Effects of high-frequency harmonics on cardiac relaxation indices

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Abstract
The degree to which the systematic distortions in the pressure curve due to recording and filtering systems influence the relaxation indices was studied. The purposes are to analyze the dependency on the high frequencies of the relaxation and contractility parameters, to determine the degree to which the catheter recordings modify those parameters and to test the monoexponential hypothesis in which the T index is based. In 17 open chest dogs, the left ventricular pressure (LVP) was recorded in 4 different ways: with a large-bored metal cannula, a catheter-tip manometer, a Cournand catheter and a pigtail catheter. The ECG and LVP were digitized by a computer. A Fourier analysis was performed. The LVP waves were resynthesized with different numbers of harmonics. The catheter recordings are not recommended to calculate relaxation indices. Relaxation parameters apparently present more sources of errors than contractility parameters. The monoexponential hypothesis of T apparently is fulfilled if the isovolumic relaxation is considered to end at the time the LVP is 10 mmHg more than left ventricular end-diastolic pressure level. The dependency on higher harmonics of T index and +dP/dtmax [maximum change in pressure over time] is similar and -dP/dtmax apparently is much more high-frequency dependent than T index.