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“Lung ultrasound score is better than diaphragm excursion at maximal deep inspiration for diagnosing severe lung hyperinflation,” researchers wrote.

Lung ultrasound score (LUS) is a useful measurement of lung hyperinflation in patients with stable COPD, according to recently published findings from researchers in China.

“Pulmonary function tests require the cooperation of patients, which is time-consuming and is likely to make the patients uncomfortable,” Yongjian Chen of the Department of Ultrasound at the Second Affiliated Hospital of Fujian Medical University, Quanzhou, Fujian, China, and colleagues wrote in the International Journal of Chronic Obstructive Pulmonary Disease. “Whether there is a more convenient auxiliary examination method for assessing the severity of lung hyperinflation in COPD patients has become a key issue in clinical research. Ultrasound has the advantages of no radiation, simple operation, and real-time observation, which has a certain research prospect.”

The researchers recruited 149 patients with stable COPD and 100 healthy control participants to undergo a series of measurements. Chen and colleagues calculated all participants’ LUS by measuring pleural sliding displacement and tracking the sliding of pleura in different sections. They also recorded patients’ total lung capacity, diaphragm excursion, residual capacity, functional residual capacity, and inspiratory capacity. The study team used multiple linear regression analysis to explore possible correlations between LUS and other measures.

The study team excluded patients from the study if they had any history of chronic respiratory diseases other than COPD, a history of surgery on the chest or abdomen, history of pleural or peritoneal diseases, respiratory infection during the month before the study, history of drug use that might affect the “skeletal muscle tissue structure,” any inability to cooperate with clinical measurements, or a history of chronic metabolic disease. The researchers wrote that both groups had similar characteristics regarding sex, age, and body mass index. Chen and colleagues drew receiver operating characteristic (ROC) curves of LUS and diaphragm excursion to determine the diagnostic efficacy of the two measurements.

LUS Correlates With Other Measurements

The researchers reported that those in the COPD group had a LUS that positively correlated with other measurements, including total lung capacity, residual capacity, functional residual capacity, and fractional residual capacity (P<0.001 for all). Ultrasound scores were negatively correlated with inspiratory and fractional inspiratory capacity (P<0.001).

The researchers determined that LUS was better suited for diagnosing severe lung hyperinflation than diaphragm excursion at maximal deep inspiration. When Chen and colleagues set the diagnostic criterion for severe lung hyperinflation as a fractional inspiratory capacity of less than 25%, the area under the ROC curve of LUS was 0.914 for diagnosing severe lung hyperinflation, whereas the area under the ROC curve of diaphragm excursion at maximal deep inspiration was 0.385, they reported. When the diagnostic criterion was a fractional residual capacity greater than 60%, the researchers reported that the area under the ROC curve was 0.845 for lung ultrasound versus 0.543 for diaphragm excursion at maximal deep inspiration (all P<0.001).

The researchers acknowledged that the study was limited because it was conducted at a single center. Furthermore, they noted that ultrasound examination could not reach deep lung tissue, which limited the examination to respiratory muscle, pleura, and subpleural lung parenchyma. Chen and colleagues wrote that a CT scan offers a more detailed view and may be used with lung hyperinflation to evaluate COPD.

“This clinical study showed that the LUS, based on pleural slip in different regions and PSD, was increased in stable COPD patients, which was correlated with pulmonary function indicators reflecting LH,” Chen and colleagues concluded. “Its correlations were stronger than those of DE at maximal deep inspiration. The diagnostic efficacy of pulmonary ultrasound scoring in the diagnosis of severe LH is better than that of DE at maximal deep inspiration, so it can be used to evaluate LH in stable COPD patients.”

Real-World Use & Limitations

Saqib H. Baig, MD, assistant professor and pulmonologist at Sidney Kimmel Medical College, Philadelphia, said the findings offered an interesting possibility of a new clinical tool but cautioned that the study had some limitations.

“The researchers utilized point-of-care ultrasound, which has become increasingly favored in recent years because of its non-invasive approach and its ability for rapid bedside diagnostics,” he said. “They developed a novel LUS to investigate its effectiveness in identifying lung hyperinflation, which is traditionally detected through pulmonary function testing.”

“I believe this is a well-done study and provides good-quality evidence for its intended purpose, which was to demonstrate a reliable correlation between lung hyperinflation detected by pulmonary function testing and lung ultrasound.”

However, Dr. Baig added that the study did have its limitations. “They don’t tell you how much time it took to do this lung evaluation,” Baig continued, pointing out that the study included numerous points for ultrasound image acquisition from patients in both a supine and sitting position.

Additionally, Dr. Baig said the article did not note which specific LUS correlated with the researchers’ definition of severe hyperinflation. Moreover, the article did not offer comparisons or contrasts with chest CT scans, which is also a potential method of identifying and measuring lung hyperinflation. It’s also important to note that only a single peer reviewer reviewed the study.

“This study convinces me that lung ultrasound can be a useful bedside tool for research. We should investigate the LUS as an additional outcome measure in studies aiming to impact lung hyperinflation.” Dr. Baig said. “But I don’t think it’s ready for primetime and will need to be evaluated further before its adoption into clinical practice.”