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

Wicharn Boonjindasup, Julie M. Marchant, Margaret S. McElrea, Stephanie T. Yerkovich, Rahul J. Thomas, Ian B. Masters, Anne B. Chang

Research output: Contribution to journalArticlepeer-review

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.

Original languageEnglish
Article number107029
Pages (from-to)1-5
Number of pages5
JournalRespiratory Medicine
Volume204
DOIs
Publication statusPublished - 1 Nov 2022

Bibliographical note

Funding Information:
The study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. WB is supported by a Charles Darwin University International PhD scholarship and an Asia Pacific Society of Respirology Fellowship. AC is supported by an Australian National Health and Medical Research Council Practitioner Fellowship (grant number APP1154302 ) and top-up from the Queensland Children's Hospital Foundation (grant number 50286 ). JM is supported by an Early Career Fellowship (grant number RPC0772019 ) from Queensland Children's Hospital Foundation.

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