Variability in Cardiopulmonary Exercise Testing Biologic Controls

BACKGROUND: Cardiopulmonary exercise testing is an increasingly common test and is consid-ered the accepted standard for assessing exercise capacity. Quantifying variability is important to assess the instrument for quality control purposes. Though guidelines recommend biologic control testing, there are minimal data on how to do it. We sought to describe variability for oxygen con-sumption (VO2), carbon dioxide production (VCO2), and minute ventilation (VE) at various work rates under steady-state conditions in multiple subjects over a 1-y period to provide a practical approach to assess and perform biologic control testing. METHODS: We performed a single-center, prospec-tive study with 4 healthy subjects, 2 men and 2 women. Subjects performed constant work rate exer-cise tests for 6 min each at 25-100 W intervals on a computer-controlled cycle ergometer. Data were averaged over the last 120 s at each work rate to reflect stepwise steady-state conditions. Descriptive statistics, including the mean, median, range, SD, and coefficient of variation (CoV) are reported for each individual across the 4 work rates and all repetitions. As these data were normative, z-scores were utilized, and a value greater than +/- 1.96 z-scores was used to define significant test variability. RESULTS: Subjects performed 16-39 biocontrol studies over 1-y. The mean CoV for all subjects in VO2 was 6.59%, VCO2 was 6.41%, and VE was 6.32%. The +/- 1.96 z-scores corresponded to a 9.4- 18.1% change in VO2 , a 9.6-18.1% change in VCO2 , and a 9-21.5% change in VE across the 4 workloads. CONCLUSIONS: We report long-term variability for steady-state measurement of VO2 , VCO2 , and VE obtained during biocontrol testing. Utilizing +/- 1.96 z-scores allows one to determine if a result exceeds expected variability, which may warrant investigation of the instrument.