Relationship between pulmonary artery diastolic pressure and left ventricular end-diastolic pressure.

The distal end of a pulmonary artery catheter is typically
directed into a branch of the right pulmonary artery. This
is due to the orientation of the natural curvature of the
catheter relative to the path of the catheter through the
right heart. During diastole, when the balloon on the tip of
the pulmonary artery catheter is inflated, a fluid chamber
connection from the tip of the pulmonary artery catheter
to the left ventricle is established. This is referred to as the
pulmonary artery occlusion pressure or “wedge” pressure.
This pressure is not equal to but is related to the pulmonary
artery diastolic pressure, which is measured when the balloon
is deflated.
Any pathology that occurs between the tip of the catheter
and the left ventricle will affect and degrade the relationship
between pulmonary artery diastolic pressure and
left ventricular end-diastolic pressure . Pulmonary artery
hypertension from changes in pulmonary vascular resistance,
whether from reversible or irreversible causes, will
have a negative impact on this relationship. This is due to
concurrent pulmonary venous hypertension. The same is
true of mitral valve stenosis. In a sense, these lesions prevent
a clear “view” of the left ventricle from the pulmonary
artery. Pulmonic stenosis, however, occurs proximal to this
fluid chamber and will not affect this “view.”