The chest wall is a critical component of the respiratory pump. Diseases that alter the structure of the chest wall affect the function of the pump, and may result in respiratory compromise or failure. The components of the chest wall include the bony structures (ribs, spine), respiratory muscles, and nerves connecting the central nervous system with the respiratory muscles.
Chest wall structure and physiology and diseases that affect the bony portion of the chest wall will be reviewed here. Included are discussions of the following conditions:
- Ankylosing spondylitis
- Congenital deformities, including pectus excavatum
- Flail chest
- Abdominal processes, including morbid obesity and ascites
- Chest wall tumors
The various forces acting upon the mechanical structure of the chest wall play a major role in determining lung volume, and chest wall abnormalities can have a significant impact on lung function. Abnormalities of the bony structures of the chest wall and abdominal processes that affect respiration will be reviewed here. Diseases affecting chest wall nerves and muscles are discussed separately. (See "Respiratory muscle weakness due to neuromuscular disease: Clinical manifestations and evaluation" and "Respiratory muscle weakness due to neuromuscular disease: Management" and "Respiratory physiologic changes following spinal cord injury".)
NORMAL STRUCTURE AND FUNCTION
The rib cage and vertebral column form the boundaries of the chest wall superiorly and laterally, while the diaphragm constitutes the inferior component. Changes in the intra-abdominal contents or compliance of the abdominal wall alter the mechanical properties of the chest wall through their effects on the motion of the diaphragm. The external boundary of the lower chest wall is the lower border of the rib cage, but internally, this boundary overlaps with the diaphragm, which covers as much as one-half of the rib cage at residual volume (RV). By virtue of this "zone of apposition" between the diaphragm and the ribs, the rib cage is exposed both to abdominal and pleural pressures, such that the normal function of the chest wall depends on the intricate interaction of the two spaces.