Abnormal thoraco-abdominal movements have been used to infer disturbances of respiratory muscle actions for more than a half century. The present chapter reviews some significant advances in analysis of respiratory muscle action, focusing largely on human studies. We review a particular contribution of neuroscience: the integration of neurophysiological principles into conventional mechanical analyses. This integration has led to our present understanding of abnormal thoraco-abdominal movements in humans. While earlier qualitative interpretations emphasized descriptions of respiratory muscle ‘disco-ordination’ or ‘asynchrony’, the present discussion develops a new perspective of co-ordinated thoraco-abdominal movements in patients with chronic lung disease (chronic airflow obstruction, CAO). We conclude that apparently abnormal thoraco-abdominal movements are accounted for by passive motions and/or local non-uniformities of thoracic or abdominal movements which occur in the context of well co-ordinated neural commands to the various respiratory muscles.

Early descriptions of respiratory muscle actions were based on visual observation of patients. While mechanical measurements of respiratory pressure and volume changes significantly improved clinicians' understanding of respiratory muscle action, it was uniquely the inclusion of neurophysiological measurements done simultaneously with mechanical studies which yielded more comprehensive advances in understanding. Important mechanical studies were contributed by several workers (Rahn et al., 1946; Campbell & Green, 1955; Campbell, 1958; Agostoni & Rahn, 1960; Agostoni & Mognoni, 1966; Grimby, Bunn & Mead, 1966). Significant studies which provided the neurophysiological infrastructure for analysis of respiratory muscle actions appeared during the 1950s and 1960s (Campbell & Green, 1953a, b; Petit, Milic-Emili & Delhez, 1960; Taylor, 1960; Delhez & Petit, 1966; Sears & Newsom-Davis, 1968).