The Ultimate Acoustic Stethoscope Review (page 3)
Subjective Clinical Testing:
We carried the test scopes on rounds and to the clinic. We tested the scopes on thin patients, obese patients, patients with COPD, patients with murmurs, gallups, clicks, patients with CHF, and patients with vascular bruits. We listened to respiratory sounds, and measured blood pressure. We identified 4 subjective differences between scopes which are summarized in the table below. Loudness is the perceived amplitude of the sound. Clarity is the ability to distinguish diagnostic cardiac sounds such as valvular clicks. Some scopes had problems with noise artifacts or external noise interference. Some scopes had poor ergonomics, aspects which interfered with their practical use. We subtracted 2 points for minor design issues, and five points for major design issues. An additional issue we investigated was the use of a Bell versus a Diaphragm. The practical benefit to the use of a Bell was that it was narrower than the diaphragm and thus could better acoustically couple to an irregular surface, such as between the ribs or above the carotid of a cachectic patient. We subjectively assigned a score of 1-10 for loudness and clarity, and subtracted points for ergonomic or other issues which interfered with our use of the scope. Our results are summarized below. The higher the number, the better the score.
|ADC Platinum Cardiology 615||6||7||Single Head (-2)||11|
|ADC Adscope Professional 603||2||8||10|
|AllHeart Cardiology||6||7||Defective Earpieces (-5)||8|
|DRG Puretone Traditional PT3||10||1||Prone To Noise Artifacts (-5)||6|
|Single Head Nursing Stethoscope||5||6||Single Head (-2)||9|
|Littmann Cardiology I||9||9||Short Tube (-5)||13|
|Littmann Cardiology III||9||8||17|
|Littmann Master Classic II||8||8||Single Head (-2)||14|
|Littmann Classic II SE||7||7||14|
|Omron Sprague Rappaport||8||9||Prone To Noise Artifacts (-2)||15|
|Prestige Sprague Rappaport Stealth||6||7||13|
|Welch Allyn Tycos Elite||4||10||Irregular Diaphram (-2)||12|
In the clinic, our subjective favorite scopes were the Littman Cardiology 3, and the Omron Sprague Rappaport. The Littman Cardiology III was great at cleanly amplifying sounds from all patients under all conditions. The Omron Sprague Rappaport was also great at amplifying sounds on all patients at in quiet environments. It had a very crisp sound, and was great at hearing the click of mitral valve prolapse, or the splitting of S2 with respiration. Like any Sprague Rappaport scope it was bulky, readily amplified external noises, and had noise artifacts if the twin tubes rubbed against each other. You probably don’t want to use this scope in a moving, noisy environment such as the back of an ambulance. The Prestige Sprague-Rappaport was similar to the Omron. But it was slightly less efficient and slightly less crisp. It had softer tubes than the Omron and was less prone to artifacts. The Littman Cardiology I, was acoustically superb, the best of the group. With its hard diaphragm it had a crisper sound than the newer Cardiology 3 model, was almost as loud, and its thick tubing was great at blocking external noises. But its short tubing made it very difficult to check blood pressures. Also with its short tubing, it placed one’s face uncomfortably close to the patient’s anatomy in certain situations. The Allheart Cardiology is a Chinese made copy of the Littman Cardiology I design, but uses a longer tube. It was fair acoustically when the defective original earpieces were replaced as noted above. It took more pressure on the patients skin for acoustic coupling, perhaps because of the thick non chill ring, and was less efficient than the Cardiology I. The DRG scope was loud, but always had a background rumble, especially when the tube was touched. We couldn’t hear clicks or physiologic splitting of the S2 at all with this scope. Tapping the diaphragm results in a musical poing, ie, the diaphragm could create its own artifactual sound. We judged it the worst of the group in listening to heart sounds. Subsequent objective testing showed unusual resonances, and poor transient response.
Most of the scopes had both bell and diaphragm. The Littman Cardiology III had two different sized diaphragms, one adult and a smaller pediatric one. Clinically the small diaphragm is as useful as a bell. The reason is that a smaller diaphragm is better able to acoustically couple to an irregular surface, such as the neck of an thin elderly patient. A dramatic demonstration of this was in a cachectic elderly woman with a loud carotid bruit. We couldn’t hear the carotid bruit at all with the single diaphragm Littmann Master Classic. However the bruit was readily heard on any scope with a small diaphragm or a bell. The thin bony irregular neck wouldn’t acoustically couple with a large diaphragm, but readily coupled with a smaller diaphragm or bell. Thus, we judged the Master Classic to be inferior to the Cardiology III, even though its diaphragm performed almost identically to the large diaphram of the Littman Cardiology III. The ADC scopes were beautifully made but less acoustically efficient. Heart sounds were faint. It was as if everyone had COPD.
The Welch Allyn was unique. When you could get good coupling the sound from the Welch Allyn ribbed diaphragm was wonderful. It was the only scope with good imaging. An analogy is the ability to pick out the individual sounds of every instrument in an orchestra. However the ribbed diaphragm made it difficult to acoustically couple to bony patients with protruding ribs. The surfaces just didn’t match. The ribbed diaphragm was much less efficient than the Littman scopes. The solution is to use both diaphragm and bell on every patient. Thus the Welch Allyn is a good scope, but it takes some getting used to. It’s not for doctors in a hurry, because you really need to use the bell and diaphragm on every patient. A photo of the Welch Allyn diaphragm is shown below:
The single headed nursing scope looked like a toy, but was acceptable. It was more efficient than the Adscope, and was cleaner sounding than the DRG. The classic dual head Littmann was slightly less efficient and slightly more muffled sounding than the more expensive Littmanns. But it was still a very good scope. Its pocket sized, and thus is a popular choice amongst surgeons.