Locations on the Chest. Be familiar with general anatomic terms used to locate chest findings, such as:
Supraclavicular—above the clavicles Infraclavicular—below the clavicles Interscapular—between the scapulae Infrascapular—below the scapula Bases of the lungs—the lowermost portions Upper, middle, and lower lung fields
You may then infer what part(s) of the lung(s) are affected by an abnormal process. Signs in the right upper lung field, for example, almost certainly originate in the right upper lobe. Signs in the right middle lung field laterally, however, could come from any of three different lobes.
The Trachea and Major Bronchi. Breath sounds over the trachea and bronchi have a different quality than breath sounds over the lung parenchyma. Be sure you know the location of these structures. The trachea bifurcates into its mainstem bronchi at the levels of the sternal angle anteriorly and the T4 spinous process posteriorly.
The Pleurae. The pleurae are serous membranes that cover the outer surface of each lung, the visceral pleura, and also line the inner rib cage and upper surface of the diaphragm, the parietal pleura. Their smooth opposing surfaces, lubricated by pleural fluid, allow the lungs to move easily within the rib cage during inspiration and expiration. The pleural space is the potential space between visceral and parietal pleurae.
Breathing. Breathing is largely an automatic act, controlled in the brainstem and mediated by the muscles of respiration. The dome-shaped diaphragm is the primary muscle of inspiration. When it contracts, it descends in the chest and enlarges the thoracic cavity. At the same time it compresses the abdominal contents, pushing the abdominal wall outward. Muscles in the rib cage and neck expand the thorax during inspiration, especially the parasternals, which run obliquely from sternum to ribs, and the scalenes, which run from the cervical vertebrae to the first two ribs.
During inspiration, as these muscles contract, the thorax expands. Intra-thoracic pressure decreases, drawing air through the tracheobronchial tree into the alveoli, or distal air sacs, and expanding the lungs. Oxygen diffuses into the blood of adjacent pulmonary capillaries, and carbon dioxide diffuses from the blood into the alveoli.
After inspiratory effort stops, the expiratory phase begins. The chest wall and lungs recoil, the diaphragm relaxes and rises passively, air flows outward, and the chest and abdomen return to their resting positions.
Normal breathing is quiet and easy—barely audible near the open mouth as a faint whish. When a healthy person lies supine, the breathing movements of the thorax are relatively slight. In contrast, the abdominal movements are usually easy to see. In the sitting position, movements of the thorax become more prominent.
During exercise and in certain diseases, extra work is required to breathe, and accessory muscles join the inspiratory effort. The sternomastoids are the most important of these, and the scalenes may become visible. Abdominal muscles assist in expiration.
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