Rationale
Pulmonary arterial compliance (PAC) represents a measure of pulsatile afterload of the right ventricle. Resting PAC has shown prognostic relevance in several cardiopulmonary conditions and may be associated with early pulmonary vascular disease. Compared to exercise PH, another indicator of early disease, the clinical relevance of exercise PAC is unknown.

Methods
We included patients with resting mPAP (mean pulmonary arterial pressure) <25mmHg who underwent symptom-limited exercise RHC in our clinic from 2005 to 2020. Exercise and resting PAC were assessed in the same body position. Survival analysis was performed using Cox-regression analysis.

Results
We included n=310 patients (median[IQR] age 64 [52-72] years, 219 (71%)females, resting mPAP 18[15-21]mmHg, pulmonary vascular resistance 1.9 [1.5-2.6]WU, pulmonary arterial wedge pressure 8 [6-10]mmHg, cardiac output 4.8 [4-5.6]L/min) with n=63 all-cause mortality events (time-to-event 7.9 [3.5-11.8] years). Exercise PAC was correlated with 6-minute walk distance (p<0.001,r=0.34), peak oxygen uptake (p<0.001,r=0.43) and N-terminal-pro-brain-natriuretic-peptide (NTpro-BNP,p<0.001,r=-0.47). In the univariate analysis, exercise PAC was significantly associated with mortality (HR:0.75 [95%CI 0.62-0.90], p<0.001), whereas resting PAC was not (HR:0.89 [95%CI 0.77-1.03], p=0.12).

Conclusion
In patients with normal or mildly elevated mPAP at rest, exercise PAC is significantly correlated with relevant clinical markers of exercise capacity and cardiac strain (NT-proBNP). Moreover, compared to resting PAC, exercise PAC is a significant predictor of all-cause mortality in univariate analysis, marking its potential clinical und prognostic relevance.