Effects of high-frequency harmonics on cardiac relaxation indices

This study was designed to determine the degree to which the systematic distortions in the pressure curve due to recording and filtering systems influence the relaxation indices. The purposes are 1) to analyze the dependency on the high frequencies of the relaxation and contractility parameters, 2) to determine the degree to which the catheter recordings modify those parameters, and 3) to test the monoexponential hypothesis in which the T index is based (Weiss, Frederiksen, and Weisfeldt, J. Clin. Invest. 58: 751-760, 1976). In 17 open-chest dogs, the left ventricular pressure (LVP) was recorded in four different ways: 1) with a large-bored metal cannula, 2) with a catheter-tip manometer, 3) with a Cournand catheter, and 4) with a pigtail catheter. The ECG and LVP were digitized by a computer. A Fourier analysis was performed, and the LVP waves were resynthesized with different numbers of harmonics. We conclude that 1) the catheter recordings are not recommended to calculate relaxation indices, 2) relaxation parameters present more sources of errors than contractility parameters, 3) the monoexponential hypothesis of T 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, 4) the dependency on higher harmonics of T index and +dP/dtmax is similar, and 5) -dP/dtmax is much more high-frequency dependent than T index.