1) A histometrical method was described, with which arterial cross sections of autopsy cases were reduced to the state, in which internal elastic membrane was perfectly stretched. The distance from the center of the arterial lumen to the middle point of the media in this condition was defined as anatomical arterial radius, R
, and the thickness of the media in this condition as anatomical medial thickness, D
. The values of R
were determined by
/2π, respectively, in which L
was the length of internal elastic membrane and S
was the surface area of the muscular coat in arterial cross section.
2) A regular relation was confirmed between R
, which was represented by a general equation D
being constants. On a logarithmic scale, the relation gave a linear regression and was represented by a linear regression equation _??_
, in which X
. Statistical treatments of the histometrical results were discussed.
3) The histometrical method was applied to renal and superior mesenteric arteries. Non-hypertensive cases were divided into 3 age groups, and in each age group common regression equations were determined of each artery to demonstrate the characteristics of arterial pattern. Each artery was composed of two parts divided at R
=100μ. In the part R
was smaller than, but very close to, 1. Superior mesenteric artery had stronger muscular coat than renal artery at R
=1000μ. In the other part, R
was remarkably lower than 1, especially in renal artery, indicating rapid elevation of the ratio D/R with reduction of arterial radius. At the point R
=10μ, renal artery had a higher value of D
. The difference of arterial pattern was discussed in relation to different regulatory function of the two arteries.
4) The ratio D
was defined as media index and employed as the estimate of medial strength. The value of the index was determined to the major part by blood pressure, arterial radius and arterial system, and to a lesser extent by age. Media index of the non-hypertensive was strikingly constant at a given radius of a given arterial system, in spite of remarkable arterial growth with age, with the exception at R
=10μ, where the index gradually fell with age. By an elevation of media index medial hypertrophy was defined and hypertension was concluded.
5) Upper rejection limit of estimated D from the regression equations of the non-hypertensive was statistically determined at R
=100μ and R
=10μ of each artery. Arteries with larger estimated D
than the upper rejection limit at any R were not regarded to belong to the non-hypertensive. The rejection limit at R
=100μ of renal artery was the most effective and reliable anatomical standard in screening hypertensive cases.
6) In the hypertensive, medial hypertrophy was confirmed in both renal and superior mesenteric arteries. Medial hypertrophy was very unequal according to the dimension of arterial branches. It was prominent in the region R
>100μ, but less pronounced in the region R<100μ, and practically ceased to be noticed at R
=10μ in the majority of cases with essential hypertension. Blood pressure was regarded to be abruptly lowered in the vicinity of R
=100μ and arterioles were in all probability not exposed to abnormally high blood pressure in an average. The unequal medial hypertrophy induced a transformation of general arterial pattern in hypertension.
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