Heart rate: Chronotropv is an important determinant of oxygen consumption that can be easily adjusted with presently available therapeutic modalities. Although the absolute amount of oxygen consumption per heart beat cannot be reproducibly measured, chronotropy is felt to be the most important contributor to the total oxygen consumption.
Contractility (velocity of contraction, dP/dT): This term refers to the rate of rise in the intraventricular pressure during isovolemic contraction. Contractility is influenced by the autonomic nervous system, heart rate, blood calcium level, temperature, and other factors. In the failing left ventricle, treatment with positive inotropic agents causes an expected increase in oxygen consumption. However, the improved systolic function and consequent decreased end-diastolic volume, wall tension, and oxygen consumption yield a net decline in oxygen demand. ventolin inhaler
Systolic wall tension: Myocardial wall tension is proportional to ventricular systolic pressure, ventricular radius, and inversely proportional to ventricular wall thickness (according to the Laplace relation). The effects of the preload and afterload are incorporated into the above parameters. Preload influences ventricular radius, whereas afterload dictates the magnitude of systolic pressure generation. Systolic wall tension decreases with increasing ventricular wall thickness.