Brief Reviews : A Systems Analysis Approach to Understanding Long-Range Arterial Blood Pressure Control and Hypertension

Abstract

• The use of systems analysis as an experimental tool for solving complex physiological problems is not new. Actually, systems analysis is merely the logical analysis of how systems perform. However, modern usage of the term implies a more formalized type of logic, especially a type of logic that includes quantification at each step in the analysis. Several of the figures in this paper illustrate systems analysis flow diagrams that show interrelationships between the different parts of simple or complex mechanisms for the control of arterial blood pressure. One can readily see that each part of each systems analysis diagram is only a symbolic way in which a composite of individual physiological phenomena fit together in a complete system.The principal advantage of the formalized systems analysis approach to understanding any physiological mechanism is that it often allows greater depth of thought than our minds can perform using simple logical procedures. The mind has the capability of holding and analyzing perhaps five to ten different sequential phenomena, each occurring at different rates and each interrelated with the other phenomena by various cross-linkages. However, beyond this size of system it is almost impossible to think through all the complex relationships simultaneously. On the other hand, the modern computer can handle literally thousands of such crosslinking interrelationships at the same time and can develop answers that the mind alone cannot achieve. Now setting aside this philosophizing about systems analysis per se, we will attempt to show how the systems analysis approach has been useful in the study of long-range arterial blood pressure control and the understanding of hypertensive

Hypertension following denervation of aortic baroreceptors in unanesthetized dogs.

“…Taken with our findings, these results argue against the importance of the nonneural "infinite gain" mechanisms that Guyton et al (1974) have emphasized. Differences between our results and those of Cowley and DeClue (1976) and Cowley and Guyton (1975), who found very little average increase in blood pressure after attempts at complete (aortic and carotid sinus) baroreceptor denervation, probably reflect differences in denervation procedures.…”

“…This reflex control is generally considered operative for short-and longterm regulation. Recently, however, Guyton et al (1974) have expressed the view that arterial baroreceptors are not important in long-term control of arterial pressure. They believe that the baroreceptor reflexes will act for only 1 or 2 days to correct alterations in arterial pressure, and they attribute long-term control of arterial pressure to nonneural mechanisms.…”

Blood pressure and diurnal variation in sodium, potassium, and water excretion

“…[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] Data from epidemiological, clinical, and animal experimental studies all indicate a direct causal association between excess salt intake and hypertension. Several investigators suggest that hypertension is the result of an inability of the kidney to excrete salt and water normally.…”

“…35,40,47-52 These investigators hypothesise that development of chronic BP elevation results from need of the kidneys to increase urine volume and sodium excretion-in the presence of habitual sodium intake several-fold above physiologic requirement-in order to maintain homeostasis of the extracellular fluid volume. 40,43,[47][48][49]52 Diurnal variations in excretion of sodium, chloride, potassium, and water have been observed in many studies. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Creatinine excretion has generally been reported to be fairly constant over 24 h, 2,7,11,26,28 and on average this was the case for the men in this study.…”

Age as a function in the development of sodium-related hypertension.

“…The renin-angiotensin-aldosterone (RAA) system has been much investigated in its relation to hypertension (64)(65)(66)(67)(68). Although it is clear that defects in the production of any of these elements can affect the ability of the body to adjust the resistance of the circulatory system and/or blood volume, the RAA system is thought to be capable only of short-term adjustments to maintain homeostasis of these systems and any continued elevation of sodium eventually overwhelms the RAA system.…”