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312 J. A. MACWILLIAM 



pressure measurement and to regard differences of 10 to 20 mm. in 

 blood-pressure readings as being of small moment in view of the larger 

 variations that may occur from time to time with apparently little 

 significance. But the importance of such differences varies greatly 

 in relation to their position in the scale of pressures. When they 

 start near the "normal" lower limits of systolic and diastolic pressures, 

 differences of 10 to 20 nxm. may mean much, e.g., between 100 and 80 

 or 90 systolic, or between 60 and 40 or 50 diastolic, such are of much 

 significance as compared with similar amounts at higher levels. 



Relations of systolic, diastolic and pulse pressures. The 3:2:1 ratio 

 commonly cited as applicable to these pressures is subject to very 

 considerable variations without coming into the category of the abnor- 

 mal. The validity of the ratio is mostly evident with certain normal 

 pressures, e.g., S. 120, D. 80, P. P. 40, the pulse pressure being one-half 

 of the diastolic and one-third of the systolic. It does not hold good in 

 such low pressures as may sometimes be found in healthy persons, 

 e.g., S. 105, D. 60; where the P. P. is three-fourths, instead of one- 

 half, of the diastolic and much nearer one-half than one-third of the 

 systolic. Again with such a high diastolic as 120 mm. (muscular 

 effort, etc.) a S. 180 and P. P. 60 are apt to be under what actually 

 occur, the high diastolic tending to give a relatively higher S. and P. P. 

 on account of the tense condition of the arterial walls; the discharge 

 from an efficient L. V. causes a disproportionately large rise of systolic 

 pressure — apart from the influence of an increased discharge per beat 

 occurring in a distended or enlarged heart. Such effects of diminished 

 distensibility of the arterial system at high diastolic pressures may also 

 be paralleled by loss of elasticity and stiffening of the arterial walls 

 from degenerative changes, apart from the presence of a high diastolic 

 pressure. These factors being operative at different ages, it is evident 

 that while the average (absolute) values of pulse pressure in large num- 

 bers of persons vary with age in the manner already stated, the actual 

 amounts in individuals may be greatly affected, apart from the in- 

 fluence of age, in the ways just stated. Pulse pressures of deficient 

 amounts associated with a high diastolic level are naturally of evil 

 significance as indicating cardiac inefficiency, provided the low P. P. 

 is not accounted for by acceleration of the pulse rate. 



Blood pressure in muscular exercise. While a rise of blood pressure 

 has long been known to be associated with muscular exertion, the 

 great majority of the measurements have been made after the period 

 of exertion has ended and have for the most part dealt only with sys- 



