Cardiopulmonary exercise testing: does a learning effect exist in vascular patients?

Anaerobic threshold, as judged by cardiopulmonary exercise testing (CPX), is a well documented measure of fitness before major surgery. Using CPX in a surgical population, it has been shown that a reduced anaerobic threshold is associated with an increased mortality rate [1]. Exercise improves fitness and as with most exercise tests individuals may display a learning phenomenon with repeated tests i.e. as patients become more familiar with the test the results obtained can improve. It is therefore important to eliminate this learning effect, with repeat CPX testing, so that improvements in anaerobic threshold can genuinely be attributed to improved patient fitness. Our group felt that it was important to establish if a learning effect exists before assessing the impact of an exercise prescription on the anaerobic threshold. Our aim was to assess the effect of repeat CPX testing on the anaerobic threshold. Sixteen patients with abdominal aortic aneurysms under surveillance (< 5.5 cm diameter) were recruited to this prospective observational study. They underwent CPX testing four times over a six-week period, in weeks 1, 2, 3 and 6 (tests 1, 2, 3 and 4, respectively). It was performed to a standardised protocol, by the same investigators, and at the same time of day, to eliminate possible factors affecting variation. A change in anaerobic threshold of >4 ml.kg.min was regarded as a significant result. Statistical analysis was performed using SPSS v13. The results of tests 1 and 3 were compared to analyse if a learning effect occurs, with tests 3 and 4 then compared to analyse if any learning is subsequently lost (using the two-tailed paired t-test). The results are presented in Table 1 and show that there was no significant change in anaerobic threshold between tests 1 and 3, or tests 3 and 4. Our results demonstrate that a learning effect does not exist for the patient population studied. This data also show that anaerobic threshold measurement is highly reproducible, making it a good objective measure of cardiopulmonary function.