Determining the role of exercise in patients with chronic pulmonary disease.

Chronic pulmonary diseases are common in the community and their pathophysiology is complex. The principal symptoms are dyspnea and limited exercise capacity. Some, but not all, patients have true ventilatory limitation where the maximal exercise ventilation (VEmax) equals the measured maximal ventilatory volume (MVV). Those with obstructive disease have impeded expiration requiring an obligatory expiratory time for adequate lung emptying (i.e., a timing constraint). In these patients, increased breathing frequency during exercise tends to lead to hyperinflation and smaller tidal volumes, circumstances that predictably worsen breathing efficiency (i.e., result in high VD/VT). Those with restrictive disease characteristically have limited inspiratory capacity but unimpeded or even accelerated expiration (i.e. tidal volume constraint). These patients characteristically exhibit rapid respiratory rates (e.g., > 50.min-1) at end exercise.