Blood Pressure

THE HEART PUMPS BLOOD DIRECTLY INTO
blood vessels called arteries, which are like a series of
pipes. The narrower the artery, the greater the resistance or
impedance to the flow of blood; therefore, the heart must
pump with greater force. The amount of force the blood is
pumped from the heart through the arteries is the blood
pressure.

I. HISTORICAL REVIEW
A. The Beginning of Sphygmomanometry
Reverend Stephen Hales is the father of sphygmomanometry.
During his seven-year course in theology at Corpus
Christi (Bene’t College), Cambridge in 1733, mathematics
and science were added to basic theology and philosophy.
It was at Cambridge where he initially experimented on
pressure, resistance, and flow. He later became curate of
Teddington outside of London, received his BA, and was
awarded an MA at Cambridge and Bachelor of Divinity
from Oxford.

Some years later he commenced his experimental scientific
work on the circulation of blood. He conducted
more than 25 experiments on dogs and horses. Figure 1 is
an artist’s impression of Hale’s experiments to determine
the blood pressure of a horse. His observations were published
in Volume II of the Statical Essays in 1733:
. . . in the summer I caused the mare to be tied down
alive on her back; having laid open the left crural artery
about three inches from her belly, I inserted into it a
brass pipe whose bore was one sixth of an inch in
diameter. . . . I fixed a glass tube of nearly the same
diameter which was 9 feet in length: then untying the
ligature of the artery, the blood rose in the tube 8 feet 3
inches perpendicular above the level of the left ventricle
of the heart;. . . when it was at its full height it would
rise and fall at and after each pulse 2, 3, or 4
inches . . . .’’

Figure 2 is a page from Haemastatics showing his
measurement for correlating blood volume with the blood
pressure. After this, it appears that there were no advances
for the next 100 years.

B. Further Advances
Poiseuille was a physician and a physicist who introduced
the mercury manometer to the world in 1833. He won the
gold medal of the Royal Academy of Medicine for his
doctoral designation of the management of arterial blood
pressure by means of the mercury manometer connected
to a cannula that was inserted directly into an artery.
Around 1881 Samuel von Basch further advanced blood
pressure measurements with the use of an inflatable
rubber bag with water (see Fig. 3). In 1889, Potain substituted
air for water and used a rubber bulb for compression
of the pulse. He recorded the pressure with a
portable aneroid manometer, but the measurements were
unreliable.

C. Advancements Leading to Current Methods
Scipione Riva-Rocci, in 1896, reported a noninvasive
method of obtaining blood pressure that led to our current
technique (see Fig. 4). He reported the appearance
of definite and pronounced oscillations in the column
of mercury which coincided with the appearance of the
radial pulse. This was taken as the systolic pressure. The
diastolic pressure was recorded when the level of the
mercury column changed from large to small oscillations.
A major defect in Riva-Rocci’s technique was the use of
a narrow 5-cm arm band. German pathologist Friedrich
Von Recklinghausen later corrected this defect by introducing
a 12-cm wide arm band in 1901.

By 1905, Nicolai Korotkoff further advanced Riva-
Rocci’s ideas. In 1898 Korotkoff obtained his medical
degree from the University of Moscow and pursued
a career in vascular surgery. As a surgeon, he often used
a stethoscope to differentiate between a solid mass and
arterial aneurysm. He was therefore concerned with sounds
made by arteries.

His main conclusions were derived from the simple
observation that a perfectly constricted artery under
normal conditions does not emit any sounds. Thus, he
proposed the sound method for measuring blood pressure
on humans. He used the Riva-Rocci sleeve on the middle
third of the arm. At first he observed no sounds, but as the
mercury in the manometer dropped to a certain height
the first short faint tones appeared. He called these tones
the maximum blood pressure. When all sounds disappeared,
the manometer reading reflected the minimum
blood pressure. The accuracy of Korotkoff’s ‘‘sound
method’’ has stood the test of time. It is presently used
worldwide with acceptable clinical accuracy; nothing has
changed except for a varied cuff size relative to the arm
width.

II. SYSTOLIC AND DIASTOLIC BLOOD PRESSURE
Everyone has a blood pressure, but what does that mean?
The pressure in the arteries when the heart contracts
(systole) is called systolic blood pressure. This is usually
less than 140 millimeters of mercury (mmHg). The
pressure in the arteries when the heart is relaxed (diastole)
is called diastolic pressure, and this is usually less than
90 mmHg in adults.

