Alteration in breathing pattern with progression of chronic obstructive pulmonary disease

We examined the relationship between breathing pattern and severity of disease in patients with chronic obstructive pulmonary disease (COPD). Resting breathing pattern was recorded for 45 min using the respiratory inductance plethysmograph (RIP) in 22 patients with stable COPD. Six subjects (moderate group) had FEV1 25 to 50% predicted, 8 subjects (severe group) had FEV1 less than 25% predicted, and 8 subjects (respiratory failure group) had FEV1 less than 25% predicted and were hypoxemic. Seven of the subjects with respiratory failure were also hypercapnic. Subjects with respiratory failure were studied with and without supplemental O2. All subjects were studied in the seated position. There were no significant differences in breathing pattern between the moderate and severe groups. Tidal volume (VT) was 120 ml lower in the severe group, but breathing frequency (f) was slightly elevated, allowing minute ventilation (VI) to be maintained. The respiratory failure group demonstrated a significant decrease in VT compared with that in the moderate group and a significant decrease in VT/TI as compared with both moderate and severe groups; TI was unchanged in subjects with respiratory failure, and, as f did not increase significantly, VI was decreased. Acute relief of hypoxemia had no effect on breathing pattern in respiratory failure. Variability was assessed by comparing the coefficients of variation for each timing component. There was no difference in intraindividual variability of breathing pattern between all groups. These results suggest that changes in ventilatory control as reflected by breathing pattern are to some extent independent of mechanical abnormalities.