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Definition.—This term is employed to designate alterations in arterial blood-pressure in which the systolic blood-pressure curve maintains an average level below the established normal minimum. The actual level of this pressure will be affected to some degree by the age and other physiologic factors, which control the normal level of pressure (see page 42).

The Lower Normal Limits.—The limits are, of course, largely arbitrary, depending as they do upon so many variable and varying factors. To maintain their full value, they must be modified to conform to our knowledge of the many so-called physiologic factors active in each individual case (see Chapter VI).

Experience teaches that 105 mm. may be taken as the low limit of normal blood-pressure in young men, and 95 mm. as the normal low limit in young women. This will of necessity be modified slightly by the age, occupation and muscular development of each individual. The only way to estimate the degree of abnormality in the bloodpressure is to apply the knowledge obtained from experience in examining a large number of cases. Therefore it is usually advisable to employ the blood-pressure test as a routine in all cases, in order to develop one's ability to interpret the significance in each individual case. Unfortunately, literature almost entirely lacks exhaustive studies of low systolic pressures, with the exception of certain definite conditions, as acute and chronic infections, shock, hemorrhage, Addison's disease, etc., where the references are many and the data conclusive.

Varieties of Hypotension.-We must admit the possibility of a relative hypotension, in which the curve of pressure, while above the established normal is yet so far below a previous long-continued high pressure, that it presents the physical phenomena of a pathologic low pressure. This point is discussed more fully below.

Hypotension is also encountered as a coincident phenomenon of many pathologic conditions in which it is usually the result of the effect of some substance or substances affecting the cardiac output, the arterial coats or the vasomotor mechanism. These include infections, certain metabolic diseases, shock, hemorrhage, etc. Such conditions occasion a temporary hypotension, which is relieved, as the patient recovers or is relieved of the metabolic fault. These conditions will be considered in detail in appropriate sections and need not now be discussed.

In order to fully comprehend the discussion which follows, some form of clinical classification of low bloodpressure must be formulated. The following seem to be the most satisfactory subdivisions:

(a) Terminal hypotension, (b) essential hypotension, (c) relative hypotension and (d) temporary or secondary hypotension.

(a) Terminal Hypotension. The term is used to indicate the more or less marked fall in systolic pressure, usually accompanied by a diminishing pulse pressure which indicates the approaching end of life (see Fig. 43).

Usually before death, irrespective of the cause, the bloodpressure tends more or less rapidly toward zero.

The rate at which this occurs and its relation to the actual cause of death, is determined by so many factors about which almost nothing is known, that as yet little may be said with

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Fig. 43.-Chronic interstitial nephritis. Male. Aged fifty-six. This chart shows the rapidity of the rise in systolic pressure in a case of chronic interstitial nephritis and myocarditis in a patient of fifty-six who failed to appreciate the necessity of care or treatment and was willing to, as he said "take his chances.” Cardiac dilatation began when the systolic pressure reached 230 and rapidly advanced. The patient died in an attack of pulmonary edema with systolic pressure 185. Observations before 1914 recorded on chart are yearly averages. 1914 observations show average systolic pressures by months.

certainty. According to Janeway, in protracted illness pressures as low as 60 mm. (5-cm. cuff) may exist for several days before death (note). In such cases the hypotension may be of some value as a sign of impending dissolution, but as a rule the terminal fall in pressure is usually a matter of hours or even minutes. Occasionally the fall is too rapid to be observed and an apparently normal systolic pressure may be demonstrated almost up to the moment of death.

NOTE.— I have seen a case of acute bichlorid poisoning in which a systolio pressure of 65 was recorded several days before death.

(6) Essential Constitutional or True Hypotension.Definition.—This type of hypotension may be defined as that form of lowered systolic blood-pressure met in a certain class of individuals who, though not distinctly ill, do not show evidences of robust health. These persons do not seem to have the physical development, or circulatory power to maintain normal blood-pressure values even under the most favorable circumstances. Systolic pressures of 100 or lower are the rule (see Fig. 42, page 231).

Since the pioneer work of L. F. Bishop in this field, a few spasmodic efforts have been made to assign a definite symptomatology to this condition, and recently Goodman' has contributed a valuable paper upon this condition.

Symptomatology. These cases are not actually ill, nor are they ever well, but complain of all sorts of symptoms which can be traced directly to low pressure as the only assignable cause.

Such individuals are unable to withstand any prolonged or severe physical exertion without fatigue.

They have not only a habitually low pressure but they also respond very poorly and uncertainly to measures directed toward improving the circulation or to those stimuli which in the normal person result in a rise in pressure. The pulse pressure is usually smaller than normal, indi

1 E. H. Goodman, Am. Jour. Med. Sci., April, 1914.

cating a defective cardiac output, while there is no relation between blood-pressure and pulse rate.

These cases are usually associated with enteroptosis and may have a tendency to attacks of temporary dizziness, upon sudden change of posture; many are undoubtedly of intestinal toxemic origin. Constipation tends to keep the pressure down, as does also a marked indicanuria, which is so frequently encountered in these cases. Headaches are frequent, and are often relieved by measures directed toward increasing the pressure. These cases wake up tired, then improve during the early hours of activity, only to become exhausted long before the end of the day.

Many are thin and poorly nourished, and suffer continually from chilly hands and feet, which are often moist and may be actually wet. The dependent hands are bluish and when one is elevated to above the head for a short time it becomes abnormally pale.

Those patients lack initiative, and every movement seems to be an effort; even when shaking hands, it is done in a half-hearted manner, and life is generally viewed through dark glasses. They are decidedly of the depressive neurasthenic type. Mental tire is often extreme in spite of the evidently active mind. Some of these cases undoubtedly belong to the class of congenitally small hearts and arteries.

(c) Relative Hypotension.—This term would seem to be a necessary one and should be applied to those cases whose actual pressure, while still above the estimated normal, has fallen from a former pathologic high level to such a degree that symptoms due to the fall have developed. A fairly common example of this is the frequent occurrence of edema

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