ABDOMINAL MUSCLE RECRUITMENT AND PEEPI DURING BRONCHOCONSTRICTION IN CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Background - It has been recently shown that, when breathing at rest, many patients with severe chronic obstructive pulmonary disease (COPD) contract abdominal muscles during expiration, and that this contracti on is an important determinant of positive end expiratory alveolar pre ssure (PEEPi). In this study the effects of acute bronchoconstriction on abdominal muscle recruitment in patients with severe COPD were stud ied, together with the consequence of abdominal muscle action on chest wall mechanics. Methods - Breathing pattern, pleural (PPL) and gastri c (PGA) pressures, and changes in abdomen anteroposterior (AP) diamete r were studied in 14 patients with COPD (mean forced expiratory volume in one second (FEV1) 1.06 (0.08) 1) under control conditions and duri ng histamine-induced bronchoconstriction. Results - The analysis of pl ots of PGA versus the AP diameter of the abdomen revealed that during maximal bronchoconstriction (decrease in FEV1 of 34.8% (95% confidence intervals (CI) 29.9 to 39.7)) the expiratory rise in PGA increased si gnificantly whereas end expiratory abdomen AP diameter decreased, indi cating marked abdominal muscle recruitment. As a consequence, the rib cage compartment accounted for all of the volume of hyperinflation dur ing bronchoconstriction (mean value 0.66 1, 95% CI 0.49 to 0.83). Posi tive end expiratory alveolar pressure during progressive bronchoconstr iction was related directly to the expiratory rise in PGA and inversel y to the expiratory time. Conclusions - The results indicate that, in patients with severe COPD, the abdominal muscles are recruited during acute bronchoconstriction. This recruitment probably preserves diaphra gm length at the beginning of inspiratory muscle contraction despite t he hyperinflation, and contributes significantly to positive end expir atory alveolar pressure. The degree of dynamic pulmonary hyperinflatio n during bronchoconstriction can be overestimated if abdominal muscle contraction is not assessed.