Harvard Psychological Studies, Volume 2

by Unknown

(3) Inhalation of amyl nitrite makes the dicrotic almost disappear. The adherents of the theory of the peripheral origin of the dicrotic wave explain this fact by supposing that this drug dilates the arterioles and makes little reflection possible. Their opponents say that the action of the heart and the resistance of the system are so enfeebled that the backward flow is slight and gives rise only to a small wave.

(4) If an artery is opened and the blood allowed to spurt on a revolving drum of white paper a curve is obtained which shows the dicrotic elevation (the hemautographic curve of Landois). The resistance of the periphery is totally lacking in this case and the dicrotic elevation could not appear if it were due to a wave reflected at the periphery.

(5) The appearance of the dicrotic is not retarded if an elastic tube is placed between the periphery and the place where the instrument is adjusted. If the dicrotic were due to a wave reflected at the periphery it would be retarded because the wave would have to travel a distance so much greater.

These arguments prove the impossibility of the theory of the peripheral origin of the dicrotic wave. Also the other hypothesis meets with a number of serious difficulties, and we mention the following facts which are arguments not against any special form of this theory, but against any hypothesis which starts from the assumption that the dicrotic elevation is due to a wave travelling from the heart to the periphery.

(1) The descent of the catacrotic phase ought to be a succession of diminishing waves, but not a slow descent with merely small elevations.

(2) This hypothesis accounts for none of the abnormal pulse forms.

(3) The blood ought to push against the semilunar valves with a force not less than 1/2 - 2/3 of the force of the contraction of the ventricle, because this is about the relative height of the first secondary elevation with regard to the primary wave, which is due to the contraction of the ventricle.

(4) It does not account for the disappearance of the dicrotic elevation through lack of elasticity of the arterial wall: for the dicrotic elevation is most marked in youth, becomes lower in old age, and disappears in diseases like atheroma and arteriosclerosis, which impair the elasticity of the arterial wall. Landois's theory overcomes this theory only apparently, although the dicrotic would be absent, yet in that case the descent of the primary wave ought to be as steep as its ascent.

(5) This theory is refuted by the experiment of v. Kries, who proved the existence of the dicrotic if the heart is replaced by a valveless bag.

The obvious impossibility of making the theories agree with the facts does not permit one to accept any of them. All of them are based on the supposition that the dicrotic elevation is due to a wave travelling in the blood, and this belief is founded on the following argument: If a wave travels in the blood the sphygmographic curve shows an elevation; the dicrotic elevation is an elevation in the sphygmographic curve. Therefore, the dicrotic elevation is due to a wave travelling in the blood. This fallacy is responsible for the astonishing fact that the refutation of one of two apparently contradictory statements does not prove the other. It is characteristic of the present state of the problem concerning the origin of the dicrotic elevation, that a modern writer[63] calls it "inextricably complicated."