Here is another way of looking at blood pressure. Each
contraction of the heart causes blood to be pushed
(propelled) through the arteries in the form of a pulse
wave; thus the flow of blood in the arteries is pulsatile.
A wave must have a crest and a trough. The crest is caused
when the heart contracts (systole) and is the highest
pressure. Systolic blood pressure coincides with the first
Korotkoff sounds heard with the stethoscope over the
brachial artery at the cubital fossa just below the level of
the inflated cuff on the arm. The trough is caused when
the heart relaxes (diastole), producing the lowest pressure,
or diastolic pressure at which instant all Korotkoff sounds
disappear, and no sounds are heard with the stethoscope.
Resistance in the arteries against which the heart must
pump is called the total vascular resistance. If the total
vascular resistance increases, blood pressure increases. This
vascular resistance is increased when the arteries are
constricted by disease, aging, drugs, or naturally occurring
chemicals in the body such as adrenaline and noradrenaline.
Sudden alarming stress, fright, and situations that
provoke sudden anxiety may cause secretion of excess
adrenaline and noradrenaline, which causes sudden and
considerable elevation in systolic blood pressure. In these
situations the systolic blood pressure, which may have been
135 mmHg, may shoot up suddenly, and within minutes
be 175–200 mmHg.

The amount of blood expelled by the heart into the
arteries in one minute is called the cardiac output and is
about 5 L/minute. Blood pressure is equal to the total
vascular resistance multiplied by the cardiac output.
Hypertension is the medical term for high blood pressure
and has nothing to do with excessive nervous tension.
High blood pressure in individuals older than age 18
is defined as a systolic blood pressure of greater than
140 mmHg and/or a diastolic blood pressure of greater
than 90 mmHg based on the average of two or more
readings taken at each of two or more visits after an initial
screening (average of at least four readings taken days or
weeks apart).

III. CLASSIFICATION
The classification of blood pressure (BP) for adults age
18 years and older as given in the Seventh Report of the
Joint National Committee on Prevention, Detection,
Evaluation, and Treatment of High Blood Pressure
(JNC 7) is as follows:

Normal: BP<120>160; >100

IV. NORMAL FLUCTUATIONS IN BLOOD PRESSURE
A. Marked Variability
Marked variability in blood pressure is normal. It varies
from minute to minute and from day to day like the waves
of a sea, fluctuating with the force of the prevailing winds.
Blood pressure is different at night, during sleep, and the
early morning, fluctuating considerably during the day.
The systolic pressure may differ from 5 to 15 mmHg
during these moments.

Ambulatory blood pressure recordings may be needed in
some individuals to verify the correct levels of hypertension.
The blood pressure readings in a doctor’s office or
clinics are often higher than they are in a home setting.
Blood pressure readings taken at home are important,
but it is necessary to have the pressure recorded outside
the home in different settings to arrive at conclusive
documentation that high blood pressure is indeed present.
The variability of the blood pressure recorded on repeated
measurements, both at a single visit and on separate
occasions at a clinic or physician’s office, is much greater
than most doctors and patients realize. Individuals are
often falsely labeled normotensive or hypertensive. Because
of the lifelong commitment to antihypertensive medications,
the diagnosis must be carefully established, particularly
with borderline hypertension. Because of this marked
variability in recorded blood pressure from day to day,
individuals with borderline hypertension may require
observation for up to two years before a correct diagnosis
is made and the commencement of medications.

B. Daytime and Nighttime Variability
Daytime blood pressure is mainly determined by the
degree of physical and mental activity and is under the
control of baroreflexes that operate through adjustments in
heart rate and peripheral vascular resistance. The usual fall
in blood pressure at night is a result of sleep and inactivity
rather than the time of day; pressure falls during the
day if an individual sleeps. Blood pressure may fall
10–20 mmHg during sleep as the baroreflex sensitivity
decreases sympathetic nervous activity.
There is a usual abrupt rise in blood pressure within
minutes of arising in the early morning caused by
catecholamine release; it is a critical period that coincides
with an increased incidence of sudden cardiac death,
stroke, and myocardial infarction. An increase in catecholamines
increases blood pressure, which causes increased
stickiness of platelets that may aggregate and predispose
the formation of clots in coronary arteries or arteries that
supply the brain. The activity of the heart increases as more
oxygen is required to cope with the stimulation caused by
the release of catecholamines.

Beta-blocking drugs counteract the deleterious effects of
catecholamines, and they have been shown in sound,
randomized clinical trials to decrease the early morning
incidence of sudden deaths and fatal and nonfatal myocardial
infarction. These sudden deaths are not prevented
by aspirin or antiplatelet agents. This information is probably
known to less than 25% of practicing doctors
worldwide.

C. White-Coat Hypertension
The definition of white-coat hypertension awaits clarification.
The prevalence in a population of untreated hypertensive
patients has been reported to vary from 12% to as
high as 53%. It is estimated, however, that about 10% of
these individuals have genuine hypertension; they do not
require medication and their hypertension should be
defined by blood pressures taken outside the physician’s
office. Home measurements and the use of finger blood
pressure measurements should be used.
The acute elevation of blood pressure in the office
setting is presumably a conditional reflex that increases
sympathetic nervous arousal each time the blood pressure
is taken by the physician. In a study of 292 patients with
diastolic blood pressures ranging from 90 to 104 mmHg
during multiple physician’s visits over a period of
6 years, 21% had persistently normal readings during a
24-hambulatory recording.

