Pulse (Lat. pulsare, to beat), the throbbing of the arteries caused by the intermitting impulses communicated to the blood by the heart's contractions, propagated as a wave by the elasticity of the arteries, perceptible to the touch in all but the smallest vessels, and visible when they are superficial or exposed; the pulsation being nearly synchronous with the contraction of the left ventricle. At each pulsation the capacity of the artery is augmented by an increase of diameter and by a partial elongation, the vessel being thereby lifted from its bed; this increase has been estimated for the carotid artery as 1/23 part, but this can be only an approximation. The pulsation of the larger arteries in the immediate neighborhood of the chest, as for example the carotids, is perceptibly synchronous with that of the heart; but for those at a distance, a slight interval of time is required for its propagation. Thus the pulse of the radial artery at the wrist is sensibly later than that of the heart, and that of the posterior tibial artery, at the ankle joint, later still. But this interval in each instance is very short, and requires careful attention to be distinguished.

The pulse is liable to vary, within the limits of health, from the diversities of age, sex, stature, muscular exertion, condition of the mind, state of the digestive process, and period of the day. The following table is given by Carpenter as an approximation to the average frequency of the pulse per minute at different ages:

In the foetus.................................. 140 to 150

Newly born infant............................. 130 to 140

During the 1st year............................ 115 to 130

" " 2d ".................................................... 100 to 115

" " 3d ".................................................... 95 to 105

" " 7th to 14th year...................................................... 80 to 90

" " 14th to 21st " ....................................................... 75 to 85

" " 21st to 60th " .................................... 70 to 75

In old age....................................................................................................... 75 to 80

According to Dr. Guy, the pulse of the adult female usually exceeds that of the adult male of the same age by 10 to 14 beats a minute; according to Volkmann, the pulse is less frequent as the stature is greater, about four beats for half a foot in height. It is well known that muscular exertion increases the frequency of the pulse. The effect of posture has thus been expressed by Dr. Guy:

Average beats per minute in

Standing.

Sitting.

Lying.

Healthy males.................................

81

71

66

Healthy females..............................

91

84

79

According to this, the difference between standing and lying in the former is one fifth of the whole, in the latter one eighth; when this change is effected by muscular effort the variation is greater, accounting for many cases of sudden death in persons with disease of the heart or in very weak conditions on quickly assuming an erect position. Mental excitement, the digestive process, alcoholic drinks, and elevation above the sea level, accelerate the pulse; as a general rule, though with numerous exceptions, it is more frequent in the morning than in the evening, and in sanguine than in lymphatic temperaments. The pulse is slower during sleep, and from the effect of rest, diet, cold, venesection, and the action of many drugs, especially digitalis, aconite, and hellebore. The pulse may be counted in any artery, and in a manner familiar to all, but most conveniently in the radial at the wrist, in the carotids, temporals, brachial, or femoral. The average numerical proportion of the arterial pulsations to the respiratory movements is 4 or 5 to 1; when this proportion is widely departed from, there is either some general diseased condition of the system accompanied with fever, some obstruction to the proper aeration of the blood, or some disorder in the nervous system; in inflammatory or acute diseases, the pulse may rise to 120 and 160 in the adult, and so that it cannot be counted in the child; in pneumonia, with the quickened pulse the number of respirations increases more rapidly, the above proportion becoming as 3 or even 2 to 1; in hysteria a similar increase may occur in both without any serious cause. - The exact form of the arterial pulse has been determined by means of a contrivance termed the "sphygmograph," which consists of a small metallic or ivory plate, held in contact with the integument immediately over the vessel by means of a delicate spring, and lifted from its bed by each pulsation of the artery.

The plate carries an upright rod, which in its turn moves a long but light index, the end of which traces an alternately ascending and descending line upon the surface of a strip of paper moving with uniform velocity. Thus the extent of the vertical motion measures the width of the arterial expansion; and its greater or less obliquity, as traced upon the paper, indicates its rapidity or slowness, as compared with the horizontal movement of the paper itself. Such a trace is very useful, first by showing minute peculiarities of the arterial pulsation, too small to be distinctly perceptible by the touch; and secondly, by leaving them in the form of a permanent record, suitable for subsequent study and comparison. The ordinary trace of the radial pulse, taken in this way, consists of a nearly vertical ascending line, which indicates the sudden and rapid expansion of the artery, followed by an oblique and somewhat undulating descent, showing the comparatively slower and more irregular collapse of the vessel.

These two ascending and descending lines are repeated for every pulsation of the artery.

Trace of the Radial Pulse, taken by the Sphygmograph.

Fig. 1. - Trace of the Radial Pulse, taken by the Sphygmograph.

Sometimes the undulations of the descending line become more perceptible, owing to an increase of temperature or some other cause which diminishes the resistance of the arterial walls to the heart's impulse; and under these circumstances the expansion of the vessel is more sudden and vertical, while its collapse is indicated by one or two well marked oscillations, in the trace of the descending line. In certain cases of disease this oscillation of the artery at the period of collapse becomes so marked that a sort of secondary beat, or reduplication of the pulse, is perceptible even to the touch; and this constitutes what is known as the double or dicrotic pulse, in which there are two perceptible pulsations of the artery for every contraction of the heart. Of these two pulsations, only the first is directly caused by the impulse of the heart; the second is due to the oscillation of the blood in the relaxed arterial tube. Dr. E. R. Hun, who at that time was special pathologist to the New York state lunatic asylum at Utica, published in the "American Journal of Insanity" for January, 1870, the results of a series of investigations, in which he found that the pulse of the insane "always tends toward the dicrotic or monocrotic type, being never tricrotic in uncomplicated cases.

It becomes more characteristic as the mental condition degenerates, and assumes its typical form in the most profound state of dementia," as shown in the following sphyg-mographic tracing of the pulse of a patient 37 years of age. The trace given in fig. 5 shows a marked dicrotic form in a patient having slight symptoms of mania. This became irregularly tricrotic under excitement, and more regular after an outburst of excitement. - Usually the pulsating movement of the blood is not continued into the capillary vessels; but when the arteries are dilated in the glandular organs at the time of their increased functional activity, the pulsation is communicated to the capillaries, and even through them to the veins. This condition, however, lasts only during the period of increased vascular excitement; and as it subsides, the movement of the blood in the capillaries again becomes uniform, and the pulsation is limited as before to the arterial system.

Trace of the Radial Pulse under the influence of Increased Temperature.

Fig. 2. - Trace of the Radial Pulse under the influence of Increased Temperature.

Trace of a Dicrotic Pulse, in Typhoid Fever.

Fig. 8. - Trace of a Dicrotic Pulse, in Typhoid Fever.

Trace of Pulse in Dementia.

Fig. 4. - Trace of Pulse in Dementia.

Trace of Dicrotic Pulse in Mania.

Fig. 5. - Trace of Dicrotic Pulse in Mania.