Measurement of cardiac output during exercise by open-circuit acetylene uptake

Rebecca C. Barker, Susan R. Hopkins, Nancy Kellogg, I. Mark Olfert, Tom D. Brutsaert, Timothy P. Gavin, Pauline L. Entin, Anthony J. Rice, Peter D. Wagner

Research output: Contribution to journalArticlepeer-review

53 Scopus citations


Noninvasive measurement of cardiac output (Q̇T) is problematic during heavy exercise. We report a new approach that avoids unpleasant rebreathing and resultant changes in alveolar PO2 or PCO2 by measuring short-term acetylene (C2H2) uptake by an open-circuit technique, with application of mass balance for the calculation of Q̇T. The method assumes that alveolar and arterial C2H2 pressures are the same, and we account for C2H2 recirculation by extrapolating end-tidal C2H2 back to breath 1 of the maneuver. We correct for incomplete gas mixing by using He in the inspired mixture. The maneuver involves switching the subject to air containing trace amounts of C2H2 and He; ventilation and pressures of He, C2H2, and CO2 are measured continuously (the latter by mass spectrometer) for 20-25 breaths. Data from three subjects for whom multiple Fick O2 measurements of Q̇T were available showed that measurement of Q̇T by the Fick method and by the C2H2 technique was statistically similar from rest to 90% of maximal O2 consumption (V̇O(2max)). Data from 12 active women and 12 elite male athletes at rest and 90% of V̇O(2max) fell on a single linear relationship, with O2 consumption (V̇O2) predicting Q̇T values of 9.13, 15.9, 22.6, and 29.4 l/min at V̇O2 of 1, 2, 3, and 4 l/min. Mixed venous PO2 predicted from C2H2-determined Q̇T, measured V̇O2, and arterial O2 concentration was ~20-25 Torr at 90% of V̇O(2max) during air breathing and 10-15 Torr during 13% O2 breathing. This modification of previous gas uptake methods, to avoid rebreathing, produces reasonable data from rest to heavy exercise in normal subjects.

Original languageEnglish (US)
Pages (from-to)1506-1512
Number of pages7
JournalJournal of Applied Physiology
Issue number4
StatePublished - Oct 1999


  • Inert gas
  • Maximal exercise
  • New methodology

ASJC Scopus subject areas

  • General Medicine


Dive into the research topics of 'Measurement of cardiac output during exercise by open-circuit acetylene uptake'. Together they form a unique fingerprint.

Cite this