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J Thorac Cardiovasc Surg 1999;118:568
© 1999 Mosby, Inc.

Letters to the Editor

Fourier analysis of the intra-aortic balloon pump

Michael Poullis, MD

Department of Cardiothoracic Surgery
National Heart and Lung Institute
Hammersmith Hospital
Du Cane Rd, East Acton
London W12 0NN, United Kingdom

Reply to the Editor:

Arterial impedance can be represented by the term fa({omega}) + 2{surd}–1 · fb({omega}), where fa({omega}) and fb({omega}), are algebraic functions involving heart rate. Systemic vascular impedance is the modulus of this term, |fa2({omega} + fb2({omega})|. This term will have a fundamental frequency, resulting in maximum blood flow and minimum work by the heart. Hence matching the heart rate to the fundamental frequency could have beneficial effects.Go 1

The aim of Fourier analysis was to show that with a constant heart rate, the fundamental frequency and harmonics of an arterial blood pressure trace are different when a balloon pump is initiated in 1:1, 1:2, or 1:3 ratios of augmentation; that is, the fundamental frequency has shifted even though the heart rate is constant. The shift developed is dependent on the augmentation ratio.

The three Fourier analysis results presented were all carried out with the same underlying heart rate of 60 beats/min; thus the deduction by Grossi, that spectral analysis of a blood pressure tracing reveals the patient’s heart rate, although true in all situations in the absence of a balloon pump, is completely incorrect in the presence of an intra-aortic balloon pump.

The aforementioned principle of two frequencies (heart rate and balloon frequency) being combined to create a third different frequency (Fourier fundamental frequency) is a widely established phenomenon in the field of electronics. It explains the operation of radio frequency sideband generation.

Fourier analysis does not interfere with ventricular afterload reduction and increasing diastolic blood pressure augmentation, because these will be optimized via balloon inflation and deflation timing, before Fourier analysis is performed.

With regard to the impossibility of quantifying arterial impedance without measuring blood flow, calculation of the augmentation index (the ratio of the difference between systolic blood pressure and blood pressure at the point of inflection to pulse pressure) can provide an indication of impedance matching via semiquantification of the peripherally reflected pressure wave.

12/8/100081

References

  1. Poullis M. Fourier analysis of the intra-aortic balloon pump. J Thorac Cardiovasc Surg 1999;117:827-8.[Free Full Text]



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[Abstract] [Full Text] [PDF]

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