Study of systolic pressure variation (SPV) in presence of mechanical ventilation.

The application of technological support to differentphysiological systems requires the knowledge of theireffects on daily clinical monitoring parameters. It is well known that mechanical ventilation affectsorgans (lungs) outside of the cardiovascular systeminfluencing however cardiovascular parameters (arterialpressure). This phenomena must be considered inmonitoring critically ill patients, particularly in assessingcardiopulmonary response to different treatments.However the “side effects” of ventilation can be utilisedby clinicians to improve both their diagnostic andtherapeutic capability. This requires the understanding ofcardiopulmonary interaction, especially when mechanicalassistance is used. Attention has been paid in recentyears to the relationships between circulatory andrespiratory systems (1, 2). Some studies have proposedmechanical ventilation as a tool to improve cardiacfunction (1, 3, 4) and new monitoring parameters havebeen proposed to analyse the influence induced onhemodynamics by mechanical ventilation (2, 5).As left ventricular preload has been demonstrated to bea valuable parameter in assessing cardiac function andvolemic status of patients, its monitoring is one of theimportant problems in anaesthesiology and in theintensive care unit (ICU). Usually, clinical assessment ofpreload is performed measuring cardiac filling pressure(through central venous pressure (CVP) or pulmonarycapillary wedge pressure (PCWP)) or the left ventricularend-diastolic area using transesophageal echocardio-graphy. Recently, a new method based on the study of effectsof mechanical ventilation on arterial pressure waveformhas been proposed. Changes in lung volume andintrathoracic pressure due to mechanical ventilationaffect cardiac function and cardiac output due to thechanges in right ventricular afterload and changes in