To investigate the utility of the breathing reserve index at the lactate treshold (BRiLT), defined as the ratio of the minute ventilation (VE) at LT/maximal voluntary ventilation (MVV= FEV1X40) to differentiate ventilatory (VL) from cardiovascular exercise limitation (CVL).
Prospective determination of BRiLT in 356 consecutive symptom-limited cycle-ergometer tests in 323 patients, 178 men and 145 women, performed between Januari 2000 and December 2003. Tests were considered maximal if a VL, defined as VEmax/MVV >80%, was reached or if a CVL,defined as achieving >80% of the predicted maximum heart rate, or a combination of both was reached. Breath-by-breath expired gas analysis was used and LT was determined non-invasively by the dual-methods approach (V-slope combined with ventilatory equivalents).The cut-off for BRiLT was set at >42% as proposed by Medoff et al. (1).
For all patients, the BRiLT >42% predicted a VL at maximal exercise with a sensitivity of 71% and a specificity of 95%. In the 110 tests performed in 95 COPD patients the sensitivity increased to 82% and the specificity decreased to 92%. The best results were obtained in COPD patients with pure VL. 7/8 had a BRiLT of >42%. However a LT could not be determined in 43% of the COPD patients compared to 15% of the non-COPD patients.
The BRiLT, a variable measured at submaximal exercise, accurately distinguishes COPD patients with and without a ventilatory limitation to exercise but has a poor discriminatory sensitivity in non-COPD patients especially if they attain both a CVL and VL.
The use of the BRiLT is valuable in the interpretation of cardiopulmonary exercise tests in COPD patients who have reduced effort or perform submaximal exertion.
M. Meysman, None.