Myocardial oxygen consumption involves a balance between oxygen demand and oxygen supply.
Myocardial oxygen supply depends on:
Oxygen content of the coronary arterial blood.
Coronary vessel calibre (concentration of myocardial metabolic products and the pCO2).
Coronary perfusion pressure, which is diastolic and dependent on the LVEDP. It is equal to the difference between the aortic diastolic blood pressure (driving pressure) and the LVEDP or coronary pressure (back pressure), whichever is greater.
Coronary perfusion time, which equates to 1/heart rate. With faster heart rates J
r diastole is shorter. a r
Myocardial oxygen demand depends on: C
Basal oxygen requirements. |'
External work (mean arterial pressure x stroke volume), which is determined jj by LV preload, myocardial contractility or inotropic state (measured by the s velocity of contraction), and LV afterload (dependent upon aortic contractility and arteriolar run-off).
Internal work (during isovolumetric contraction), which is pressure generated and dependent on the ventricular radius.
Heart rate: tachycardia increases demand.
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