Non-invasive evaluation of left ventricular power output by simultaneous recordings of applanation tonometry and echocardiographic Doppler signals

Ventricular hydraulic power is defined as the instantaneous product of flow and pressure at the aortic root. This paper describes a system for non-invasive determination of LV power output based on simultaneous acquisition of applanation tonometry for aortic blood pressure (BP) evaluation and echo-Doppler signals for flow measurement. Acquisition is performed with a dedicated A/D system allowing on-line visualisation of Doppler power spectra and calibrated tonometric signals (using mean and diastolic cuff BP at brachial level). Aortic BP is estimated either using an aorto-radial transfer function, either untransformed carotid BP. This method has been investigated in 10 normal volunteers. Visualisation of calibrated data during acquisition allowed recordings with a low variability (mean standard deviation of reconstructed systolic BP<5 mmHg). Expected increase in systolic BP was observed from carotid to radial sites. Mean peak power was 6+/-2W micromanometer-tipped probe against an arterial wall. When a sufficient force is applied over the center of the artery to distort the vessel wall, the normal contact stress between the skin and the tonometer tip approximates the instantaneous intraluminal pressure [5]. Instantaneous aortic flow can be calculated as the product of the area of the left ventricular outflow tract and the Doppler blood velocity, both measured by echocardiography. This has been correlated with invasive measurements realised with electromagnetic flow probes [6]. Combination of tonometry and echocardiography has already been described [7,8], but in order to facilitate such recordings and to minimise variability of the measurements, we sought a system allowing on-line visualisation of tonometric recordings combined with processing of simultaneously acquired Doppler signals. The aim of this study was therefore to develop an integrated PC based system for the evaluation of left ventricular peak power using applanation tonometric signals calibrated on-line and visualised together with simultaneously acquired Doppler power spectra.