Correlation of diaphragm thickness with pulmonary function test in Parkinson's disease

Dopaminergic neurons are lost in Parkinson's disease (PD), a degenerative neurological condition. While the effects of PD on motor functions are well understood, its impact on respiratory function is less clear. In PD patients with suspicious pulmonary symptoms, the presence and degree of impairment in lung function often cannot be optimally assessed through pulmonary function tests (PFTs) due to the patients' neurological symptoms.

To examine the relationship between diaphragmatic thickness as determined by ultrasonography (US) and conventional PFTs in PD patients. Additionally, we evaluated the potential use of diaphragmatic thickness as an alternative measure for assessing respiratory function in PD patients who are unable to perform PFTs.

A total of 43 PD patients who presented to the clinics between June 15, 2021, and June 30, 2022, were included. Patients with coronavirus disease 2019 infection history, conditions affecting diaphragmatic motility, recent thoracic or abdominal surgery, or imaging showing restrictive masses were excluded. Demographic data, disease duration, Hoehn-Yahr stage, and medication use were recorded. PFTs were used to evaluate forced vital capacity, forced expiratory volume in the first second, and other parameters, while US was used to measure diaphragmatic thickness. Breathlessness was assessed using the modified medical research council dyspnea scale.

Significant correlations were found between peak expiratory flow (PEF) and diaphragm fraction (P = 0.019), as well as between PEF percentage and diaphragmatic thickness during expiration (P = 0.023). In early-stage PD, diaphragmatic thickness during inspiration correlated with oxygen saturation (P = 0.048). In advanced-stage PD, PEF and PEF% were significantly correlated with diaphragm thickness during expiration [r = 0.405, P = 0.049 (for PEF); r = 0.463, P = 0.023 (for PEF%)] and diaphragm fraction [r = -0.476, P = 0.019 (for PEF); r = -0.617, P = 0.001 (for PEF%)].

Present study assessed the relationship between PFTs and diaphragmatic thickness in PD patients. Diaphragmatic thickness measured by US was found to correlate with certain PFT parameters, suggesting it could be used as an alternative measure for assessing respiratory function in Parkinson's patients who have difficulty performing PFTs.