Invasive Cardiopulmonary Exercise Testing Identifies Distinctive Hemodynamic Phenotypes in Patients with Interstitial Lung Disease and Exercise Intolerance

Introduction: Pulmonary vascular abnormalities coexist with interstitial lung disease (ILD), leading to a spectrum of physiologic impairments. We hypothesized that ILD patients with exercise intolerance have a heterogenous hemodynamic profile when assessed by invasive cardiopulmonary exercise testing (iCPET). Methods: From January 2018 to December 2023, we prospectively performed iCPET for several conditions. The primary outcome of the study was to assess the hemodynamic phenotypes both at rest and during exercise of ILD patients with exercise intolerance, which cannot be fully explained by the severity of ILD. Results: Of the 43 ILD patients included in the study, 10 (23%) had no pulmonary hypertension (PH), 16 (37%) had no PH with pulmonary vascular resistance (PVR) >2 WU, 7 (16%) had precapillary PH, 7 (16%) had postcapillary or combined pre- and postcapillary PH, and 3 (7%) had unclassified PH. Four (9%) patients had exercise PH. Forced vital capacity, diffusion capacity for carbon monoxide, peak oxygen consumption, and resting partial pressure of oxygen (PaO₂) were significantly lower across the no PH to precapillary PH spectrum. Peak exercise PaO₂ decreased (97 ± 25, 73 ± 15, and 62 ± 10 mm Hg, p = 0.001) while mPAP/CO slope (1.9 ± 1.1, 3.1 ± 2.1, and 5.1 ± 2.7, p = 0.009) and PAWP/CO slope (0.9 ± 0.7, 0.9 ± 0.7, and 3.0 ± 3.0, p = 0.007) increased from no PH, to no PH with high PVR, to precapillary PH. No associations were noted for gender, presence of fibrotic ILD and scleroderma, and mPAP/CO >3 WU across this spectrum. Conclusion: Patients with ILD and exercise intolerance have several hemodynamic phenotypes with parameters that reveal worse exercise performance from no PH to no PH with elevated PVR to precapillary PH.