Respiratory muscle insufficiency in acute respiratory failure of subjects with severe COPD: treatment with intermittent negative pressure ventilation.

Nine subjects with severe chronic obstructive pulmonary disease (COPD) in acute respiratory failure (ARF) and with marked weakness of the respiratory muscles (Group A) underwent intermittent negative pressure ventilation by means of an iron lung (8 h daily for 7 days). Seven subjects with COPD in stabilized chronic respiratory failure (Group B) were studied as controls and submitted to the same medical therapy without ventilator treatment. Functional respiratory tests were performed before and after 7 days of treatment. After ventilatory treatment, Group A showed an increase of maximum inspiratory pressure (PImax), maximum expiratory pressure (PEmax), vital capacity (VC), arterial oxygen tension (PaO2), pH and a decrease of residual volume (RV), total lung capacity of (TLC) and arterial carbon dioxide tension (PaCO2) (all statistically significant). No improvement was ascertained in the functional parameters of Group B. The expiratory muscles seem to play a determining role in ARF. We conclude that the iron lung is a useful therapeutic defence in removing muscular fatigue and in restoring a good level of respiratory compensation of ARF in severe COPD.