Cardiorespiratory Fitness and Pulmonary Function in Parkinson’s Disease: A Cross- Sectional Study with Clinical Correlations

Background Parkinson’s disease (PD) is frequently accompanied by impairments in cardiorespiratory fitness (CRF) and pulmonary function (PF), which may diminish quality of life and limit functional independence. This study aimed to assess CRF and PF in patients with PD and explore their interrelationship. Methods This cross-sectional study enrolled 48 patients with PD (Hoehn-Yahr stage 1–4) and 17 age-matched healthy controls. All participants underwent comprehensive assessments, including pulmonary function testing (PFT) and cardiopulmonary exercise testing(CPET), alongside the systematic collection of demographic and clinical characteristics. PD patients were additionally evaluated for motor symptoms using the Unified Parkinson’s Disease Rating Scale part III (UPDRS-III), disease severity (Hoehn-Yahr stage, H-Y stage), cognitive function (Montreal Cognitive Assessment, MoCA), and activities of daily living (Modified Barthel Index, MBI). Correlation analyses were conducted to investigate the relationship between PFT and CPET outcomes, with a focus on identifying potential associations between respiratory impairment and exercise capacity in PD. Results Compared to controls, PD patients demonstrated significantly reduced PF and markedly impaired exercise capacity. Although 84% of PD patients showed preserved PF, 96% exhibited severe reductions in CRF. Strong correlations were observed between pulmonary measures and exercise capacity. Higher CRF levels were associated with better cognitive function and greater independence in daily activities. Disease severity was inversely related to CRF. Conclusions PD patients experience significant declines in both PF and CRF, which are linked to worse clinical and functional outcomes. The discordance between preserved PF and severely reduced CRF suggests that non-pulmonary mechanisms may contribute to exercise intolerance. CPET should be integrated into PD assessments to guide personalized rehabilitation strategies. Trial registration: Not applicable.