Effect of Portable NIV on Operational Chest Wall Volumes in COPD

The VitaBreath (Philips, Respironics) is a portable, handheld, battery powered, non-invasive ventilation device, that has been shown to reduce activity-related shortness of breath in patients with COPD. The VitaBreath device delivers 18 cmH2O inspiratory and 8 cmH2O expiratory pressures, but can only be used during recovery periods. A previous study (REC: 17/NE/0085) showed that use of the VitaBreath device during the recovery periods interspersing successive exercise bouts enhances exercise tolerance and reduces breathlessness compared to pursed lip breathing in patients with COPD. This was attributed to faster recovery from exercise-induced dynamic hyperinflation, assessed by volitional inspiratory capacity manoeuvres using a spirometer. However, inspiratory capacity manoeuvres are effort dependent, thus limiting the number of repetitions the patient can perform during exercise. In addition, investigation of the direct effect of the application of the VitaBreath device on dynamic hyperinflation was not possible due to the need to employ a spirometer for assessing inspiratory capacity. Optoelectronic plethysmography (OEP) allows continuous non-invasive assessment of end-inspiratory and end-expiratory volumes of the thoracoabdominal wall and its compartments, thereby facilitating assessment of dynamic hyperinflation on a breath-by-breath basis without the necessity to breathe via a spirometer. Unfortunately, OEP technology was not available at the time of our previous study. The investigators will use OEP to provide accurate breath-by-breath volume measurements during exercise and recovery to evaluate whether the VitaBreath device reduces total and compartmental thoracoabdominal wall volumes compared to the pursed lip breathing technique. Furthermore, the investigators will investigate the effect of use of the VitaBreath device on respiratory muscle activation and respiratory muscle oxygenation using OEP technology in conjunction with electromyography (EMG) and near inferred spectroscopy (NIRS), respectively to appreciate how the application of the VitaBreath device impacts on the operation and energy demands of the respiratory muscles as compared to control pursed lip breathing. The investigators hypothesised that the use of the VitaBreath device during the recovery periods interspersing successive exercise bouts will reduce the magnitude of dynamic hyperinflation in a greater extent compared to the pursed lip breathing technique.