Nature of Peripheral Resistance in Arterial Hypertension.

The nature of the arteriolar resistance and its distribution in the body remain the fundamental problem in the study of arterial hypertension in man. Since the cardiac output is normal in this state (1), the " average arteriolar resistance " at rest must be increased. The extent to which the peripheral resistance is increased in various tissues can be determined by comparing the blood flow in the different tissues in both normal and hypertensive subjects under similar conditions. If in arterial hypertension the peripheral resistance in any one part is not increased, the blood flow in that part will be greater than in normal subjects. Since the cardiac output at rest is normal in arterial hypertension, the "average tissue blood flow " must also be normal. This has been confirmed by the demonstration that in hypertensive subjects the blood flow is normal in the hand and forearm (2, 3). While it is of interest to gather further information on the " resting " blood flow in other organs in normal and hypertensive subjects , it is of particular importance to ascertain whether the increased peripheral resistance in arterial hypertension can be lowered to a normal level in any one organ by potent vasodilating stimuli. If the increased peripheral resistance which exists at rest in arterial hypertension can be lowered to normal in any one organ, as manifested by a faster blood flow than is present in that organ in normal subjects under similar conditions , then the increased peripheral resistance at rest is the result of functional vasoconstric-tion, and is not the result of permanent, irreversible structural changes in the vessels. If the increased peripheral resistance present in arterial hypertension, however, cannot be reduced to normal by powerful vasodilating stimuli, as indicated by the finding of the same blood flow in the tissues of both normal and hypertensive subjects when the vessels are maximally dilated, then there are at least two obvious explanations: The chemical or other factors, which cause the vasoconstric-tion and the increased peripheral resistance, remain active in the presence of the various physiological stimuli applied and prevent the vessels from dilating as widely as normally; or the increased peripheral resistance is the result of permanent structural changes and, therefore, the vessels cannot dilate as widely as normally. Other investigators have shown that the increased peripheral resistance, which is present in the usual types of clinical arterial hypertension, …