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Pituitrin.-1 c.c. 10 per cent. sol. Same as epinephrin but less marked effect.

Caffein.-Caffein sodium benzoate 72 to 2 gr., no effect.

Strychnin Sulphate.—No effect except in toxic quantities, then a rapid rise in venous pressure.

The Nitrites.-Amyl nitrate and nitro-glycerin 150 to Yso gr. caused a decided fall in venous pressure.

Morphine.-48 to y gr. No effect on venous pressure. ¥4 to 42 gr. Slight fall in venous pressure.

Alcohol.—25 to 30 per cent. strength 10 to 50 c.c. in amount. Small doses no effect, large doses rise in venous pressure. This rise was in proportion to the degree of disturbance of heart action.



Absolute and Relative Blood-pressure.—Throughout the discussion of this subject, the relative blood-pressure only has been considered, that is, the degree of arterial pressure over and above barometric pressure at the time of the observation. This has, from a clinical standpoint, been clearly demonstrated to be the important factor, as ordinary studies do not involve a determination of the absolute blood-pressure, i.e., the systolic pressure plus the actually determined barometric pressure at the time of the observation. It may be stated in passing that changes in atmospheric pressure are accompanied by approximately equal changes in the absolute blood-pressure, usually in the same direction.

Altitude.—In approaching the subject of the effect of
altitude on blood-pressure and pulse rate, a sharp line
must be drawn between the influence of changes in altitude
(atmospheric pressure) upon normals and other individ-
uals, particularly the tuberculous; otherwise confusion will
surely follow, because the great bulk of clinical data dem-
onstrates that altitude affects normal and pathologic in-
dividuals differently.

Effect of High Altitude on Healthy Individuals.-
Gardner and Hoagland, at an altitude of 6000 ft., meas-

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1 Gardner and Hoagland, Trans. Amer. Climat. Assn., 1905.

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ured large numbers of normals who had lived in Colorado for more than a year, and concluded that the average bloodpressure was slightly lower than at the sea level, although prolonged residence at that altitude does not materially affect blood-pressure.

Experiments showed that an ascent from 6000 to 14,000 lowered pressure and increased pulse rate. The fall was apparently a permanent one, although the fall which immediately follows the change in altitude is temporarily greater than is the case after the individual becomes accustomed to the alteration in altitude.

Smith at Ft. Stanton' (6200 ft.) states that, “It has been scientifically established that blood-pressure is lowered with increased altitude."

Pomeroy2 in order to determine the degree of variation in the systolic and diastolic blood-pressure, caused by changes of altitude, averaged the observations of eighteen investigators, dating from 1878 up to the date of this writing and including himself. He found that the fall in systolic blood-pressure ranged between 1 and 22 mm. Hg., and the diastolic fall was between 1 and 11 mm. Hg.

The effect of sudden changes in altitude in the upward direction results usually in an increase in systolic pressure, an increase in diastolic pressure, with very little if any significant change in pulse pressure. These changes were accompanied by nose-bleed and headache. In another group which were largely pathologic, no such changes were noted. In order to determine the effect of increased atmospheric 1 Reprint No. 51, Public Health Rep., P. H. and M. H. Service. 2 Int. Med. Jour., Vol. xviii, p. 731. • Personal communication from Dr. Harley Stamp.

pressure upon the blood-pressure and pulse rate, Brooks studied seventy-five compressed-air workers, when contrary to the findings of earlier investigators, he found that only rarely did there occur a marked rise in arterial pressure, even in workers subjected to a pressure of plus 31 lb., as in no cases examined by him was blood-pressure or pulse rate materially altered. Further observations, if in accord with these, would be of value in demonstrating the degree of danger involving cassion workers who are subjects of cardiovascular and renal impairments.

Blood-pressure in Deep Mines.- Investigations after descent into the Butte mines, to a depth of 2600 ft. below the surface, was made in an effort to determine the effect of this change upon blood-pressure. The usual effect was found to be a fall in both systolic and diastolic pressure with a primary increase in pulse pressure, which tended in a short time to return toward normal values.2

Schneider and Hedbloms present a very concise and accurate summary of present knowledge bearing on this point.

1. A considerable elevation in altitude tends to lower systolic and diastolic blood-pressure and to increase the heart rate.

2. The fall of systolic pressure is slightly greater and more certain to occur than the fall of diastolic pressure.

3. A rise in diastolic pressure occurs in some individuals.

4. The influence of such factors as psychic states, eating and exercise may obscure the findings.

1 H. Brooks, Med. Rec., May 25, 1907. 2 Personal communication from Dr. Harley Stamp. 8 Am. Jour. Physiol., Vol. xxiii, No. 2.

5. The fall in blood-pressure and increase in heart rate are more marked in the early part of stay in high altitudes.

6. With prolonged stay in high altitudes the heart rate probably returns more nearly to normal than the bloodpressure of all individuals.

7. High altitudes do not affect in the same degree all individuals.

8. Small elevations in altitude do not materially influence blood-pressure.

9. Those individuals most affected by high altitudes seem to sustain the greater fall in systolic blood-pressure and the greater acceleration in heart rate.

10. The heat of the summer season probably accelerates the pulse rate.

11. Moderate variations in altitude are not of themselves inimical to residence or physical activity in persons having definite cardiovascular or nephritic lesions.

Tuberculosis.—LeRoy S. Peters, pointed out in 19081 that altitude usually caused a rise in blood-pressure in the tuberculous. He made his observations at an altitude of 6000 ft. (For effect of tuberculosis on blood-pressure see Chapter XIV.) Bullock confirms the observations of Peters. The

. blood-pressure raising effect of altitude on persons suffering from pulmonary tuberculosis appears to be of distinct advantage to the patient, as it directly combats the bloodpressure reducing acting of tuberculotoxins by altering metabolism, modifying and stimulating tissue change, and aiding elimination.

1 Arch. Int. Med., August, 1908. : Jour. A. M. A., June 19, 1909.

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