovolumetric contraction phase no ∆ in volume b/c aortic and mitral valves are closed
• aortic valve opens and blood leaves ventricle => volume decreases

Question 5

What are the four phase of the cardiac cycle?

Answer 5

1) Filling phase
2) Isovolumetric contraction phase
3) Ejection phase
4) Isovolumetric relaxation phase

Question 6

Describe the filling phase

Answer 6

• At end of diastole, LA has filled w/ blood from pulm vein
• Contraction triggered by electrical signal originating from SA node
• As LA starts to contract, atrial pressure ^ => no ∆ in volume

Question 7

Describe the isovolumetric contraction phase

Answer 7

• As wave of depolarization reaches ventricle, it contracts and ventricular pressure ^
• This pushes mitral valve closed b/c pressure exceeds that in atrium
• Ventricular pressure increases rapidly b/c ventricle contracts but blood has no place to go

Question 8

Describe the ejection phase

Answer 8

• As the ventricle contracts, ventricular pressure exceeds that in aorta => aortic valve opens, blood flow begins
• Decreased ventricular volume
• Increased and then decreases in ventricular pressure

Question 9

Describe the isovolumetric relaxation phase

Answer 9

• As ventricle relaxes, pressure falls
• when ventricular pressure goes below aortic pressure => aortic valve closes
• Ventricles continues to relax => both valves closed, pressure falls rapidly (slowly at first)
• as ventricle relaxes, pressure eventually falls below that of atrium => mitral valve opens
• cycle begins again

Question 10

Describe the Frank-Starling Law of the Heart

Answer 10

• Instrinsic mechanism by which the heart adapts to changes in preload
• Heart response to ^ EDV by increasing force of contraction
• Heart always functions on ascending limb ventricular function curve

Question 11

Describe the PV loop diagram

Answer 11

Just go look at the ppt

Question 12

Define stroke volume

Answer 12

SV = EDV - ESV

Question 13

Define ejection fraction

Answer 13

Fraction of EDV ejected during systole

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

Question 14

Define stroke work

Answer 14

• energy per beat (Joules)
• corresponds to area inside PV loop diagram

NOT the same for left and right sides of the heart

Question 15

Define pulse pressure

Answer 15

End diastolic pressure - peak systolic pressure

Question 16

Where are SV, EF, SW, and PP in the PV loop diagram?

Answer 16

GO LOOK AT THE PPT

Question 17

Define preload

Answer 17

Pressure stretching the ventricle prior to contraction

Question 18

Define afterload

Answer 18

resistance the LV must overcome to circulate blood

LV afterload: aortic pressure

Question 19

Define contractility

Answer 19

• Inotropy
• Force of contraction that’s independent of fiber length
• describes systolic function of heart
• sympathetic tone is biggest factor affecting inotropy
• changes => new ventricular function

Reflects the strength of contraction at any given preload and afterload

Question 20

Describe how altering preload, afterload, or contractility changes ventricular function

Answer 20

Increase in preload:

• results in ^ SV for next beat
• same ESV, EF ^

Increase in afterload:

• decrease in SV
• ventricle has to work harder against the increased aortic pressure => less blood ejected
• EDV unchanged, EF decreased, ESV increased

∆ in contractility:

• new starling curves
• corresponds to greater systolic pressure development
• Associated with ^ stroke risk
• ^ SV

Question 21

Describe generally the systolic/diastolic pressure-volume relations and ventricular functions curves

Answer 21

• Pressure and volume changes in LV bound by 2 curves

1) systole pressure-volume relationship
2) end-diastolic pressure-volume relationship

Question 22

Describe the end-diastolic pressure volume relationship

Answer 22

• Pressure-volume relationship during filling of heart BEFORE contraction
• Corresponds to passive elastic properties of ventricle
• Slope of EDPVR is shallow in normal physiological range
• represents PRELOAD on LV

Question 23

Describe the systolic pressure volume relationship

Answer 23

• Curve at peak of isometric contraction
• Maximum pressure that can be developed for a given set of circumstances
• Steeper than EDPVR — pressure ^ a lot for small changes in volume
• Includes active plus passive properties