Assisted ventilation as an aid to exercise training: a mechanical doping?

Exercise training as a part of multidisciplinary pulmonary rehabilitation can improve both exercise tolerance and health-related quality of life in patients with chronic obstructive pulmonary disease (COPD) 1. The following physiological changes contribute to these improvements: reduction of lactic acidosis; minute ventilation and heart rate for a given work rate; and enhanced activity of mitochondrial enzymes and capillary density in the trained muscles. Intensity of exercise training is of key importance. High-intensity training has improved both maximal and submaximal exercise tests and has induced both cardiorespiratory and peripheral muscle adaptations 2. Nevertheless, in patients with severe COPD, extreme breathlessness and/or peripheral muscle fatigue may prevent higher levels of intensity training. As a consequence of flow limitation, in order to cope with the increased ventilatory demands of exercise, these patients show a breathing pattern that ultimately places greater demands on their inspiratory muscles. Indeed, in these patients, a pattern of low tidal volume and high-frequency breathing is unlikely to be advantageous, but it is the only pattern available in the presence of expiratory flow limitation and dynamic hyperinflation. Increased inspiratory muscle work may contribute to dyspnoea and exercise limitation in such patients, even before their ventilatory ceiling is attained. To the extent that intrinsic mechanical loading and functional inspiratory muscle weakness in COPD contribute to dyspnoea, assisted ventilation should provide symptomatic benefit by unloading and assisting such overburdened ventilatory muscles. Reducing exercise dyspnoea by assisted ventilation might allow for higher levels of exercise intensity. Several studies have examined the acute effects of different modalities of ventilatory assistance on dyspnoea and exercise tolerance in advanced COPD. The message of these physiological studies could be summarised as follows: assisted ventilation delivered as noninvasive positive pressure ventilation (NPPV), either as continuous positive airway pressure (CPAP), inspiratory pressure support (IPS) or proportional assist …