Effects of Inspiratory Muscle Training on Shortness of Breath (Dyspnea) and Postural Control in Patients With COPD

The purpose of this clinical trial is to elucidate mechanisms of dyspnea relief and improvements in postural control after inspiratory muscle training (IMT) in patients with COPD.

An endurance cycle exercise test (Constant work rate (CWR) test) will be used to evaluate dyspnea intensity and unpleasantness at comparable breathing efforts, at comparable work rates on the cycle ergometer, before and after IMT. Patients will be performing a CWR test at 75% of the peak work rate achieved during a maximal incremental cardiopulmonary exercise test (CPET). Before, during and after CWR cycling tests patients will rate their intensity of dyspnea, unpleasantness of dyspnea, breathing related-anxiety and leg discomfort using a modified 10- point Borg scale. Patients will be asked to report qualitative descriptors of dyspnea at the end of the CWR cycling test. Maximum duration of the CWR test will be recorded and levels of minute ventilation will be registered continuously throughout the exercise protocol. With this endurance exercise test the investigators will be able to assess changes in the onset of dyspnea (intensity and unpleasantness) and the performance in endurance exercise before and after IMT.

Surface electromyography (EMG), and a multipair esophageal electrode catheter system will be used during CWR exercise to evaluate respiratory muscle recruitment, respiratory effort and neural drive to the different respiratory muscles. The catheter will be inserted to continuously record Pes (esophageal pressure), Pgas (gastric pressure) and EMGdi (electromyogram of the diaphragm muscle). PesMax (maximal esophageal pressure), PgasMax (maximal gastric pressure) and PdiMax (maximal transdiaphragmatic pressure) will be obtained during maximal sniff and cough maneuvers. Transcutaneous surface electromyography (sEMG) techniques will be applied to scalene, sternocleidomastoid and parasternal intercostal muscles to register neural drive to these respiratory muscles. With this measurements, the investigators will be able to assess whether there are any changes in respiratory muscle recruitment patterns and respiratory neural drive to the different respiratory muscles after IMT.

During exercise 'Respiratory Muscle Metaboreflex' will lead to sympathetically mediated vasoconstriction of limb locomotor muscle, less blood and oxygen supply to active limbs muscle there by locomotor muscle fatigue occurred. Quadriceps twitch forces evoked by magnetic stimulation of femoral nerve will be assessed to measure locomotor muscle fatigue at identical exercise time points during CWR test before and after the intervention. With this technique, the investigators will be able to assess whether the onset of locomotor muscle fatigue is delayed after IMT.

An isocapnic hyperpnea trial will be performed to assess respiratory muscle perfusion, dyspnea intensity and unpleasantness, respiratory muscle recruitment pattern, respiratory effort and neural respiratory drive without the work of locomotor muscle before and after IMT. Patients will be asked to maintain a targeted minute ventilation pattern equal to their breathing frequency, tidal volume and minute ventilation recorded at rest and during the final minute of constant load exercise test (at ~75% WRpeak). Experimenters will provide verbal guidance to patients to adjust the rate and depth of their breathing such that the target ventilation will be obtained and maintained constant within ±5%. Isocapnia will be maintained by having subjects inspire from a Douglas bag containing 5% CO2, 21% O2, balance N2 that will be connected to a two-way non-rebreathing valve (model 2700, Hans Rudolph) by a piece of tubing.