[Blood lactate three minutes after a graded exercise test: a criterion of maximal exercise in patients with COPD]

The graded exercise test (GXT) is used to measure the exercise capacity of patients with chronic obstructive pulmonary disease (COPD). To do this GXT must be maximal (exhaustive). However, the value of the blood lactate at the GXT endpoint [La(-)max] or after a recovery period of three minutes [La(-)recovery], to confirm that the GXT is maximal, remains controversial. The purpose of the present study is to determine a threshold of [La(-)max] and/or [La(-)recovery], which confirms the exhaustiveness of GXT in patients with COPD.

Thirty-six patients with COPD performed a GXT until exhaustion on a cycle ergometer. During the GXT cardiorespiratory parameters, [La(-)max] and [La(-)recovery] were measured. When at least three out of five of the most frequently used criteria to confirm exhaustion were met, GXT was considered as maximal. Conversely, GXT was considered as sub-maximal when less three criteria were observed. The receiver operating characteristic (ROC) curves were analyzed.

For [La(-)max] the areas under the ROC curve and the areas under the diagonal were not significantly different (P=0.16). For [La(-)recovery] the ROC curve inflected itself at 5.8mmol/L (sensitivity=0.92 and specificity=0.56).

It was not possible to use [La(-)max] to confirm exhaustion in our population. However, [La(-)recovery]<5.8mmol/L may help to confirm non-exhaustion during GXT in patients with COPD. Below this blood lactate threshold 93% patients performed a sub-maximal GXT.