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History of Stethoscopes and Sphygmomanometers

Stethoscopes

 

For decades, physicians relied almost solely on the stethoscope

From the time it was invented in 1816 until early this century, the stethoscope was the most reliable and informative tool available for diagnosing cardiovascular disease. Although other, more sophisticated diagnostic methods have come into use since then, the stethoscope has never been discarded.

"At the turn of the century...diagnosis relied on taking a history and examining the heart with a stethoscope, and treatment consisted mainly of rest and a few standard oral medications." said W. Bruce Fye, a University of Wisconsin cardiologist and historian.

The stethoscope battles embarrassment

Since the time of Hippocrates, physicians listened directly to patients' chests as they tried to assess cardiac health. The inventor of the stethoscope, Rene Theophile-Hyacinthe Laennec, relied on this method, too.

 


The inventor of the stethoscope listens directly to a patient's chest to hear the effect of tuberculosis on the lungs.

 

 

One day, when he needed to examine an obese young woman, Laennec hesitated to put his head to her chest. Remembering that you can hear a pin scraping one end of a plank by putting your ear to the other end, he came up with the idea for a stethoscope prototype. He rolled a stack of paper into a cylinder, pressed one end to the patient's chest, and held his ear to the other end.

"I was surprised and pleased to hear the beating of the heart much more clearly than if I had applied my ear directly to the chest," Laennec said in 1816.

Laennec's first manufactured stethoscope was a simple wooden tube. A succession of different designs followed his, including, eventually, a "binaural" type with two ear pieces. In 1850, George Camman substituted rubber for stiffer materials and made a more comfortable model—the forerunner of today's stethoscopes.

The use of the stethoscope led to better descriptions of heart sounds and improved ability to distinguish among various murmurs and rhythmic disturbances. It increased understanding of how blood moves through the heart in each cardiac cycle, under normal and abnormal conditions.

"A wonderful instrument called the stethoscope, invented a few months ago ... is now in complete vogue in Paris."
(London Times December 19, 1824)

Convertible monaural stethoscope, 1860
(Wood)

 

Monaural stethoscope, 1865
(Ivory, steel, wood)

 

 

Monaural stethoscope, 1880
(Brass, chrome, plastic)

 

 

Camman's binaural stethoscope, ca. 1870
(Steel, rubber, cotton)

 

 

Modern binaural stethoscope, 1998
(stainless steel, rubber, nylon, plastic)

 

What are the sounds that a stethoscope reveals?

A normal heartbeat makes a lub-dup sound. This sound is created when the heart tissue vibrates when blood is thrown into turbulent oscillations as it is pushed against the heart valves and bounces back.

heart
(Click image to rotate object)

 

Lub

You hear the first part of a heartbeat when the ventricles contract and the blood is pushed against, and bounces back from, the closed valves between the atria and ventricles.

Dup

You hear the second part of a heartbeat when the blood exiting the heart via the aorta and the pulmonary artery bounces back from the closed pulmonary and aortic valves.

What's a heart murmur?

A variety of heart conditions can change the shape of heart valves or chambers and cause abnormal sounds. If the valves don't close completely, for example, some blood leaks back through the valve, making a whooshing, rasping, or blowing sound called a murmur.

 

Sphygmomanometers

 

What is blood pressure?

Blood pressure is the force exerted by the blood on blood vessel walls. Today, it's measured in millimeters of mercury, units that refer to the height to which a column of mercury is raised by an equivalent pressure.

Recording blood pressure leads to the discovery of hypertension

Although physiologists who studied animals knew about the phenomenon of blood pressure in the 1700s, it was many years before physicians figured out how to measure it in humans. As soon as doctors had an accurate device and a simple procedure for measuring blood pressure, it became a normal part of a medical exam. Physicians could detect and monitor blood pressure over time, and they soon discovered hypertension, or chronic high blood pressure, a widespread and life-threatening condition.

Unfortunately, doctors had few options for treating hypertension and little understanding of its causes. Sometimes kidney disease was associated with hypertension, but in most cases, no cause could be identified.

This 1863 sphygmograph was an early attempt to measure blood pressure that proved to be cumbersome and inaccurate. A spring pressed one end of a lever onto the wrist, compressing an artery. The lever rose and fell with each pulse wave. A recording device traced the movements on smoked paper.

 

This 1898 sphygmomanometer had a cuff that was too narrow. Later models with wider cuffs gave more accurate readings.

 

This 1901 model had a wide cuff, but doctors used their fingers to detect arterial blood flow as they watched for changes in pressure.

 

In 1905, Russian surgeon Nikolai Korotkoff developed the modern technique of using a stethoscope to listen for the sounds of blood flowing through the artery. His method proved to be extremely accurate and led to the discovery of hypertension.

 

1920 mercury sphygmomanometer, the "Pilling Midget"

How to take a blood pressure reading, based on Korotkoff sounds


A modern sphygmomanometer

  1. Place cuff snugly around the middle of the upper arm.
  2. Place the bell of your stethoscope over the pulse point just below the cuff.
  3. Pump up the cuff until it's tight enough to stop blood flow.
  4. Slowly deflate the cuff and listen.
  5. Note the pressure reading when you hear the first faint sounds—that means some blood has started to pass through the vessels under the cuff. This is the maximum, or systolic, pressure.
  6. When all sounds stop, note the pressure reading again. Now blood is flowing freely. This is the minimum, or diastolic, pressure.
  7. Record the blood pressure as systolic over diastolic.
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