Therapeutic implications of the pathophysiology of COPD
This review examines 18 studies published > or =30 yrs ago. They show that the earliest manifestation of chronic obstructive pulmonary disease (COPD) is an increase in residual volume suggesting that the natural history of COPD is a progressive increase in gas trapping with a decreasing vital capacity (VC). The reduction in VC forces the forced expiratory volume in 1 s to decline with it. This is aggravated by rapid shallow breathing leading to dynamic hyperinflation. The earlier studies show that this is energetically opposite to a minimal work or force pattern and is responsible for dyspnoea and exercise limitation. This information, available for >30 yrs leads to three virtually untested hypotheses: 1) training patients to breathe slowly and deeply transiently during exercise should decrease the work of breathing, dynamic hyperinflation and improve exercise performance; 2) rapid shallow breathing is caused by alveolar and bronchial inflammation that stimulates non-myelinated vagal C-fibre afferents, which are known to cause this breathing pattern; and 3) if so, therapeutic efforts to block these afferents might restore a slow-deep pattern and be beneficial, particularly in COPD exacerbations.