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Nonpharmacological modulation of dynamic hyperinflation

CORRESPONDENCE: E. F. M. Wouters, Dept of Respiratory Medicine, University Hospital Maastricht, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands. Fax: 31 433875051. E-mail: e.wouters{at}lung.azm.nl

Expiratory flow limitation is the pathophysiological hallmark of chronic obstructive pulmonary disease (COPD), but dyspnoea is the most prominent and distressing symptom. Acute dynamic hyperinflation (DH), which refers to the temporary increase in operating lung volumes above their resting value, is a key mechanistic consequence of expiratory flow limitation and has serious mechanical and sensory consequences. In flow-limited patients, pharmacological interventions using bronchodilating agents act by improving dynamic airway function: enhancing lung emptying and reducing lung hyperinflation. Besides bronchodilators, other factors that reduce the ventilatory demand at a given level of exercise or interventions that aim to improve lung emptying or to reduce resting levels of hyperinflation decrease the rate of development of DH in COPD patients. The different nonpharmacological intervention strategies that aim to reduce lung hyperinflation are summarised in the present article, as well as the different underlying mechanisms contributing to lung deflation. The following interventions are systematically reviewed in the present article: breathing supplemental oxygen or low-density gas mixtures of helium and oxygen, pulmonary rehabilitation and noninvasive positive pressure ventilation. Pulmonary rehabilitation and noninvasive pressure ventilation reduce the DH; the effects of heliox-breathing and hyperoxia are more variable. These nonpharmacological interventions have importantly contributed to the present understanding of the role of hyperinflation in COPD patients.

KEYWORDS: Chronic obstructive pulmonary disease, heliox breathing, hyperinflation, hyperoxia, noninvasive ventilation, pulmonary rehabilitation