Control Of Cardiac Output Flashcards
After load
Load the heart must eject blood against (aortic pressure)
Pre load
Amount the ventricles are stretched (filled) in diastole (end diastolic volume/central venous pressure)
Central venous pressure
Pressure in large veins draining to heart
Total peripheral resistance
Systemic vascular resistance - resistance to blood flow offered by systemic vasculature
What happens to pressure as it encounters resistance on the other side
Drops
How do arterioles increase resistance
Constriction - pressure in capillaries and venous side will fall
Arterial pressure will rise
What happens if total peripheral resistance decreases (CO unchanged)
Lower resistance =
arterial pressure fall (easier to flow)
Venous pressure increase (builds up venous side)
What happens if total peripheral resistance increases (CO unchanged)
Arterial pressure increases
Venous pressure fall
What happens if cardiac output increases
Increase arterial pressure (more blood pumping out)
Decrease venous pressure (easier for blood to flow into empty heart)
What happens if CO decreases?
Arterial pressure decreases (less blood out)
Venous pressure increases (heart isn’t as empty so less easy to flow in)
What happens when tissues need more blood?
Arterioles and precapillary sphincters dilate
Less resistance
Arterial pressure falls - heart needs to pump more to maintain pressure
Venous pressure raises - heart pumps more to ensure doesn’t rise
2 ways which heart responds to changes in CVS and aBP
Intrinsic and extrinsic
Cardiac output
Stroke volume x heart rate
Stroke volume
End diastolic volume (finished filling) - end systolic volume (finished emptying)
EDV - ESV
Typical cardiac output
5L per minute
Typical stoke volume
70ml
67% of EDV
How can you increase stroke volume
Increase end diastolic volume (fill blood more)
Decrease end systolic volume (pump more blood out)
When does ventricular filling occur?
Diastole
AV valves open
Aortic and pulmonary closed
When do the ventricles stop filling?
Until the intraventicular pressure is equal to venous pressure
Higher venous pressure = more filling of heart = higher ventricular pressure
What is the ventricular compliance curve?
Higher venous pressure = more filling of heart = higher ventricular pressure
Frank starling law of the heart
If you stretch fibres of heart before contracting it will contract harder
More the heart fills = harder contraction
Harder contraction = bigger stroke volume
What is how much the ventricles fill dependent on?
Compliance -
Increased compliance - dilated walls, thinner (less pressure exerted)
Decreased compliance - hypertrophy (stiff and high pressure)
Starling curve
Increase venous return = Left ventricular end diastolic pressure increase = increase in stroke volume = increase preload
Length tension curve cardiac muscle
If sarcomere length too short - filament overlap interferes with contraction (decreases force)
