An intracardiac manometer: its evaluation and application.

The miniature intracardiac manometer supplied a method for recording artefact-free pressure tracings from the heart and great vessels of man and the intact animal. This instrument has been applied to the procedure of cardiac catheterization. It has also been used to demonstrate that if motion artefacts can be minimized, the central pulse can be recorded with reasonable accuracy by means of manometric systems with relatively poor dynamic response. Illustrations of pulse waves within the heart and great vessels of man and dogs and the effects of varying the dynamic response of the recording system are included. T HE WIDESPREAD acceptance and application of cardiac catheterization in diagnosis of congenital heart disease has required the accurate recording of changes in intracardiac pressure. In spite of the physical difficulties of recording through a long, narrow-bore cardiac catheter, it has been found that manometer-catheter systems with reasonably adequate dynamic response can be evolved.'-' Even when such manometer-catheter systems are used, the recordings of pressure obtained from the right ventricle and pulmonary artery of human beings are often obviously distorted by artefacts.' 2 The artefacts are, for the most part, produced by pressures generated in the lumen of the catheter by the acceleration and deceleration of the contained column of fluid, associated with movements of the catheter imparted by the heart beat.1' 2 This type of motion artefact can be minimized if the movable mass coupled to the manometer is very small so that the reactive forces and consequent pressures generated by movement are correspondingly reduced. A manometer made sufficiently small to be attached to the intracardiac end of a cardiac catheter would have this characteristic. It would also avoid other serious difficulties associated with recording through a long narrow plastic tube, such as damping factors, entrapped air bubbles and variation of physical characteristics of the catheter which accompany change of temperature. Gauer and Gienapp" 5 designed such an instrument according to the principles first outlined by Wetterer.6 The manometer as applied in cardiac catheterization is illustrated in figure 1. The brass housing of the miniature manome-ter accommodates two transformers, the secondary coils of which are wound in opposite directions. The relative coupling of the coils varies with the movements of a soft iron core mounted on the base of a tiny piston which is pressurized by the intracardiac or vascular pressure. The manometer is attached to an 8 F. cardiac catheter and projects …