Analysis of ventilation profile during six minutes walking test: Preliminary study

Background: The evolution of the Respiratory Therapy has led us to cure the patients with comorbidities and/or chronically ill. Moreover, it has induced us to suspect that the six-minutes walking test (6-MWT) might be maximal for subgroup of patients. Aim: Firstly, verify the percentage of patients of whom the 6-MWT has a maximal trend (6-MWT max) by analyzing their ventilation profile during the test. Secondly, identify the threshold characteristics and predictor parameters of patient’ 6-MWT max. Methods: 97 COPD patients performed forced vital capacity (FVC), forced espiratory volume in 1 sec (FEV1), FEV1/FVC%, maximal voluntary ventilation, inspiratory capacity (CI), minute ventilation (VE) with portable spirometer Spiropalm®, before and immediately after 6-MWT. In the 6-MWT max we calculated the best thresholds using the resampling procedure called “bootstrapping”, in order to discriminate whether the test was a maximal performance or not. The discrimination capability of each threshold was evaluated in terms of accuracy of classification. Results: About 70% of patients recruited achieved a 6-MWT max for symptoms, HR or VE max. About 57% of patients had a maximal performance exclusively from the ventilatory index. The most predictive parameters for a maximal test were: FEV1/FVC < 46% (p < 1x10 -5), FEV1% < 44% (p < 1x10 -5) e MVV < 46.5 (p < 1x10 -5). Conclusion: Preliminary data suggest that FEV1/FVC%, FEV1% and MVV are predictor factors for a maximal performance. The 6MWT may underestimate the real potential of the patient. Instead, it would be more useful to assess, before starting the training, weather the 6-MWT was a maximal test or not.