The majority of the pleural cavity is filled with the lungs, heart and great vessels. In between the parietal and visceral pleural membranes is the pleural space that is normally filled with serous fluid that allows both pleural membranes to slide past each other easily. A second visceral pleural membrane covers the lungs and other structures lying within the cavity.

The interior wall of the chest cavity is lined with the parietal pleural membrane. Abdominal muscles can also be used during active exhalation, as might occur during periods of severe bronchoconstriction. As breathing difficulty worsens, accessory muscles, such as the sternocleidomastoid and scalene in the neck, contract to elevate the upper portion of the ribcage. The diaphragm and intercostal muscles provide most of the effort of normal breathing, as well as the beginning stages of respiratory distress. The diaphragm will move downward 1-2 cm in normal breathing, but can move up to 10-12 cm (3.9-4.7 inches) with deep inspiration. At rest, the superior position of the diaphragm is at the level of the fifth intercostal space. The thoracic cavity is separated from the abdominal cavity by the diaphragm, a broad structure of muscle and fibrous tissue that is responsible for most of the effort of normal breathing. The rest of the bony structure of the chest includes the clavicles, scapula and the spinal column. Just below each rib lies a bundle of arteries, veins and nerves. In between each rib is an intercostal space, consisting of muscle and connective tissue that, when stimulated by the respiratory center, contracts and pulls the ribs outward. This rather intricate connection of bones and ligaments provide the ribcage with strength, yet provide elasticity to allow the chest cavity to expand and contract during ventilation. In addition, the last two pairs of false ribs are known as floating ribs, as they do not attach to the sternum at all. These are called true ribs, compared to the remaining five pairs of false ribs which do not attach directly to the sternum.

Anteriorly, the first seven rib pairs directly connect to the sternum through cartilaginous attachments. The first rib pair lies just under the clavicles. Twelve pairs of ribs connect posteriorly to the spinal column vertebrae with bands of ligaments that hold them in place. The thoracic or chest cavity is cylindrical in shape, and contains organs of the cardiovascular, respiratory and gastrointestinal systems. Together they make up almost 20 percent of all major trauma cases. The most common causes of penetrating trauma are from stabbing and gunshots. The most common cause of blunt force chest injuries is the motor vehicle crash, accounting for 70-80 percent of such injuries. Approximately 16,000 deaths occur from chest trauma annually. Over 100,000 people die from trauma every year in the U.S. It is critical that EMS providers rapidly recognize and, when necessary, treat and transport chest injuries without delay. Chest injuries range from minor abrasions and contusions, to major blunt and penetrating traumatic events that cause compromise to the airway, breathing and/or perfusion. The thoracic, or chest area of the body contains major organs and structures essential to human survival and well-being. Jugular venous distention was noted, and radial pulses were weak and thready. Auscultation of the chest revealed near-absent lung sounds over the right side. The pulse oximeter provided an initial reading of 79 percent on room air. As they disrobed the patient, they determined that the patient was dyspneic, with rapid breathing. Under the bright lights of the patient care compartment, the crew noted the man was neatly dressed, although his jacket was torn and his shoes were missing. With resignation, the medics lift the patient onto their gurney and wheeled him into their unit. The man responded by grunting and feebly trying to push them away. Knowing that the area is frequented by homeless people, the crew made an attempt to awaken him, first verbally and then with a painful stimulus. At 0200 hours Medic 772 is dispatched for a report of a “man down.” The crew arrives to find a young male on the sidewalk, apparently sleeping and lying on his side.

Lungs sound like rice krispies