Asynchronous Thoracoabdominal Movements in Chronic Airflow Obstruction (CAO)

Abstract

Thoracoabdominal movements (TAM) represent two parallel pathways for the distribution of body wall volume displacements. Thoracic and abdominal pathways provide two “degrees of freedom” by which body wall movements accommodate lung volume changes (12). During spontaneous breathing in normal humans, inspiration is the “active phase” of respiration, and expiration is normally passive. Respiratory movements of the thorax and abdominal wall are both driven by the actions of the diaphragm, as well as by muscles intrinsic to each structure. To a useful approximation, abdominal movements reflect directly the movements of the diaphragm in quiet breathing. Thoracic movements may be passive (caused by the action of the diaphragm, using the abdominal contents as a fulcrum to lift the lower rib cage) or active (caused by action of the intercostal and thoracic “accessory” inspiratory and expiratory muscles). During normal quiet breathing, thoracic and abdominal movements are in large part, passive, closely synchronized (in phase), reflecting primarily the action of the diaphragm driving both structures (8). It may be said that TAM during resting breathing are relatively unitary: not only are thoracic and abdominal movements in phase, but their relative amplitudes are nearly constant. This constitutes TAM manifesting only one “degree of freedom,” (despite the potential for utilizing two degrees of freedom).