The lungs of patients with COPD can be hyperinflated both at rest (static hyperinflation) and/or during exercise (dynamic hyperinflation
Pulmonary rehabilitation is an integral component of the management of patients with chronic lung disease, and results in decreased ventilatory requirements and respiratory rate during ambulation, thereby decreasing the risk of developing dynamic hyperinflation
The depth of inhalation, dynamic hyperinflation
, and barotrauma may be important factors in some patients who develop emphysema related to cigarette smoking or other factors, as well.
and auto-PEEP remained clinically unrecognized long after the era of positive pressure ventilation had begun.
Symptom control is achieved predominantly by improving airflow limitation and reducing dynamic hyperinflation
. Airflow limitation is mainly treated with bronchodilators.
This approach has proven clinical utility: it permits the estimation of expiratory flow limitation, the extent of dynamic hyperinflation
, and tidal volume ([V.sub.T]) constraints  (Figure 1(a)).
Many factors may contribute to the sense of dyspnea people with COPD experience during and following exercise including poor physical fitness, (1) hypercapnia, (2) hypoxemia, (3) and dynamic hyperinflation
Forced expiration associated with the increased ventilatory demands of exercise can induce premature airway closure (O'Donnell 1994, Rabe et al 2007) leading to air trapping and dynamic hyperinflation
. Dynamic hyperinflation
contributes to increased elastic and mechanical loads on the inspiratory muscles and to neuroventilatory dissociation which further exacerbate the shortness of breath, leading to exercise intolerance, limited physical activity, and thus to a poor quality of life (Christopher 2006, O'Donnell 1994, O'Donnell et al 2007).
In addition, Heliox (BOC Medical, Priestley Road, Worsley, Manchester M28 2UT, UK) was entrained into the inspiratory limb of the Puritan Bennett ventilator as a strategy to reduce dynamic hyperinflation
and improve gaseous exchange (1,2).
has been identified as a possible mechanism which limits exercise in patients with COPD (O'Donnell and Webb, 1993).
An additional advantage of plotting tidal breaths over the MEFV curve is that dynamic hyperinflation
can be detected as a decreasing IC with exercise ([V.sub.T] curves become shifted to the left, towards TLC).
As mentioned above, the rationale for the potential superiority of interval exercise is that it is associated with a small increase in arterial lactate concentration (less than 4 mmol/L), reduced ventilatory demand (lower ventilation and degrees of dynamic hyperinflation
), (23), (25), (26), (27) and lower symptoms of dyspnea (23), (28) and leg discomfort (22), (27), (28) during the training sessions compared to continuous training.