Helium is used to inflate the balloon, its low density facilitating rapid transfer from pump to balloon. Inflation is commonly timed to the 'R' wave of the ECG, although timing may be taken from an arterial pressure waveform. Minor adjustment may be made to the timing to ensure that inflation occurs immediately after closure of the aortic valve (after the dicrotic notch of the arterial pressure waveform) and deflation occurs at the end of diastole. The filling volume of the balloon can be varied up to the maximum balloon volume. The greater the filling volume, the greater the circulatory augmentation. The rate at which balloon inflation occurs may coincide with every cardiac beat or every 2nd or 3rd cardiac beat. Slower rates are necessary in tachyarrhythmias. Weaning of intra-aortic balloon counterpulsation may be achieved by reducing augmentation or the rate of inflation.
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