LITMIR.BIZ

Figure 2.4 Summary of sound transmission in the lung. Sound is generated either by turbulence in the larynx and large airways or by the voice. Both sources are a mixture of high (H)‐ and low (L)‐pitched components. Normal aerated lung filters off the high‐pitched component but transmits the low‐pitched component quite well. This results in soft, low‐pitched breath sounds and low‐pitched vocal resonance. Consolidated lung transmits high‐pitched sound particularly well. This results in loud, high‐pitched breath sounds (bronchial breathing), high‐pitched bleating vocal resonance (aegophony) and easy transmission of whispered (high‐pitched) speech (whispering pectoriloquy). Pleural effusion causes reduction in the transmission of all sound, probably because of reflection of sound waves at the air–fluid interface. Breath sounds are absent and vocal resonance is much reduced or absent.

      A solid medium (consolidated lung) conducts sound better, particularly high‐pitched sound. Breath sounds heard over a consolidated lung are therefore similar to those heard with the stethoscope held over the larynx and are referred to as bronchial breathing. The sound is louder and harsher, has a higher frequency ‘hiss’ and tends to be similar in inspiration and expiration.

      Vocal resonance is assessed by listening over the chest with the stethoscope as the patient says ‘ninety‐nine’. Normal aerated lung transmits the ‘booming’ low‐pitched components of speech and attenuates the high frequencies. Consolidated lung, however, transmits the higher frequencies better, so that speech takes on a bleating quality known as aegophony. Whispering ‘ninety‐nine’ produces only high‐pitched sounds. This can barely be heard over normally aerated lung but is transmitted surprising well over consolidated lung and is referred to as whispering pectoriloquy.

Figure 2.5 Signs of localised lung disease.

A reduction in the intensity of breath sounds (diminished breath sounds) over an area of lung may indicate obstruction of a large bronchus and collapse of a lobe of the lung. A pleural effusion produces an air–fluid interface, which sound just bounces off. Breath and voice sounds are usually absent over an effusion.

      Added sounds

      In normal individuals, at auscultation, the inspiratory phase of respiration seems longer than the expiratory phase. Prolongation of the expiratory phase is a feature of airway obstruction and is often accompanied by wheeze (‘rhonchi’ is redundant and should be avoided): a high‐pitched whistling or sighing sound. Diffuse wheeze is a feature of asthma. Despite the presence of airway obstruction, wheeze is unusual in COPD; diminished breath sounds are more common.

      Wheeze localised to one side, or one area of the lung, suggests obstruction of a bronchus by a carcinoma or foreign body (e.g. an inhaled peanut). Remember, inspiratory wheeze is not wheeze, it’s stridor. Stridor indicates the site of obstruction as being in the trachea or main bronchi.

      Avoid the term ‘crepitations’ or ‘crepes’ when describing crackles; the existence of two terms only causes confusion. (Most people have a clear idea of the difference in meaning between the two terms; unfortunately, everyone’s idea is different.) Language should facilitate communication, so keep it simple. If the crackles are coarse, they should be described as coarse crackles; if they are fine, they should be called fine crackles. (Reserve the term ‘crepes’ for those thin pancakes you get in France.) It is thought that crackles are produced by the opening of previously closed bronchioles. Early inspiratory crackles are sometimes heard in patients with a little excess airway mucus (e.g. COPD), but these may diminish or even disappear when the patient is asked to cough. Late inspiratory crackles can sometimes be heard at the lung bases in obese individuals as the poorly ventilated areas open at the end of a deep breath. Paninspiratory crackles can be fine (like Velcro), representing lung fibrosis or pulmonary oedema. Coarse paninspiratory crackles usually imply excess purulent airway secretions, as seen in bronchiectasis. Remember: distinguishing coarse from fine is much easier if you remembered to ask the patient to cough at the start of the examination.

      Pleural rubs are ‘creaking’ sounds. They are often quite localised and indicate roughening of the normally slippery pleural surfaces. They are heard in the context of pleural inflammation due to either infection or infarction (pulmonary embolism).

Signs

See Fig. 2.5 for signs of localised lung disease. It is important to realise that major disease of the lungs may be present without any detectable physical signs, and it is therefore essential to obtain a chest X‐ray when there is good reason to suspect localised lung disease.

      KEY POINTS

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