Lung Ultrasound Assessment of Lung Hyperinflation in Patients with Stable COPD: An Effective Diagnostic Tool

Abstract

Purpose

To evaluate the degree of lung hyperinflation (LH) in patients with stable chronic obstructive pulmonary disease (COPD) by lung ultrasound score (LUS) and assess its value.

Patients and Methods

We conducted a study of 149 patients with stable COPD and 100 healthy controls recruited by the Second Affiliated Hospital of Fujian Medical University. The pleural sliding displacement (PSD) was measured, the sliding of the pleura in different areas was observed, and LUS was calculated from both of them. The diaphragm excursion (DE), residual capacity (RV), total lung capacity (TLC), inspiratory capacity (IC) and functional residual capacity (FRC) were measured. We described the correlation between ultrasound indicators and pulmonary function indicators reflecting LH. Multiple linear regression analysis was used. The ROC curves of LUS and DE were drawn to evaluate their diagnostic efficacy, and De Long method was used for comparison.

Results

(1) The LUS of patients with stable COPD were positively correlated with RV, TLC, RV/TLC and FRC and negatively correlated with IC and IC/TLC (r₁=0.72, r₂=0.41, r₃=0.72, r₄=0.70, r₅=−0.56, r₆=−0.65, P < 0.001). The correlation was stronger than that between DE at maximal deep inspiration and the corresponding pulmonary function indices (r₁=−0.41, r₂=−0.26, r₃=−0.40, r₄=−0.43, r₅=0.30, r₆=0.37, P < 0.001). (2) Multiple linear regression analysis showed that LUS were significantly correlated with IC/TLC and RV/TLC. (3) With IC/TLC<25% and RV/TLC>60% as the diagnostic criterion of severe LH, the areas under the ROC curves of LUS and DE at maximal deep inspiration for diagnosing severe LH were 0.914 and 0.385, 0.845 and 0.543, respectively (P < 0.001).

Conclusion

The lung ultrasound score is an important parameter for evaluating LH. LUS is better than DE at maximal deep inspiration for diagnosing severe LH and is expected to become an effective auxiliary tool for evaluating LH.

Keywords:

• chronic obstructive pulmonary disease
• lung hyperinflation
• ultrasound
• pleural sliding displacement
• pulmonary function

Abbreviations

COPD, chronic obstructive pulmonary disease; LH, lung hyperinflation; FRC, functional residual capacity; IC, inspiratory capacity; sLH, static lung hyperinflation; dLH, dynamic lung hyperinflation; TLC, total lung capacity; RV, residual volumetotal; AreaFE, area under the forced expiratory flow-volume loop; AreaFE%, AreaFE expressed as a percentage of reference value; MPT, manually/metronome paced tachypnea; MPIH, metronome-paced incremental hyperventilation; IOS, impulse oscillometry system; DE, diaphragm excursion; FEV₁, forced expiratory volume; FVC, forced vital capacity; mMRC, modified Medical Research Council; CAT, COPD Assessment Test; PSD, pleura sliding displacement; ROC, receiver operator characteristic; LUS, lung ultrasound score; AUC, area under curve.

Ethics Approval and Informed Consent

This study was approved by the Ethics Committee of the Second Affiliated Hospital of Fujian Medical University (reference number: 2019-223). This study was conducted in accordance with the Declaration of Helsinki and all participants gave informed consent.

Acknowledgments

We are grateful for the support of the Department of Respiratory Medicine of the Second Affiliated Hospital of Fujian Medical University.

Disclosure

The authors declare that they have no competing interests in this work.

Additional information

Funding

This project was financially supported by Natural Science Foundation of Fujian Province, China (NO:2022J01783).