Lecture 9: Determinants of Cardiac Output Flashcards Preview

Cardiovascular System > Lecture 9: Determinants of Cardiac Output > Flashcards

Flashcards in Lecture 9: Determinants of Cardiac Output Deck (16):
1

what are some key measures of the heart

- stroke volume
- heart rate
- cardiac output

2

what are some measures of cardiovascular performance?

flow = pressure gradient/ resistance

3

why is the maintenance of a pressure gradient critical?

maintains flow and perfusion to tissues

4

what is M.A.P?

quality monitored by the system, controls flow
MAP = CO x resistance

5

what is CO?

HR x SV

6

what is SV?

EDV - ESV

7

what is TPR?

overall resistance to flow through the entire circulation

8

MAP = CO X RESISTANCE

CO = HR x SV , SV = EDV - ESV = VR
RESISTANE = TPR

TPR & ESV= after load
EDV = preload

9

what is preload?

the force stretching a relaxed myocardium
--> amount of stretch on myocardial muscle before heart contracts, VR will determine PRELOAD

10

what is after load?

force opposing the shortening of myocardium during contraction
arterial pressure will determine after load (TPR)
ventricular wall pressure

11

determinants of stroke volume - frank

VR determines EDV, increase EDV = increase SV
sympathetic drive modifies contractility, for any fixed length this will increase output.

increased SV achieved by :
- increased muscle length = increase VR = increase EDV
- increased contractility by increased calcium

12

effect of cell length w/ EDV

cell length determined overlap of thick and thin filaments
length of relaxed cells determined by amount of blood in ventricle

13

physiological significance of the frank-starling relationship

length-tension relationship of the heart allows for equalisation of output from left and right sides of the heart
eg/ increase in output from RS = increase ventricular filing = increased EDV = increase stretch of cardiac muscle fibres = increased force development in ventricle = increased left ventricular output.

increased arterial output = increased after load, reduced ejection fraction, increased in ESV and EDV = increased cardiac stretch and contractility

14

how can you modulate contractility?

with use of a positive ionotrope
- any agent that increase peak isometric tension at a fixed length
ionotropes act through modulated intracellular calcium

15

how can you increase force f contraction in cardiac muscle?

- can't increase AP like in skeletal muscle because set by pacemaker cells
- can't increase # of fibres stimulated because they're all already contracting
SO..
dependent on intracellular calcium levels

16

explain the cascade of binding NA to beta adrenergic receptors

activation of adenyl cyclase
increase intracellular cAMP
phosphorylation of VOCC
inward movement of calcium
increase calcium release from SR
increase actin-myosin cross binding
increase force of contraction