Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/120

104 VASCULAR SYSTEM lever, which is moved near the fulcrum by a screw acting on a small horizontal wheel, from whose axis there projects a long, light, wooden lever. The point of the screw rests on a flat disk of steel or ivory, at the end of an elastic spring, which presses the ivory disk or pad on the artery. The lever inscribes the movements on a blackened surface, usually a strip of paper smoked in the flame of a lamp burning turpentine, carried in front of the point of the lever by clock-work. In the instrument as modified by Mahomed, Byrom Bramwell, and others there is an arrangement for adjusting the amount of pressure made on the artery by the ivory pad, so that tracings may be taken at different times from the same artery with different or with the same pressures. The tracings are " fixed " by passing them through shellac or photographic varnish. Sphyg- The following changes take place in an artery when it pulsates : mograph (1) it dilates and at the same time lengthens to a small extent ; or pulse (2) the pressure of the blood increases iu the artery, and a feeling tracing, of hardness and resistance is experienced when the artery is com pressed with the finger. These facts are illustrated in the sphygmo- graphic curve shown diagrammatically iu fig. 17. The ascending line ab (line of ascent, up-stroke, or percussion stroke) corresponds to the distension of the ar tery produced by the systole of the left ventricle, and the descending line bed to its elastic recoil ; the length of the line ad represents the total duration of the movement, which is divided into two portions by the perpendicular line be. The FIG. 17. Diagram of distance ac measures the duration of the disten- a sphygmographic sion of the artery and cd the time of its elastic traciu S- recoil. In a continuous tracing the durations of the individual pulsations are equal, and in inverse ratio to the number of pulsa tions in a unit of time. In a normal pulse the distension and the elastic recoil of the vessel succeed each other without interruption, so that there is no period of repose in the artery. When, however, the pressure of blood in the artery falls below a certain point, these characters disappear or are modified. Fig. 17 shows that the duration of the distension of the artery is only about one-third of that of its contraction. The rapidity and slowness of the pulse depend on the ratio of these periods. The pulse is quick when the duration of the arterial distension diminishes, and slow when it increases. The line ab becomes less oblique and more nearly ver tical, in proportion as the time of the distension is short, quick, and nearly instantaneous. The rapidity of the pulse is increased by quick action of the heart, considerable power of yielding in the arterial walls, easy afflux of blood owing to dilatation of smaller vessels, and nearness to the heart. The term quickness has reference to a single pulse-beat, and frequency to the number of beats in a given time, say, one minute. The line bed is always more oblique than ab, and in careful tracings it presents several elevations or notches (see fig. IS). If we refer the different portions of the curve to their origin the re sult is as fol lows : (1) the up-stroke corre- FIG. 18. Sphygmogram of radial artery; pressure 2 oz. Each sponds to the part of the curve between the base of one up-stroke and systole of the tlie laase f * lle nex * corresponds to a beat of the heart, , - f, , -I so that this figure shows five heart-beats and part of a ventricle, sixth ; a&, the ascent ; b, apex of up-stroke ; 6 to h, the opening the aor- descent, with an elevation d, the first tidal or predicrotic tic valves pour- wave ; e, aortic notch ; /, a second elevation, the dicrotic ti-r l 1,1 wave ; g, a slight curve, sometimes called the second tidal ing the blood waye (Landois and Stirling.) into the arter ies, arid distending them ; (2) the dovnstroke represents the time during which the blood is flowing out of the arteries at their peri phery into the capillaries ; (3) the larger wave in the descent, i.e., the dicrotic, recoil, or aortic systolic wave, represents the time of the closure of the aortic valves; (4) the predicrotic, first tidal, or second ventricular systolic wave occurs after the first systolic wave and during the ventricular contraction (Byrom Bramwell). In many pulse-tracings there are still smaller secondary waves, due to elastic vibrations of the wall of the vessel. The three factors causing an arterial pulsation are (1) the more or less energetic contraction of the ventricle, (2) the quantity and pressure of the blood, and (3) the elastic and contractile properties of the arterial Avail. If these factors be in any way modified there will be a corresponding modi fication in the physical characters of the pulse. The character of a pulse-tracing is affected by the amount of pressure applied to the artery. With a light pressure the dicrotic wave is relatively less ; with a moderate pressure (3 to 7 oz. ) it is well marked, whilst the curve is lower ; and with greater pressure it is again reduced. With 7ij to 10 oz. pressure small secondary waves appear before the dicrotic. The normal pulse-rate in man is about 72 per minute, in woman about 80 per minute ; but in some individuals a state of health is consistent with a pulse-rate as rapid as 100 or as slow as 50 beats Physio logical char acters of pulse. per minute. The pulse-rate is influenced by the undermentioned