Not only did Ti/Ttot decrease during the course of threshold breathing training, but this training led to substantial improvements in maximum inspiratory pressure, training pressure, and the work and pressure-time integral of threshold breathing. These improvements leave little doubt that IMT did train the inspiratory muscles of our patients.
We cannot exclude the possibility of improvement in inspiratory muscle performance being due to placebo effects of the training device or frequent contact with a physiotherapist.
Our control patients were not submitted to sham training or to training on a very low threshold load, and only restricted measurements were made in this group. Furthermore, they were recruited after increases were observed in the training group, and we may have been biased against detecting improvement in the control subjects. However, the trainees showed no improvement in 12 MWD, which is subject to motivational factors, nor in cycle exercise performance, which may also improve due to placebo factors. fully
Furthermore, it is unlikely that a decrease in lung volume accounted for the increase in inspiratory pressures in the training group. No consistent trend was observed in the four patients in whom lung volumes were measured.
Despite marked improvement in inspiratory performance, we observed no change in MSBC, maximum ventilation, or oxygen uptake during exercise, or in overall exercise performance as assessed by 12 MWD. The failure of the training-induced reduction of Ti/Ttot to occur during exercise may well be relevant to the absence of improved exercise tolerance. The rationale for supposing that IMT might lead to an improved exercise performance is based on the assumption that minute ventilation and breathing pattern during exercise are going to be appropriately altered by inspiratory muscle training. A reduced inspiratory time, achieved by increased inspiratory flow, would allow greater time for expiration, and therefore allow an increased exercise maximum ventilation to be achieved without any change in lung mechanics.
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