Encyclopedia of Family Health - Vol. 15

By David B. Jacoby; Robert M. Youngson | Go to book overview

Sphygmomanometer

Questions and Answers

Will it hurt to have my blood
pressure taken?

No, not at all. The most that you
will feel is a tightness on your arm
when the cuff is fully inflated; but
this lasts for only a few seconds
and amounts to mild discomfort
rather than pain.

When my blood pressure is taken
I get a thumping feeling in my
arm. Why?

This is the equivalent to what the
doctor hears with a stethoscope
and represents the moment at
which the pressure in the cuff is
dropped to a point at which
blood can flow into the lower arm
again. It can do so only at the
peak of the heart’s pumping
action, called systole, so you feel a
thump in your arm each time your
heart beats. When the pressure in
the cuff is lowered again, and the
blood flows freely again, the
thumping disappears. The reading
on the scale then represents the
diastolic blood pressure.

I understand that having your
blood pressure taken involves
cutting off the blood supply to
one arm. Isn’t this dangerous?

No; the blood supply is cut off for
only a few seconds; it would have
to be interrupted for at least 10
minutes to cause damage to the
tissues of the arm.

My doctor always takes my blood
pressure on the left arm, but
other doctors use the other arm.
Which method is correct?

Both. Except in people with a very
rare disease, the blood pressure is
the same throughout the body, so
it doesn’t matter which arm is
used. It may be that in the doctor’s
office, the left arm is nearest to
the sphygmomanometer, so that
the patient need not move.

Our circulatory system needs a consistent pressure if it is to function efficiently. The machine used to measure this pressure is called a sphygmomanometer; it can be a mercury gauge or an aneroid device.

The pressure of blood in the arteries fluctuates, about 80 times each minute, between a maximum that occurs at the height of the heart’s contraction (the systolic pressure) and a minimum that occurs when the heart muscle relaxes between beats (the diastolic pressure). The sphygmomanometer works by comparing the pressure in the arteries with that required to support a standard column of mercury at a certain height. The familiar figures for normal blood pressure, 120/80, mean that the systolic pressure is equivalent to the force required to support a column of mercury 120 mm (4.75 inches) high, and the diastolic pressure would support a column of mercury 80 mm (3.15 inches) high. An upright glass tube (a manometer), which is graduated in millimeters and closed at the top, is connected at the bottom to a glass bulb containing mercury. It is fixed on to a backboard for support. There is an armlet or cuff for compressing the upper arm; and the rubber bulb for pumping it up is fitted with a screw valve to enable air to be released from the cuff at the right time. The three parts of the apparatus are connected by short lengths of rubber tubing. The cuff and the pressure gauge are connected so that the pressure in one is the same as the pressure in the other.


Measuring the blood pressure

The cuff is wrapped firmly around the arm just above the elbow and the doctor pumps air into it until the pressure is sufficient to stop blood from flowing into the lower arm. He or she listens with a stethoscope over the brachial artery at the elbow. At this point the doctor will hear nothing. Continuing to listen, the doctor slightly unscrews the valve on the bulb so that air is released from the cuff and the pressure in it slowly falls. When the pressure in the cuff and in the artery are the same, the blood can flow again, but only at the systolic part of the heart’s action, since the diastolic pressure is insufficient to get past the inflated cuff. The doctor will hear a series of thuds each time the heart beats and squeezes blood past the cuff. The reading on the scale then represents the systolic blood pressure (see Blood Pressure). Once the systolic level is recorded, the doctor loosens the valve further. When the thumping dies away, the reading on the scale represents the diastolic blood pressure.

Blood pressure can be measured using
a mercury gauge sphygmomanometer
.

See also: Heart; Heart disease; Kidneys and
kidney diseases; Salt; Stress; Stroke

-2036-

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Encyclopedia of Family Health - Vol. 15
Table of contents

Table of contents

  • Title Page iii
  • Contents v
  • Spastic Colon 2022
  • Specimens 2024
  • Speculum 2027
  • Speech 2028
  • Speech Therapy 2032
  • Sperm 2034
  • Sphygmomanometer 2036
  • Spina Bifida 2037
  • Spinal Cord 2040
  • Spleen 2044
  • Splinters 2047
  • Splints 2048
  • Sports Injury 2050
  • Sports Medicine 2052
  • Sprains 2056
  • Stammering and Stuttering 2058
  • Staphylococcus 2062
  • Starch 2063
  • Stem Cell 2065
  • Stenosis 2067
  • Sterilization 2068
  • Steroids 2072
  • Stethoscope 2074
  • Stiffness 2076
  • Stillbirth 2080
  • Stimultants 2083
  • Stitch 2086
  • Stomach 2088
  • Stomach Pump 2091
  • Strangulation 2094
  • Streptococcus 2097
  • Stress 2098
  • Stress Management 2103
  • Stretch Marks 2105
  • Sty 2112
  • Subconscious 2114
  • Sudden Infant Death Syndrome 2116
  • Suffocation 2118
  • Sugars 2120
  • Suicide 2122
  • Sunburn 2126
  • Sunstroke 2130
  • Suppositories 2132
  • Surgery 2134
  • Surrogacy 2141
  • Sutures 2144
  • Swellings 2145
  • Symptoms 2149
  • Syphilis 2153
  • Syringing 2156
  • Index 2158
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