Open-circuit acetylene uptake methods (OpCirc1 and OpCirc2) correlated highly with the direct Fick method for measuring cardiac output during exercise (R2 = 0.90 and 0.89, respectively).
Observational (n=6)
Does the open-circuit acetylene uptake method accurately measure cardiac output during exercise compared to the direct Fick method?
Open-circuit acetylene uptake methods provide reliable cardiac output measurements during mild to moderate exercise, but may underestimate values at high exercise intensities compared to the direct Fick method.
Effect estimate: R2 = 0.90 and 0.89
An open-circuit (OpCirc) acetylene uptake cardiac output (QT) method was modified for use during exercise. Two computational techniques were used. OpCirc1 was based on the integrated uptake vs. end-tidal change in acetylene, and OpCirc2 was based on an iterative finite difference modeling method. Six subjects 28-44 yr, peak oxygen consumption (VO(2)) = 120% predicted performed cycle ergometry exercise to compare QT using OpCirc and direct Fick methods. An incremental protocol was repeated twice, separated by a 10-min rest, and subsequently subjects exercised at 85-90% of their peak work rate. Coefficient of variation of the OpCirc methods and Fick were highest at rest (OpCirc1, 7%, OpCirc2, 12%, Fick, 10%) but were lower at moderate to high exercise intensities (OpCirc1, 3%, OpCirc2, 3%, Fick, 5%). OpCirc1 and OpCirc2 QT correlated highly with Fick QT (R(2) = 0.90 and 0.89, respectively). There were minimal differences between OpCirc1 and OpCirc2 compared with Fick up to moderate-intensity exercise (70% peak VO(2). These differences became significant for OpCirc1 only. Part of the differences between Fick and OpCirc methods at the higher exercise intensities are likely related to inhomogeneities in ventilation and perfusion matching (R(2) = 0.36 for Fick - OpCirc1 vs. alveolar-to-arterial oxygen tension difference). In conclusion, both OpCirc methods provided reproducible, reliable measurements of QT during mild to moderate exercise. However, only OpCirc2 appeared to approximate Fick QT at the higher work intensities.
Johnson et al. (2000) reported an observational. Open-circuit acetylene uptake cardiac output (OpCirc) methods vs. Direct Fick method was evaluated on Cardiac output (QT) correlation (R2 = 0.90 and 0.89). Open-circuit acetylene uptake methods (OpCirc1 and OpCirc2) correlated highly with the direct Fick method for measuring cardiac output during exercise (R2 = 0.90 and 0.89, respectively).