factors. (1) Age : a newly-born child, 130 to 140 beats per minute ; 1 year, 120 to 130 ; 2 years, 105 ; 3 years, 100 ; 4 years, 97 ; 5 years, 94 to 90 ; 10 years, about 90 ; 10 to 15 years, 78 ; 15 to 50 years, 70 ; 60 years, 74 ; 80 years, 79 ; 80 to 90 years, over 80. (2) Length of body : Ozarnecki, Yolkmann, and Rameaux have shown that as the height increases the pulse slows. (3) Bodily states : active muscular exercise, increased blood-pressure, active digestion, pain, nervous excitement, extreme debility quicken the pulse. (4) Tem- 2Jerature : increase of temperature quickens the pulse. An increase of 1 above 98 Falir. is associated with an increase of 10 beats per minute : thus, at 98 Falir. the pulse-rate will be 60 per minute ; at 99, 70 ; at 100, 80 ; at 101, 90 ; at 102, 100 ; at 103, 110 ; at 104, 120 ; at 105, 130 ; and at 106, 140 (Aitken). (5) Posture: the pulse is more frequent when one stands than when one sits, and still slower when one lies down. (6) Sensory imjjrcssions : music is said by Dogiel to quicken the pulse. (7 ) Pressure ; increased barometric pressure slows the pulse. (8) Diurnal rhythm : 3 to 6 A.M., 61 beats ; 8 to 11.30 A.M., 74 ; towards 2 P.M., a decrease ; towards 3 (at dinner-time) another rise, which goes on until 6 to 8 P.M., when it may be 70 ; towards midnight, 54 ; a rise again to wards 2 A.M., when it soon falls again, and afterwards rises, as before, towards 3 A.M. (Landois and Stirling). Colin gives the following pulse-rates in various animals : elephant, 25 to 28 beats per minute ; camel, 28 to 32 ; giraffe, G6 ; horse, 36 to 40 ; ox, 45 to 50 ; tapir, 44 ; ass, 46 to 50 ; pig, 70 to 80 ; lion, 40 ; lioness, GS ; tiger, 74 ; sheep, 70 to 80 ; goat, 70 to 80 ; leopard, 60 ; wolf (female), 96 ; hyaena, 55 ; dog, 90 to 100 ; cat, 120 to 140; rabbit, 120 to 150; mouse, 120; goose, 110; pigeon, 136; hen, 140; snake, 2-1; carp, 20; frog, 80; salamander, 77. A pulse is said to be strong or weak according to the weight it is able to raise. The strength is usually estimated by pressing the finger on the artery until the pulse-beat beyond the point of pressure disappears. The pulse is said to be hard or soft according to the degree of resis -nce experienced. In feeling the pulse it is import ant to notice whether the tension is great during the distension of the vessel, or whether it is hard during the intervals between the pulse-beats as well as during the beats themselves. On the other hand, it may be soft in these intervals in consequence of the semi- lunar valves at the aorta not closing perfectly (aortic incompetence), thus allowing the blood partially to flow back into the ventricle. This softness and the feeling of sudden collapse of the arterial wall are the pulse characteristics of unfilled arteries. A pulse may be large in volume, as where a large amount of blood is thrown into the aorta, owing to hypertrophy of the left ventricle, or it may be small and thready when a small quantity of blood passes into the aorta, either owing to a diminished total amount of blood, or from constriction of the aortic orifice (aortic stenosis), or from disease of the mitral valve allowing the blood to regurgitate into the left auricle, or when the ventricle contracts feebly. The pulse becomes later and later in time as we recede from the heart. Czermak estimated the delay as follows : carotid pulse, after the cardiac beat, 087 second ; radial, 159 second ; posterior tibial, 193 second. By placing delicate tambours or electromag netic sphygmographs at different points of the circulation and re cording the movements on a rapidly moving surface, E. H. Weber found the velocity of the pulse- wave to be 30 31 feet per second ; Garrod found it to be from 29 52 to 35 43 feet per second ; Crashey determined it at 27 89 feet per second ; and Moens at 27 23. In the arteries of the upper limb it is stated to be 30 84 and in those of the lower limb 31 82 feet per second. The wave-length is ob tained " by multiplying the duration of the inflow of blood into the aorta = 08 to 09 second by the velocity of the pulse-wave." This would give the wave-length at 2 46 feet. As already pointed out, inspiration favours the flow of blood into the veins and retards the flow in the arteries, whilst expiration has the reverse effect. The tension of the arteries during inspiration is therefore less than in expiration, and this affects the form of the pulse-curve, as is seen in fig. 19. (1) " The greater distension of the Strengt of puls Tension Volunn Velocit of pulsi wave. Influen of respi ration c pulse. FIG. 19. Sphygmographic tracing showing influence of respiration on pulse. J, during inspiration ; E, during expiration. (Riegel.) arteries during expiration causes all the parts of the curve occurring during this phase to be higher ; (2) the line of ascent is heightened during expiration, because the expiratory thoracic movement helps to increase the force of the expiratory wave ; (3) owing to increase of the pressure the dicrotic wave must be less during expiration ; and (4) for the same reason the elastic elevations (secondary waves) are more distinct and occur higher in the curve near its apex" (Landois and Stirling, op. cit.}. See also p. 102 above. Non-striated muscle, as has been already stated, exists to a con- Contrac sidcrable amount in the walls of the smaller arteries, and the calibre tility of of these vessels may consequently be changed by the activity of the arteries,

contractile coat. The contractility of vessels may appear under two