by the modern sphygmomanometer. While it may be true that extremes in pressure might be recognized, it is also true that the smaller variations, which are after all often the most important clinically, cannot be detected with any degree of certainty, if at all.

We will consider therefore, that no further argument is necessary, but will assume it to be an accepted fact that the accurate estimation of arterial tension is to be accomplished only by means of sphygmomanometry.

With the older instruments it was possible to roughly estimate the systolic pressure. At the present time approximate estimations are no longer sufficient as we now believe it essential to determine with accuracy not only the systolic pressure but also the diastolic and pulse pressures, as well. Experience has taught us that while the systolic pressure is important, it is nevertheless only a part, and frequently but a small part of the information sought.

It, therefore, becomes extremely important to consider clinically the accepted methods of sphygmomanometry and to possess a working knowledge of the methods and instruments employed.

There are a large number of instruments, mostly of very recent devising, which may be relied upon in competent hands for this estimation, and the choice between them is largely a personal matter. So that in the pages to follow all statements referring to specific instruments are intended only to supply a certain amount of working knowledge, obtained through actual experience, which may save the reader unnecessary experimentation when selecting an instrument.

METHOD OF EMPLOYING THE MODERN SPHYGMOMANOMETER

Having already considered the subject of blood-pressure in the abstract and having reviewed the critera surrounding the proper performance of the study, we are now in a position to consider the actual clinical employment of the sphygmomanometer.

All modern clincial instruments are operated in conjunction with the elastic cuff or arm-band, which after encircling one of the extremities is inflated, so that by compression it will obliterate the arterial pulse. The measure of air pressure at the moment of complete obstruction is the measure of the systolic pressure. This has already been shown on page 50 to approximate the actual arterial pressure, as determined simultaneously by the direct introduction of a canula, so closely that the difference (a few mm. Hg) may be ignored. These readings if made with any modern type of instrument are comparable, as they all give the pressure readings in terms of millimeters of mercury. The several forms of apparatus will be discussed in detail later. Except for the style and construction of the manometer there is very little difference in the several apparatus either as regards their modus operandi or their clinical use, the only differences being slight variations in minor details such as the material forming arm-band, the location of tubes and other attachments, etc.

SUGGESTIONS TO BE FOLLOWED AND PRECAUTIONS TO BE OBSERVED WHILE USING THE SPHYGMOMANOMETER

Position of the Patient.-Whether the observation is made in the reclining or sitting posture will be determined

by the nature of the case and by exigencies of practice. In the critically ill the horizontal posture is preferable, although it will not always be found convenient or possible in the presence of orthopnea, while in ambulatory cases it will not always be found convenient to employ the horizontal. One point to be borne in mind is that for purposes of comparison it is essential, whenever possible, to make all subsequent observations in a case in the same posture as was the first. At all events the location of the arm-band, irrespective of the patient's posture, should be at the heart-level, thus eliminating the error due to gravity. Under all circumstances the patient should be in a comfortable position, and one favoring muscular relaxation.

Application of Cuff.-The cuff is usually applied to the arm above the elbow and should be maintained at the heart-level, Fig. 6. It should be applied directly to the bared arm or over very thin coverings and wrapped firmly; this will avoid the unnecessary delay required to fully inflate a loosely applied arm-band. The arm-band should not exert pressure. This point is also of importance in using any method other than the auscultatory, since the greater the volume of confined air the less marked will be the rhythmic impulse transmitted to the manometer.

Time of Observation. Whenever possible observations should be made at about the same time of day, and in the same relation to the taking of food. Observations should not be made during periods of excitement, or after exercise, or in periods of profound fatigue, neither after the ingestion of large amounts of fluid or of stimulants, as tea, coffee or alcohol. An overheated or unduly chilled extremity

will affect the arterial pressure in the part (see page 145). Observations made under pathologic conditions, such as edema or spasms, are absolutely unreliable.

Fear and psychic disturbances markedly influence the readings (see page 59); for this reason, in the nervous and excitable, the initial reading is often higher than those made subsequently.

Condition of Indicator and Cuff.-A leaky apparatus will give unreliable readings; old rubber parts are often responsible for this. When properly connected the apparatus should be able to sustain the mercury column without receding. A rapid fall indicates a leak somewhere in the air system and should be corrected. At the beginning of each test the indicator, irrespective of type, should register zero and in the mercury instruments the mercury

column should not be broken. This latter condition may be overcome by abruptly jarring the apparatus until the mercury unites.

The Performance of the Test.-The greatest rapidity compatible with accuracy is essential, since undue delay while the arm is under compression will, through vasomotor influences, give a disagreeable sensation, and may also affect the systolic pressure. Two or more readings should be made whenever possible for purposes of verification and to eliminate psychic and other transitory sources of variation, and no single observation should be accepted when it is possible to make additional ones.

The Keeping of Records. Whenever possible bloodpressure records should be preserved, this not only makes for accuracy in individual readings but also furnishes valuable data for comparison, not only in the same case, but also in statistical studies.

For this purpose the author has for some time employed a small card upon which individual daily records are made and filed (see Fig. 7) and from which, when desired, graphic charts, similar to those shown throughout this work, are easily compiled.