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Sphygmomanometry: The Study of Blood Pressure
By Jennifer Louya
Throughout history the practice of medicine has been influenced by the scientific
technologies of the time. One example of this is the observation of the pulse. Through changes
and improvements in technology, researchers began to observe blood pressure in a more accurate
manner. Through scientific developments blood pressure measurement went from being
qualitative to quantitative—this means that blood no longer had to be physically seen rising and
falling in a glass tube to be recorded, but instead could be documented with a noninvasive
method that resulted in accurate numerical data.1 As the science evolved, so did the medical
instruments. Instruments for recording blood
pressure went from being invasive, sometimes
harmful devices to being sophisticated, accurate
instruments. One of the key devices in this
development was the Baumanometer, a device
displayed in the Special Collections at the Health
Science Library. This instrument was crucial
because it made sphygmomanometers more accurate
and available to the scientific community.
Historians such as N.H. Naqvi and M.D.
Blaufox, authors of Blood Pressure Measurement:
An Illustrated History, have agreed that Stephen
Figure 1: A drawing of Stephen Hales
performing his first experiment to record
blood pressure. Source: “History of Blood
Pressure”
(http://www.instantbloodpressure.com/history
-of-blood-pressure/)
Hales was the first to measure blood pressure.
1
N.H. Naqvi and M.D. Blaufox, “Sphygmography,” in Blood Pressure Measurement: An Illustrated History, New
York: The Parthenon Publishing Group, 1998, 31-47.
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Stephen Hales was a clergyman who was interested in botany and physiology. In 1733 he
published Haemastaticks, a book that discussed his experiments in the discovery of blood
pressure.2 In it, Hales writes:
Having laid open the left crural artery about three inches from her belly, I inserted into it
a brass pipe which was one sixth of an inch in diameter; and to that, by means of another
brass pipe which was fitly adapted to it, I fixed a glass tube, of nearly the same diameter,
which was nine feet in length: then untying the ligature on the artery, the blood rose in
the tube eight feet three inches perpendicular above the level of the left ventricle of the
heart: but it did not attain to its full height at once; it rushed up about half way in an
instant and afterwards gradually at each pulse twelve, eight, six, four, two, and sometimes
one inch…3
This was the first record of blood pressure. By inserting a glass tube in a mare’s artery, Hales
was able to observe the blood rise and fall with each heartbeat, proving there was blood pressure.
Hales repeated this experiment several times and with each trial noticed that blood pressure
depended on the size and condition of the animals.4
After this initial discovery many scientists started to look into blood pressure
measurement and how to improve its accuracy. In 1828, a French physiologist created the
haemodynamometer, device that consisted of a graduated U-shaped glass tube filled with
mercury called the manometer. Later in 1842, Professor Carl Ludwig, a German professor of
physiology, connected this U-shaped manometer to a kymograph and was the first to graphically
record blood pressure. Both of these inventions were major improvements upon the first
measurement where blood pressure was recorded by using only a glass tube in an artery.
In the latter half of the nineteenth century, scientists were still trying to find a way to
record blood pressure in a non-invasive manner. In 1877, Samuel Ritter van Basch created a new
sphygmomanometer that closed the artery by outside pressure. Blood pressure was found by
2
Naqvi and Blaufox, Blood Pressure Measurement, 49-65.
Stephen Hales, Statistical Essay, Containing Haemastaticks, London: Hafner Publishing Co., 1733.
4
Ibid.
3
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recording the location of the mercury in the glass tube at the first pulse and once more at the final
pulse before the pulse could no longer be heard. This was a great improvement because in earlier
models of sphygmomanometers the skin was cut and a tube was inserted into the artery.5 As time
went on other models of sphygmomanometers were created but it was not until 1896 that the
model for modern day sphygmomanometers was invented.
Figure 2: Carl Ludwig's kymograph. Source: “History of Blood
Pressure” (http://www.instantbloodpressure.com/history-of-bloodpressure/).
Scipione Riva-Rocci, an Italian pediatrician, created a sphygmomanometer that used an
arm cuff to obstruct the flow of the brachial artery in 1896. This invention marked the start of
the modern era of sphygmomanometry. The only major flaw in this design was the width of the
armband. Since the original armband was too narrow, the readings were at first inaccurate. Later
it was determined that the proper width of the armband is four and a half inches to five inches
wide. A band too narrow gave high blood pressures, while bands too thick gave blood pressures
too low. This improvement shows that medicine was starting to become more standardized. With
physicians now using the same width of armbands, the results were becoming more accurate and
5
Naqvi and Blaufox, Blood Pressure Measurement, 49-65.
