COMPARISON BETWEEN 3-ELEMENT AND AND 4-ELEMENT WINDKESSEL MODELS TO CHARACTERIZE VASCULAR PROPERTIES OF PULMONARY CIRCULATION

In 11 anaesthetised pigs the accuracy of the three-element (WK3) and t he foul-element (WK4) Windkessel models to describe hemodynamic proper ties of the pulmonary circulation was compared during six different ex perimental conditions increasing pulmonary arterial pressure: increase in left atrial pressure, increase in alveolar pressure, increase in p ulmonary blood flow, endotoxin shock, mechanical obstruction of left p ulmonary artery or histamine infusion. Our results show ed that WK4 fi tted better the data than did WK3 because values of 1-R-2 decreased fr om 6 percent (WK3) to 1.4 percent (WK4) when WK4 was used (P < 0.0005) . 1-R-2 was an adequate marker of the accuracy of the linear regressio n used to solve equations of both models. Compliance values estimated by WK4 were decreased by 5% comparatively to WK3 (P = 0.008). However this difference can be considered as not physiologically relevant. Val ues of characteristic resistance corresponding to R-1 + (L/R2C) in WK4 and to R-1 in WK3 were not different (P = 0.22). The relative changes in R-1, R-2, and C observed due to the different experimental conditi ons were comparable regardless of the model. In conclusion, the conver sion of WK3 in WK4 by adding an inductance, whose physiological meanin g is not clear resulted in an increased statistical accuracy of the mo del, but did not seem to have relevant influence on parameters or thei r evolution during experimental conditions.