Anaerobic threshold (AT) is one of the central parameters reported in cardiopulomonary exercise testing. The ATS/ACCP 2003 statement recommends its derivation in a noninvasive protocol be based on the V-slope method and/or the ventilatory equivalents method. Both methods require data reviewer subjective inputs for identifying an inflection point. Our study proposes that the Respiratory Exchange Ratio (RER) at unity be used as a surrogate for its derivation.
The first part of our study included a retrospective assessment of ten cardiopulmonary exercise cases. For the surrogate AT, data were not subjected to any filtering or statistical manipulations, e.g. time averaging. The RER, the oxygen uptake (VO2), and the work rate as a function of time were analyzed by linear regression. The corresponding value when RER is unity defined the proposed AT at a specific time, from which a specific work rate or VO2 was obtained. These estimates for AT were compared to conventional measurements of AT based on 20-second data averaging and visual inspection for inflection points on V-slope, ventilatory equivalents, and end-tidal O2 and CO2 graphs. The second part of the study tested the proposed AT surrogate method against data from forty published case studies, and the comparison of the AT surrogate to the conventional AT evaluation.
Good agreement was noted in both parts between conventional AT and the AT surrogate. In the ten case studies, work rate, VO2, and percent of predicted maximum VO2 at the AT surrogate were compared with the conventional AT. The standard deviation (SD) ranged from 15-29%, Figure 1. When published data were added to the ten case studies, the SD for VO2 improved to 13%, Figure 2.
In this limited evaluation, there appears to be good agreement between the AT surrogate approach and the conventional AT methods. Future studies using larger databases would be needed to further validate this concept.
This alternate approach holds the promise of reducing both intra- and inter-observer variability in the determination of AT.
K.K. Shiu, None.