Respiration is gas exchange at both a tissue level (through the blood stream) and with the external environment (by the mechanical act of breathing). Diaphragmatic contraction, expanding the capacity of the thoracic cavity, is essential for inspiration. The upper ribs are fixed by the scalene muscles, and the intercostals and levator costae muscles approximate and elevate the ribs, further increasing the chest capacity (table 1).

By fixing the upper limbs, e.g. by gripping the head of the bed, the muscles of the neck and shoulder girdle can become accessory muscles of respiration.

Table 1 Muscles of the Thorax

Expiration is by diaphragmatic relaxation, and recoil of the lungs and rib cage. It can be accentuated by contraction of the abdominal wall muscles, as in coughing and straining.

The upper airway is usually through the nose (page 27) and the naso- and oropharynx, into the larynx and trachea, but breathing may also be through an open mouth, particularly if the nose is blocked, and in deep breathing, as after severe exercise or in pulmonary disease. Mouth breathing is also required when you are listening to the chest, to allow the rapid intake of large breaths

The larynx is a tube between the pharynx and the trachea. It protects the tracheal inlet in swallowing and contains the vocal cords for vocalisation. It is surrounded by a number of cartilages; the lowest, the cricoid, is the only complete cartilaginous ring in the respiratory passage, adding stability and maintaining an open airway. The thyroid cartilage has two laminae that meet anteriorly in V shaped fashion, the apex producing the prominent Adam’s apple of the male (page 65). The vocal folds are attached behind the apex. The posterior end of each fold is attached to the muscular process of an arytenoid cartilage, the two arytenoids rest on either side of the posterosuperior border of the cricoid. Movement at the joints, between the arytenoid and cricoid cartilages, allows widening of the opening between the vocal folds (rima glottides), either in a V or a diamond shape, thus adjusting the airflow between them. The joints between the inferior horns, at the back of the thyroid laminae, and the cricoid cartilage allow adjustment of the length and tension in the vocal folds, altering the pitch of the emitted sound.

The epiglottis is also attached to the back of the V of the thyroid cartilage and extends upwards. The laryngeal opening is closed during swallowing, by a combination of raising the larynx and pulling down the epiglottis towards it. This upward movement of the larynx can be observed by asking a subject to swallow (page 65), or watching your own larynx in a mirror; it is easier to see in the male because of the Adam’s apple.

The trachea descends from the larynx through the lower neck into the thorax. It divides at the level of the manubriosternal joint into right and left main bronchi; these enter the hilum of each lung, together with a pulmonary artery, two pulmonary veins and surrounding lymphatics.

In development, the pleural cavity on each side starts as an empty epithelial lined space, but the lung pushes into it from the medial side, like a fist into a balloon (letting out most of the air in the process!). The lining on the outside remains attached to the chest wall as the parietal pleura. The evaginated medial wall remains, separating the pleural cavity from the mediastinum, but the expanding lung takes with it a covering of visceral pleura that is continuous with the mediastinal pleura around the lung root (hilum). The cavity remains only as a potential space, the parietal and visceral pleura are in contact, a little fluid lubricating the surfaces to aid movement of the expanding and collapsing lung, during respiration.

The surface markings of the parietal pleura can be remembered from what happens on the even numbered ribs (figure 4). The apex of the lung domes upwards within the circumference of the first rib, to about 2 cm above the level of the clavicle. From here the pleura on the two sides, passes medially and they meet opposite the second costal cartilage. At the fourth, the pleura on the left is pushed laterally by the developing heart (costomediastinal pleural recess). At the level of the sixth costal cartilage, the pleura on both sides passes laterally crossing the midclavicular line at the eighth costal cartilage and reaching the midaxillary line at the tenth. Posteriorly (figure 5) the pleura follows the twelfth rib before ascending along the line of the transverse processes.

The trachea descends from the larynx through the lower neck into the thorax. It divides at the level of the manubriosternal joint into right and left main bronchi; these enter the hilum of each lung, together with a pulmonary artery, two pulmonary veins and surrounding lymphatics.

In development, the pleural cavity on each side starts as an empty epithelial lined space, but the lung pushes into it from the medial side, like a fist into a balloon (letting out most of the air in the process!). The lining on the outside remains attached to the chest wall as the parietal pleura. The evaginated medial wall remains, separating the pleural cavity from the mediastinum, but the expanding lung takes with it a covering of visceral pleura that is continuous with the mediastinal pleura around the lung root (hilum). The cavity remains only as a potential space, the parietal and visceral pleura are in contact, a little fluid lubricating the surfaces to aid movement of the expanding and collapsing lung, during respiration.

