During the isotime, we observed a reduction in DH represented by a higher IC under PLB
than in CB in IMPROVER. In this subgroup, the increase in IC was correlated with the increase in
endurance time obtained with PLB and with the decrease in dyspnoea intensity. These findings
demonstrate that the reduction in DH is one of the factors that contributed to the increase in exercise
tolerance during PLB in these patients (Figure 1). Another factor that may have contributed to the
improvement in exercise tolerance is the higher SpO2 in patients under PLB. The improvement in
blood oxygenation in patients that exhibit impaired gas exchange and oxygenation limits may
contribute to a reduction in the stimulation of peripheral chemoreceptors (loss of the hypoxic
stimulus) and a reduction in the production of lactic acid by the muscles. As a result, ventilatory
demand falls and exercise tolerance increases. Improved blood oxygenation at rest was reported by
several authors but only Faager et al.16 described a reduction in oxygen desaturation under PLB
during exercise. Our study confirms these findings both at rest and during highintensity
exercise in the total group and in IMPROVER subgroup.