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comparable. Unfortunately, with many different models and brands of sphygmomanometers,
blood pressure measurement was not yet standardized—not until William Baum’s invention.6
In 1916 William Baum created a highly accurate and portable line of
sphygmomanometers that are still used
today. William Baum worked at the
Life Extension Institute, an institution
founded in the United States in 1913 to
extend life and prevent disease. There
he noticed that the blood pressure
measurements made by doctors were
Figure 3: Riva-Rocci’s sphygmomanometer. Source: “Other
Devices in Sphygmomanometry” (http://vlp.mpiwgberlin.mpg.de/).
inaccurate. Due to his frustration with
the instruments of the time, William
Baum created the Baumanometer, a new breed of sphygmomanometer.7 Baum stated in his
application for a patent:
Closed end or compromised air or fluid instruments…operate at the expense of accuracy,
due to variations in the compressibility of the tube-confined air…the open end
instruments problems are…spilling of fluid…adjustable scale whose ‘zero’ mark is
required to be brought to the level of the fluid…fluctuation of the fluid column…’air
pockets’…breakage…8
The major disadvantage of earlier devices was their need for calibration. This created
inaccuracies if the scale was to drift or if the wrong amount of fluid was poured. The
Baumanometer, however, did not need to be calibrated. The Baumanometer came in two
different models in 1921: the desk model and the wall model. The desk model in 1921 came in a
6
Naqvi and Blaufox, Blood Pressure Measurement, 67-91.
Ibid.
8
William A. Baum, "William A. Baum of New York Manometer," United States Patent Office, Application
1594039, filed 8 October 1920; patented 27 July 1926.
7
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walnut wooden case while the 1924-1926 models came in metal cases.9 One of these
Baumanometers can be observed in the University of North Carolina at Chapel Hill’s Health
Science Library. On the inside of the device, there is a graduated glass tube containing a mercury
ball at the bottom measuring in calibrated millimeters. The glass tube is connected with a rubber
hose to a metal cylinder mounted on the inside of the case. This metal cylinder is connected to
the rubber pump with a long rubber tube. Another rubber tube connects the rubber air pump to an
air pouch inside of the armband. The armband is an olive green while the tubing and the rubber
air pump are black. There is a knob on the side of the rubber pump to release air from the
armband to find the final pulse. This device stands about a foot tall and is approximately 6 inches
wide.
The Baumanometer
was an everyday device used
in both hospitals and offices as
well as in homecare. Due to
the desk model
Baumanometer’s ability to
latch shut, it was easily
transported. Setup for a
Baumanometer was also very
easy. All the user had to do
Figure 4:
The 1921
Baumanometer in
UNC
Health
Sciences
Library.
Source:
Photo by
author.
was open the case and take out
the armband and pump. The device was noninvasive and caused the patient no harm. The
armband was tied around the patient’s upper arm above the elbow and inflated to measure blood
9
Baum, “Manometer.”
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pressure. The devices reflected the science of the time. As science and medicine became more
about collecting accurate results, instruments were designed to do just that. It was no longer
about just getting the results, but actually obtaining correct and standardized results that could be
compared to one another.10 Due to the ability to be compared, blood pressure started to be used
to detect acute diseases.
Blood pressure became more significant to medicine and science due to its availability
and easy, quick method of collecting data. Blood pressure has had a large impact on diagnosis
and treatment with medications. R. O. Butterfield, a physician in Los Angeles during the 1920s
states in a letter titled, “The Sphygmomanometer and the Endocrines”:
In the days of our childhood, the old-fashioned family physician used to judge our fever
by the pulse rate, and by the sense of touch determined the quality of the pulse or blood
pressure. He might or might not have used the stethoscope. Then came the clinical
thermometer and other instruments of diagnostic value, but without a doubt the most
important one of recent years is the sphygmomanometer.11
Butterfield goes on to say that in some of the infectious diseases of the time arterial
hypertension, detected by measuring blood pressure, was a precursor.12 In modern medicine,
blood pressure is measured often to detect acute diseases and cure them early on.
In history, medicine has been influenced by the scientific advancements and
developments of the time. Throughout time the medical instruments of the time evolved with the
science. Instruments for recording blood pressure went from being invasive, sometimes harmful
devices to being sophisticated accurate instruments.13 This means that blood no longer had to
physically seen rising and falling in a glass tube to be recorded, but instead could be documented
with a noninvasive method that resulted in accurate numerical data. The Baumometer was
10
Baum, “Manometer.”
R.O. Butterfield, “The Sphygmomanometer and the Endocrines,” in Essays on the Internal Secretions, Glendale,
CA: The Harrower Laboratory, 1920, 136-146.
12
Ibid.
13
Naqvi and Blaufox, Blood Pressure Measurement, 31-47.
11
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created in 1916 and is the basis for modern day blood pressure devices because of its accuracy
and portability. Due to the availability this new and accurate device, blood pressure measurement
began to be used as a precursor to trace some acute diseases.