Adaptation of the inert gas FRC technique for use in heavy exercise

B. D. Johnson, K. C. Seow, D. F. Pegelow, J. A. Dempsey

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


We automated the inert gas rebreathe technique for measurement of end-expiratory lung volume (EELV) during heavy exercise. We also assessed the use of two gas tracers (He and N2) vs. a single gas tracer (He) for measurement of this lung volume and compared the two-tracer EELV to changes in the inspiratory capacity (defined with transpulmonary pressure) and shifts in the end-expiratory pressure from rest through heavy exercise. A computer program switched a pneumatic valve when flow crossed zero at end expiration and defined points in the He and N2 traces for calculation of EELV. An inherent delay of the rebreathing valve (50 ms) caused virtually no error at rest and during light exercise and an error of 74 ± 9 ml in the EELV at peak inspiratory flow rates of 4 l/s. The measurement of EELV by the two gas tracers was closely correlated to the single-gas tracer measurement (r = 0.97) but was consistently higher (120 ± 10 ml) than when He was used alone. This difference was accentuated with increased work rates (2-5% error in the EELV, rest to heavy exercise) and as rebreathe time increased (2-7% error in the EELV with rebreathe times of 5-20 s for all work loads combined). The double-gas tracer measurement of EELV agreed quite well with the thoracic gas volume at rest (P > 0.05). Repeat measurements performed during the same exercise load were in close agreement (r = 0.97, coefficient of variation ± 3%), and changes in the EELV from rest through heavy exercise agreed with changes in the inspiratory capacity (r = 0.86) and with positive shifts in the end-expiratory esophageal pressure (r = -0.66). The automated technique, with two gas tracers, appears to give sensitive, reproducible, and accurate measurements of EELV during heavy exercise.

Original languageEnglish (US)
Pages (from-to)802-809
Number of pages8
JournalJournal of applied physiology
Issue number2
StatePublished - Jan 1 1990


  • end-expiratory lung volume
  • rebreathing technique
  • switching valve
  • two-tracer method

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


Dive into the research topics of 'Adaptation of the inert gas FRC technique for use in heavy exercise'. Together they form a unique fingerprint.

Cite this