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 As
useful as it has been throughout the millennia, the pulse is but a
crude and imprecise representation of the blood pressure. The first
direct blood pressure measurement is attributed to the Reverend
Stephen Hales in 1733. After inserting a glass tube into a horse’s
artery, he measured a column of blood eight feet three inches tall
above the level of the horse’s left ventricle. By
the nineteenth century, scientists began to experiment with various
devices to measure the amplitude of the pulse wave. A designer of such
a device, Vierodt suggests that the back-pressure necessary to remove
the beats of the pulse makes it possible to appreciate the value of
the blood pressure.
In
1881 in Vienna, Samuel Von Basch records the first noninvasive
measurement of systolic blood pressure needed to obliterate the
arterial pulse with a tonometer.
In
the late nineteenth century, other devices were introduced, but of
little significance. |
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The
modern era of blood pressure measurement starts with the introduction
of the sphygmomanometer by Scipione Riva-Rocci in 1896. He created an
inflatable rubber cuff designed to obstruct the blood flow of the
brachial artery. A column of mercury was used to quantify the pressure
required to inflate a rubber cuff at the moment the pulse became
unpalpable distal to the cuff. Although revolutionary, Riva-Rocci’s
invention was limited by inherent problems; specifically, his cuff was
too narrow, resulting in inaccurate measurements. Von Recklinghausen
later recognized this error and widened the cuff from 5 to 13 cm.
Source of illustration: Zimmermann, E. (1903). XVIII. Preis- Liste
über psychologische und physiologische Apparate (p. 89). Leipzig:
Eduard Zimmermann.
Aneroid
manometers were subsequently introduced. The oscillations of a
manometer allowed for better visualization of pulsations compared to
fluctuations in the level of the mercury column. This allowed for the
development of the oscillometric method of measuring the blood
pressure. It is important to note that oscillometry is the only
non-invasive method that directly estimates the mean blood pressure:
The minimal occlusive pressure at which maximal oscillation occurs.
In
1905, a Russian Surgeon, Nikolai Sergeyevich Korotkof ,described the
sounds heard with a stethoscope placed over the brachial artery below
the Riva-Rocci-von Recklinghausen cuff during slow deflation. This is
still the most widely used method worldwide today.
Further
refinement to using Riva-Rocci’s method includes the use of the
Doppler, which is independent of the audible vibrations needed with
Korotkoff’s method.
In
recent decades, both automatic non-invasive blood pressure measuring
devices and direct measurement with small arterial lines have become
widespread. Other approaches have been introduced to measure the
arterial blood pressure, including the Penaz method, which is based on
unloading the arterial wall to measure a calibrated waveform in a
finger.
All
of these methods possess advantages and disadvantages. Invasive
monitoring provides the most reliable beat-to-beat measurement of the
blood pressure and allows frequent blood sampling. However, besides
being sometimes technically challenging, invasive procedures increase
the risk of infection. On the other hand, non-invasive methods such as
the arm cuff, although ubiquitous, can traumatize tissues, which may
lead to paresthesias associated with nerve damage with prolonged use.
The
quest for the ideal blood pressure measurement technique, both
invasively and non-invasively, continues today. The most recent
introduction is Medwave’s Vasotrac, a non-invasive device that
provides blood pressure information on a continual basis. |
