Inspiratory muscle training in clinical practice. Physiologic conditioning or habituation to suffocation?

Six healthy volunteers and 19 patients with stable chronic obstructive pulmonary disease underwent a multistage, maximal, ventilatory stress test, ie, serial imposition of increasingly severe resistances to inspiration by means of a commercially available device (Pflex Inspiratory Trainer). Patients consistently underventilated and suffered desaturation during the test; healthy individuals did not. Eight patients completed three weeks or more of daily training stints using the inspiratory resistive device. There was no significant improvement in performance of the test after training. Those individuals whose condition improved showed no discernible change in ventilatory pattern but did suffer further desaturation.