Ventricular Function Flashcards Preview

Cardiovascular > Ventricular Function > Flashcards

Flashcards in Ventricular Function Deck (31):
1

resting tension

the amount of tension that develops passively by stretching muscle

2

active tension

the amount of tension that is developed by the muscle by an active process (contraction) at a particular length

3

preload

force placed on muscle before contraction beings (pre)

muscle is passive as preload is applied

causes muscle to passively lengthen

intact heart, preload is the volume that fills the chamber during the diastolic phase

4

isometric contraction

contraction without change in length

5

isotonic contraction

contraction with shortening and constant muscle tone

6

effects of increasing preload on isometric contraction

increasing preload increases amount of tension developed

time to peak tension unchanged

increases dT/dt

7

optimal length

the sarcomere length that produces the maximal tension development - due to better crossbridge alignment

8

length dependent calcium sensitivity

as length of muscle increases, so does the sensitivity to calcium

9

contractility

a change in force development, independent of change in muscle length due to load

changing contractility alters the amount of tension developed and the time to peak tension (isometric)

10

increasing preload at constant afterload and contractility

• Decreases the time to the onset of shortening. (Note the dotted vertical lines in A)

• Increases the amount of shortening. (A, B, C)

• Increases shortening velocity. (Note differences in dL/dt in A).  Shortening velocity increases with increased preload.

• Does not affect the maximum tension reached (This is determined by the afterload!).

11

increasing afterload at constant preload and contractility

• Increasing afterload decreases the amount of shortening

• Increasing afterload decreases the velocity of shortening

• Increasing afterload increases the total tension developed in the muscle.

12

What happens to Vmax when contractility is increased?

increased

13

ejection fraction equation

EF= { EDV-ESV } / EDV * 100

14

preload in the heart

stretches cardiac muscle passively toward its optimal length

passively positions contractile elements for interaction

alters calcium sensitivity

equivalent to EDV

15

afterload in the heart

opposes shortening (ejection)

analogous to arterial pressure

in some diseases, also due to obstrictive structures such as aortic valve stenosis or hypertrophied muscle

16

contractility of the heart

force development independent of length changes

in intact heart, contractility changes due to changes in sympathetic nerve activity

increased sympathetic activity leads to greater calcium release and greater ejection

17

What is the adult normal value for ejection fraction?

about 60%

18

How do you maximize shortening in isolated cardiac muscle or stroke volume in the heart?

increase preload

decrease afterload

increase contractility

19

heart failure

a condition in which the heart fails to provide a cardiac output sufficient to meet the needs of the body

20

reasons for decreased contractility in the heart

decrease calcium availability

ischemia

myocardial depressants

chronic volume overload

21

reasons for decreased compliance

scar tissue

elevated pericardial fluid

pericardial constriction

22

mechanisms of heart failure

impaired contractility

impaired diastolic filling

increased afterload

23

causes of impaired diastolic filling

left ventricular hypertrophy

restrictive cardiomyopathy

myocardial fibrosis

transient myocardial ischemia

pericardial constriction or tamponade

24

reason for increased afterload (chronic and severe)

advanced aortic stenosis

uncontrolled severe hypertension

25

factors affecting stroke volume

force of contraction

afterload

ventricular size

hypertrophy

26

determinants of preload

pressure gradient

time for filling

compliance

atrial function

27

determinants of contractility

neurotransmitters

drugs

disease

28

determinants of afterload

aortic pressure

ventricular outflow tract resistance

29

absolute heart rate

heart rate affects the time for ventricular filling

30

factors influencing "heart rate" (ventricular rate)

pacemaker function

AV nodal conduction

ventricular conduction

autonomic nervous system

31

external work

external work = stroke volume x mean aortic pressure