Normal Breath Sounds

What is bronchial breathing sounds?

Normal breathing is not a silent process. Air flow through the large airways is turbulent and causes a rustling or blowing type of sound. It is most prominent in the upper respiratory tract (nasal cavity, pharynx and larynx) and the upper part of the lower respiratory tract (trachea). Inspiration is usually louder than expiration. This type of normal breathing sound is known as bronchial breathing.

What is vesicular breathing sounds?

Once air enters the bronchial tree and lung tissue, the sound is diminished. However, the movement of air from the upper respiratory tact may resonate in the lung tissue itself and cause a quiet, wispy sound that is more pronounced on inspiration and almost silent on expiration. This type of sound over the lung is known as vesicular breathing and should not be the same amplitude and quality as bronchial breathing sounds.

Soft Breathing Sounds

Sometimes the normal vesicular breathing sounds are diminished. This change will be more evident at the region where the sound is most affected and can be compared to the other lung if it is unaffected by any pathology. The reason for these diminished sounds may either be hampered by the overlying tissue (conduction) or impaired air flow (ventilation).

Causes of Diminished Vesicular Breathing Sounds

Impaired Sound Conduction

  • Thick chest wall – obesity, excessively muscular chest wall
  • Fluid around the lungs – pleural effusion
  • Thickening around the lungs – pleural thickening/fibrosis
  • Air around the lungs – pneumothorax

Reduced Ventilation

  • Obstruction – foreign body especially in one bronchus
  • Diminished lung elasticity – COPD (chronic obstructive pulmonary disease)
  • Collapsed lung due to obstruction within the airway (obstructive atelectasis – example in lung cancer)

Loud Breathing Sounds

At other times the breathing sounds over the lung are loud and clearly audible, above and beyond the norm. It is similar in volume and nature to bronchial breathing (bronchophony/bronchial breath sounds). This indicates that the resonance is pronounced. To identify loud sounds from normal sounds, transmission tests to assess vocal resonance will be conducted.

Vocal Resonance

Vocal resonance refers to the vibration created by sound production (phonation) and this is evident throughout the respiratory tract and adjacent structures, similar to breathing sounds. In terms of diagnosing any lung abnormality the vocal resonance over lung tissue may need to be assessed to establish if the loud breathing sounds detected upon ausculation (bronchophony) over the lung is indeed present and whether it is due to any specific pathology. This may also be confirmed by touch (tactile fremitus).

Voice transmission tests

This assess the conduction of sound through lung tissue or the manner in which it is manipulated by any pathology – fluid in the lung or around it  or consolidation of the lung tissue. The patient will be asked to say “ninety nine” repeatedly while the doctor auscultates the chest (listens with a stethoscope).

  • The normal lung transmits low-pitched sound and filters (attenuates) high-pitched sound. The sound of the numbers “ninety nine” will be indistinct and reverberating.
  • The consolidated lung will transmit higher frequencies and the numbers will be clearly audible and even louder. This can be confirmed by asking the patient to whisper “ninety nine”. Normally it would be difficult to hear the whisper but if the sound is clear then this indicates consolidation of the lung tissue, which is the most common cause. This is known as  whispering pectoriloquy. Other causes of loud breathing sounds are discussed below.
  • If the space or lining around the lung is affected, as is the case with fluid around the lungs (pleural effusion) or pleural thickening,  or lung collapse, vocal resonance is significantly diminished, muffled or possibly even absent.

Causes of Loud Breathing Sounds

  • Consolidation of the lung tissue as is the case with pneumonia is the most common cause.
  • Fibrosis of a part of the lung (localized pulmonary fibrosis).
  • Collapsed lung
    • Tension pneumothorax
    • Non-obstructive atelectasis. This includes atelectasis due to a massive pleural effusion although the bronchial breath sounds will be evident at the top of the effusion.

Related Articles

  1. Abnormal Breathing Sounds
  2. Causes of Stridor and Wheeze

Article reviewed by Dr. Greg. Last updated on September 11, 2010