Is measuring ventilation during the six minutes walking test (6MWT) important?

Background: 6MWD and FEV1 are used as a one-time measure of functional status, as predictors of morbidity and mortality, and for measuring the response to medical interventions. The additional value of ventilation (VE) monitoring during the 6MWT is unknown. Aim: Evaluation of VE during the 6MWT and it's correlation with the validated parameters (6MWD and FEV1). Method: Patients (P) and healthy subjects (H) performed two standard 6MWT (S6MWT) and one 6MWT with VE monitoring (V6MWT), at minimum 1 hour intervals. The inspiratory capacity (IC) was measured before and after the V6MWT. VE profile and correlations between parameters were assessed. Results: 23P (15 COPD cases) and 5H performed the tests. The baseline VE did not correlate with FEV1 and 6MWD nor with the baseline or end-of-test IC. Most subjects reached a VE plateau within the first 3 minutes of the test. The time to a stable VE did not correlate with the V6MWD or FEV1, but with baseline IC (r 0.428). The peak VE, as well as the difference between initial and final (delta) VE, did however significantly correlate with FEV1 (r 0.696 and 0.686 respectively) and 6MWD (r 0.515 and 0.476 respectively). Strong correlations were found between FEV1, V6MWD and baseline and end-of-test IC (r > 0,7), but not with the delta IC. The correlation of ventilatory parameters (IC, peak VE, delta VE) with the 6MWD was proven to be FEV1 dependent as, when controlled for FEV1, these correlations did not remain significant. Conclusions: Some ventilatory parameters measured during the 6MWT did correlate with the 6MWD and FEV1. The importance of VE profile evaluation during the 6MWT needs further assessment.