Two variants of nephrosclerosis separately related to age and blood pressure

Two variants of nephrosclerosis, roughly corresponding to the arterial and the arteriolar forms, have been examined in a series of autopsy kidneys by five observers using quantitative morphometry. These two variants are both marked by fibroplastic intimal thickening and medial wastage in the arteries, but one of these affects vessels of sizes that are closer to the heart, whereas the other affects sizes that are more remote from the source of arterial pressure. Both types of nephrosclerosis were found to increase with aging in subjects without hypertension. Each year of aging added 0.15 units of intimal thickening to the close vessels and 0.11 to the remote vessels. Each millimeter of mercury of elevated blood pressure was equivalent to 1 year of aging in the close and 2 years in the remote levels of the arterial tree. The four variables, age, blood pressure, remote level intimal thickness, and close level intimal thickness, were found to hold complex curvilinear interrelationships when examined by regression analysis. A dynamic model was suggested by the following findings: The earliest changes shown by young normotensives are in the close vessels, possibly because of the aging effect of the normal pulse wave. Later, the changes extend into the remote level, perhaps because the thickened intima is rigid and propagates the pulse wave abnormally far into the smallest arteries. Hypertension could then be viewed either as a cause for an exaggeration of this normal process or as a consequence of its extension into the remote level vessels where resistance to blood flow is greater or both. The objective morphometric method showed good agreement in the findings by independent observers and is considered to be suitable for epidemiologic studies of nephrosclerosis.