Vol. 21 Issue 13
Breath Sounds Revealed
Listening to the 'Orchestra' Can Help Determine Medical Status
By Chris Wookey, RRT
The other day I listened to a concert by the Florida Orchestra and found I could close my eyes and separate the strings from the horns, the woodwinds from the percussion and listen to each section independently.
It occurred to me that I do the same thing when I listen to breath sounds. No lung has just one sound any more than an orchestra or a band has just one instrument. If you listen carefully, it's possible to hear all the sounds while at the same time listening to each one: "That's a flute, that's a violin, that's a horn," or "That's a wheeze, that's rhonchi, those are rales."
Understanding breath sounds is like understanding music. It requires education and listening.
The key to education: a good teacher; the key to listening: concentration. You'll need to tune out all other noise and focus on the breath sounds.
Most of us learned breath sounds using complicated terms like "adventitious," "bronchovesicular" and so on. Who cares? The goal when assessing breath sounds is to effectively describe what's going on in the patient's chest, not to confuse others with descriptions virtually meaningless to anyone except a therapist.
In the real world, we use adjectives like, "crackles," "congested," "squeaky" or "wheezy." These terms better describe a patient's condition than do textbook names. Unfortunately, they're at the other end of the complicated terminology we learned in school.
Respiratory therapists need to understand only five breath sounds in everyday clinical practice: clear, rhonchi, wheezes, rales and stridor.
When air flows through a tube, it creates a sound. Sounds have a high and low "pitch" depending on how fast or slow the air moves through the tube (or how many holes you cover up on a flute).
If we view the bronchial tree as a series of tubes, we'll see air flows in and out of them either smoothly or turbulently. The sound created is determined by the smoothness or roughness of the flow, much like the difference in the sound of a calm river or a set of rapids.
The same physics affect air and water. Viewing air as "thin" water will help to understand how the sound changes when the flow changes.
In an unobstructed tube (bronchus), air flows in and out easily and creates a very low-pitched, blowing sound that we equate with clear or healthy breath sounds. We all understand clear breath sounds and know they occur in a healthy tracheobronchial tree.
But what about the other four?
In a hollow tube, such as the trachea or bronchi, air flows smoothly as long as a patient has no obstructions or "bumps." When bumps occur, such as globs of mucus, the air must flow around them.
As air flows around obstructions in the tube, it must change direction and becomes "turbulent." The air speeds up to go around the obstruction, and the sound it makesthe pitchchanges. In general, the pitch goes up depending on the size of the obstruction, much like a voice does when it goes from a whisper to scream.
The change in pitch determines whether the sound will be called a rhonchi or a wheeze. The greater the airway obstruction, the higher the pitch.
Rhonchi are continual low-pitched sounds; wheezes are continual high-pitched sounds. Both are caused by airway obstructions.
This explains why patients sometimes sound "worse" after a breathing treatment. They are moving more air and creating a louder sound, but they're actually better than before.
Rhonchi and wheezes occur in the larger airways and can be heard on both inspiration and expiration.
The trachea divides 24 times before it reaches the lung. In the terminal airways like the bronchioles, there's little or no air flow. There, all gas exchange occurs as a result of diffusion and brownian movement.
Breath sounds caused by turbulent air flow causing rhonchi and wheezes cannot be heard. Another sound, however, indicates a completely different pathology: rales.
Imagine wetting your palms and pushing them together and then pulling them apart. It makes a "popping" or "smacking" sound. Now imagine thousands of little palms being pulled apart. In the lung, this sound is commonly called "crackles" or rales.
It's the sound of wet or moist bronchioles and alveoli popping open when inflated on inspiration. Rales are heard in some patients with congestive heart failure or pulmonary edema and occur in the tiny distal airways and alveoli. They occur intermittently only on inspiration and aren't the product of large airway obstructions like rhonchi and wheezes.
Stridor, the last of the five, is a "boring" breath sound. It's easily identified by a unique "whistling" or "barking" sound and is most commonly found in children with subglottic edema or croup. Typically heard only on expiration, stridor is caused by exhaled air squeezing through a narrowed trachea or around an aspirated foreign body.
Armed with this new simplified version of breath sounds, you should be able to identify the various sounds and understand what they mean to the patient's medical status.
Now, put on your stethoscope and listen to the band!
Chris Wookey is a staff therapist at North Okaloosa Medical Center in Crestview, Fla.