Objective: To analyze the correlation between quadriceps contraction index (Qci) and diaphragmatic function in patients with chronic obstructive pulmonary disease (COPD), and explore its clinical significance.

Methods: A total of 100 patients with stable COPD admitted to the Second Affiliated Hospital of Ningxia Medical University from October 2024 to December 2025 were enrolled. They were divided into the mild-to-moderate COPD group (48 cases) and severe-to-very severe COPD group (52 cases) according to pulmonary function grading criteria. Meanwhile, 50 healthy subjects undergoing physical examination during the same period were recruited as the healthy control group. General baseline data of the three groups were collected. The anterior thigh thickness in supine position, quadriceps thickness (Qthick), diaphragmatic thickness at end-inspiration (TDI) and end-expiration (TDE), and diaphragmatic excursion (DE) during quiet breathing were measured. The thickening fraction of the diaphragm (TFDI) and Qci were calculated. The differences in indicators among groups were compared, and the correlations of Qthick, Qci with TD, DE and TFDI were analyzed.

Results: Qthick, Qci, DE, TDE, TDI and TFDI in the mild-to-moderate COPD group and severe-to-very severe COPD group were significantly lower than those in the healthy control group (P < 0.05). Qci in the severe-to-very severe COPD group was lower than that in the mild-to-moderate COPD group (P < 0.05). Pearson correlation analysis showed that Qci was positively correlated with TDI, TDE, quiet breathing DE and TFDI, with statistically significant differences (P<0.05). Qthick was only positively correlated with TFDI (P < 0.05).

Conclusion: Qci is correlated with diaphragmatic function in patients with COPD. B-ultrasound measurement of quadriceps function can indirectly assess diaphragmatic function, providing a simple and feasible examination method for the evaluation of respiratory function in patients with chronic respiratory diseases.

Keywords: COPD; Quadriceps Contraction Index; Diaphragm Function

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