Effect of duration of data averaging interval on reported peak VO2 in patients with heart failure

To describe the effect of the duration of the data averaging interval on the calculated peak oxygen uptake (VO2) reported from a symptom-limited maximal exercise test in patients with heart failure.

Maximal exercise test results from 275 patients diagnosed with stable heart failure due to left ventricular systolic dysfunction (ejection fraction<45%; age: 45-75 years; peak VO2: 8.0-20.0mL/kg/min), were examined. Sampling rates of 10, 20, 30 and 60s were used to calculate peak VO2, which was identified as the highest interval value that occurred during the final minute of exercise or the first interval in immediate recovery.

Mean peak VO2 (mL/kg/min) across the four sampling periods was as follows: 14.0±3.0 (10s), 13.7±3.0 (20s), 13.5±3.0 (30s) and 13.2±2.9 (60s) and there was a significant reduction with increasing averaging duration (p<0.0001). Peak VO2 was significantly different between the 10s and 60s sampling times (p<0.0001). Peak respiratory exchange ratio (RER) was also significantly different between 10 and 60s sampling rates (p<0.0001). Sub-analyses showed peak VO2 values in those people achieving RER>1.05 to be +0.8±0.7mL/kg/min higher than those who had not achieved RER values>1.05; similar findings, +0.8±0.7mL/kg/min, were seen in those patients achieving RER>1.10 versus those who did not.

Sampling rate method has a significant effect on calculated peak VO2 and RER. We suggest that laboratories standardize their sampling rate method to ensure consistency.