THE HISTORY OF BLOOD PRESSURE MESUREMENT

The ancient Greek physician Galen first proposed the existence of blood in the human body. Building on ideas conceived by Hippocrates, the body was comprised of three systems. The brain and nerves were responsible for sensation and thought. The blood and arteries filled the body with life-giving energy. He also believed that the liver and veins provided the body with nourishment and growth.

It was not until 1616 when William Harvey announced that Galen was wrong in his assertion that the heart constantly produced blood. Instead he proposed that there was a finite amount of blood that circulated the body in one direction only. But Harvey's views were initially met with a lot of resistance and scepticism. The idea that blood was not constantly produced in the body raised doubts about the benefit of bloodletting, a popular medical practice at the time.

Harvey was neither the only nor the first to question Galen's ideas. The Egyptians knew that blood flowed through the body and used leeches to unblock what they thought were passages of blood.

The first recorded instance of the measurement of blood pressure was in 1733 by the Reverend Stephen Hales. A British veterinarian, Hales spent many years recording the blood pressures of animals. Fifteen years beforehand, he took a horse and inserted a brass pipe into an artery. This brass pipe was connected to a glass tube. Hales observed the blood in the pipe rising and concluded that this must be due to a pressure in the blood. At this time the technique was invasive and highly inappropriate for clinical use.

It was not until 1847 that human blood pressure was recorded. The method used Carl Ludwig's kymograph with catheters inserted directly into the artery. Ludwig's kymograph consisted of a U-shaped manometer tube connected to a brass pipe cannula into the artery. The manometer tube had an ivory float onto which a rod with a quill was attached. This quill would sketch onto a rotating drum hence the name 'kymograph', 'wave writer' in Greek. However blood pressure could still only be measured by invasive means.

The lack of a non-invasive method of determining this new idea of blood pressure lead to many physicians working in this field. Once such man, Karl Vierordt, found in 1855 that with enough pressure, the arterial pulse could be obliterated. Vierordt used an inflatable cuff around the arm to constrict the artery.

Etienne Jules Mary, a French physician/cinematographer, developed this idea further in 1860. His sphygmograph could accurately measure the pulse rate, but was very unreliable in determining the blood pressure. Yet this design was the first that could be used clinically was a small degree of success.

In 1881, Samuel Siegfried Karl Ritter von Basch invented the sphygmomanometer. His device consisted of a water-filled bag connected to a manometer. The manometer was used to determine the pressure required to obliterate the arterial pulse. Direct measurement of blood pressure by catheterisation confirmed that von Basch's design would allow a non-invasive method to measure blood pressure. Feeling for the pulse on the skin above the artery, was used to determine when the arterial pulse disappeared.

However von Bacsh's design never won a keen following, many physicians of the time being sceptical of new technology, claiming that it sought to replace traditional ideas of diagnosis. In addition, many questioned the medial usefulness of information about the blood pressure. This did not stop some from attempting to produce a more useful device. A spring-based sphygmomanometer won some support, but they were difficult to calibrate and were very unreliable when dealing with acutely ill patients.

Scipione Riva-Rocci developed the mercury sphygmomanometer in 1896. This design was the prototype of the modern mercury sphygmomanometer. An inflatable cuff was placed over the upper arm to constrict the brachial artery. This cuff was connected to a glass manometer filled with mercury to measure the pressure exerted onto the arm.

Riva-Rocci's sphygmomanometer was spotted by the American neurosurgeon Harvey Cushing while he was travelling through Italy. Seeing the potential benefit he returned to the US with the design in 1901. After the design was modified for more clinical use, the sphygmomanometer became commonplace. Cushing and George Crile were major advocates of the benefits.

This sphygmomanometer could only be used to determine the systolic blood pressure. Observing the pulse disappearance via palpitation would only allow the measuring physician to observe the point when the artery was fully constricted. Nikolai Korotkoff was the first to observe the sounds made by the constriction of the artery in 1905. Korotkoff found that there were characteristic sounds at certain points in the inflation and deflation of the cuff. These Korotkoff sounds were caused by the abnormal passage of blood through the artery, corresponding to the systolic and diastolic blood pressures.

A crucial difference in Korotkoff's technique was the use of a stethoscope to listen for the sounds of blood flowing through the artery. This auscultatory method proved to be more reliable than the previous palpitation techniques and thus became the standard practice.

Modern developments have led to more accurate auscultatory sphygmomanometers, and newer oscilliometric models. These sphygmomanometers measure the pressure imparted onto the cuff by the turbulent blood squirting through the constricted artery over a range of cuff pressures. This data is used to estimate the systolic and diastolic blood pressures.

Development of the stethoscope

The development of the stethoscope owed much to the work of Leopold Auenbragger. Auenbragger believed that the sounds heard from tapping on the patient's chest would reveal any irregularities. This technique, 'thoratic percussion' was published in 1761, but was largely ignored until the early 19th Century.

Next came Nicolas Corvisart. He was a supporter of Auenbragger's thoratic percussion and was vigorous in his promotion of 'auscultation', listening to the sounds body cavities made when tapped firmly. One follower of Corvisart was René Laennec. Laennec took a particular interest in the auscultation of the thorax.

The standard auscultatory technique for the physician would be to press their head against the patient's chest in order to listen to the resonations. However this left Laennec in an awkward situation, if the following anecdote is to be believed. During his days as a young doctor, in 1816, he was presented with a young buxom lady who was showing all the signs of heart disease. Wanting to ascultate the chest for confirmation of his diagnosis, the tenderness of Laennec's years left him too inhibited to act. Rather than cause himself undue embarrassment, he rolled a piece of paper into a tube, and used that rather than plant his head into her chest. To his astonishment, he could hear the heart just as well as if he had been diagnosing a man instead.

After careful experimenting, Laennec decided upon a hollow tube 3.5cm in diameter, and 25cm long. He investigated the sounds made by the heart and lungs with his new stethoscope and published the results in 1819. He found that his diagnosis was backed up with the observations in the autopsies.

Using Laennec's stethoscope was no more accurate than placing the head to the chest. Thus the benefit of the stethoscope was more social than clinical. It allowed the doctor some dignity during diagnosis and later became a 'badge of office' for the physician.

There were many alterations to Laennec's original idea such as one developed by N.P. Commins in 1828. He added a hinge and connected the two halves with tubing. This design allowed more flexibility to observe parts of the body hard to reach with the rigid design. There were many attachments available to the physician. One such was an extension that could be screwed in. This was of great benefit to the timid physician, or the doctor whose next patient had a particularly unique aroma.

The binaural stethoscope was developed in the 1890s complete with the recognisable rubber tubes. The onset of radiography has rendered the stethoscope obsolete in hospitals. However it is still a useful diagnosis tool for a GP or a cardiologist, so the humble stethoscope will remain a doctor's trusted friend for a little while longer.