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Respiratory exacerbations are associated with muscle loss in current and former smokers
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  • Published on:
    Erector spinae muscle area is not associated with mortality in the COPDGene cohort
    • Stefanie E Mason, Pulmonary and Critical Care Physician Brigham & Women's Hospital
    • Other Contributors:
      • George R Washko, Pulmonary and Critical Care Physician

    We thank Tanimura and colleagues for their thoughtful commentary on our recent manuscript, “Respiratory exacerbations are associated with muscle loss in current and former smokers” and read their analysis of erector spinae muscle area (ESMA) with interest (1). In their commentary, they note that muscle loss can occur heterogeneously, with the greatest expected impact on the muscles of ambulation. They suggest that erector spinae muscles, due to their fiber composition and anti-gravity role, are a better reflection of inactivity-related muscle loss and posit that changes in pectoralis muscle area (PMA) may only reflect changes in nutrition (as measured by body mass index, BMI).

    We agree that muscle loss is unlikely to be uniform; however, a disconnect has been reported between the postural muscles of the trunk and ambulatory muscle (e.g. quadriceps) weakness, despite similar fiber types (2). Few studies measure both groups of muscles simultaneously, but there is evidence that inspiratory force is more affected than peripheral muscle force in patients with COPD; implying that deconditioning is not the sole driver of muscle dysfunction (3). While the pectoralis muscle potentially underestimates inactivity-related atrophy, these studies suggest its role as an accessory muscle of inspiration makes it a reasonable target for capturing any underlying systemic process.

    In contrast to Tanimura et al’s findings, in the COPDGene participants (n=8,603) BMI was more stro...

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    Conflict of Interest:
    None declared.
  • Published on:
    Frequent exacerbations of COPD can contribute to accelerated loss of antigravity muscles rather than pectoralis muscles
    • Kazuya Tanimura, Pulmonologist Department of Respiratory Medicine, Graduate School of Medicine, Kyoto University
    • Other Contributors:
      • Susumu Sato, Pulmonologist
      • Shigeo Muro, Pulmonologist
      • Toyohiro Hirai, Pulmonologist

    To the editor,

    We read the interesting report by Mason et al, “Respiratory exacerbations are associated with muscle loss in current and former smokers”.[1] In this study, the authors demonstrated that exacerbations are associated with accelerated loss of pectoralis muscles (PMs) in two large observational cohorts and quantified the impact of each annual exacerbation as the equivalent of 6 months of age-expected decline.
    Skeletal muscle loss is one of the major systemic manifestations associated with mortality in patients with COPD. Not only systemic muscle loss but also loss of specific muscle groups are associated with clinical outcomes such as exacerbations and mortality in patients with COPD.[2, 3] Moreover, muscle loss can occur heterogeneously.[4] This may be partially because each muscle group has its physiological function or biological characteristics such as muscle fiber composition. This supports that loss of specific muscle groups may have different implications in the clinical course of COPD.
    We previously analyzed the cross-sectional area of erector spinae muscles (ESMCSA) and that of PMs (PMCSA) in male patients with COPD using chest CT.[3] ESMs are ones of antigravity muscles which are involved in maintaining an upright posture. PMs play an important role in the movement of upper limbs. Both muscles also act as accessory inspiratory muscles. ESMs are composed of 60% type 1 fibers and 40% of type 2 fibers and PMs are composed in the reverse...

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    Conflict of Interest:
    None declared.