Effects of portable non-invasive ventilation on exercise tolerance in patients with COPD

Breathlessness is the dominant symptom that limits exercise tolerance in patients with COPD. Several ergogenic approaches have been employed to improve exercise tolerance in this population including bronchodilators, oxygen and heliox supplementation, intermittent exercise and non-invasive ventilation (NIV). Although application of NIV during exercise is beneficial for increasing exercise capacity in patients with COPD, there are several disadvantages that limit its wider application during exercise, including lack of compliance with the equipment, and the time required to set up and supervise the equipment in the setting of pulmonary rehabilitation. Recent advances in technology have facilitated the development of portable non-invasive ventilation (pNIV) devices aiming to alleviate breathlessness during activities of daily living. The VitaBreath (Philips, Respironics) was developed in 2016 as a portable, handheld, battery powered, bi-level, NIV device, providing fixed positive inspiratory and expiratory airway pressure support (IPAP:18 and EPAP: 8 cmH2O, respectively). Accordingly, this dissertation aimed to investigate the physiological effects of pNIV application during controlled laboratory exercise conditions and activities of daily living, in patients with advanced COPD. As the VitaBreath device is no longer commercially available, but similar devices may come to market, the present dissertation provides proof of concept on how pNIV can be applied intermittently during exercise in patients with COPD, and how to select patients most likely to respond to pNIV. This in turn may encourage the development of more suitable devices. Intermittent exercise was chosen to evaluate the effects of pNIV in comparison to the commonly adopted pursed lip breathing (PLB) technique, as this type of exercise allowed regular application of the pNIV device or the PLB technique during recovery periods. Patients retained the device for 3 months to investigate the acceptability, comfort and usability of the device during activities of daily living. Twenty-four COPD patients were randomised to perform two intermittent exercise protocols sustained at different work intensities (60% WRpeak for 6-min and 80% WRpeak for 2-min) alternated with 2-min rest periods. Within each intermittent exercise modality, patients performed two identical exercise tests using either pNIV or the PLB technique in a balanced order sequence, during the recovery phases of intermittent exercise. The findings of this study showed that with both intermittent protocols average endurance time was greater when pNIV was applied compared to PLB. Improvements in exercise tolerance were due to lower degrees of dynamic hyperinflation (DH) and breathlessness with pNIV compared to PLB. An important finding of the aforementioned study was that a subgroup of patients (8/24) failed to show a clinical important improvement in DH with pNIV compared to PLB and did not improve exercise tolerance. Analysis identified that these 8 patients experienced greater resting lung hyperinflation, greater exercise-induced DH and breathlessness, secondary to the adoption of a tachypnoeic breathing pattern with pNIV compared to PLB. Interestingly, these patients also reported less benefit from using the device at home, in terms of anxiety around breathlessness and recovery time from breathlessness. Considering the variation of response reported in the present thesis it is important that clinicians assess the response to pNIV on an individual basis. As with any new method, it was important to appreciate the physiological consequences of the acute application of pNIV on thoracoabdominal volume regulation and respiratory muscle recruitment (assessed by optoelectronic plethysmography), and central hemodynamic responses. Compared to PLB, acute application of pNIV was associated, in the majority of patients, with increased end-inspiratory and end-expiratory rib cage volumes and greater rib cage muscle recruitment, as well as decreased end-expiratory abdominal volumes reflecting reduced expiratory abdominal recruitment. Measurement of cardiac output revealed no adverse circulatory responses with the application of positive airway pressures provided by pNIV during the recovery periods. However, the pattern of thoracoabdominal volume regulation and respiratory muscle kinematics confirmed the findings of the original studies, thereby identifying responders and non-responders to pNIV. Interestingly, responders to pNIV exhibited greater recruitment of the expiratory abdominal muscles compared to non-responders, thereby facilitating them to combat end-expiratory rib cage dynamic hyperinflation effectively. When patients used the VitaBreath device during their daily physical activities, the majority of patients felt less anxious about becoming breathless and felt that their breathlessness recovered faster when using the device at home for 3 months. Moreover, almost all patients used the device at least weekly and all patients rated the ease of VitaBreath use to be between good and excellent. Additionally, most patients felt that using the device had benefited them and that they would recommend the device to other patients. The main disadvantage of the device was reported to be the high cost and its portability. The pNIV method provided fixed IPAP and EPAP. This represents a very important disadvantage of this particular pNIV device, which clearly mitigated the beneficial impact it had on some patients. Future research into pNIV devices should examine how best to identify patients who benefit from a pNIV method in everyday life. On-going development of auto-adjusted ventilators would facilitate a larger fraction of COPD patients to be physically active and experience a better quality of life