Adventitious sounds are abnormal pulmonary sounds that can be divided into:
- pleural adventitious sounds
- bronchopulmonary adventitious sounds
When describing adventitious sounds it is important to indicate in which section of the breathing cycle these noises are audible.
Pleural adventitious sounds
Pleural adventitious sounds (pleural rubs) are usually easy to recognise as rubbing or crackling (‘footsteps in the snow’). They occur during breathing as the result of the rubbing together of irritated or inflamed pleural membranes, separated by very little fluid (pleuritis sicca). A rubbing noise will not be audible if a substantial amount of fluid is present between the inflamed pleural membranes.
Pleural rub is audible most clearly at the end of inspiration because movement of the visceral pleura is faster than the parietal pleura. However, in contrast to most other adventitious sounds, pleural rub is audible both during inspiration and expiration.
Bronchopulmonary adventitious sounds
Bronchopulmonary adventitious sounds are abnormal sounds that can be divided on the basis of their duration:
- wheezing and rhonchi
- crackles
Wheezing and rhonchi
High-frequency wheezing and low-frequency rhonchi are continuous adventitious sounds lasting longer than 250 milli-seconds and caused by vibration of fairly large airways which are constricted. Such constriction can be the result of swelling and mucous membrane oedema, smooth muscle spasms or stasis of bronchial secretions. Depending on the degree of narrowing , these adventitious sounds can be audible either with breathing at rest or during deep breathing. Wheezing is identified particularly in constricted airways (as with asthma), whereas rhonchi are predominantly found in the presence of thick secretions (such as bronchitis).
Crackles
Crackles are discontinuous adventitious sounds that last for less than 20 milliseconds and have a much more explosive character than wheezing and rhonchi. One should describe where they are heard and whether they disappear upon coughing or deep sighing.
Crackles can be subdivided into fine (high-frequency) crackles or coarse (low-frequency) crackles. During inspiration, early inspiratory (often coarse) crackles are probably caused by the opening of larger airways (e.g. in COPD). Late inspiratory (often fine) crackles are probably caused by the opening of smaller airways (e.g. with pulmonary oedema). Furthermore, coarse and fine crackles can also occur during expiration. Expiratory coarse crackles usually occur as a result of bronchial secretion and often disappear with coughing. Expiratory fine crackles occur with respiratory tract weakness and deformation, such as emphysema and bronchiectasis, and often do not disappear upon coughing.
Procedure
Ask the patient to sigh deeply with their mouth open. Then, auscultate with the membrane side of the stethoscope, pressing the stethoscope firmly against the thorax to prevent it shifting when the patient breathes; this can lead to incorrect suspicion of adventitious sounds, particularly in the presence of hair growth.
Systematically listen to all lung fields. Move in a downwards direction and each time, for both the anterior and the posterior aspect, start at the lung apices. Always immediately compare left and right. At each location, listen to at least one complete inspiration and expiration cycle. Constantly assess the nature of the breath sounds and the presence and nature of possible adventitious sounds.
Listen at the level of:
- the posterior thorax [Figures 31a and 31b]
Figure 31a: auscultation; posterior thorax
Figure 31b: auscultation points; posterior thorax
- the lateral thorax [Figures 32a and 32b]
Figure 32a: auscultation; lateral thorax
Figure 32b: auscultation points; lateral thorax
- the anterior thorax [Figures 33a and 33b]
Figure 33a: auscultation; anterior thorax
Figure 33b: auscultation points; anterior thorax