Assessment of Pulmonary Function Tests in Patients with Hypothyroidism

Hypothyroid patients often complain of shortness of breath, fatigue, and exercise intolerance. Both inspiratory and expiratory muscles' weakness is present, and the impairment of pulmonary function may be initiated at the subclinical stage of hypothyroidism. Hence, this study aimed to assess the pulmonary function tests (PFTs) in hypothyroid patients.

This cross-sectional observational study was undertaken on patients attending the medicine outpatient department and indoor, in the Department of Medicine at Rajendra Institute of Medical Sciences, Ranchi, Jharkhand, from May 2023 to June 2024. Thyroid profile was estimated by enzyme-linked immunosorbent assay. PFTs (forced expiratory volume in 1 s [FEV1], forced vital capacity [FVC], and FEV1/FVC) were assessed by spirometry. Data were analyzed using SPSS software (version 22.0). Descriptive analysis was done for almost all variables along with t -test and Chi-square test wherever applicable for finding a significant difference using P value. Pearson's correlation was used to determine the correlation between the variables.

The study was conducted on 136 patients, of whom 26% were male and 74% were female. In this study, the mean thyroid-stimulating hormone, free triiodothyronine (T3), and free thyroxine (T4) levels were 19.6 ± 34.7 μIU/ml, 1.1 ± 0.794 ng/ml, and 2.9 ± 2.47 ng/ml, respectively. Spirometry results revealed a predominant restrictive pattern (75.74%). Peak expiratory flow rate (PEFR) had a mean value of 5.89 ± 1.91 L/min. This low level of PEFR suggests restrictive lung disease. Correlation analyses demonstrated a positive relationship between serum T4 levels with FVC ( P = 0.006) and serum T3 level with PEFR ( P = 0.041), indicating lower T3 and T4 levels associated with restrictive lung disease.

Pulmonary function tests can be affected in hypothyroidism with increased risk of restrictive lung disease.