ABSTRACT
During normal inspiration, when the diaphragm and external intercostal m uscles o f t he r ibcage c ontract, e xpansion o f t he internal d imensions o f t he t horax d raws t he v isceral p leural membrane outwards, thus stretching open the lungs. is results in the creation of subatmospheric pressure within the chest; air moves into the lungs to equilibrate pressure. E ective inspiration is t hus rel iant on t he integrity of neural control mechanisms a nd t he s tructural c haracteristics o f t he c hest w all. Musculoskeletal disease and other factors that a ect chest wall mechanics can have a large impact on the function of the respiratory system (e.g., preterm neonates have compliant chest walls that tend to retract, rather than expand, during diaphragmatic contraction). Rel axation o f t he i nspiratory m uscles re sults i n passive recoil of the lungs and chest wall, and causes expiration. During exercise or forced expiration, contraction of the expiratory m uscles ( the i nternal i ntercostals o f t he r ibcage a nd t he muscles of the abdominal wall) generates a positive intrathoracic pressure, thus forcing air from the lungs.
