Heart Vessels (1999) 14:67-71 Heart andVessel S © Springer-Verlag 1999 Mechanism of pulmonary venous pressure and flow waves L.R. Hellevik 1, P. Segers 2, N. Stergiopulos 3, F. Irgens 1, P. Verdonck 2, C.R. Thompson 4, K. Lo 4, R.T. Miyagishima 4, and O.A. Smiseth 5 1 Department of Applied Mechanics, Thermodynamics and Fluid Dynamics, The Norwegian University of Scie Technology, N-7491 Trondheim, Norway HBiTech, University of Gent, Gent, Belgium 3 Biomedical Laboratory, EPFL, Switzerland 4St. Paul's Hospital, Vancouver, BC, Canada 5 Rikshospitalet, Oslo, Norway Summary. The pulmonary venous systolic flow wave has been attributed both to left heart phenomena, such as left atrial relaxation and descent of the mitral annu- lus, and to propagation of the pulmonary artery pres- sure pulse through the pulmonary bed from the right ventricle. In this study we hypothesized that all waves in the pulmonary veins originate in the left heart, and that the gross wave features observed in measurements can be explained simply by wave propagation and reflec- tion. A mathematical model of the pulmonary vein was developed;the pulmonary vein was modeled as a lossless transmission line and the pulmonary bed by a three-element lumped parameter model accounting for viscous losses, compliance, and inertia. We assumed that all pulsations originate in the left atrium (LA), the pressure in the pulmonary bed being constant. The model was validated using pulmonary vein pressure and flow recorded 1 cm proximal to the junction of the vein with the left atrium during aortocoronary bypass sur- gery. For a pressure drop of 6mmHg across the pulmo- nary bed, we found a transit time from the left atrium to the pulmonary bed of • --~ 150ms, a compliance of the pulmonary bed of C ~ 0.4 ml/mmHg, and an inertance of the pulmonary bed of 1.1mmHgsVml. The pulse wave velocity of the pulmonary vein was estimated to be c ~ 1 m/s. Waves, however, travel both towards the left atrium and towards the pulmonary bed. Waves traveling towards the left atrium are attributed to the reflections caused by the mismatch of impedance of line (pulmonary vein) and load (pulmonary bed). Wave in- tensity analysis was used to identify a period in systole of net wave propagation towards the left atrium for both measurements and model. The linear separation technique was used to split the pressure into one corn- Address correspondence to: L.R. Hellevik Received December 24, 1998; revision received May 17, 1999; accepted June 19, 1999 ponent traveling from the left atrium to the pulmonary bed and a reflected component propagating from the pulmonary bed to the left atrium. The peak of the re- flected pressure wave corresponded well with the posi- tive peak in wave intensity in systole. We conclude that the gross featuresof the pressure and flow waves in the pulmonary vein can be explained in the follow- ing manner: the waves originate in the LA and trave towards the pulmonary bed, where reflections give rise to waves traveling back to the LA. Although the gross features of the measured pressure were captured well by the model predicted pressure, there was still som discrepancy between the two. Thus, other factors initi- ating or influencing waves traveling towards the LA cannot be excluded. Key words: Pulmonary venous flow - Wave reflection - Pressure pulse - Flow pulse Introduction The normal flow pattern in extraparenchymal pulmo- nary veins (PV) is characterized by antegrade flow peaks during systole (S waves) and early diastole (D wave), and by strongly reduced or retrograde flow (R wave) into the PV during atrial contraction in late dias- tole (Fig. 1). The pulmonary D wave is caused by LV relaxation and the subsequent opening of the mitral valve and pressure reduction in the left atrium (LA). The factors that determine the D wave are largely the same as those determining early transmitral filling [1]. The pulmonary venous S wave is composed of an early ($1) and a late ($2) systolic flow pulse. The origin of the pulmonary venous S wave, and in particular the $2 wave, is not clear. Several experimental studies in dog models conclude that the S wave is generated pre-