Limitation of correction of frequency dependent artefact in pressure recordings using harmonic analysis

Abstract

Frequency dependent phase and amplitude distortion may theoretically be minimized using correction formulae derived from a model which assumes that water filled catheter manometer systems are analogous to an oscillating mass attached to a spring and damping pot. This study defines the practical limits of this correction technique using harmonic analysis of simultaneously recorded water filled and catheter tip manometer systems. Some improvement was obtained in tracings recorded with underdamped, high frequency response systems. In no case were exact duplications of the catheter tip tracings obtained. Divergence of measured in vitro frequency response from actual in vivo frequency response was one source of these discrepancies. Loose coupling of the components of the system also changed the behavior from that of the assumed simple mechanical models and at times prevented adequate correction. Catheter tip manometers, in spite of their expense and relative fragility, still appear to be the best means at present of obtaining accurate pressure tracings, particularly at high heart rates or where time derivatives are to be computed.