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Imparting Information to the patient.—Except in rare instances the patient should not be given specific information regarding his blood-pressure, as it is extremely easy for certain individuals to become so imbued with the importance or omnipotence of this observation, that they develop a distinct neurasthenic stripe. There are, however, certain types of cases in which much good will follow a frank discussion of this subject with the patient, as for example, in the case of one who is firmly of the opinion that the height of his blood-pressure indicates a grave and rapidly fatal condition and who may be relieved permanently of this anxiety by demonstrating a physiologic level in the absence of such a condition. The other type is the neurasthenic who has inordinate reliance in this test and who if he can be shown a distinct improvement in pressure during the physician's conduct of his case, will naturally be helped to a recovery.
The Personal Equation of the Examiner.- Fortunately, for clinical medicine this factor is largely eliminated by the auscultatory method and now really exists only in determining the diastolic point according to the present interpretation of the sound phases (see Chapter V, page 90).
In the tactile method there is often an element of error of from 5 to 10 mm. between different observers. This may be due either to lack of experience and hence untrained tactile acuity, or to subjective pulsations felt by the observer. The frequency with which this subjective pulse becomes evident cannot be determined, but if suspected it can easily be eliminated by a simultaneous observation of the pulse of both the operator and the patient.
In my experience with students employing the auscultatory method there is rarely any appreciable element of error after the students have once learned to appreciate the significance of the sounds.
By tactile sense the determination of the diastolic pressure cannot be relied upon except when determined by those of constant and wide experience. Another source of error will depend upon whether the readings are made as the pressure in the instrument is ascending or descending (see page 141). It will be found here that, owing often to slight obstruction to the free passage of air in the apparatus, the pressure in the manometer will not immediately respond to the changes of pressure in the cuff. Another element of error may arise from the fact that, when using a pump or bellows, the rising pressure is not as easily controlled as the descending. Therefore, except under special conditions, all observations should be made after first rapidly and completely obliterating the pulse. There is one exception to this which has recently been called to my attention by Dr. Francis J. Dever, namely, in aortic regurgitation. Here in determining the diastolic pressure during the release the change from the third to the fourth phase may be so slight that it is missed, whereas with a rising pressure, after the diastolic pressure has been approximately determined, it will be found that the passage from the fourth to the third phase will be very sharp and distinct.
METHOD OF ITS USE AND DESCRIPTION OF INSTRUMENTS
The use of manometers or upright tubes filled with fluid, in the study and measurement of blood-pressure in man is attributed to an English clergyman, Stephen Hales,' who published the results of his experiments in 1733, but it was not until recently that a systematic study of the circulation as shown by the blood-pressure was undertaken.
With our increasing knowledge of the circulatory mechanism, both in health and disease, it has become increasingly essential to have instruments of precision which will enable physicians to study circulatory phenomena, estimate circulatory efficiency and measure the work of the heart.
With the earlier instruments and the former methods only the systolic pressure could be gauged; but this is no longer sufficient, as the systolic pressure by itself may fail to give the information required. Both the systolic and the diastolic readings are now determined and in addition we have also learned to depend much upon other collateral data, coincidentally acquired with modern instruments and improved methods.
A great variety of apparatus for the estimation of human blood-pressure has been devised, the development and application of which having now become almost
Stephen Hales, "Statistical Essays," London, 1733, Vol. ii.
"ancient history," they will be just touched upon here. In many of these older instruments either the principal or the technique or both were at fault; hence consideration need be given only to a few of the representative modern instruments of the last few years. These are great improvements over the previous ones, and have demonstrated their ability to give dependable and accurate blood-pressure values.
DEVELOPMENT OF THE SPHYGMOMANOMETER
Graphic methods for determining blood-pressure in man began with Vierordt in 1855 who attempted to measure blood-pressure by placing weights on the radial artery until the pulse was obliterated.
The first practical instrument, however, was introduced by Marey in 1876, but his work seems to have been practically forgotten until von Basch, in 1887 devised an instrument which at that time found some favor. This instrument recorded only the systolic pressure, and is important chiefly because it was the direct forerunner of all modern instruments. The instrument of von Basch employed intermediate compression-a rubber bulb filled with water and communicating by a tube with a mercury manometer, by which the radial artery was compressed. The systolic pressure was determined by measuring the amount of pressure necessary to obliterate the lumen of the artery and obstruct the pulse, which was indicated by the mercury column. In a later model von Basch substituted a spring manometer for the mercury column. In 1889 Potain replaced the water of the earlier instruments with air, and modified the pressure in the circuit at will by means of a bulb, connected with the apparatus by a branch tube. He also improved his apparatus by using the chamber of an aneroid barometer for measuring pressure.
In 1896 Riva-Rocci' and Hill” published almost simultaneously articles descriptive of new sphygmomanometers. The important feature of each of these instruments was the introduction of a rubber bag or tube encircling the arm and inflated by a bulb or a pump. This improve ment surmounted the most serious defect in the earlier instruments, which was the difficulty of accurately adapting the small round pelote to the arm, thereby compressing the artery (the radial) directly over the bone. By the method of Riva-Rocci and Hill, the pressure is everywhere exerted at right angles to the tangent of the circumference of the arm, and the artery therefore compressed equally from three sides against the bone (see page 66, Fig. 8).
Since this time there has been practically no change in the principles of sphygmomanometry. Improvements have tended toward perfecting the apparatus and simplifying the technique, changes having been directed chiefly toward portability, in means of circular compression and source of pressure, and the style of the manometer.
From the narrow arm-band as originally employed by Riva-Rocci (4.5 cm.—2 in.) to the extremely wide band of von Recklinghausen, numerous investigators have de termined that a cuff 11 to 13 cm. (442–5 in.) in width
1 Gaz. Med. di Torino, 1896, Nos. 50 and 51. 2 Brit. Med. Jour., 1897, Vol. ii, p. 904.
3 For the accuracy of this method as compared with the direct or canular method, see page 39.