. Diseases of the heart and thoracic aorta. hroughthe aortic valves, the line of descent becomes more and morevertical in proportion to the freeness of the outflow and therapidity of the action of the heart. The dicrotic wave, or the aortic systolic wave, as it maybe called, is usually present in a normal pulse tracing, and The line of descent is sloping, because the recoil of the artery is gradual. Inthis respect there is, therefore, a marked difference between the upstroke and theline of descent 252 Diseases of the Heart. corresponds to that period of the cardiac cycle which imme-diately fol
. Diseases of the heart and thoracic aorta. hroughthe aortic valves, the line of descent becomes more and morevertical in proportion to the freeness of the outflow and therapidity of the action of the heart. The dicrotic wave, or the aortic systolic wave, as it maybe called, is usually present in a normal pulse tracing, and The line of descent is sloping, because the recoil of the artery is gradual. Inthis respect there is, therefore, a marked difference between the upstroke and theline of descent 252 Diseases of the Heart. corresponds to that period of the cardiac cycle which imme-diately follows the closure of the aortic valve cusps: whilethe point of the tracing which immediately precedes it {e infig. 78), and which is generally, but not universally/ believedto correspond in time to the closure of the aortic segments,is termed the aortic notch. Where the vaso-motor tone is very good, and the arterialtension high,— as it is in some healthy persons,—the dicroticwave is very feebly marked or altogether absent. (See%• 83.). Fig. 83.—Pulse tracing of good tension (pressure 3 oz.) The pulse is slightlyirregular, but otherwise normal ; the dicrotic wave is scarcely perceptible. The exact cause of the dicrotic wave has given rise to much debate ;but most physiologists are agreed that it is in great part due to therecoil current from the closed aortic valve,—an opinion which is con-firmed by clinical observation. Dr Galabin, while agreeing that thegreat cause of the dicrotic wave is a recoil current from the aorticvalves, thinks that its production is aided by the inertia of the Dr Roy differs from this opinion. As the result of careful experiment,he suggests that the secondary waves which appear in the unopenedartery under normal blood-pressure, are the result of an active vermi-cular contraction of the muscular coat of the arteries. He completelyrejects the theories which would ascribe these undulations to reflected, A Text Book of Physiology, /\.\
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