Pulmonary capillary wedge pressure augments right ventricular pulsatile loading

Background - Right ventricular failure from increased pulmonary vascular loading is a major cause of morbidity and mortality, yet its modulation by disease remains poorly understood. We tested the hypotheses that, unlike the systemic circulation, pulmonary vascular resistance (R _PA) and compliance (C _PA) are consistently and inversely related regardless of age, pulmonary hypertension, or interstitial fibrosis and that this relation may be changed by elevated pulmonary capillary wedge pressure, augmenting right ventricular pulsatile load. Methods and Results - Several large clinical databases with right heart/pulmonary catheterization data were analyzed to determine the R _PA-C _PA relationship with pulmonary hypertension, pulmonary fibrosis, patient age, and varying pulmonary capillary wedge pressure. Patients with suspected or documented pulmonary hypertension (n=1009) and normal pulmonary capillary wedge pressure displayed a consistent R _PA-C _PA hyperbolic (inverse) dependence, C _PA=0.564/(0.047+R _PA), with a near-constant resistance-compliance product (0.48±0.17 seconds). In the same patients, the systemic resistance-compliance product was highly variable. Severe pulmonary fibrosis (n=89) did not change the R _PA-C _PA relation. Increasing patient age led to a very small but statistically significant change in the relation. However, elevation of the pulmonary capillary wedge pressure (n=8142) had a larger impact, significantly lowering C _PA for any R _PA and negatively correlating with the resistance-compliance product (P<0.0001). Conclusions - Pulmonary hypertension and pulmonary fibrosis do not significantly change the hyperbolic dependence between R _PA and C _PA, and patient age has only minimal effects. This fixed relationship helps explain the difficulty of reducing total right ventricular afterload by therapies that have a modest impact on mean R _PA. Higher pulmonary capillary wedge pressure appears to enhance net right ventricular afterload by elevating pulsatile, relative to resistive, load and may contribute to right ventricular dysfunction.