Measurement of cardiac output during exercise by open circuit
acetylene uptake.
Barker, Rebecca C., Susan R. Hopkins, Nancy Kellogg, I. Mark Olfert,
Tom D. Brutsaert, Timothy P. Gavin, Pauline L. Entin, Anthony J. Rice
and Peter D. Wagner.
1Department of Medicine, University of California, San Diego, La
Jolla, CA and 2Department of Thoracic Medicine, Royal Adelaide
Hospital, Australia
APStracts 6:0275A, 1999.
Non-invasive measurement of cardiac output (Q. T ) is problematic
during heavy exercise. We report a new approach which avoids
unpleasant rebreathing and resultant changes in alveolar Po2 or Pco2
by measuring short-term acetylene (C2H2) uptake by an open circuit
technique, applying mass balance for the calculation of cardiac
output. 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 helium in the inspired mixture. The
maneuver involves switching the subject to air containing trace
amounts of C2H2 and helium; 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 Q. T were available showed that Fick and C2H2
measurement of Q. T were statistically similar from rest to 90% V.
o2max. Data from 12 active women and 12 elite male athletes at rest
and 90% V. o2max fell on a single linear relationship with V. o2
predicting Q. T _s of 9.13, 15.9, 22.6 and 29.4 l/min at V. o2 of 1,
2, 3, and 4 l/min. Mixed venous Po2 predicted from C2H2 -Q. T,
measured V. o2 and arterial [O2 ] was about 20-25 Torr at 90% V.
o2max during air breathing and 10-15 Torr breathing 13% O2 . This
modification of previous gas uptake methods, to avoid rebreathing,
produces reasonable data from rest to heavy exercise in normal
subjects.
Received 22 March 1999; accepted in final form 7 June 1999.
APS Manuscript Number A221-9.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 25 June 1999