Theoretical analysis of occlusion techniques for measuring pulmonary capillary pressure

Abstract

We have developed a model including three serial compliant compartments (arterial, capillary, and venous) separated by two resistances (arterial and venous) for interpreting in vivo single pulmonary arterial or venous occlusion pressure profiles and double occlusion. We formalized and solved the corresponding system of equations. We showed that in this model 1) pulmonary capillary pressure (Pc) profile after arterial or venous occlusion has an S shape, 2) the estimation of Pc by zero time extrapolation of the slow component of the arterial occlusion profile (Pcao) always overestimates Pc, 3) symmetrically such an estimation on the venous occlusion profile (Pcvo) always underestimates Pc, 4) double occlusion pressure (Pcdo) differs from Pc. We evaluated the impact of varying parameter values in the model with parameter sets drawn either from the literature or from arbitrary arterial and venous pressures, being respectively 20 and 5 mmHg. Resulting Pcao-Pc differences ranged from 0.4 to 5.4 mmHg and resulting Pcvo-Pc differences ranged from -0.3 to -5.0 mmHg. Pcdo-Pc was positive or negative, its absolute value in general being negligible (< 1.1 mmHg).

Capillary pressure estimates from arterial and venous occlusion in intact dog lung

“…The later observation agrees with those of DAWSON et al [1] and YAMADA et al [16]. The fit of the arterial and venous occlusion pressure-time profiles by the sum of two exponentials, rather then by an instantaneous drop followed by a single exponential, suggests that compliant rather than resistive components predominate near the arterial and venous occlusion sites [17]. This suggests that the techniques of analysis of these profiles should be based on a model of the pulmonary circulation where the vascular compliance is presumably partitioned into arterial, middle, and venous compartments separated by an arterial and a venous resistance.…”

“…Because the data of the initial component of the pressure profiles characterized by a short time constant could not be used for the estimation of capillary pressure, the value of 10±6% that was observed in the present study is considered an upper limit for the middle fraction of the Pa-Pv difference [17].…”

“…We did not use the data of the initial components or the pressure profiles characterized by a short time constant for the estimation of capillary pressure, because potential deformations may affect this component [2,18,19]. As the inflection point cannot be formalized mathematically on a biexponential curve [17], we used the zero-time extrapolation of the slow segment to estimate Pc,ao and Pc,vo. This choice implies that Pc,ao would overestimate Pc and that Pc,vo would underestimate Pc, if the arterial and venous compartments represent a substantial percentage of the middle compartment compliance [17].…”

“…As the inflection point cannot be formalized mathematically on a biexponential curve [17], we used the zero-time extrapolation of the slow segment to estimate Pc,ao and Pc,vo. This choice implies that Pc,ao would overestimate Pc and that Pc,vo would underestimate Pc, if the arterial and venous compartments represent a substantial percentage of the middle compartment compliance [17].…”

Preoperative Partitioning of Pulmonary Vascular Resistance Correlates With Early Outcome After Thromboendarterectomy for Chronic Thromboembolic Pulmonary Hypertension

“…A biexponential fitting of the pressure decay curve between the moment of occlusion and the pulmonary artery occluded pressure (Ppao), with normalization to the mean pulmonary artery pressure (mPpa), has been previously described and is used here to derive Poccl ( Figure 1). 8,10,11 Rup was calculated as follows: Rup% ϭ 100 ϫ (mPpa Ϫ Poccl) / (mPpa Ϫ Ppao).…”