3M Littmann Stethoscope
Seen by many in the medical community as one of the better stethoscope brands, Littmann stethoscopes are named after David Littmann, MD, the creator of what is known as a "combination" or "double-headed" stethoscope. In the November 1961 issue of the Journal of the American Medical Association, Dr. Littmann laid out the groundwork for most modern stethoscopes. Previous stethoscopes used two separate tubes made of spirals of wire with gum elastic and silk on the exterior. These were not good for sound insulation, and could rub together and create unwanted noise. Littmann proposed using a single solid tube with only one bore, known as a single-lumen tube. He also proposed using a chestpiece that had two sides, one which was open (no plastic diaphragm) for low-frequency sounds, called a bell, and another with a solid head for high-frequency sounds (the plastic diaphragm would filter out the low-frequency noise). Littman also worked to shorten the length of the stethoscope from head to earpieces (reducing sound loss), and wanted to make stethoscopes lighter.
In 1963, Littmann began producing his "ideal" stethoscopes under the company Cardiosonics, Inc. that he formed along with Gus Machlup, and the company was acquired by 3M just four years later. 3M expanded the line from the original model and a "nurses' version" produced by Littmann and Machlup to over 10, with such features as aluminum instead of stainless steel to reduce weight, and pediatric models with smaller chestpieces. Development continued, and in 1970, 3M brought out the Cardiology series, which featured a double-lumen design (two bores in one solid tube), along with a host of other improvements recommended by cardiologists. The line was also the first to feature a single-headed model that could vary between high- and low-frequency sounds (called a tunable head) by varying the pressure applied to the stethoscope. The first electronic stethoscope was introduced in 1999.
The 3M Littmann brand now includes ten models, ranging from the Lightweight line (single-belled, designed mainly for nurses) to the Model 4100, an electronic stethoscope that both amplifies and records sounds. The following detail all of the different lines of Littmann stethoscopes, and their characteristics.
The only model currently available under the Lightweight line is Lightweight II S.E. Designed for doing basic physical assessments and taking blood pressures, the Lightweight is a basic model. The chestpiece is made of a resin (as compared to stainless steel or metal alloys for all other models), and is specially shaped for use with blood pressure cuffs. It also features the same style combination design that Littmann's original model used (one solid end and one open one).
The Select features a single-lumen tube and a tunable, single-sided chestpiece. Its acoustic quality is less than the other models but is good for initial assessments and auscultation of blood pressures. Though the design appears similar to that of the original Master Classic model, the Select's chestpiece is made of different materials, resulting in a lower-cost product.
The Classic II is actually four separate models. Two (the Infant and Pediatric versions) are designed specifically for younger patients. They feature 0.75 and 1 inch bells, respectively; the smaller diameter is better for smaller patients, as the doctor can focus on sounds from a specific area of the body. The Classic II S.E. is the adult version of the Classic II, featuring a "standard" size chestpiece (1.75 inches). All three of these models have single-lumen tubing, and machined stainless steel bells.
The Master Classic II is the "deluxe" version of the Classic II. Though its chestpiece is only single-sided (compared to two-sided for the other three models), the tubing is thicker (helping to preserve sound quality), and uses a "Master" chestpiece, made from plated and polished alloy. This model also features a tunable diaphragm, which allows the examiner to hear high- or low-frequency sounds depending on the pressure applied.
These three models are specifically designed for use in examining cardiology patients, as their names imply. The Cardiology III features a two-sided tunable chestpiece, and double-lumen tubing. The second diaphragm is 1.3 inches wide, designed for more focused auscultation. The Cardiology S.T.C. is similar to the Cardiology III, with the exception of the head. Instead of a steel double-sided chestpiece, the S.T.C. features a specially designed chestpiece, making it easier for the clinician to grasp the chestpiece and helps achieve a better seal on the patient. The Master Cardiology model reverts back to the traditional single-sided steel chestpiece, and has better acoustical quality than the other Cardiology models. The Master Cardiology also comes with an additional adaptor that fits over the chestpiece, converting it from a regular-sized diaphragm down to a small-sized (pediatric) one.
3M Littmann has two models of electronic stethoscopes. Both feature the added benefits of electronic amplification and noise-filtering technology. One difference between the two models (the 3000 and the 4100) is in the process by which the diaphragm is "tuned": the former uses analog electronic frequency filtering, while the latter uses digital. The 4100 also features slightly better amplification (25dB vs. 20dB for the 3000), and the ability to record six tracks worth of chest sounds. The 4100 also comes with an IR port, allowing stored sounds to be transmitted to another 4100 Stethoscope, or to a PC (most 4100 models are now also packaged with heart sound analysis software). In addition, the 4100 will calculate heart rate and display it on an LCD screen. The 3000 uses 1 AAA battery, providing forty hours of battery life, while the more gadget-intensive 4100 requires two AAA batteries, and has a battery life of only twenty hours.
Purchasing 3M Littmann Stethoscopes
Littmann stethoscopes can be purchased from most medical supply companies, uniform shops, and even some university bookstores. Used stethoscopes can also sometimes be found on eBay and other online retailers. 3M provides a list of authorized distributors on its website at http://solutions.3m.com/wps/portal/3M/en_US/Littmann/stethoscope/purchase/where-to-buy/, and recommends that their stethoscopes be purchased from an authorized distributor to avoid purchasing a counterfeit stethoscope.