Patrick Segers

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.

Monitoring Left Heart Performance in the Critically Ill

Pre-existing ventricular dysfunction in the critically ill patient significantly determines outcome. The importance of this feature has been demonstrated both in septic and in perioperative non-cardiac surgical patients [1, 2]. When admitted to the ICU, patients with extensive hemodynamic deterioration, either due to distributive shock, cardiogenic shock or posttraumatic hypovolemia, should be examined rapidly to correctly assess the main determinants of cardiovascular function. Table 1 summarizes intrinsic and extrinsic determinants governing ventricular function. Rapid decision making will have a major impact on further therapeutic strategies [3, 4]. In this respect, it is of paramount importance to estimate accurately both changing loading conditions and cardiac function. Traditional measures, such as stroke volume, cardiac output, and ejection fraction have proven their validity in clinical practice, although caution is warranted because of their strong load dependency. The load dependency precludes the use of ejection fraction as a parameter in patients with either disturbed preload or afterload. Left ventricular (LV) ejection fraction does not show any prognostic value with respect to outcome prediction in patients with normal systolic LV function in septic shock [5]. With the advent of more powerful and more specific technology, a different framework for evaluating LV performance must be proposed.