Linearity Of Systolic Blood Pressure Response To Angiotensin Ii Stimulation In A Rat Model

BACKGROUND: The regulation of blood pressure is a dynamic process in which myriad mechanisms operate simultaneously. The renin-angiotensin system is one of the most studied blood pressure control systems because the rise of circulating angiotensin II levels is associated with the development of hypertension and renal damage. In control theory, the field of system identification is focused on the development of mathematical models based on experimental determination of a system's temporal behaviour.OBJECTIVE: The aim of the present study was to use experimental and theoretical analyses to characterize whole organism response to stimulus with angiotensin II (the input variable) using systolic blood pressure as the output variable.METHODS : Nine normotensive male Wistar rats (250 g to 300 g), six weeks of age, were housed under standard laboratory conditions. The animals were anesthetized with sodium pentobarbital (65 mg/kg) to implant a catheter in the aorta. The systolic arterial pressure was continuously recorded using a pressure transducer attached to the intra-arterial cannula. Animals were stimulated with at least four boluses of angiotensin II, at fixed time intervals. A mathematical model was proposed to reproduce the systolic blood pressure response at each stimulus with angiotensin II.RESULTS: Three static properties were demonstrated: homogeneity, additivity and shift invariance. These results agree with linear systems requirements.CONCLUSIONS: The whole-body response to angiotensin II stimulus behaves linearly, despite the high complexity of the blood pressure regulation subsystems and their simultaneous interactions; specifically, there is a linear relationship between the observed rise in systolic blood pressure and angiotensin II concentration.