Breath sounds are the sounds made by air as it moves through the respiratory system.  Breath sounds are also called lung sounds or respiratory sounds.  Sometimes they can be heard by anyone; other times they can be heard only by listening to the lungs and airways with a stethoscope.

To describe and identify breath sounds, medical professionals usually use auscultation (they listen with a stethoscope).  They listen while the patient is breathing in, and while they are breathing out.  They listen to both lungs, at both the chest and the back, starting at the bottom and working their way up.  They listen to whether the pitch of the breath sounds is low, medium or high.  They also listen to whether the sounds are soft, medium, loud, or very loud).

Abnormal Breath Sounds

There are many kinds of breath sounds that are not normal.  These are called adventitious breath sounds.  Each different kind of abnormal breath sound is a sign of a different problem.  Some of the most common abnormal breath sounds are:

Wheezing

Wheezing is usually high-pitched.  It sounds musical, like whistling.  Usually, wheezing is heard first when a person is breathing out.  If it gets worse, wheezing starts happening when the patient breathes in and out.

Wheezing is caused by the airways being too narrow.  This can happen because of diseases like asthma or chronic obstructive pulmonary disorder (COPD).

If the airways are too narrow, the oxygen the body needs cannot get through.  This can become a medical emergency.

There are a few different treatments that can be used for wheezing:
 The patient can be given supplemental (extra) oxygen through a mask.
 Sometimes, moist, hot air can help wheezing.  Sitting in an area like a shower, or using a vaporizer (which creates moist, warm air) may be helpful for mild wheezing.  Emergency medical technicians or hospitals can also give humidified oxygen, which is mixed with warm water to make the oxygen into a warm steam.
 There are medicines called bronchodilators that relax and open up the airways.  This reverses the cause of wheezing and makes it easier to breathe.  Albuterol is a very common bronchodilator and is carried on many ambulances.  Bronchodilators can be given in inhalers or in a nebulizer (which mixes the medicine with warm water to make the medicine into steam).

Stridor

Stridor is a high-pitched sound that usually happens when a person breathes in.  It may sound a lot like wheezing.  Medical professionals can tell the difference by listening to the throat with a stethoscope.  If the sound they hear is louder in the throat, it is stridor, not wheezing.

Stridor is usually caused by something blocking the larynx (voice box).  This can happen because:
 A person is choking and an object is blocking the larynx
 A person has an infection, and swelling in the throat or airways blocks the larynx
 The muscles in the airway or vocal cords spasm (suddenly get tighter); this is called laryngospasm

Like wheezing, stridor can signal a medical emergency if not enough oxygen is able to get through the airways.

Treatment for stridor depends on the cause:
 Helping a person stop choking by using choke saving (like the Heimlich maneuver)
 Treating the infection that is causing swelling in the larynx
 Giving medicines to help the muscles in the airway or vocal cords relax
 No matter what the cause is, giving extra oxygen may also help

Children are more likely to have stridor because of choking.  They are more likely to choke because their airways are smaller.  They are also more likely to get childhood infections like croup or epiglottitis that can cause stridor.

Rales (fine crackles)

Rales are also called fine crackles, because they often sound like a fine crackling noise.  They are heard when a person breathes in, on both sides (in both lungs).  Rales may also sound like bubbling, rattling, or small clicking sounds.

Rales are heard when a person has fluid in their lungs.  This is called pulmonary edema.  Pulmonary edema may happen for many reasons, like:
 Congestive heart failure (CHF)
 Pneumonia or other infections in the lungs
 Injury to the lung
 Blood clot in the lung (pulmonary embolism)
 Breathing in smoke
 Drowning

Rales signals pulmonary edema, no matter what is causing that pulmonary edema.  When a medical professional listens to the lungs, rales usually start at the bottom of the lungs.  As the pulmonary edema gets worse and fluid fills the lungs more, rales can be heard closer and closer to the top of the lungs.

Rhonchi (coarse crackles)

Rhonchi are also called coarse crackles, because they sound like coarse, rattling, crackling sounds.  Rhonchi and rales can sound a lot alike.  The main differences are:
 Rales start at the bottom of the lungs and can be heard farther up as the patient gets sicker.  They are heard on both sides (in both lungs) together.
 Rhonchi are often heard just in certain spots in the lungs.  They do not always start at the bottom of the lungs.  They may be heard only on one side, or in different spots on both sides.

Rhonchi are usually caused by mucus in the bronchi, the tubes that lead to the lungs.  For example, if a person has pneumonia, mucus can build up in their bronchi and the bronchi's airways, and cause rhonchi.

Unequal breath sounds

In a healthy person, breath sounds should always sound the same on both sides.  This signals that both lungs are working well.  If breath sounds cannot be heard in one lung, this can signal a serious problem.  It means that air is not getting in and out of that lung.

One of the most common causes of unequal breath sounds is a collapsed lung (pneumothorax).  A lung can collapse for many different reasons:
 A very bad injury to the lung
 Lung diseases like asthma, COPD, tuberculosis (TB), whooping cough, pneumonia, or cystic fibrosis
 Sometimes air blisters called blebs form on the top of the lungs.  If these air blisters break, air can leak out of the lungs and cause the lung to collapse.  
 Sometimes, a lung can collapse on its own.  This is called a spontaneous pneumothorax.

A pneumothorax is often a medical emergency and needs to be treated in a hospital.

References

Respiratory system