A new approach for a minimally invasive measurement of cardiac contractility via ventricle elastance

Elastance, derived from the pressure-volume diagram, has been shown to be a reliable quantitative description of heart contractility which is not dependent on the load conditions of heart. However, its measurement involves the monitoring of the ventricle volume and intraventricular blood pressure with an invasive procedure. While the ventricle volume can be computed from an area measurement, obtained by echocardiography, intraventricular blood pressure still requires a highly invasive measurement procedure. We propose here a new method, which has been implemented and tested, in which this pressure is approximated by the peripheral arterial pressure. A proper signal processing is required in order to solve the problems due to the distortion and delay introduced in the pressure signal by its propagation from the ventricle to the peripheral artery. To this end, suitable signal synchronization procedures have been designed and implemented. Using currently available biomedical instrumentation (echocardiographic scanner and patient monitor) interfaced to a PC and developing a software package with LabVIEW, a prototype system has been developed, which can compute on-line the contractility parameters. Preliminary tests on 10 ICU patients have confirmed the clinical feasibility of this minimally invasive approach and the diagnostic importance of having contractility indices which are independent of the load conditions of heart.