The impression must not be gained that hypertension in itself always constitutes a disease or even a symptom of disease. Hypertension itself is practically always a compensatory process. That is to say, it is the attempt on the part of the body to equalize the distribution of blood in the body when there is some poison causing constriction of the small arteries. In this sense hypertension is not only essential, but actually life-saving. A heart which is so diseased that it can not respond to the call for increased action by hypertrophy of its fibers, would shortly wear out. The very fact that the heart becomes enlarged and the tension in the arteries becomes high, indicates that in such a heart there was great reserve power. But while hypertension is largely an effort at adjustment among the various parts of the circulation, it nevertheless tends to increase, provided the cause or causes which produced it act continuously. Moreover, as has been said (Chap. II), the arterioles do not respond to increased work on the part of the heart by expanding, but by contracting. A vicious circle is thus maintained which eventually must lead to serious consequences.
Hypertension is then, if anything, only a symptom which may or may not demand treatment. That hypertension leads to the production of sclerosis of the arteries has been repeatedly affirmed here. In certain cases it is good and should not be experimented with. In other cases it is bad and some treatment to reduce the tension must be tried. The main point is to regard hypertension as one regards a compensated heart lesion.
Prof. T. Clifford Allbutt divides the causes of arteriosclerosis clinically into three classes: (1) The toxic class—the results of poisons of the most part of extrinsic origin, chiefly those of certain infections. In some of these diseases, the blood pressures, as for example, in syphilis, are ordinarily unaffected; in others, as in lead poisoning, they are raised. (2) The class he calls hyperpietic,[15] in which an arteriosclerosis is the consequence of tensile strength, of excessive arterial blood pressure persisting for some years. A considerable example of this class is the arteriosclerosis of granular kidney, but in many cases kidney disease is, clinically speaking, absent. (3) The involutionary class, in which the change depends upon a senile, or quasisenile degradation. This may be no more than wear and tear, a disposition of all or of certain tissues to premature failure—partly atrophic, partly mechanical—under ordinary stresses; or it also may be toxic, a slow poisoning by the "faltering rheums of age." In ordinary cases of this class the blood pressures for the age of the patient are not excessive. Although the toxins of the specific fevers, notably typhoid, as stated above, and influenza, have been shown to produce arteriosclerosis, this, under favorable circumstances he believes tends to disappear. This has been shown by Wiesel.
As the blood pressure is dependent on the resistance offered by the capillaries and arterioles, there are only two ways in which increased pressure can be brought about; either by rendering the blood more viscous, or by the generation of some poison from the food taken into the body which, acting on the vasomotor center or directly on the finer vessels, arteriolar or capillary, sets up a constriction over any large area, and mainly in the splanchnic area. In regard to the liability to arteriosclerosis, this area stands second only to the aortic and coronary areas. He believes that arteriosclerosis itself has little effect in raising arterial pressure. Many cases are seen in which with extreme arteriosclerosis there was no rise in blood pressure, and some in which pressures have been rising even long before the appearance of arterial disease. Prof. Allbutt also believes that in the hyperpietic cases the arteries undergo a transient thickening, which can be removed if the causes can be reached and overcome.
Clinically speaking, then, hyperpietic arteriosclerosis is not a disease, but a mechanical result of disease. If the narrowing of the arterioles is brought about by thickening due to arteriosclerosis, then it would seem a priori that such obliteration should cause a rise in pressure. Were the vascular system a mere mechanical set of tubes and a pump, this would happen, but other factors of great importance must be taken into consideration besides the mechanical factors; viz., chemical and biological factors. Thus, whole parts may be closed and with compensatory dilatation in other parts there would be little or no change in pressure, unless there were hyperpiesis. In established hyperpiesis, we note two conditions in the radial artery: first, a comparatively straight vessel with a small diameter; secondly, a larger, more tortuous vessel, "the large leathery artery." In the cases of the first group, hyperpiesis is often more marked, although not appearing so to the examining finger, than in the second class. In view of the difficulty of estimating by touch alone the amount of hyperpiesis in a contracted hard artery, it is often overlooked until a ruptured vessel in the brain startles us to a realization of our mistake. The "narrow" artery is more dangerous than the tortuous one, for with every change in pressure the passive vessels of the brain must receive blood that under normal conditions would go to other parts of the circulation.
In involutionary sclerosis there is a gradual thickening and tortuosity of the vessel, which although it may be greater than in the hyperpietic cases, yet is never so dangerous to life. The heart in hyperpiesis hypertrophies and dilates, but such a heart is the result, not an integral part, of the arterial disease.
The Heart
When the arterial tree becomes narrowed and the resistance offered to the flow of blood thereby is increased, more muscular work is required of the left ventricle and according to the general laws which govern muscles the ventricle hypertrophies. There is an actual increase in number of fibers as well as an increase in the size of the individual fibers. Some of the best examples of simple hypertrophy of the left ventricle are found under such circumstances. The chambers as a rule do not dilate until the resistance becomes greater than the contraction can overcome, when symptoms of broken compensation of the heart take place. The hypertrophy of the left ventricle brings more of this portion of the heart toward the anterior chest wall. The enlargement is toward the left, also, consequently the apex-beat is found below and to the left of its usual site, even an inch or more beyond the nipple line. The impulse is heaving, pushing the palpating hand forcibly up from the chest wall. The visible area of pulsation may occupy three interspaces and the precordium is seen to heave with every systole. On auscultation the second sound at the aortic cartilage is ringing, clear, and accentuated. Not infrequently, too, the first sound is loud and booming, but has a curious muffled sound that may even be of a murmurish quality. The leaflets of the mitral valve may be the seat of sclerosis, the edges are slightly thickened and do not quite approximate, thus causing a definite murmur with every systole. This murmur may be transmitted out into the axilla and be heard at the inferior angle of the left scapula.
Palpable Arteries
Not every artery that can be felt is the subject of arteriosclerosis, and, as has been stated, palpable arteries being more or less a condition of advancing years, judgment as to whether the artery is pathologically or physiologically thickened may be a matter of individual opinion. A radial artery that lies close to the lower end of the radius and can actually be seen to pulsate when the hand is held slightly extended on the back of the wrist, is easily felt, but must not, therefore, be considered a sclerosed artery. The radial may be so deeply situated in the wrist of a fat subject that it is difficultly palpable. Yet the two cases just described may have arteries of identical structure, there being no more retrogressive changes in the one than in the other. "Experience is fallacious and judgment difficult."