Cardiac Mechanics - Pressure-volume relationships Flashcards
ESP
aortic pressure = afterload
EDP
venous pressure = preload
Preload
load on heart during diastole (before contracting), RAP, CVP, Pv, EDV, EDP
Afterload
load on heart during systole (while contracting), TPR, MAP
Preload (EDP)^
ESV constant, SV^, CO ^
Frank Starling law
as the heart fills up with more blood during diastole (EDV^), it contracts harder and pumps out more blood during systole –> SV^
Afterload (ESV/ESP^)
SV decreases and CO decreases
Contractility
Depends upon intrinsic strength of the muscle [Ca++] inside cell
Depends upon the total amount of heart muscle which is fixed in the short term but can change with aerobic exercise
Increases with sympathetic stimulation
Ejection fraction ^
(SV/EDV)^
At any given EDP and ESP
as contractility ^, SV^
Stroke work
deltaP * deltaV = work performed by the heart to eject a volume of blood (stroke volume) at a specific pressure (mean arterial pressure)
Total energy required
External work + Internal work
External work
SV * MAP
Internal work
1/2 * MAP * ESV
Efficiency
work accomplished (SW)/ total energy used
As PV area increases
need more O2
During systole
Pcoronary - Pheart = 0
Flow in coronary arteries is
greatest during diastole, and very low during systole
If aortic valve leaks
no isovolumic contraction, LVV ^, always leaking blood from aorta into ventricles
Aortic stenosis
valve doesn’t completely open –> increase velocity in order to get blood out through smaller opening, large pressure drop across the valve, must ^LVP to account for pressure loss
Cardiac output
= venous return
As preload (EDP)^
stretch the ventricular muscle so that [Ca++]^ resulting in a stronger contraction
As afterload (ESP)^
heart needs to pump against a higher pressure to eject. Valves close sooner, leaving more blood in the heart (ESV^ so SV decreases)
Vascular system affects
EDP and ESP and consequently CO