White-coat hypertension has been observed in more
than 20% of individuals diagnosed as hypertensive,
including elderly patients with systolic hypertension.
In one study approximately 50% of patients who were
not believed to be responding to medications based on
physician’s blood pressure readings were shown on
ambulatory monitoring to have controlled blood pressures.
Overuse of medications in this large population of
individuals is a real problem.

D. Pseudohypertension
Pseudohypertension is a false reading of high blood pressure.
It is not unusual for this to occur in patients with
arteriolosclerosis, calcification, and diffuse hardening of
the arteries, particularly in the upper limbs. With hardening
of the arteries, the rigid, pipe-like arteries resist
compression by the sphygmomanometer cuff, and the
pressure in the cuff wrapped around the arm fails to
constrict and collapse the brachial artery. Because of this,
blood continues to flow through the artery into the
forearm causing a false high reading. A reading in the range
of 180 to 220 is not unusual.

Pseudohypertension should be excluded in elderly
individuals whose brachial arteries characteristically feel
rigid and pipe-like and in individuals who have no effects
of hypertension after several years of abnormal readings
such as evidence of hypertension in the retina or cardiovascular
or renal disease. Pseudohypertension may also
be suspected in these individuals with blood pressure
apparently resistant to therapy and in those who develop
dizziness and lightheadedness related to change in posture.
Recordings over a period of weeks in the home, particularly
with a simple finger blood pressure measurement,
should resolve the diagnosis of pseudohypertension in
virtually all patients. An automatic oscillometric recorder
may be required to verify the blood pressures, and rarely,
a direct intra-arterial reading may be necessary.

E. Home Measurements
Home measurements of blood pressure are crucial for the
adequate management of hypertension in more than 33%
of hypertensives. A record of home measurements verified
by measurements outside the physician’s office is an
important strategy to prevent overmedication.
Measurements in the home have been shown to give
virtually all of the information provided by ambulatory
blood pressure monitoring. The home or ambulatory
readings have been shown in studies to be comparable,
reproducible, and considerably lower than office readings.
Home blood pressure measurements are strongly indicated
for the following:

To assist the physician with the diagnosis of borderline
or stage 1 hypertension (see stages given above in
Section III)

To exclude short term hypertension that may occur for
a few months because of stressful situations at work or
at home and do not require lifelong medications

To exclude white-coat hypertension

To exclude pseudohypertension in the elderly

To monitor response to therapy to avoid the addition
of another antihypertensive agent to achieve control,
thus preventing overmedication for so-called uncontrolled
blood pressure in an office setting

V. FINGER CUFF METHOD OF PENAZ
This method works on the principle of the unloaded
arterial wall. Arterial pulsation in a finger is detected
by a photoplethysmograph under a pressure cuff. The
plethysmograph’s output drives a servoloop which changes
the cuff pressure to maintain constant output so that the
artery is held in the partially opened state. The pressure
oscillations in the cuff are measured and resemble the
intra-arterial pressure wave in most individuals tested.
Finometer and Portapres recorders are available and are
useful for the diagnosis of pseudohypertension that may
occur in the elderly who may be overmedicated because
of the finding of high blood pressure readings obtained
with the usual cuff method.

VI. TECHNIQUE AND PITFALLS OF MEASUREMENT
The cuff size must the appropriate for the blood pressure
measurement to be accurate. The arm and the mercury or
aneroid manometer must be at the same level as the heart.
The patient should be seated for about 5 minutes with
the back supported and with the arm supported at heart
level. If the arm is not supported than readings are
approximately 8 mmHg higher than those taken with
arm supported. If the back is not supported, readings may
be as much as 10 mmHg higher because of the isometric
exertion needed to support the body and arm.
Inflate the bladder quickly to a pressure about
20mmHg above the systolic pressure as recognized by
disappearance of the radial pulse. Inflating the bladder too
slowly may cause errors. Deflate at a rate of 2–4 mmHg
per second; a slower rate of deflation may cause false high
readings. If a second blood pressure reading is to be taken,
the cuff must be completely emptied of air and the arm
band removed and reapplied. Many erroneous readings are
obtained if proper technique is not stringently applied.

VII. EFFECTS OF HIGH BLOOD PRESSURE
A moderate degree of hypertension for more than five
years causes severe damage to vital organs. Complications
include:
1. Hypertrophy or enlargement of the heart
2. Heart failure that causes fluid to accumulate in the
lungs and the legs manifested by severe shortness of
breath
3. Myocardial infarction
4. Atrial fibrillation, a serious arrhythmia which causes
palpitations, leads to stroke, and requires a bothersome
commitment to anticoagulation with blood thinners
5. Stroke that may be thrombotic or hemorrhagic
6. Damage to the kidney that leads to renal dysfunction
and renal failure
7. Aortic aneurysm prone to rupture

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