Non-invasive measurement of cardiac output (QT) is problematic during heavy exercise. We report a new approach avoiding intolerable rebreathing by using short-term acetylene (C2H2) uptake and applying mass balance, assuming that alveolar and arterial C2H2 pressures are the same. To account for C2H2 recirculation, end tidal [C2H2] is extrapolated back to breath 2 of the maneuver, which involves simply switching the subject to air containing trace amounts of C2H2 (and helium to correct C2H2 for incomplete mixing). The two gases are measured continuously by mass spectrometer for 20-25 breaths. Results for two subjects for whom Fick O2 measurement of QT were available revealed statistical similarity from rest to 90% V̇O2MAX. Data from 9 active women at rest and 90% of V̇ O2MAX, and from 12 elite athletes also at rest and 90% V̇O2MAX fell on a single, linear relationship with V̇O2 predicting QT of 8.8, 15.4, 22.0, and 28.7 1/min at V̇O2 of 1,2, 3 and 4 1/min. Mixed venous PO2 predicted from C2H2-QT, measured V̇O2 and arterial [O2] was about 20-25 Torr at 90% V̇ O2MAX (room air) 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.
|Original language||English (US)|
|State||Published - Mar 20 1998|
ASJC Scopus subject areas
- Molecular Biology