Pressure-flow relationships interpretation in idiopathic pulmonary arterial hypertension

Objective: We analyze exercise-derived mean pulmonary artery pressure/cardiac index relationship to expand the concepts regarding its nature and to better identify "responders" in idiopathic pulmonary arterial hypertension patients.

Methods: Mean pulmonary artery pressure/cardiac index relationship and extrapolated pressure to zero flow were obtained in 40 patients' breathing room air, oxygen 99.5% and hydralazine. The hemodynamic characteristics were analyzed for the cohort and separate for responders (n = 20) and non responders (n = 20) according to the acute response to vasodilator. We tested this previous criteria versus the Task Force on diagnosis and treatment prescribed by the European Society of Cardiology.

Results: The mean pulmonary arterial pressure-flow diagram of the total cohort (p < 0.01). No alterations in gas exchange or lung mechanics. For patients responders versus non-responders, the slope was abnormal 2.2(95%CI: 1.1-3.3) vs 5.89 (95% CI: 4.69 - 7.11), mmHg/L min/m2 and increased extrapolated pressure to zero flow (38.2 + 7.5 to 66.3 + 7.5 mmHg, p < 0.01). Without difference with oxygen 99.5%. With vasodilator effect, mean pulmonary arterial pressure decreased (52.1+9.5 a 40 + 5.5 mm Hg, p< 0.01) versus it did not change (96.2 + 8.5 vs 90 + 7.5 mmHg, p = 0.3), slope 1.15 (95% CI: 0.68 - 1.62) vs. 1.28 (95% CI: 0.78-1.78) mmHg/L min/m2, the extrapolated pressure to zero flow did not change (69.4 + 7.8 a 85.1 + 8.5 mmHg), p < 0.01 compared to control. In non-responders with vasodilator, mean pulmonary arterial pressure/cardiac index (90 + 7.5 mmHg, pendiente: 1.28, 95%IC: 0.78 - 1.78 mmHg/L min/m2) was different between responders 40 mm Hg mean pulmonary arterial pressure. Pressure were 34 + 3 vs 45 + 4 mm Hg and slopes 1.14 (95%IC: 0.67 - 1.61 vs 2.22 (95%IC: 1.35 - 3.09 mm Hg/L min/m2) p < 0.01 respectively.

Conclusions: Abnormalities of the mean pulmonary arterial pressure/cardiac index relationship exercise-derived seems to reflect "mainly arteriolar" increased lineal pulmonary vascular resistance in idiopathic pulmonary arterial hypertension patients. Both acute vasodilator response criteria are useful to identify responders and not responders in this patient population.