Objectives: The purpose of this study is to evaluate the impact of Parkinson’s disease (PD) on respiratory function using spirometry. In addition, the study aims to investigate the relationship between the severity of PD and any impairments in a respiratory capacity as measured by forced vital capacity (FVC%). Methods: This case–control study (40 cases of PD vs. 40 healthy controls) was conducted from July 1, 2021, to October 31, 2022, in a tertiary care hospital of New Delhi. Clinical symptoms and severity (Movement Disorder Society Unified Parkinson’s Disease Rating Scale [MDS-UPDRS] part-III score and Modified H and Y Scale) of the patients of PD were noted. A pulmonary function test (by spirometry) was performed and parameters such as forced expiratory volume in 1 s (FEV1), FVC, FEV1/FVC, and peak expiratory flow rate (PEFR) were noted. Mann–Whitney U-test (for two groups) and Chi-square test were used for the comparison of variables. Spearman rank correlation coefficient was used for the correlation of FVC (% predicted) with MDS-UPDRS part-III score and Modified H and Y stage. Results: Compared to controls, cases had significantly lower FVC% (70.5 vs. 88, P < 0.01), significantly lower FEV1% (68 vs. 83.5, P < 0.01), comparable FEV1/FVC (% predicted) (97 vs. 96, P = 0.805) and significantly lower PEFR (% predicted) (80.5 vs. 92, P < 0.01). The pattern of lung involvement was restrictive, normal, and obstructive in 72.50%, 20%, and 7.50% of cases, respectively. FVC (% predicted) showed a significant negative correlation with MDS-UPDRS part-III score (r = −0.895, P < 0.01) and with Modified H and Y Scale (r = −0.792, P < 0.01). Conclusion: Patients with PD had significantly more deranged respiratory dysfunction and there was significantly higher respiratory dysfunction with increasing severity of PD. A proper screening of lung functions may allow an early detection of respiratory dysfunction, thereby helping to initiate an early pulmonary rehabilitation to prevent respiratory complications.

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