cardiac physiology Flashcards
what is the purpose of the cardiovascular system?
to deliver nutrients, oxygen, immune cells etc. to tissues and the rapid removal of metabolic waste products2t
what can be used to see the coronary arteries in a patient
coronary angiogram
when is coronary blood flow greatest and why
during diastole as the vessels a compressed by the contracting myocardium during systole
what is the significance of the coronary arteries being end arteries
they don’t form anastomoses and so if there is a blockage in one artery, ischaemia occurs in all areas downstream
structural adaptation of the heart to meet the high O2 requirement
very high myocardial capillary density - more blood per mm^2 of muscle fibre allowing for great O2 deliver
functional adaptations the heart to meet the high O2 requirement (3)
high basal flow/O2 extraction; metabolic hyperaemia (myocardial cell release vasodilating factors which cause the coronary vessels to dilate when more O2 is needed due to increasing work being done); autoregulation (blood flow to the heart is maintained even if BP is low)
what is cardiac output + typical value at rest
the volume of blood ejected by 1 ventricle in 1 minute; 5L/min
what is stroke volume + typical value at rest
the volume of blood ejected from the ventricle in sytole; 75ml
cardiac output equation
CO = HR x SV
where is the majority of the blood found in the body and why is this important
in the veins (2/3 of the blood found here); acts as a blood reservoir so if HR increases then blood is moved small veins -> large veins -> heart to increase cardiac output, this is essential in topping up the heart/arteries after a haemorrhage
why is there a disparity between kidney CO and O2 consumption
they filter the blood and so require more blood flowing through them than O2 they carry
what is the significance of the myocardium receiving a small proportion of the CO but requiring a high O2 conc (2)
coronary blood has little spare reserve O2; cardiac pain due to O2 drop (angina) can be triggered by just a modest fall in blood flow
what factors affect stroke volume (3)
preload (↑SV) ; contractility (↑SV) ; afterload (↓SV)
what is preload
the stretch on ventricular fibres before contracting; the greater the stretch, the greater the contraction
what can be used as a surrogate marker of preload and why/how
end diastolic volume/pressure; pressure is exerted on the walls of the heart as it stretched (stretch on ventricular fibres) which can be detected using a specialised catheter
what is the relationship between central venous pressure and right ventricular preload?
CVP = vena cava pressure at the entrance to the RA => CVP can be used to estimate RA pressure; in diatole RA pressure = RV pressure => CVP can be used to estimate RV end diastolic pressure (which = preload)
what is end diastolic pressure/volume
the volume/pressure of blood in the ventricle at the end of ventricular filling
what is the frank-starling mechanism (law of the heart)
the greater the preload the greater the force of contraction (frank), the greater the stroke volume (starling)
what is starling’s law (from frank-starling)
the more the ventricle is stretched in diastole (preload), the greater the stroke volume; the energy of contraction is proportional to muscle fibre length at rest
what is the starling curve (ventricular function curve) - draw it out
stroke volume/CO on the y-axis, and central venous pressure/end diastolic volume on the x-axis; A shift along the same line indicates a change in preload, while shifts from one line to another indicate a change in afterload or contractility; A blood volume increase would cause a shift along the line to the right, which increases left ventricular end diastolic volume (x axis), and therefore also increases stroke volume (y axis)
