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The ‘knee’ pattern in spirometry flow-volume curves in children: Does it relate to tracheomalacia?

  • Wicharn Boonjindasup
    Correspondence
    Corresponding author. Australian Centre for Health Services Innovation, Queensland University of Technology, 62 Graham Street, South Brisbane, Brisbane, Queensland, 4101, Australia.
    Affiliations
    NHMRC Centre for Research Excellence in Paediatric Bronchiectasis (AusBREATHE), Child Health Division, Menzies School of Health Research, Charles Darwin University, PO Box 41096, Casuarina, Darwin, Northern Territory, 0810, Australia

    Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, 1873, Rama 4 Road, Pathumwan, Bangkok, 10330, Thailand

    Australian Centre for Health Services Innovation @ Centre for Healthcare Transformation, Queensland University of Technology, 62 Graham Street, South Brisbane, Brisbane, Queensland, 4101, Australia
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  • Julie M. Marchant
    Affiliations
    Australian Centre for Health Services Innovation @ Centre for Healthcare Transformation, Queensland University of Technology, 62 Graham Street, South Brisbane, Brisbane, Queensland, 4101, Australia

    Department of Respiratory & Sleep Medicine, Queensland Children's Hospital, 501 Stanley Street, South Brisbane, Brisbane, Queensland, 4101, Australia
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  • Margaret S. McElrea
    Affiliations
    Australian Centre for Health Services Innovation @ Centre for Healthcare Transformation, Queensland University of Technology, 62 Graham Street, South Brisbane, Brisbane, Queensland, 4101, Australia

    Department of Respiratory & Sleep Medicine, Queensland Children's Hospital, 501 Stanley Street, South Brisbane, Brisbane, Queensland, 4101, Australia
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  • Stephanie T. Yerkovich
    Affiliations
    NHMRC Centre for Research Excellence in Paediatric Bronchiectasis (AusBREATHE), Child Health Division, Menzies School of Health Research, Charles Darwin University, PO Box 41096, Casuarina, Darwin, Northern Territory, 0810, Australia

    Australian Centre for Health Services Innovation @ Centre for Healthcare Transformation, Queensland University of Technology, 62 Graham Street, South Brisbane, Brisbane, Queensland, 4101, Australia
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  • Rahul J. Thomas
    Affiliations
    Australian Centre for Health Services Innovation @ Centre for Healthcare Transformation, Queensland University of Technology, 62 Graham Street, South Brisbane, Brisbane, Queensland, 4101, Australia

    Department of Respiratory & Sleep Medicine, Queensland Children's Hospital, 501 Stanley Street, South Brisbane, Brisbane, Queensland, 4101, Australia
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  • Ian B. Masters
    Affiliations
    Australian Centre for Health Services Innovation @ Centre for Healthcare Transformation, Queensland University of Technology, 62 Graham Street, South Brisbane, Brisbane, Queensland, 4101, Australia

    Department of Respiratory & Sleep Medicine, Queensland Children's Hospital, 501 Stanley Street, South Brisbane, Brisbane, Queensland, 4101, Australia
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  • Anne B. Chang
    Affiliations
    NHMRC Centre for Research Excellence in Paediatric Bronchiectasis (AusBREATHE), Child Health Division, Menzies School of Health Research, Charles Darwin University, PO Box 41096, Casuarina, Darwin, Northern Territory, 0810, Australia

    Australian Centre for Health Services Innovation @ Centre for Healthcare Transformation, Queensland University of Technology, 62 Graham Street, South Brisbane, Brisbane, Queensland, 4101, Australia

    Department of Respiratory & Sleep Medicine, Queensland Children's Hospital, 501 Stanley Street, South Brisbane, Brisbane, Queensland, 4101, Australia
    Search for articles by this author
Published:October 28, 2022DOI:https://doi.org/10.1016/j.rmed.2022.107029

      Highlights

      • In this study, we found that the ‘knee’ in spirometry flow-volume curves was often associated with an airway condition in children.
      • Tracheomalacia diagnosed by flexible bronchoscopy was found in 65% of children with the ‘knee’ pattern.
      • A scoop before plateau of the ‘knee’ was significantly associated with tracheomalacia diagnosed by flexible bronchoscopy.

      Abstract

      Background

      There is little data on patterns of spirometry curves in children with tracheomalacia but convex inflection on flow-volume curves (identified as the ‘knee’) is thought to represent tracheomalacia.

      Objectives

      To determine (a) the prevalence of tracheomalacia in children with the ‘knee’ pattern on spirometry, and (b) whether spirometry parameters and visual characteristics of the ‘knee’ can identify presence/absence or severity of tracheomalacia.

      Patients/methods

      We reviewed the spirometry undertaken at Queensland Children's Hospital between 2016 and 2019 and retrieved spirometry with the ‘knee’ pattern in the flow-volume curves. Flexible bronchoscopy videos of these children were reviewed for tracheomalacia diagnosis and severity in a blinded manner. We also evaluated several ‘knee’ characteristics (onset of inflection, angle of inflection, a scoop before plateau, plateau progression), spirometry parameters and tracheomalacia severity.

      Results

      Of the 78 children with the ‘knee’, 51 (65.4%) had tracheomalacia. Spirometry values were significantly lower in those with tracheomalacia, compared to those without (predicted FEV1 = 86.1% vs 99.9%, FVC = 95.1% vs 104%, FEF25–75% = 68.6% vs 89.6%, all p < 0.02). A scoop before plateau was significantly associated with tracheomalacia (66.7% vs 40.7%, p = 0.03). There was no significant difference in spirometry parameters or the ‘knee’ characteristics between children with mild versus moderate-to-severe tracheomalacia.

      Conclusion

      Most but not all children with the ‘knee’ pattern have flexible bronchoscopy-defined tracheomalacia. Those with tracheomalacia had lower spirometry values and the presence of a scoop before plateau was the most characteristic feature. A prospective longitudinal study is required to determine the diagnostic value of spirometry flow-volume curve characteristics in children.

      Keywords

      Abbreviations:

      TM (tracheomalacia), FB (flexible bronchoscopy), ERS (European Respiratory Society), FEV1 (forced expiratory volume in first second), FVC (forced vital capacity), FEF25–75% (forced expiratory flow between 25% and 75% of vital capacity), PEF (peak expiratory flow)
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