Effects of sampling interval on peak oxygen consumption in patients evaluated for heart transplantation

Background and methods: Peak oxygen consumption is a commonly accepted criterion in patient selection for cardiac transplantation. To determine the effect of various gas exchange sampling intervals on the variability of peak oxygen consumption, 15 consecutive patients evaluated for cardiac transplantation performed maximal treadmill testing using a ramped protocol. Oxygen consumption was measured via breath-by-breath analysis of expired air. Peak oxygen consumption was determined for each test using the following sampling intervals: 60-, 30-, and 15-s averages, eight breath rolling average, and true breath by breath. Variability of the mean peak oxygen consumption for each sample average was compared using analysis of variance on repeated measures. Results and conclusions: Measures of peak oxygen consumption differed significantly (p < 0.001) between sampling averages. A maximum variability of 20% was noted between the largest and smallest averages (13.8 +/- 4.2 mL/kg/min for 60 s vs 17.3 +/- 4.2, mL/kg/min for breath by breath). No significant difference was found between the 30-s, 15-s, and eight breath rolling averages (14.2 +/- 3.7 vs 14.5 +/- 3.9 vs 14.7 +/- 4.3 mL/kg/min), respectively. Results of the study suggest (1) the sampling average can have a significant effect on peak oxygen consumption influencing patient selection for transplantation, and (2) sample averages larger than breath by breath but smaller than 60 s be used for determination of peak oxygen consumption.