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gives the most accurate readings, with the possible exception of the extremely obese. A special narrow cuff may also be found advantageous in work with very young children, manufactured at my suggestion by the G. P. Pilling and Son Company, Philadelphia, Pa.

Technique and Employment of the Sphygmomanometer. -From the practical clinical standpoint all modern sphygmomanometers are applied and measure bloodpressure in the same manner. Therefore, a general description will explain the manner of application of all. For convenience of description the modern sphygmomanometer may be divided into the following parts:

1. The source of air pressure.
2. The compression device.
3. The manometer or indicator.

1. The source of air pressure may be a compressed air supply similar to that employed to operate atomizers, a rubber bulb, or a small metal force pump. The function of this portion of the instrument is merely to inflate the compression member and by so doing to exert a variable degree of pressure upon the artery under examination. The source of pressure is joined by suitable tubular means to the compression member.

2. The compression member is composed of a hollow elastic air-containing portion and a rigid, leather or fabricretaining portion. These are so arranged that when applied to an extremity, the hollow elastic portion is in contact with the skin surface of the arm or leg, which it encircles either partially or completely. Outside this the restraining portion is fastened, in a suitable manner, to restrain the elastic portion and to force the pressure 'inward against the member and so through it to the artery.

Fig. 8, A and B, shows the relation of the compression bag to the artery. In Fig. A, the pressure within the cuff

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B Fig. 8.—Diagram of relations of armlet to brachial artery. A. Pressure in “b” 135 mm. Hg., pressure in “a” 130 mm. Hg., B is therefore collapsed, pulse cannot pass. B. Pressure b129 mm. Hg., pressure in “a” 130 mm. Hg., pulse passes. Explanation of systolic reading: a, artery; b, compressing armlet; c, retaining cuff; d, tube to manometer; e, humerus.

is greater than the blood-pressure within the artery, which is therefore collapsed and the pulse in the distal end of the vessel cut off. In Fig. B, the pressure in the cuff has been reduced so that it is a fraction of a millimeter less than the systolic pressure within the vessel. Now at each systole, a small amount of blood will pass beyond the constriction and will reach the distal end of the artery, where the wave can be felt by the palpating finger at the wrist.

Fig. 9, A and B, represents the conditions existing

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B Fig. 9.-A. Systolic pressure in "a" 130 mm. Hg., pressure in "b" 101 mm. Hg., artery not compressed. B. Diastolic pressure in “a” 100 mm. Hg., pressure in “b101 mm. Hg., artery collapsed. Diagram of relation of armlet to brachial artery. Explanation of diastolic reading; a, artery; b, compressing armlet; c, retaining cuff; d, tube to manometer; e, humerus.

between the constricting cuff and the vessel at the diastolic time of pressure. A represents a pressure within the cuff less than the systolic pressure in the vessel. This is insufficient to affect the vessel during the systolic period, while B shows the artery and cuff during the diastolic period, at the moment when the pressure within the artery is at its lowest point, a fraction of a millimeter less than the pressure within the cuff. Consequently the artery is collapsed at this time. The effect of each succeeding systole is to alternate between a round and a flat vessel at the point of compression. This affects the pressure of air within the cuff which is in turn transmitted to the mercury column of the manometer and becomes visible in the rhythmic fluctuation of the column of mercury which is synchronous' with the pulse beat.

3. The indicator, manometer or gauge, is a device for measuring the amount of air pressure exerted against the artery. The modern types give the measure of pressure in terms of millimeter Hg., rendering the readings of all instruments comparable. The indicator is the part of the modern sphygmomanometer, which has had focussed upon its construction the greatest inventive skill and ingenuity. Many medical men of mechanical ability have made slight changes in minor or superficial details; as in shape and size of the manometer tube, or in the location of attachments for tubular connections in the mercury instruments, and in the form of the containing case in the aneroids. Hence we find a multiplicity of names attached to many slightly varying instruments.

Blood-pressure instruments are usually classified according to the style and type of measuring device employed. These may be grouped as follows:

CLASSIFICATION OF BLOOD-PRESSURE INSTRUMENTS

Modified from G. W. Norris, “Blood-pressure, its Clinical Applications,” Lea and Febiger, 1914.

I. Mercury manometers:
1. Reservoir, Riva-Rocci, Cooke, Stanton, Pilling-

Special and Pilling-Midget, Nicholson, Hill,

Kercher, Hollman, Gärtner, Westenrijk. 2. U-shaped: Janeway, Faught, Martin, Linnell,

Fellner. II. Compressed-air manometers: Oliver, Benedick, Herz. III. Aneroid manometers: Rogers, Brunton, Faught,

Pachon, Jacquet. IV. Spring manometers: von Recklinghausen, Stern. V. Instruments for graphic registration: Erlanger, Gib

son, Bingel, Singer, Uskoff, Silbermann, Brugsch, Stursberg, Muenzer, Strauss-Fleischer, Bussenius,

Wybauw VI. Instruments constructed with, or to which may be

fitted, special oscillating indices, such as the Fedde or Pal oscillometers, Bing, Faught, Vaquez, Widmer. Rodgers.

DESCRIPTIONS OF MODERN INSTRUMENTS

1. Riva-Rocci Sphygmomanometer (Fig. 10).—This mercury manometer is of cistern form, and is constructed of heavy glass from which emerge two tubes, one for the inflating apparatus and one for the attachment of the armband. The latter is provided with a release valve for gradually lowering the pressure in the circuit during the test. The scale engraved upon the glass tube reads up to 260 mm. Hg.

The armlet consists of a hollow rubber tube covered with silk having a width of 4.5 cm. (2 in.), which is fastened

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