Circulatory effects

Approximately three-quarters of the left ventricular coronary flow occurs during diastole. The IABP is precisely timed with the onset of diastole and therefore augments both the diastolic pressure and the coronary perfusion pressure.

The deflation of the balloon is precisely timed just prior to the onset of systole, thus creating a relative 'vacuum' in the aorta and reducing the afterload ( Weber and

Janicki. . .1974). The left ventricular wall tension developed is decreased and the myocardial oxygen demand is reduced. Therefore IABP improves the function of the failing heart by improving the myocardial oxygen supply-to-demand ratio.

The synergistic effects of diastolic augmentation and afterload reduction exert beneficial effects on the failing circulation ( Bardet etal; 1977). IABP improves the cardiac output and as a result reduces the left atrial filling pressure. The stroke volume increases significantly but the heart rate is not usually altered significantly. The systemic blood pressure drops and the diastolic pressure is increased, but the effect on the mean systemic arterial pressure is variable. The systemic vascular resistance is usually reduced, but this is also manipulated by pharmacological intervention.

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