Arterial pressure and stroke volume variability as measurements for cardiovascular optimisation

➥ lation are familiar and the ‘swing’ of the pressure trace during inspiration and expiration is easily seen on a standard monitor display. These changes are largely the consequence of alterations in intrathoracic pressure (PIT). It is important to recognise that PIT greatly influences the transmural pressure (PTM), which is the actual effective distending pressure of the cardiac chamber, and represents chamber volume (preload) and afterload. As PTM is the difference between the measured (or transduced) pressure inside the cardiac chamber of interest (PMEAS) and the PIT outside the chamber, it follows that as the PIT increases so the PTM falls: