[Study of the precision and limitations in measuring left ventricular pressure and its first time-derivative...

The precision in measuring left ventricular pressure and its first time-derivative has been evaluated with the study of the physical caracteristics of a system currently used for pressure wave sampling. Besides the different catheters, the set-up tested consists of a nylon connector (110 cm) and of two three way stopcocks. Amplitude and phase response, from 1 to 60 Hz, have been obtained testing the system with sinusoidal pressure waves generated by an hydraulic oscillator. Despite mild differences dependent on the different catheters, the system amplifiers remarkably at frequencies above 5 Hz. Above this limit the harmonic content of the left ventricular pressure wave is negligible and can be ignored in defining the basic morphology and the absolute values of the curve. Similary, the amplification of these high frequency harmonics operated by the system does not affect appreciably pressure measurements. In the case of the pressure time-derivative the significant harmonic content is shifted toward higher frequencies. For this reason a reliable dp/dt cannot be obtained with this hydraulic set-up. A maximal hypothetic error, utilizing a Cook 5.2 F 105 cm catheter, of 8-9% and 28-31% has been estimated for pressure and time-derivative measurments respectively.