The surface markings of the parietal pleura can be remembered from what happens on the even numbered ribs (figure 4). The apex of the lung domes upwards within the circumference of the first rib, to about 2 cm above the level of the clavicle. From here the pleura on the two sides, passes medially and they meet opposite the second costal cartilage. At the fourth, the pleura on the left is pushed laterally by the developing heart (costomediastinal pleural recess). At the level of the sixth costal cartilage, the pleura on both sides passes laterally crossing the midclavicular line at the eighth costal cartilage and reaching the midaxillary line at the tenth. Posteriorly (figure 5) the pleura follows the twelfth rib before ascending along the line of the transverse processes

1. Dome of pleura/apex of lung
2. Lung and pleural markings
3. Pleural layers coming together at manubriosternal joint 4. Cardiac notch of left lung
5. Costomediastinal pleural recess
6. Transverse fissure of right lung
7. Oblique fissure of lungs
8. Lower border of lungs
9. Lower limit of pleural cavities

1. Dome of pleura
2. Oblique fissure
3. Lower border of lung
4. Lower limit on pleural cavity

Inferiorly, the diaphragm bulges into the pleural cavity on each side, reaching, during expiration, the fourth interspace on the right and the fifth on the left. The outer gutter, between the diaphragm and ribs, is known as the costodiaphragmatic recess. Radiological examination is routinely used to screen for unsuspected, as well as suspected disease (figure 6a,b)

Each lung has an upper and lower lobe divided by the oblique fissure, this follows the line of the sixth rib posteriorly, running obliquely downwards and forwards. On the right side, the transverse fissure, at the horizontal level of the fourth costal cartilages, produces a separate middle lobe. On the left, the ventricles bulge into the lung and the middle lobe is represented as the lingula, a part of the lower lobe.

The bronchial division follows that of the lobes, with further division into functional bronchopulmonary segments, each with its own major vessels. The upper lobes have three (apical, anterior and posterior), the middle lobe two (medial and lateral), the lingula two (superior and inferior) and the lower lobe on the right five (apical, anterior, posterior, median and lateral). The left lung has no medial bronchopulmonary segment of the lower lobe, on account of the space taken by the heart. This lobe has a cardiac notch over the heart, corresponding to the costomediastinal recess of the pleural cavity.

The surface markings of the lungs follow those of the pleura, except inferiorly, where the base is approximately two rib spaces higher. Needles and drains can be introduced in the pleural cavity to inject or withdraw fluid, gasses and drugs, a needle can be passed directly into the pericardial cavity and heart, below the cardiac notch of the left lung, although in an emergency, it is inserted at a lower level (page 233).

Abnormalities of the larynx, such as inflammation and neoplasia, may interfere with the airway and/or produce voice changes. Damage to the recurrent laryngeal nerve may be produced by cancers of the thyroid, cervical esophagus or the apex of the lung. The interior of the larynx may be observed by laryngoscopy or endoscopy

Pulmonary diseases present with dyspnea, cough, cyanosis, chest pain, clubbing and the signs of cardiac failure. Common chest diseases encountered are asthma, chronic bronchitis, emphysema, pneumonia, pneumothorax (figure 7) and cancer of the bronchus. The latter produces local respiratory problems and its metastases may also produce symptoms in the bone, brain and liver. The lung is also a common site for metastases from other sites (figure 8).

Figure 7 Pneumothorax – large right upper lobe congenital lung cyst has leaked, but not collapsed. Associated pneumothorax in lower lateral aspect of right pleural cavity has collapsed underlying lung.

Figure 8 Pulmonary metastases: these “cannon ball” deposits are typical of renal carcinoma.

Pulmonary infection may progress to a pulmonary abscess and, in the pleural cavity, to an empyema. Blocking of a bronchus may produce collapse of part or all of a lung (atelectasisfigure 9); this can occur postoperatively as well as with infection and malignancy. Chronic infection of the bronchi can lead to destruction of their lining and abscess formation of the wall (bronchiectasis). Pulmonary embolus (figure 10) is also a postoperative problem, following lower limb deep venous thrombosis.

Figure 9 Atelectasis: collapse of right upper lobe has produced linear white shadow; lower lobe expanded to fill upper pleural cavity. Linear shadows are a common finding in segmental and lobar pulmonary collapse.

Figure 10 Left pulmonary artery embolus: from lower limb venous thrombosis, completely blocked upper lobe artery, only trickle passing to left lower lobe

Severe trauma may produce a palpable sternal fracture, but also consider associated myocardial contusion and spinal injury. Similarly, with rib fractures, look for a pneumothorax, hemothorax (figure 11) a flail chest, and damage to the liver and spleen.

NB Pulmonary disease may give rise to abdominal pain; abdominal disease may produce a pleural effusion; diaphragmatic pain may be referred to the tip of the shoulder (phrenic nerve C3,4,5); and pus somewhere, pus nowhere, pus under the diaphragm.

Figure 11 Pneumohemothorax: combination of fluid and air in pleural cavity produces distinctive horizontal level. Fractured ribs, from trauma to lower left chest, are not visible.