Use the diaphragm of the stethoscope to assess the breath sounds (figure 24a–l). Ask the patient to take moderately deep breaths and to breathe in and out through their open mouth; excessive inspiration, and too complete an expiration, may precipitate the symptoms and signs of hypocarbia, the patient feeling faint.

Normal breath sounds are produced by the airways rather than the alveoli. They have been likened to wind rustling in leaves, and are called vesicular sounds. Vesicular sounds are louder and longer on inspiration than expiration, there is no gap between inspiration and expiration. These sounds are generated by the turbulence of air in the large airways filtering through the normal lung to the chest wall.

Bronchial breath sounds have a more hollow and blowing nature. They are audible throughout expiration and there is often a gap between inspiration and expiration. The expiratory sound has a higher intensity than the inspiratory sound. They are normally audible over the trachea and the main bronchi, as well as over areas of consolidation.

Breath sounds are described as normal or reduced in quality. Causes of reduced breath sounds include emphysema, pleural effusion, pneumothorax and pleural thickening.

Adventitious sounds are either wheezes (rhonchi) or crackles (râles). Wheezes have a musical quality and may be heard both on inspiration and expiration. They are caused by continuous oscillation of opposing airway walls and imply airway narrowing. The pitch depends on the speed of airway flow.

Auscultation over the chest while the patient utters some words (e.g. ninety nine), vocal resonance, gives further information about the lung’s ability to transmit sound. Over the normal lung, the low-pitched components of speech are heard with a booming quality and high- pitched sounds are attenuated. In consolidation, high-pitched sounds are preferentially transmitted and the speech heard through the stethoscope has a bleating or egophonous quality. When the vocal resonance is increased to a great extent, even whispered speech may become audible, a sign known as whispering pectoriloquy.