Central venous pressure is one of the most misunderstood numbers in critical care. It is often treated as a preload measurement.
That is not quite right.
CVP is a pressure measured in the thoracic vena cava near the right atrium.
Preload is better understood as myocardial fiber stretch before contraction. Pressure and volume are related, but they are not the same.
A stiff ventricle can have a high pressure at a relatively low volume. A compliant ventricle can accommodate more volume with less pressure rise.