It is especially important to note the influence of moderate activity upon the heart, particularly upon the blood pressure, as shown by careful measurements of blood pressure prior to a walking period and immediately following the walking period for the several men. To secure a base-line, the cuff was adjusted prior to the walking test and a number of observations made with the subject in the standing position. After the completion of the walking, which usually occupied about 26 minutes, the cuff was immediately inflated and both the systolic and diastolic blood pressures noted. At the end of one minute a second observation was made, and the observations continued at intervals for 2 to 2 1/2 minutes. These measurements, it is only fair to state, were taken under very great tension on the part of all operators and are not so free from extraneous influences as one could wish. Furthermore, the cuff had to be repeatedly inflated somewhat rapidly, and there was hardly time for the circulation to be fully established in each case.1 On the other hand, it is highly improbable that with the group of men as a whole, any disturbance of the general picture could have been made by a fault in technique. The readings were frequently checked by one of us and we have every confidence that they were both taken and recorded as accurately as they could be under the experimental conditions. We believe that they present a true picture of the blood pressures immediately following walking at a rate of about 69 meters per minute. The effects of walking upon the action of the heart will be further considered in the discussion of the pulse-rate. (See p. 440).

Although the first records of the blood pressures before and after walking were those for Squad B on the morning of January 28, we shall first discuss the values found with Squad A on the morning of February 3, 1918. These are given in table 78, in which both systolic and diastolic pressures and pulse pressure are recorded for each of the 11 men immediately before and after walking. Usually two additional observations were made after the cessation of walking at about the fifth and ninth minutes with the subject sitting. The systolic blood pressures as measured on these men in the standing position before work on the morning of February 3 may first be compared with the records made by Dr. Goodall on the evening of February 2 for the sitting position. The systolic pressures on the morning of February 3 averaged 101 mm., the highest being 107 mm. with Mon and the lowest 97 mm. found with 4 of the subjects. Examining the sitting blood pressures found the preceding evening (see those for February 2 in the lower part of table 76), we find that the values tend to be somewhat below 100, with an average of 95 mm. The highest, 100 mm., was found with Can, Gar, Moy, and Vea, and the lowest, 90 mm., with Bro, Gul, Pea, and Pec. Although the effect of posture on blood pressure is the subject of much discussion, the morning systolic blood pressures are reasonably well checked by these observations of the evening before. The morning values for the systolic blood pressure taken just before walking are therefore in all probability not far from the true values.

1 This criticism also applies to the technique used by Cotton, Rapport, and Lewis. Heart. 1917, 6, p. 200.

Table 78. - Blood-Pressure Measurements Prior To And Immediately After 24 Minutes Of Level Walking On A Treadmill - Squad A, February 8, 1918

The diastolic blood pressures likewise show values in the morning which are, as a rule, higher than those found the evening before. That is, in the morning records with the subject standing we find the diastolic blood pressure ranges from 81 mm. with Bro to a minimum of 60 mm. with Pec, the average value being for the morning 72 mm. The average of the records made by Dr. Goodall the evening before is 64 mm. Nevertheless, the appearance of values as low as 60 mm. in the case of Pec and 64 mm.in the case of Vea is a reasonable control upon the low values found the evening before.

The pulse pressures taken before work on February 3 are not unlike those found the evening before. The morning pulse pressures, with the subject standing before work, range from a minimum of 16 mm. with Bro to a maximum of 37 mm. with Pec and average 29 mm. On the evening before they ranged from a minimum of 20 mm. with Pec to a maximum of 40 mm. with Moy and Vea, and average 31 mm. A somewhat interesting fact is that Pec had the minimum pulse pressure in the evening but gave the maximum value the next morning prior to walking.

The effect of work upon the blood pressure can in this series of measurements be noted only in the measurement of the blood pressure in the first quarter minute after the cessation of walking. These values are likewise recorded in table 78. In this first observation immediately after work a slight tendency is shown for the systolic pressure to rise in nearly all cases, although only a few millimeters, the most pronounced rise being 11 mm. with Can. In three cases there is a slight fall. Comparing the average systolic pressure for the 11 men the first quarter minute after the end of work with that measured before work, we find a rise of but 3 mm., i. e., from 101 to 104 mm. The course of the systolic blood pressure in the next 2 minutes was essentially constant, there being hardly any changes that are truly significant, although in general there was a very slight tendency for the blood pressure to fall as time progressed. The two observations made with the subject in the sitting position show slightly lower values than those found for the standing. Except for Can and Kon, the pre-walking blood pressure level was usually regained at the end of 9 minutes. With Can the blood pressure remained at 104 mm. as compared with 97 mm. before walking and with Kon it was 98 mm. as compared with 106 mm., these men showing diametrically opposite effects. The fact should be noted, however, that the values compared were obtained in different positions.