Mechanisms of exercise limitation and prevalence of pulmonary hypertension in hypersensitivity pneumonitis

Background Hypersensitivity pneumonitis (HP) is an immune-mediated condition triggered by inhaled antigens in susceptible individuals. Patients with HP often present with exercise limitation due to multiple mechanisms, including ventilatory and cardiocirculatory impairments, particularly pulmonary hypertension (PH). Methods In this cross-sectional study, patients with HP of varying severity underwent clinical assessment, including quality-of-life questionnaires, incremental treadmill cardiopulmonary exercise testing (CPET), pulmonary function testing, 6-min walk test and transthoracic echocardiography (TTE). Patients with a diffusing capacity of the lung for carbon monoxide ( D LCO ) below 40% of predicted and/or a tricuspid regurgitation velocity >2.5 m·s −1 or pulmonary artery systolic pressure >35 mmHg on TTE were referred for right heart catheterisation. Results Among 90 patients, 65% were female, with a median age of 65.5 years, and 85% had fibrotic HP. CPET was performed in 51 patients (56%), with a mean peak oxygen consumption of 58±13% of predicted. Exercise capacity was reduced in 98% of patients, with multifactorial limitation in 88%, primarily due to cardiocirculatory impairment (76%) and impaired gas exchange (66%). The mean 6-min walk distance was 334±116 m. Mean forced vital capacity and D LCO were 56±20% and 42±22% predicted, respectively. PH was identified in 59% of patients (95% CI 48–72%), predominantly with combined post- and pre-capillary involvement. Conclusions Reduced exercise capacity is highly prevalent in patients with HP and is typically multifactorial. PH is also common, with a predominance of combined post- and pre-capillary patterns. These findings underscore the need for a comprehensive evaluation strategy in symptomatic HP patients.