[Relationship between expiratory muscle dysfunction and dynamic hyperinflation in advanced chronic obstructive pulmonary disease].

BACKGROUND AND OBJECTIVES: Dynamic hyperinflation (DH) and expiratory flow limitation (EFL) are physiologically linked and seem to be involved in the genesis of dyspnea and the quality of life (QL) impairment in chronic obstructive pulmonary disease (COPD). Advanced COPD patients often show expiratory muscles dysfunction that could be involved in DH development.

AIM: Study the relationships between expiratory muscle dysfunction and DH, and their association with dyspnea and QL, in advanced COPD.

PATIENTS AND METHODS: In 25 patients we measured lung function, exercise capacity (incremental ergometry and walking test), EFL and end-expiratory lung volume (EELV) at rest and during exercise, respiratory muscles strength and endurance, dyspnea and QL (Saint George Respiratory Questionnaire, SGRQ).

RESULTS: The patients (mean FEV(1)=31% predicted) showed a moderate decrease of respiratory muscles strength and endurance. Nineteen patients exhibited EFL at rest and 24 at 70% of maximal workload (W(max)). The EELV increased from rest to 70% W(max) (9% of predicted FVC). At 70% W(max) EELV correlated inversely with the EFL amount (rho=-0.42), the inspiratory and expiratory muscles endurance (rho=-0.43 and -0.42 respectively) and y VO(2max) (rho=-0.52). The EELV increase from resting to 70% W(max) correlated with dyspnea (rho=0.53) and the amount of EFL at 70%W(max) with the activity score of SGRQ. The FEV(1,) expiratory muscles endurance and LFE amount were independent predictors of EELV at 70% W(max).

CONCLUSIONS: In advanced COPD a poorer expiratory muscles endurance is related with higher DH during exercise (and lower EFL), which is correlated with higher dyspnea and worse QL.