The linear relationship between systolic pulmonary artery pressure and mean pulmonary artery pressure is maintained regardless of autonomic or rhythm disturbances

Pulsatile pulmonary artery pressure in a large animal model of chronic thromboembolic pulmonary hypertension: Similarities and differences with human data

A striking feature of the human pulmonary circulation is that mean (mPAP) and systolic (sPAP) pulmonary artery pressures (PAPs) are strongly related and, thus, are essentially redundant. According to the empirical formula documented under normotensive and hypertensive conditions (mPAP = 0.61 sPAP + 2 mmHg), sPAP matches ~160%mPAP on average. This attests to the high pulsatility of PAP, as also witnessed by the near equality of PA pulse pressure and mPAP. Our prospective study tested if pressure redundancy and high pulsatility also apply in a piglet model of chronic thromboembolic pulmonary hypertension (CTEPH). At baseline (Week‐0, W0), Sham (n = 8) and CTEPH (n = 27) had similar mPAP and stroke volume. At W6, mPAP increased in CTEPH only, with a two‐ to three‐fold increase in PA stiffness and total pulmonary resistance. Seven CTEPH piglets were also studied at W16 at baseline, after volume loading, and after acute pulmonary embolism associated with dobutamine infusion. There was a strong linear relationship between sPAP and mPAP (1) at W0 and W6 (n = 70 data points, r² = 0.95); (2) in the subgroup studied at W16 (n = 21, r² = 0.97); and (3) when all data were pooled (n = 91, r² = 0.97, sPAP range 9–112 mmHg). The PA pulsatility was lower than that expected based on observations in humans: sPAP matched ~120%mPAP only and PA pulse pressure was markedly lower than mPAP. In conclusion, the redundancy between mPAP and sPAP seems a characteristic of the pulmonary circulation independent of the species. However, it is suggested that the sPAP thresholds used to define PH in animals are species‐ and/or model‐dependent and thus must be validated.

Measuring pulmonary arterial compliance: mission impossible? Insights from a novel in vivo continuous-flow based experimental model

Arterial compliance (C) is related to the elasticity, size, and geometrical distribution of arteries. Compliance is a determinant of the load that impedes ventricular ejection. Measuring compliance is difficult, particularly in the pulmonary circulation in which resistive and compliant vessels overlap. Comparing different methods for quantification of compliance to a method that involves a continuous flow might help to identify the optimal method. Pulmonary arterial compliance was computed in six pigs based on the stroke volume to pulse pressure ratio, diastolic decay exponential fitting, area method, and the pulse pressure method (PPM). Compliance measurements were compared to those obtained under continuous flow conditions through a right ventricular bypass (Heartware Inc., Miami Lakes, FL, USA). Compliance was computed for various flows using diastolic decay exponential fitting after an abrupt interruption of the pump. Under the continuous flow conditions, resistance (R) was a decreasing function of the flow, and the fitting to P = e^-t/RC yielded a pulmonary time constant (RC) of 2.06 s ( ± 0.48). Compliance was an increasing function of flow. Steady flow inter-method comparisons of compliance under pulsatile flow conditions showed large discrepancies and values (7.23 ± 4.47 mL/mmHg) which were lower than those obtained under continuous flow conditions (10.19 ± 1 0.31 mL/mmHg). Best agreement with steady flow measurements is obtained with the diastolic decay method. Resistance and compliance are both flow-dependent and are inversely related in the pulmonary circulation. The dynamic nature of the pulsatile flow may induce a non-uniformly distributed compliance, with an influence on the methods of measurement.

Reappraisal of the reliability of Doppler echocardiographic estimations for mean pulmonary artery pressure in patients with pulmonary hypertension: a study from a tertiary centre comparing four formulae

Different Doppler echocardiography (DE) models have been proposed for estimation of mean pulmonary arterial pressures (PAMP) from tricuspid regurgitation (TR) jet velocity. We aimed to compare four TR-derived DE models in predicting the PAMP measured by right heart catheterization (RHC) in different groups of precapillary pulmonary hypertension (PH). A total of 287 patients with hemodynamically pre-capillary PH were enrolled (mean age = 51 ± 17.4 years, 59.9% female). All patients underwent DE before RHC (< 3 h) and four formulae (F) were used for TR-derived PAMP estimation (PAMP-DE). These were as follows: F1 = Chemla (0.61 × systolic pulmonary artery pressure [PASP] + 2); F2 = Friedberg (0.69 × PASP - 0.22), F3 = Aduen (0.70 × PASP); and F4 = Bech-Hanssen (0.65 × PASP - 1.2). The PASP and PAMP (mmHg) measured by RHC were 89.1 ± 30.4 and 55.8 ± 20.8, respectively. In the overall PH group, DE estimates for PASP (r = 0.59, P = 0.001) and PAMP (r = 0.56, P = 0.001 for all) showed significant correlations with corresponding RHC measures. Concordance was noted between Chemla and Bech-Hanssen, and Aduen and Bech-Hanssen. The Bland-Altman plot showed that Chemla and Bech-Hanssen overestimated and Friedberg and Aduen underestimated PAMP-RHC measures. Paired-t test showed significant systematic biases for Aduen and Bech-Hanssen while Passing-Bablok non-parametric analysis revealed significant systematic biases all four PAMP-DE estimates. There was poor agreement between PAMP-RHC measures and PAMP-DE deciles (Kappa values were 0.112, 0.097, 0.095, and 0.121, respectively). This study showed a poor agreement between PAMP-DE estimates by four TR-derived formulae and PAMP-RHC in patients with PH, regardless of the etiology. However, these results can not be fully extrapolated to a normal population and did not address the reliability of DE estimates for PH screening procedures.