Flashcards in Lecture 9: Determinants of Cardiac Output Deck (16):
what are some key measures of the heart
- stroke volume
- heart rate
- cardiac output
what are some measures of cardiovascular performance?
flow = pressure gradient/ resistance
why is the maintenance of a pressure gradient critical?
maintains flow and perfusion to tissues
what is M.A.P?
quality monitored by the system, controls flow
MAP = CO x resistance
what is CO?
HR x SV
what is SV?
EDV - ESV
what is TPR?
overall resistance to flow through the entire circulation
MAP = CO X RESISTANCE
CO = HR x SV , SV = EDV - ESV = VR
RESISTANE = TPR
TPR & ESV= after load
EDV = preload
what is preload?
the force stretching a relaxed myocardium
--> amount of stretch on myocardial muscle before heart contracts, VR will determine PRELOAD
what is after load?
force opposing the shortening of myocardium during contraction
arterial pressure will determine after load (TPR)
ventricular wall pressure
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
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
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
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
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
dependent on intracellular calcium levels