The former is not normal for any age. Low pulse pressure usually means a weak vasomotor control and is only found in failing circulation or in markedly run down states, such as after serious illness or in tuberculosis. Therefore, it is most important to estimate accurately the diastolic pressure as well as the systolic pressure, for only in this way can we obtain any data of value regarding the driving power of the heart and the condition of the vasomotor system. A high systolic pressure does not necessarily mean that a great deal of blood is forced into the capillaries. Actually it may mean that very little blood enters the periphery. The heart wastes its strength in dilating constricted vessels without actually carrying on the circulation adequately. =Normal Pressure Variations= The systolic pressure varies considerably under conditions which are by no means abnormal. Thus, the average for men at all ages is about 127 mm. Hg. (All measurements are taken from the brachial artery, with the individuals in the sitting posture.) For women the average is somewhat lower, 120 mm. Hg. The pressure is lowest in children. In children from 6-12 years the average systolic pressure is 112 mm. Normally, there is a gradual increase as age comes on, due, as will be shown in the succeeding chapter, to physiologic changes which take place in the arteries from birth to old age. In the chart here appended is graphically shown the normal variations in the blood pressure at different ages compiled from observations made on one thousand presumably normal persons. (Fig. 28.) [Illustration: Fig. 28.--Chart showing the normal limits of variation in systolic blood pressure. (After Woley.)] The diastolic pressure has been estimated to be about 35 to 45 mm. Hg lower than the systolic pressure, and consequently these figures represent the pulse pressure in the brachial artery of man. This is equivalent to saying that every systole of the left ventricle distends this artery by a sudden increase in pressure equal to the weight of a column of mercury 2 mm. in diameter and 35 to 45 mm. high. Naturally, at the heart the pressure is highest. As the blood goes toward the capillary area the pressure gradually decreases until, at the openings of the great veins into the heart, the pressure is least. At the aorta (A) the pressure (systolic) is approximately 150 mm. Hg, at the brachial artery (B) it is 130 mm., in the capillary system (C) it is 30 mm., in the femoral vein (F) it is 20 mm., at the opening of the inferior vena cava (I) it is 3 mm.