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

1999; American Physiological Society; Volume: 87; Issue: 4 Linguagem: Inglês

10.1152/jappl.1999.87.4.1506

8750-7587

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

Blood Pressure and Hypertension Studies

Noninvasive measurement of cardiac output (Q˙t) is problematic during heavy exercise. We report a new approach that avoids unpleasant rebreathing and resultant changes in alveolar[Formula: see text] or[Formula: see text] by measuring short-term acetylene (C 2 H 2 ) uptake by an open-circuit technique, with application of mass balance for the calculation ofQ˙t. The method assumes that alveolar and arterial C 2 H 2 pressures are the same, and we account for C 2 H 2 recirculation by extrapolating end-tidal C 2 H 2 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 C 2 H 2 and He; ventilation and pressures of He, C 2 H 2 , and CO 2 are measured continuously (the latter by mass spectrometer) for 20–25 breaths. Data from three subjects for whom multiple Fick O 2 measurements ofQ˙t were available showed that measurement ofQ˙t by the Fick method and by the C 2 H 2 technique was statistically similar from rest to 90% of maximal O 2 consumption (V˙o 2 max ). Data from 12 active women and 12 elite male athletes at rest and 90% ofV˙o 2 max fell on a single linear relationship, with O 2 consumption (V˙o 2 ) predictingQ˙t values of 9.13, 15.9, 22.6, and 29.4 l/min atV˙o 2 of 1, 2, 3, and 4 l/min. Mixed venous [Formula: see text] predicted from C 2 H 2 -determinedQ˙t, measuredV˙o 2 , and arterial O 2 concentration was ∼20–25 Torr at 90% ofV˙o 2 max during air breathing and 10–15 Torr during 13% O 2 breathing. This modification of previous gas uptake methods, to avoid rebreathing, produces reasonable data from rest to heavy exercise in normal subjects.