Lung Auscultation – Vocal Resonance

Vocal resonance is the sound of the patient’s voice detected through the stethoscope. Unlike breath sounds it’s generated in the patient’s larynx. In certain diseases it can be abnormally transformed giving valuable clue to the diagnosis.

  1. Lung Auscultation – Normal Breath Sounds
  2. Lung Auscultation – Adventitious Breath Sounds
  3. Lung Auscultation – Vocal Resonance

History

René Laennec – the inventor of stethoscope – was the first one to describe abnormal vocal resonance. He described and named three types of abnormal vocal resonance – bronchophony, pectoriloquy and egophony, the last of which he likened to the sound of “bleating of a goat”.

Almost two centuries later in 1922 Shibley and Föschel simultaneously described more recent variant of the egophony – E-to-A change. Some of the authors refer to it as a distinct physical sign.

Clinical Vignette

To be added at later date.

Physical Examination

  1. Room and patient setup. Room should be quiet and patient sitting up, decently exposed. Female patients should have only front or back of the chest exposed at once. If the patient is not able to sit up, roll the patient to each side to examine the back.
  2. Warming up. Warm up the cold stethoscope by rubbing the membrane. Even if it’s not cold it’s a nice gesture of special care.
  3. Crossing arms. When listening to the back of a chest, ask the patient to cross arms over the front chest to evert shoulder blades, giving more space to listen to the lungs.
  4. Repeat ‘toy boat’. Ask the patient to repeat ‘toy boat’ each time the stethoscope is placed on the chest. Other phrases can be used as well. The key is to use words with as many diphthongs as possible, like ‘no highway cowboys’ or ‘oink-oink’ for instance. ‘Ninety-nine’ is not as suitable – see Caveats and Errors. For pectoriloquy, phrase ‘one-two-three’ is commonly used.
  5. Compare. Listen to and compare identical places on each sides. Focus especially on unusually distinct or different sounds.

Interpretation

Normally when listening to the patient’s voice through the stethoscope placed on the chest wall, the sound is muffled, indistinct and words unintelligible. This is referred to as vocal resonance. It’s happening because lungs act like a low-pass filter that eliminates all high-frequency sounds over 300 Hz (including formants of the vowels), transmitting well only ones with low frequency (100-300 Hz), thus making voice incomprehensible.

In certain diseases like pneumonia or effusion or lung consolidation in general, the sound is transformed and higher frequencies (>300 Hz)are transmitted as well. This is called abnormal vocal resonance. There are three types of abnormal vocal resonance – bronchophony, egophony and pectoriloquy.

Bronchophony refers to patient voice heard through the stethoscope that is louder regardless of the intelligibility of the words. The sound is clear and loud as if listening over the bronchi or larynx, hence the name.

Egophony is goat-like nasal quality of the patient voice. Physician asks patient to say “eee” and listens to the chest wall. Normally, all vowel sounds are altered, even by a healthy lung. “Eee” is therefore changed to a “aahh”. The difference is the sudden change over a small area of chest and unusually loud sound. This is sometimes referred to as E-to-A change.

Pectoriloquy is sound of a patient’s voice if words are intelligible. The sign is called spoken or whispered pectoriloquy when patient is speaking in normal voice or is whispering, respectively.

Here is an example. Patient is whispering ‘one two three’.

In pneumonia all the frequencies, both high and low, are transmitted well. In pleural effusion, low frequencies (100-300 Hz) are attenuated while higher ones (>400 Hz) are augmented. This explains why in pneumonia abnormal vocal resonance (>300 Hz) as well as increased tactile vocal fremitus (100-200 Hz) is present. On the other hand, in pleural effusion tactile fremitus is decreased and abnormal vocal resonance is present.

Tactile vocal fremitus Vocal resonance
Pneumonia Increased Abnormal
Pleural effusion Decreased Abnormal

Caveats and Errors

Using ‘ninety-nine’. Many physical examination textbooks use phrase ‘ninety-nine’ as one suitable for examining vocal resonance. Even though almost any words can be used to elicit the sign, based on the pathogenesis described above, ones with most diphthongs are the most suitable. Ninety-nine is a result of unfortunate literal translation from German ‘neunundneunzig’ that German physicians use in their clinical practice because it has many diphthongs.

Asymmetry. As mentioned above, all vowel sounds are altered even by healthy lungs. The key to the diagnosis is sudden change over the small area of the chest.

Other common errors are the same as in Lung Auscultation – Normal Breath Sounds.

Clinical Significance

To be added at later date.

References

Chi, J., Artandi, M., Kugler, J., Ozdalga, E., Hosamani, P., Koehler, E., … Verghese, A. (2016). The Five-Minute Moment. The American Journal of Medicine, 129(8), 792–795. https://doi.org/10.1016/j.amjmed.2016.02.020

McGee, S. R. (2018). Evidence-based physical diagnosis (4th edition). Philadelphia, PA: Elsevier.

Mangione, S. (2012). Physical Diagnosis Secrets: With STUDENT CONSULT Online Access. London: Elsevier Health Sciences.

Fremitus. (2018, April 21). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Fremitus&oldid=837548961

Whispered pectoriloquy. (2017, February 13). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Whispered_pectoriloquy&oldid=765196512

50 Heart & Lung Sounds Library : 3MTM Littmann® Stethoscopes : 3M Gulf. (n.d.). Retrieved 5 June 2018, from http://solutions.3mae.ae/wps/portal/3M/en_AE/3M-Littmann-EMEA/stethoscope/littmann-learning-institute/heart-lung-sounds/heart-lung-sound-library/#all