Pascal Verdonck

Principles of vascular physiology

The basis of modern cardiovascular hemodynamics was established in the 1960s and 1970s. Invasive measurements of aortic pressure and flow in mammals and humans demonstrated that the cardiac pulsation generates pressure and flow waves, traveling along the arterial tree. Arterial pressure and flow were studied as wave phenomena and it was realized that relevant, quantitative hemodynamic assessment of the cardiovascular system required measurement of both pressure and flow. The concept of arterial impedance was introduced. Wave reflection was found to be an important determinant of the pressure and flow wave contours, altering with age, in cardiovascular disease or in response to drugs.

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 the 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). The expected increase in systolic BP was observed from carotid to radial sites. The mean peak power was 6/spl plusmn/2 W.

Interactive control of hydraulic structures

In normalized or canalized rivers the waterlevel is kept within small limits by hydraulic control structures (weirs, gates,...). These structures ensure the protection of riparians from inundation, while at the same time optimal navigation conditions are created. In flood periods, many movements are needed to maintain the optimum waterlevel. Different hydraulic control structures on one river reach, has as consequence that control actions of one affect the others, resulting in an increase of movements of the downstream ones. In order to avoid this inconvenience, an interactive control procedure is developed and tested. A case study is presented.