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When airway obstruction is present, tidal breathing occurs at a higher lung volume; in part, this is an unconscious attempt to hold the airways open. This hyperinflation can be even more pronounced if the obstruction is due to emphysema, when the loss of lung elastic recoil allows the chest wall to find its neutral rest position with the lung at a more expanded volume (see Chapter 1). Many of the physical signs of airway obstruction are actually signs of hyperinflation.

Table 2.3 Causes of clubbing

Respiratory

NeoplasticBronchial carcinomaMesothelioma

InfectionsBronchiectasisCystic fibrosisChronic empyemaLung abscess

FibrosisIdiopathic pulmonary fibrosisAsbestosis

CardiacBacterial endocarditisCyanotic congenital heart diseaseAtrial myxoma

GastrointestinalHepatic cirrhosisCrohn’s diseaseCoeliac disease

CongenitalIdiopathic familial clubbing

Look at the chest from the front, back and sides, noting the overall shape and any asymmetry, scars or skeletal abnormality. The normal chest is flattened anteroposteriorly, whereas the hyperinflated chest of COPD is barrel‐shaped, with an increased anteroposterior diameter. In airway obstruction, patients tend to adopt a high shoulder position (assisting the lungs in holding a more inflated volume).

Watch the pattern of breathing. In health, a breath in takes about as long as a breath out. In airway obstruction, careful observation will reveal the prolonged expiratory phase to respiration. Pursed lips during expiration maintain a positive back pressure, holding small airways open longer, reducing gas trapping and allowing patients with airway obstruction to achieve better tidal ventilation at a more comfortable lung volume.

Watch the movement of the chest carefully as the patient breathes in and out. The ribs move in a way akin to the handle on a bucket. At low lung volume, the movement is predominantly outward; at high lung volume, it is predominantly upward. If, on observation, the front of the chest is seen to move upward on inspiration, hyperinflation (airway obstruction) is present. Diminished movement of one side of the chest is a clue to disease – on that side (see below). Overall movement is reduced if the lungs have reduced compliance (e.g. fibrosis).

In health, the whole ribcage expands during inspiration, the lower costal margins moving upwards and outwards as the chest expands. This is due to the downward discursion and stiffening of the diaphragm (see Chapter 1). In a chest that is already severely overinflated (e.g. in COPD), inspiration begins with the diaphragm already in a low, flat position. The contraction it undergoes during inspiration therefore tends to pull in the lower costal margin (to which it is attached). This inward movement of the lower costal margin during inspiration appears paradoxical. Costal margin paradox (Fig. 2.3) is the single most reliable sign of airway obstruction. It is both sensitive and specific, and is far more reliable than wheeze. All doctors remember to listen for wheeze; few remember to look for lower costal margin paradox.

The abdominal wall normally moves outwards on inspiration, as the diaphragm descends. Abdominal paradox, in which the abdominal wall moves inwards during inspiration when the patient is supine, is a sign of diaphragm weakness.