More Crackles

More Crackles

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 Quoting the NEJM's Resident e-Bulletin 2/20/2014 Teaching Topic Lung Auscultation

"Q. What are the differences between fine and course crackles?

A. Two categories of crackles have been described: fine crackles and coarse crackles. On auscultation, fine crackles are usually heard during mid-to-late inspiration, are well perceived in dependent lung regions, and are not transmitted to the mouth. Uninfluenced by cough, fine crackles are altered by gravity, changing or disappearing with changes in body position (e.g., bending forward). Coarse crackles tend to appear early during inspiration and throughout expiration and have a “popping” quality. They may be heard over any lung region, are usually transmitted to the mouth, can change or disappear with coughing, and are not influenced by changes in body position. Typically, fine crackles are prominent in idiopathic pulmonary fibrosis, appearing first in the basal areas of the lungs and progressing to the upper zones with disease progression. However, fine crackles are not pathognomonic of idiopathic pulmonary fibrosis; they are also found in other interstitial diseases. Coarse crackles are commonly heard in patients with obstructive lung diseases, including COPD, bronchiectasis, and asthma, usually in association with wheezes. They are also often heard in patients with pneumonia and congestive heart failure."

Who is to argue with the NEJM, documented with modern auditory recordings and referenced with a pear reviewed lead article, Fundamentals of Lung Auscultation: Abraham Bohadana, M.D., Gabriel Izbicki, M.D., and Steve S. Kraman, M.D. N Engl J Med 2014; 370:744-751February 20, 2014DOI: 10.1056/NEJMra1302901, "Computer-assisted techniques allow detailed analysis of the acoustic and physiological aspects of lung sounds." 

From a teaching viewpoint there probably is no higher authority than that quoted above, yet some of the computer-assisted observations run contrary to my clinical experience and the teachings from the pre-crackles era. In my experience, fine rales at the left base are the hallmark of left lower lobe pneumonia. They are a fine low pitched sound similar to the sound of rubbing your hair together just above your ear. They do not go away with change in position and they occur in early to mid inspiration. I am not so interested in the computer findings as I am concerned by the missed or misdiagnosed early pneumonia and the sound in my own stethoscope. Pneumonia in the early stages, coincides with the patient's complaint of chills fever and a productive cough. X-Rays are not yet positive but a gram stain confirms the diagnosis. Unfortunately, this is the stage of pneumonia that is often misdiagnosed as a virus and sent home without adequate consideration. The above description of course crackles with pneumonia might come at a later stage of pneumonia's progress when a school teacher can make the diagnosis.

The problem may be that all the pre-crackles physicians are gone now or retired. I read that crackles live only in America. I doubt that with the distribution of today's journals, but I rather imagine that Europe, especially France, would be less willing to give up Rene' Laennec's terminology or diagnostic acumen. I do wonder about the digital rendition of rales, however. Harmonics plays a significant role in the low frequencies and digital may not be able to capture these low frequency analog harmonics. Furthermore, as one of my students commented speakers cannot reproduce the low frequencies. This is evident in the class room when attempting to broadcast heart and lung sounds over the speaker system. When I was in medical school, we had tubes from the examining table in the front of the amphitheater to the back of the chair in front of us with a lure-lock fitting. Our stethoscopes had a lure-lock fitting on a detachable head. We were thus able to attach our stethoscope to the closed system and hear the sounds from the examiner's stethoscope in real time without electronic distortion.

One cannot argue with the NEJM, but medicine is not immune to mistakes and bad ideas. Once they are in print it takes a long time to change them.