Patients with chronic airflow obstruction (CAO) frequently develop abnormal thoraco-abdominal excursion, but the patterns described are inconsistent and the factors that relate to their development remain unknown. We studied 45 stable patients with FEV1 ranging from 0.36 to 2.1 L. A pattern of ventilatory muscle recruitment (VMR) was established by simultaneously measuring gastric (Pg) and pleural (Ppl) pressures and rib cage (Vrc) and abdominal (Vab) volume displacement with inductance plethysmography. From these tracings, Pg-Ppl plots were constructed and the delta Pg/delta Ppl values were calculated. The delta Pg/delta Ppl was validated in 15 patients with simultaneous analysis of Vab-Pg plots. Pearson's test and multiple regression analyses were used to correlate delta Pg/delta Ppl to factors thought to influence respiratory muscle function such as age, sex, nutritional status (weight/height, albumin), hyperinflation, airflow obstruction, and arterial blood gases. We found a direct correlation between a more positive delta Pg/delta Ppl value and increasing hyperinflation (r = 0.69, p less than 0.0001), increasing airflow obstruction (r = -0.55, p less than 0.001), and decreasing diaphragmatic strength (r2 = 0.32, p less than 0.001). We also found that expiratory Ppl became more positive with decreasing FEV1 (r2 = 0.33, p less than 0.001). This change in VMR was independent of age, sex, nutritional status, and arterial blood gas determinations.(ABSTRACT TRUNCATED AT 250 WORDS)