Abstract
IntroductionPulmonary capillary pressure (PCP), together with the time constants of the various vascular compartments, define the dynamics of the pulmonary vascular system. Our objective in the present study was to estimate PCPs and time constants of the vascular system in patients with idiopathic pulmonary arterial hypertension (IPAH), and compare them with these measures in patients with acute respiratory distress syndrome (ARDS).MethodsWe conducted the study in two groups of patients with pulmonary hypertension: 12 patients with IPAH and 11 with ARDS. Four methods were used to estimate the PCP based on monoexponential and biexponential fitting of pulmonary artery pressure decay curves.ResultsPCPs in the IPAH group were considerably greater than those in the ARDS group. The PCPs measured using the four methods also differed significantly, suggesting that each method measures the pressure at a different site in the pulmonary circulation. The time constant for the slow component of the biexponential fit in the IPAH group was significantly longer than that in the ARDS group.ConclusionThe PCP in IPAH patients is greater than normal but methodological limitations related to the occlusion technique may limit interpretation of these data in isolation. Different disease processes may result in different times for arterial emptying, with resulting implications for the methods available for estimating PCP.
Highlights
Pulmonary capillary pressure (PCP), together with the time constants of the various vascular compartments, define the dynamics of the pulmonary vascular system
The main objective of the present study was to compare estimates of PCP in patients with idiopathic pulmonary arterial hypertension (IPAH) obtained through different methods; all of these methods assumed the three-compartment model of pulmonary circulation, but each fits the pulmonary artery pressure (PAP) decay to the rather different algorithms proposed in the literature [8,11,17]
The major finding of the present study was that the IPAH group had a significantly higher PCP than did the acute respiratory distress syndrome (ARDS) group, independent of algorithm used for its estimation; this was accompanied by a marked increase in the time constant for the slow decay
Summary
Pulmonary capillary pressure (PCP), together with the time constants of the various vascular compartments, define the dynamics of the pulmonary vascular system. Our objective in the present study was to estimate PCPs and time constants of the vascular system in patients with idiopathic pulmonary arterial hypertension (IPAH), and compare them with these measures in patients with acute respiratory distress syndrome (ARDS). Four methods were used to estimate the PCP based on monoexponential and biexponential fitting of pulmonary artery pressure decay curves. Because of the inaccuracy of the Gaar equation and because the other methods are not suitable for clinical application, pulmonary artery occlusion is currently the most frequently used method for estimating PCP in a broad range of clinical and/or experimental conditions [8]. The pulmonary artery occlusion method is based on the assumption that one can determine the pulmonary capillaries' emptying pattern from the decaying pulmonary arterial occlusion pressure waveform. The complexity of the circuit reflects whether the initial decrease in the postocclusion pressure is linear or nonlinear
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