Respiratory muscle dysfunction is a common problem in patients with COPD, mostly related to pulmonary hyperinflation. Diaphragm shortening and deleterious changes in the muscle force-length relationship cause a reduction in the muscles’ capacity to generate pressure, placing them at a mechanical disadvantage.
Until now, the only way to assess respiratory muscle dysfunction has been by measuring the ratio between transdiaphragmatic pressure and electrical diaphragm activity, which involves invasive methods that are uncomfortable for patients.
Published in the European Respiratory Journal, the study by Raimon Jane’s group and his collaborators at the Hospital Germans Trias i Pujol and Hospital del Mar describes how they used respiratory muscle mechanomyogram (MMG) – a non-invasive way to measure vibrations related to the mechanical activation of muscles using accelerometers positioned on the skin – to assess respiratory muscle function in ten patients with severe-to-very severe COPD.
Using MMG, with the patients breathing normally through a mouthpiece and a tube while wearing a nose clip, the researchers and clinicians showed, for the first time, a direct comparison between the mechanical activation of the inspiratory muscles, estimated through the amplitude of the MMG, and the inspiratory effort at tidal volume – the volume of air moved into or out of the lungs during quiet breathing.
“Our results indicate that the amplitude of the MMG of patients with severe-to-very severe COPD is closely related to the inspiratory effort, and that the MMG is higher in more severe patients, even during quiet breathing, showing a lower efficiency of the respiratory muscles,” says Raimon. “In other words, the greater the degree of airflow obstruction, the greater mechanical activation of inspiratory muscle is required.”
The researchers are confident that his contribution can be a very useful tool to evaluate COPD progression, and could provide valuable information on the effect of treatments.
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Leonardo Sarlabous, Abel Torres1, José A.Fiz, Joaquim Gea, Juana M. Martínez-Llorens and Raimon Jané (2015). Efficiency of mechanical activation of inspiratory muscles in COPD using sample entropy. Eur Respir J. 46(6):1808-11
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