The initial peak in pulmonary venous flow occurs with atrial relaxation simulta-

neously with the reduction of left atrial pressure, and the second peak occurs with left ventricular relaxation and rapid transmitral filling of the ventricle.

The pulsatile nature of pulmonary venous flow is primarily influ-

enced by events occurring on the left side of the heart.

Reduction in left atrial pressure, secondary to left atrial

relaxation and augmented by the descent of the base of

the heart at the beginning of systole, results in the

initial flow of blood from the pulmonary veins. This J

phase corresponds in time to ventricular systole but is

not initiated by it. The K phase of pulmonary venous

flow corresponds in time to rapid flow across the mitral

valve, and is terminated by the rise in left atrial pres-

sure during atrial systole.

The Pulmonary Venous pressure reflects left ventricular changes in volume and pressure most accurately in the absence of significant Mitral Valve disease.  Mitral stenosis or Mitral regurgitation is reflected in the pulmonary venous pressure and specific portions of the wave form. The "a" wave of the pulmonary venous wave form corresponds to Left Ventricular End Diastolic Pressure (LVEDP), while the 'v' wave corresponds to Left Ventricular Systole. The pressure of the Pulmonary Veins then is classified as a/x and v/y and in the absence of significant Left Ventricular or Mitral Valve disease is 12-18 mm-Hg / 6-10 mm-Hg. These values change significantly in Left Ventricular dysfunction / Failure, Mitral Valve disease and some pulmonary diseases.      

PV pressure as it has been said above reflects changes in LA pressure (if do you want I have added a book chapter related with this topic, you can see LA pressure changes during cardiac cycle in table 1 and figure 1)  and its interaction with pulmonary venous capacitance-resistance and also importantly changes in Intrathoracic pressures.