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Related Experiment Videos

Flow limitation while breathing HeO2

L C Lands1, T D Charge, A L Coates

  • 1Respiratory Medicine Service, McGill University-Montreal Children's Hospital Research Institute, Quebec.

Clinical and Investigative Medicine. Medecine Clinique Et Experimentale
|August 1, 1993
PubMed
Summary
This summary is machine-generated.

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Investigating the volume of isoflow (VisoV) for small airways function, this study found dynamic airway compression occurs even with helium-oxygen (HeO2) breathing. This challenges the use of VisoV due to high variability in flow limitation measurements.

Area of Science:

  • Pulmonary Physiology
  • Respiratory Mechanics
  • Small Airways Function

Background:

  • Flow limitation during maximum expiratory flow-volume curves (MEFVC) typically occurs below 70% vital capacity (VC).
  • The volume of isoflow (VisoV) compares MEFVC in air to HeO2 to assess small airways, but exhibits high intra-subject variability.
  • Variability in VisoV may stem from an inability to achieve flow limitation when breathing HeO2.

Purpose of the Study:

  • To investigate if high intra-subject variability in VisoV is due to an inability to achieve flow limitation while breathing HeO2.
  • To determine if expiratory muscle contraction velocity is insufficient to overcome increased expiratory flows and cause dynamic airway compression with HeO2.

Main Methods:

  • Seven healthy adult males performed maximal vital capacity (VC) expirations with esophageal balloons in a body plethysmograph.

Related Experiment Videos

  • Subjects breathed both air and an 80% helium, 20% O2 (HeO2) mixture.
  • Transpulmonary pressure-flow plots were analyzed at 70%, 50%, and 25% VC to assess flow limitation.

    • Main Results:

    • Flow limitation in air was observed in 3, 6, and 7 subjects at 70%, 50%, and 25% VC, respectively.
    • In HeO2, flow limitation was achieved in only 1 and 4 subjects at 70% and 50% VC, respectively.
    • At 25% VC, 6 out of 7 subjects demonstrated flow limitation despite HeO2 breathing, with one subject showing glottic closure.

    Conclusions:

    • Dynamic airway compression occurs even with the increased expiratory flows associated with breathing HeO2.
    • The findings suggest that the inability to consistently achieve flow limitation in HeO2 contributes to the high variability observed in VisoV measurements.
    • This challenges the reliability of VisoV as a sole indicator of small airways function when using HeO2 mixtures.