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Flashcards in pump 2 Deck (30):
1

Frank Starling Law of the heart

1. Heart always functions on the ascending limb of the ventricular function (Starling) curve.
2. Heart responds to an increase in end diastolic volume (EDV) by increasing the force of contraction
3. What comes in, must go out.

2

Molecular basis for Starling’s law

1. Cardiac titin isoform is very stiff – resists stretch past a certain point.
2. Ca2+ sensitivity of myofilaments increases at longer sarcomere lengths
3. Longer sarcomere lengths change “lattice spacing” between actin and myosin, allows each cross bridge to generate more force.

3

Titin is

1. Titin is a gigantic protein that spans Z-line to M-line in sarcomeres .
2. “Molecular spring” that determines passive elasticity of muscle.

4

Skeletal muscle is more compliant due to

more elasticity in skeletal muscle titin isoform – can function on descending limb of length-tension relationship.

5

measures of cardiac performance

1. blood pressure
2. stroke volume
3. ejection fraction
4. stroke work

6

SV =

volume per beat
SV = EDV - ESV
typically 120-50 = 70 ml

7

ejection fraction (EF) =

proportion ejected at each beat

EF = SV/EDV
EF = (EDV - ESV) / EDV = 70/120 =58%

8

stroke work =

energy per beat (in joules)
= area under curve

9

How do changes in Preload, Afterload, and Contractility independently affect cardiac performance?

Look at effects of stroke volume on next beat…

10

determinants of cardiac output?

1. preload
2. afterload
3. inotropy

11

preload is the load/length to which a muscle is subjected before

shortening

12

factors that affect preload

1. blood volume
2. filling pressure & time
3. resistance to filling

13

resistance to filling:

1. right atrial pressure, AV valve stenosis
2. Ventricular compliance

14

what is the major determinant of preload

ventricular compliance

15

slope of EDPR is the inverse of

compliance

16

hypertrophy effect on compliance

reduces compliance

the steeper the slope, the harder it is for the ventricles to fill and the lower the EDV at any given EDP

17

dilation effect on compliance

dilation increases compliance

18

decreased compliance is

hypertrophy

19

increased compliance is

dilation

20

increased preload will cause

increase in SV on the next beat (via Starling's law)

21

afterload is the load against which a muscle

contracts

22

factors that affect afterload

1. Aortic pressure: hypertension increases afterload
2. wall thickness
3. radius
4. Aortic stenosis

23

Afterload is strictly defined as

wall stress

24

major determinant of afterload is

aortic pressure

25

increased afterload causes a

decreased stroke volume in the next beat

26

inotrophy (contractility) is the

force of contraction independent of fiber length

27

inotropy describes the

systolic function of heart

28

what is the biggest affecting factor of inotropy

sympathetic tone

29

changes in inotropy describe

new ventricular function (starling) curves

30

increased inotropy will cause

increased in stroke volume on the next AND SUBSEQUENT beats