Both scalar tracings and XY plots of rib cage (RC) and abdominal (AB) excursions were analyzed to detect asynchronous and/or paradoxic motion of one compartment with respect to the other in an effort to distinguish differences between normal subjects and patients with chronic obstructive pulmonary disease (COPD). An inspiratory asynchrony index (IAI) was obtained by connecting a straight line from beginning inspiration to end inspiration of the RC-AB loop, and dividing the area enclosed by the inspiratory portion by the tidal volume. In like manner, an expiratory asynchrony index (EAI) was computed. Values of IAI and EAI in the supine posture were greater in patients with COPD than in normal subjects, and such differences were consistently demonstrated during natural and voluntarily controlled abdominal breathing. Paradoxic motion as percent of volume or time period of inspiratory and expiratory compartmental excursions was indicated when RC or AB compartments moved in an opposite direction to the sum of the two. During natural breathing, paradoxic motion was almost absent in normal subjects and variably present in patients with COPD. Voluntarily controlled breathing patterns produced increased IAI, EAI, and paradoxic motion. Passive tilting from supine to the upright posture did not affect indexes in normal subjects but reduced asynchronous and paradoxic motion of the RC in patients with COPD. Other indexes of loop analysis, such as phase angle and maximal compartment amplitude/tidal volume, were not as consistent in distinguishing between normal subjects and patients with COPD during natural and voluntarily controlled breathing patterns.(ABSTRACT TRUNCATED AT 250 WORDS)