Blood Pressure

The study of the blood pressure has become a subject of great

importance in the practice of medicine and surgery. No condition can

be properly treated, no operation should be performed, and no

prognosis is of value without a proper consideration of the

sufficiency of the circulation, and the condition of the circulation

cannot be properly estimated without an accurate estimate of the

systolic and diastolic blood pressure. However perfectly the heart

may act, it cannot properly circulate the blood without a normal

tone of the blood vessels, both arteries and veins. Abnormal

vasodilatation seriously interferes with the normal circulation, and

causes venous congestion, abnormal increase in venous blood

pressure, and the consequent danger of shock and death. Increased

arterial tone or tonicity necessitates greater cardiac effort, to

overcome the resistance, and hypertrophy of the heart must follow.

This hypertrophy always occurs if the peripheral resistance is not

suddenly too great or too rapidly acquired. In other words, if the

peripheral resistance gradually increases, the left ventricle

hypertrophies, and remains for a long time sufficient. If, from

disease or disturbance in the lungs, the resistance in the pulmonary

circulation is increased, the right ventricle hypertrophies to

overcome it, and the circulation is sufficient as long as this

ventricle is able to do the work. If either this pulmonary increased

pressure or the systemic increased pressure persists or becomes too

great, it is only a question of how many months, in the case of the

right ventricle, and how many years, in the case of the left

ventricle, the heart can stand the strain.

If the cause of the increased systemic tension is an arterial

fibrosis, sooner or later the heart will become involved in this

general condition, and a chronic myocarditis is likely to result.

If, on the other hand, there is a continuous low systemic arterial

blood pressure, the circulation is always more or less insufficient,

nutrition is always imperfect, and the physical ability of the

individual is below par. It is evident, therefore, that an

abnormally high blood pressure is of serious import, its cause must

be studied, and effort must be made to remove as far as possible the

cause. On the other hand, a persistently low blood pressure may be

of serious import, and always diminishes physical ability. If

possible, the cause should be determined, and the condition


No physician can now properly practice medicine without having a

reliable apparatus for determining the blood pressure both in his

office and at the bedside. It is not necessary to discuss here the

various kinds of apparatus or what is essential in an apparatus for

it to give a perfect reading. It may be stated that in determining

the systolic and diastolic pressure in the peripheral arteries, the

ordinary stethoscope is as efficient as any more elaborate

auscultatory apparatus.

It is now generally agreed by all scientific clinicians that it is

as essential--almost more essential--to determine the diastolic

pressure as the systolic pressure; therefore the auscultatory method

is the simplest, as well as one of the most accurate in determining

these pressures. Of course it should be recognized that the systolic

pressure thus obtained will generally be some millimeters above that

obtained with the finger, perhaps the average being equivalent to

about 5 mm. of mercury. The diastolic pressure will often range from

10 to 15 mm. below the reading obtained by other methods. Therefore,

wider range of pressure is obtained by the auscultatory method than

by other methods. This difference of 5 or more millimeters of

systolic pressure between the auscultatory and the palpatory

readings should be remembered when one is consulting books or

articles printed more than two years ago, as many of these pressures

were determined by the palpatory method.

Sometimes the compression of the arm by the armlet leads to a rise

in blood pressure. [Footnote: MacWilliams and Melvin: Brit. Med.

Jour., Nov. 7, 1914.] It has been suggested that the diastolic

pressure be taken at the point where the sound is first heard on

gradually raising the pressure in the armlet.

In some persons the auscultatory readings cannot be made, or are

very unsatisfactory, and it becomes necessary to use the palpation

method in taking the systolic pressure. In instances in which the

auscultatory method is unsatisfactory, the artery below the bend of

the elbow at which the reading is generally taken may be misplaced,

or there may be an unusual amount of fat and muscle between the

artery and the skin.

The various sounds heard with the stethoscope, when the pressure is

gradually lowered, have been divided into phases. The first phase

begins with the first audible sound, which is the proper point at

which to read the, systolic pressure. The first phase is generally,

not always, succeeded by a second phase in which there is a

murmurish sound. The third phase is that at which the maximum sharp,

ringing note begins, and throughout this phase the sound is sharp

and intense, gradually increasing, and then gradually diminishing to

the fourth phase, where the sound suddenly becomes a duller tone.

The fourth phase lasts until what is termed the fifth phase, or that

at which all sound has disappeared. As previously stated, the

diastolic pressure may be read at the beginning of the fourth phase,

or at the end of the fourth phase, that is, the beginning of the

fifth; but the difference is from 3 to 10 mm. of mercury, with an

average of perhaps 5 mm.; therefore the difference is not very

great. When the diastolic pressure is high, for relative subsequent

readings, it is much better to read the diastolic at the beginning

of the fifth phase.

It is urged by many observers that the proper reading of the

diastolic pressure is always at the beginning of the fourth phase.

However, for general use, unless one is particularly expert, it is

better to read the diastolic pressure at the beginning of the fifth

phase. There can rarely be a doubt in the mind of the person who is

auscultating as to the point at which all sound ceases. There is

frequently a good deal of doubt, even after large experience, as to

just the moment at which the fourth phase begins. With the

understanding that the difference is only a few millimeters, which

is of very little importance, when the diastolic pressure is below

95, it seems advisable to urge the reading of the diastolic pressure

at the beginning of the fifth phase.

The incident of the first phase, or when sound begins, is caused by

the sudden distention of the blood vessel below the point of

compression by the armlet. In other words, the armlet pressure has

at this point been overcome. Young [Footnote: Young: Indiana State

Med. Assn. Jour., March, 1914.] believes that the murmurs of the

second phase, which in all normal conditions are heard during the 20

mm. drop below the point at which the systolic pressure had been

read, is "due to whirlpool eddies produced at the point of

constriction of the blood vessel by the cuff of the instrument." The

third phase is when these murmurs cease and the sound resembles the

first, lasting he thinks for only 5 mm. The third phase often lasts

much longer. He thinks the fourth phase, when the sound becomes

dull, lasts for about 6 mm.

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