CHEST INJURIES - Medicine for Mountaineering and Other Wilderness Activities - page 114

CHAPTER 9
CHEST INJURIES
Ben Eiseman, M.D.
Bruce Paton, M.D.
Ernest E. Moore, M.D.
Principal Contributors
Chest injuries are of particular significance because they interfere with the vital function of
respiration. Athighaltitude wheretheoxygencontent ofairislow,chest injuries that would
be of minor consequence at low altitude can be life threatening. In contrast to abdominal in-
juries, for which little can be done in a wilderness setting, a well-informed person can take
steps to increase the chances of survival for individuals with chest injuries.
THE MECHANICS OF RESPIRATION
During inspiration, muscles in the chest wall pull the ribs upward. Simultaneously the dia-
phragm contracts and flattens, expanding the chest and drawing air into the lungs. Expira-
tion, in contrast, is passive and requires no muscular action. Elastic tissue in the lung, which
is stretched as the lung expands during inspiration, retracts and reduces the volume of the
lung during expiration, pushing air out of the chest. (Anatomy of the respiratory system is
described more fully in Chapter 18: Respiratory Disorders . Also see Fig. 9-1 .)
Athin membrane, the pleura, foldsback uponitself andenvelops each lungandthe inner
surface of the rib cage. The potential space between the pleural layers is called the pleural
cavity. Normally the lungs fill the entire thorax and, because negative pressure is generated
in the pleural cavity, the two layers of the pleura remain in intimate contact. There is, there-
fore, no real space in the pleural “cavity” under normal conditions. However, if the chest
wall is perforated or a lung is punctured, air enters the pleural space through the defect and
theelasticityofthelungscausesthemtocollapse.Thisconditionisknownaspneumothorax
(see “ Fractured Rib ”).