INTRODUCTION The application of technological support to different physiological systems requires the knowledge of their effects on daily clinical monitoring parameters. It is well known that mechanical ventilation affects organs (lungs) outside of the cardiovascular system influencing however cardiovascular parameters (arterial pressure). This phenomena must be considered in monitoring critically ill patients, particularly in assessing cardiopulmonary response to different treatments. However the “side effects” of ventilation can be utilised by clinicians to improve both their diagnostic and therapeutic capability. This requires the understanding of cardiopulmonary interaction, especially when mechanical assistance is used. Attention has been paid in recent years to the relationships between circulatory and respiratory systems (1, 2). Some studies have proposed mechanical ventilation as a tool to improve cardiac function (1, 3, 4) and new monitoring parameters have been proposed to analyse the influence induced on hemodynamics by mechanical ventilation (2, 5). As left ventricular preload has been demonstrated to be a valuable parameter in assessing cardiac function and volemic status of patients, its monitoring is one of the important problems in anaesthesiology and in the intensive care unit (ICU). Usually, clinical assessment of preload is performed measuring cardiac filling pressure (through central venous pressure (CVP) or pulmonary capillary wedge pressure (PCWP)) or the left ventricular end-diastolic area using transesophageal echocardio- graphy. Recently, a new method based on the study of effects of mechanical ventilation on arterial pressure waveform has been proposed. Changes in lung volume and intrathoracic pressure due to mechanical ventilation affect cardiac function and cardiac output due to the changes in right ventricular afterload and changes in Artificial Heart and Cardiac Assist Devices The International Journal of Artificial Organs / Vol. 25 / no. 4, 2002 / pp. 313-320 Study of systolic pressure variation (SPV) in presence of mechanical ventilation F. CLEMENTE 1 , C. DE LAZZARI 1 , M. DAROWSKI 2 , G. FERRARI 1 , R. MIMMO 1 , M. GUARAGNO 1 , G. TOSTI 1 1 CNR - Istituto di Tecnologie Biomediche, Rome - Italy 2 Institute of Biocybernetics and Biomedical Engineering - PAN, Warsaw - Poland © Wichtig Editore, 2002 0391-3988/313-08 $04.00/0 ABSTRACT: Systolic pressure variation (SPV) and its components (dUp and dDown) have been demonstrated to be of interest in assessing preload in mechanically ventilated patients. The aim of this paper is to analyse the sensitivity of these variables to preload and volemic changes during mechanical ventilation in different conditions of the cardiovascular system. Computer simulation experiments have been done using a modular lumped parameter model of the cardiovascular system. The effect of mechanical ventilation has been reproduced operating on intrathoracic pressure. Experiments have been performed varying preload through filling pressure. Sensitivity of SVP, dUp and dDown is described varying separately left ventricular elastance (Ev), systemic arterial resistance (Ras) and systemic arterial compliance (Cas). The sensitivity of SPV and dDown to preload and filling pressure is appreciable for high values of Ev and for a wide variation of Ras. Preliminary clinical data concerning the three parameters show good correlation with simulation results. (Int J Artif Organs 2002; 25: 313-20) KEY WORDS: Mechanical ventilation, Blood pressure, Computer simulation, Systolic pressure, Hemodynamic, Signal processing