Cardiopulmonary exercise testing (CPET) offers a comprehensive assessment of the cardiac, ventilatory and musculoskeletal system during exercise. It is often used as a first line diagnostic tool in the assessment of athletes complaining of symptoms, those in the grey zone or athletes with heart disease. VE/VCO2 slop is a marker of ventilatory efficiency, offering prognostic information in several disease entities.
Athletes often exercise beyond the respiratory compensation point (VT2). This may lead to higher VE/VCO2, confounding results and leading to false positives. The absence of normative values for athletic populations remains a stumbling block, making it hard to extrapolate its relevance, especially when all other parameters are within normal limits.
In this prospective cohort study (1), the authors studied 521 athletes who had enrolled in the Massachusetts General Hospital Cardiovascular Performance Program. It was a male dominant population (33% female), aged 38±15 years. Most were endurance athletes (n=330, 63%), completing exercise testing on a treadmill (56%) or cycle ergometer (44%).
A significant proportion (13%) exceeded the prognostic VE/VCO2 threshold of 34. Only 11.4% of the latter group had a VE/VCO2 >34 from the start to aerobic threshold (VT1). Older age, female gender and treadmill testing were associated with higher VE/VCO2, remaining significant in multivariate analysis.
This study highlighted that many athletes had ‘’abnormally’’ high VE/VCO2 when measured across the entire test. This was independent of whether one uses guideline-recommended cut offs (>30, 33%), age/sex specific prediction equations (21%) or prognostically useful thresholds of >34 (13%). A higher VE/VCO2 (>34) for the whole exercise test was more common in athletic individuals when compared with the general population (13% vs 5%), despite a younger age (38±15 vs 54±9).
The data presented by the authors highlight that traditional reference ranges may not suite athletic populations. The marked increase in late exercise minute ventilation (VE) may skew results. VE/VCO2 start to VT1 or VE/VCO2-Nadir are reasonable alternatives in routine clinical practice.
This phenomenon is applicable to most CPET data. General population reference ranges perform poorly in athletic populations. Larger studies are needed to ascertain athletic specific ranges.