“Place the bag over the arm with the two tubes well under the arm and over the brachial artery. Wrap the remainder of the sleeve around the arm much the same as you would apply a bandage, tucking at least six inches of the sleeve under the last fold. Then place the sphygmomanometer in one tube and the bulb in another, and you are ready for reading. Care should be taken not to put the sleeve on tight enough to cause any apprehensive feeling in the patient.
“Place the finger lightly over the radial artery and send the pressure in the cuff to the point where the pulse has entirely disappeared, then advance the hand about 2 cm. above this point of disappearance, then release the air gradually and note the first perceptible pulse wave felt by the palpating finger at the wrist. This represents the true systolic or maximal pressure.
“Having now obtained the systolic or maximal pressure, release the air gradually by means of the escapement valve, and note where the largest oscillation or movement of the hand takes place, and the lowest point of this largest oscillation is the diastolic or minimal pressure.
“For example, if the largest oscillation occurred between the divisions 90 to 96, 90, being the lowest, would be the reading.
“It is well to bear in mind to keep the eye concentrated on the scale divisions, for the travel of the hand can be accurately determined when this is done.
“In determining systolic (maximal) pressure, the pulse becomes more feeble as the pressure advances, and when taken with the ends of the fingers, the pressure of the fingers is involuntarily increased, so that a very sensitive pulse may be closed off entirely by the finger pressure; while, if taken with the ends of the fingers resting on the upper curve of the bone of the wrist, permitting the balls of the fingers to rest lightly over the radial, thus bringing in contact with the pulse the most sensitive part of the fingers, any extra pressure that might result would be directed against the bone and not the pulse.
“Method by Auscultation.—This is by far the most accurate method of determining the blood-pressure, and the results obtained in this way should be free from error, or the dangers of personal equation in palpating the artery at the wrist.
“Systolic or Maximal Pressure.—Bare the arm and adjust the sleeve well up; place the stethoscope over the brachial artery about 1 cm. below the border of the cuff, then constrict the arm by inflating the bag until no sound is heard in the artery through the stethoscope. At this point release the air slowly by means of the escapement valve, and soon a clear, clicking sound will be heard, which indicates the first passage of the blood stream below the constricting arm band and is the true systolic or maximal pressure.
“Diastolic or Minimal Pressure.—Still gradually releasing the air, this clear, clicking tone (first phase) is followed by a low tone or murmur (second phase), and this murmur is followed by a loud, clear tone (third phase), this in turn by a perceptibly dull tone (fourth phase), and this dull tone represents the diastolic or minimal pressure.
“Below are given the five different phases of tone to be heard in the auscultatory blood-pressure phenomena as found by Louis M. Warfield, A.B., M.D., and confirmed by his clinical observations on animals.