Principles of Respiratory Mechanics and Clinical Correlations

Abstract

During the past 50 years, there have been a number of studies investigating the relationship of forced expiratory volume in the first second (FEV₁) to exercise tolerance and chronic (MRC) dyspnoea in chronic obstructive pulmonary disease (COPD) patients. Because poor correlations were usually found, it was concluded that: a) lung function impairment is a poor predictor of both exercise capacity and dyspnoea; b) the degree of airway obstruction, dyspnoea and exercise curtailment are independent markers of COPD severity; and c) factors other than lung function impairment (e.g. deconditioning and peripheral muscle dysfunction) play a predominant role in limiting exercise capacity in patients with chronic airway obstruction. Recent work, however, suggests that: a) the main cause of exercise intolerance and dyspnoea is dynamic pulmonary hyperinflation (DH) due to tidal expiratory flow limitation; and b) the inspiratory capacity (IC) and FEV₁/ forced vital capacity (FVC), which reflect DH at rest and during exercise, are more powerful predictors of exercise intolerance than FEV₁.