Systolic pressure variation
This shows arterial pressure (red), airway pressure (green) and central venous pressure (blue). The vertical lines show the beginning and end of a ventilatory cycle.
The patient was a 64 year old man who had had an aortic valve replacement and coronary artery bypass grafts. This recording was made while the chest was still open about twenty minutes after cardiopulmonary bypass was discontinued. It is clear from the figure that as the lungs are inflated the arterial pressure increases. This is due to blood being squeezed out of the lungs into the left atrium and so producing an increase in left atrial pressure and left ventricular stroke volume.