Lecture 9: Determinants of Cardiac Output

Question 1

what are some key measures of the heart

Answer 1

• stroke volume
• heart rate
• cardiac output

Question 2

what are some measures of cardiovascular performance?

Answer 2

flow = pressure gradient/ resistance

Question 3

why is the maintenance of a pressure gradient critical?

Answer 3

maintains flow and perfusion to tissues

Question 4

what is M.A.P?

Answer 4

quality monitored by the system, controls flow

MAP = CO x resistance

Question 5

what is CO?

Answer 5

HR x SV

Question 6

what is SV?

Answer 6

EDV - ESV

Question 7

what is TPR?

Answer 7

overall resistance to flow through the entire circulation

Question 8

MAP = CO X RESISTANCE

Answer 8

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

TPR & ESV= after load
EDV = preload

Question 9

what is preload?

Answer 9

the force stretching a relaxed myocardium

–> amount of stretch on myocardial muscle before heart contracts, VR will determine PRELOAD

Question 10

what is after load?

Answer 10

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

Question 11

determinants of stroke volume - frank

Answer 11

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

Question 12

effect of cell length w/ EDV

Answer 12

cell length determined overlap of thick and thin filaments

length of relaxed cells determined by amount of blood in ventricle

Question 13

physiological significance of the frank-starling relationship

Answer 13

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

Question 14

how can you modulate contractility?

Answer 14

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

Question 15

how can you increase force f contraction in cardiac muscle?

Answer 15

• 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

Question 16

explain the cascade of binding NA to beta adrenergic receptors

Answer 16

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