Heart as a pump

Question 1

Define Cardiac output, including equation and average CO at rest

Answer 1

volume of blood pumped per minute by left ventricle
CO= HR x Stroke volume
CO= arterial pressure/ total peripheral resistance
Avg CO = 4-6L/min

Question 2

Define stroke volume

Answer 2

volume of blood pumped per beat

Question 3

What is Cardiac index?

Answer 3

CO normalized to body size, measured as surface area in m2. Normal range is 2.6 to 4.2 L/min/m2

Question 4

High HR alone leads to what?

Answer 4

Less time for filling = decreased stroke volume (in absence of other regulation)

Question 5

What determines stroke volume?

Answer 5

strength of contraction of the heart, venous return (“preload”), and vascular resistance (“afterload”)

Question 6

How is strength of contraction of heart controlled?

Answer 6

1. Length-dependent intrinsic mechanism = Frank-Starling Law of the Heart
2. Length-independent mechanism = Inotropy (or “contractility”), regulated via sympathetic nervous system stimulation

Question 7

Can you draw the pressure volume changes during cardiac cycle? (Wiggers diagram)

Answer 7

See notes

Question 8

What is the “a wave”?

Answer 8

In diastole: A bump in the atrial and ventricular pressure that occurs as the atrium begins to contract (atrial systole) and blood flows into the ventricle

Question 9

What is the isovolumetric contraction phase of cardiac cycle?

Answer 9

Ventricle begins contracting but both the mitral valve and aortic valve are closed, but the blood has no where to go yet

Question 10

What is the ejection phase?

Answer 10

Ventricle continues to contract, ventricular pressure exceeds that in the aorta, thus the aortic valve is pushed open and blood begins to flow

Question 11

What is the isovolumetric relaxation phase?

Answer 11

The ventricle continues to relax with both valves closed, so the pressure falls rapidly

Question 12

Know what the pressure volume curves look like for systolic and end diastolic

Answer 12

See notes

Question 13

End diastolic volume is approximated by what?

Answer 13

preload (for left ventricle)

Question 14

Explain the end diastolic pressure volume relationship

Answer 14

Pressure-volume relationship during filling, before contraction. Corresponds to passive elastic properties of ventricle (slope is inverse of compliance).

Question 15

Explain the systolic pressure volume relationship

Answer 15

Pressure-volume relationship at peak of isometric contraction. Depends on the afterload (~aortic pressure)

Question 16

How is EDPVR affected by decreased compliance?

Answer 16

EDPVR becomes steeper

Question 17

What is active tension?

Answer 17

difference in force between peak systolic pressure and end diastolic pressure curves, i.e., tension developed by the contraction itself, independent of the preload.

Question 18

What is a starling curve?

Answer 18

• aka ventricular function curve: Curve that represents active tension. -Y-axis: pressure, tension, cardiac output, or stroke volume
• X-axis: volume or length
• Has ascending and descending limb

Question 19

What is Frank-Starling law of the heart?

Answer 19

INTRINSIC mechanism by which the heart adapts to changes in preload (in the normal physiological range).
a) Heart responds to an increase in EDV by increasing the force of contraction
b) Healthy heart always functions on the ascending limb of the ventricular function curve
.c) Cardiac output MUST equal venous return and cardiac output from left and right ventricles MUST match

Question 20

What is the Bainbridge reflex?

Answer 20

Increased venous return stretches sinus node which increases heart rate

Question 21

Be able to draw a PV loop diagram

Answer 21

See notes

Question 22

Which points on the PV loop represent filling phase?

Answer 22

A-c

Question 23

Which points on the PV loop represent isovolumetric contraction? What is the volume called?

Answer 23

C-D

End diastolic volume

Question 24

Which points on the PV loop represent Ejection phase?

Answer 24

D-F

Question 25

Which points on the PV loop represent Isovolumetric relaxation phase?

Answer 25

F-A

Question 26

How Do you measure blood pressure on PV loop?

Answer 26

o End diastolic pressure at point D (~80 mm Hg)
o Peak systolic pressure at point E (~130 mm Hg)
o Difference = pulse pressure (~ 50 mm Hg)

Question 27

What is stroke volume on PV loop?

Answer 27

SV = EDV -  ESV
SV= C-A

Question 28

What is ejection fraction on PV loop?

Answer 28

o The fraction of the EDV ejected during systole.
o EF = SV/EDV = (EDV – ESV) / EDV
-EF= (C-A)/ C
normal= 50-70%

Question 29

What is stroke work on PV loop?

Answer 29

o Stroke work = energy per beat (in Joules), corresponds to the area inside the PV loop diagram
o NOT the same for left & right sides of heart

Question 30

What factors affect preload?

Answer 30

• blood volume
• filling pressure & time
• resistance to filling (right atrial pressure, AV valve stenosis ,Ventricular compliance)

Question 31

What factors affect ventricular compliance?

Answer 31

Hypertrophy reduces compliance, Dilation increases compliance

Question 32

how does increased EDV affect stroke volume?

Answer 32

increases it on the next beat

Question 33

Factors that affect afterload?

Answer 33

Aortic pressure is the major determinant of afterload – hypertension increases afterload
aortic stenosis

Question 34

how does increased afterload affect stroke volume?

Answer 34

decreases it on the next beat

Question 35

How does ionotropy affect ventricular function?

Answer 35

Changes in inotropy describe new ventricular function (Starling) curves.

Question 36

What affect does increased ionotropy have on stroke volume?

Answer 36

increases stroke volume on the next AND SUBSEQUENT beats