Contribution of renal nerves to renal blood flow  variability during hemorrhage

Malpas, Simon C.; Evans, Roger G.; Head, G. A.; Лукошкова, Е. В.

doi:10.1152/ajpregu.1998.274.5.r1283

Cited by 58 publications

(82 citation statements)

References 28 publications

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“…In rabbits, stimuli that increase the mean level of renal SNA, such as hypoxia and hemorrhage, have been shown to increase the strength of 0.3-Hz oscillations in SNA (22,28). In the past, we proposed that the increase in the power of the oscillation was due to the increase in the mean SNA level.…”

Section: Discussionmentioning

confidence: 99%

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Slow oscillations in blood pressure via a nonlinear feedback model

Ringwood

Malpas

2001

American Journal of Physiology-Regulatory, Integrative and Comp

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101

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Ringwood, John V., and Simon C. Malpas. Slow oscillations in blood pressure via a nonlinear feedback model. Am J Physiol Regulatory Integrative Comp Physiol 280: R1105-R1115, 2001.-Blood pressure is well established to contain a potential oscillation between 0.1 and 0.4 Hz, which is proposed to reflect resonant feedback in the baroreflex loop. A linear feedback model, comprising delay and lag terms for the vasculature, and a linear proportional derivative controller have been proposed to account for the 0.4-Hz oscillation in blood pressure in rats. However, although this model can produce oscillations at the required frequency, some strict relationships between the controller and vasculature parameters must be true for the oscillations to be stable. We developed a nonlinear model, containing an amplitude-limiting nonlinearity that allows for similar oscillations under a very mild set of assumptions. Models constructed from arterial pressure and sympathetic nerve activity recordings obtained from conscious rabbits under resting conditions suggest that the nonlinearity in the feedback loop is not contained within the vasculature, but rather is confined to the central nervous system. The advantage of the model is that it provides for sustained stable oscillations under a wide variety of situations even where gain at various points along the feedback loop may be altered, a situation that is not possible with a linear feedback model. Our model shows how variations in some of the nonlinearity characteristics can account for growth or decay in the oscillations and situations where the oscillations can disappear altogether. Such variations are shown to accord well with observed experimental data. Additionally, using a nonlinear feedback model, it is straightforward to show that the variation in frequency of the oscillations in blood pressure in rats (0.4 Hz), rabbits (0.3 Hz), and humans (0.1 Hz) is primarily due to scaling effects of conduction times between species. sympathetic nervous system; baroreflex; stability; describing function; artificial neural network IT IS WELL ESTABLISHED that blood pressure in humans can contain a distinct oscillation at 0.1 Hz, often referred to as the Mayer wave (26,38). Experiments in a variety of animal models have shown that this oscillation is due to the action of the sympathetic nervous system on the vasculature. Although the oscillation in blood pressure is shifted to 0.4 Hz in the rat (7) and to 0.3 Hz in the rabbit (22), changes in the strength of this oscillation have been proposed to reflect changes in the mean level of sympathetic nerve activity (SNA) and/or baroreflex gain (6), raising the possibility that measurement of the strength of this oscillation may be used as a diagnostic measure of neural control of the cardiovascular system in humans (1,10,26).Current evidence favors the concept of feedback in the baroreflex loop as the origin for the 0.1-Hz oscillation in blood pressure (5,6,13,25,41). In this model, a change in blood pressure is sensed by the arterial barorece...

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Section: Discussionmentioning

confidence: 99%

“…Animals underwent surgery, at least 7 days before the recording, to implant a recording electrode around the left renal sympathetic nerve as previously described (28). Experiments were previously approved by the University of Auckland Animal Ethics Committee.…”

Section: Methodsmentioning

confidence: 99%

Slow oscillations in blood pressure via a nonlinear feedback model

Ringwood

Malpas

2001

American Journal of Physiology-Regulatory, Integrative and Comp

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101

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“…For example, our previous work demonstrated that ten percent of subjects fail to demonstrate significant coherence between the two signals at rest, (Taylor, et aL 1998b) and others have failed to find any coherence without vasodilator inti.rsions to stimulate sympathetic outtlow, (Saul, ct aL 1990) Findings in the animal literature may be even more equivocaL Generally, coherence is found only in a narrow l!·cquency band around the heart rate, (Kenney, et aL 1994) unless the animal is under severe stress. For example, Malpas et aL (Mal pas, et aL 1998)found little relationship between renal pressure and sympathetic nerve activity at 0.3Hz or below in rabbits until a severe hemorrhage was induced, increasing sympathetic activity 1 0-fold.…”

Section: Discussionmentioning

confidence: 99%

A model for the genesis of arterial pressure Mayer waves from heart rate and sympathetic activity

Myers

Cohen

Eckberg

et al. 2001

Autonomic Neuroscience

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“…The stimuli we tested are likely to be relevant to physiological stressors that increase the risk of tubular necrosis and acute renal failure (26). For example, dehydration is associated with increased circulating levels of arginine vasopressin (8,9) and acute hemorrhage is associated with increased circulating levels of ANG II (13) and increased renal sympathetic nerve activity (20).…”

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Renal medullary tissue oxygenation is dependent on both cortical and medullary blood flow

O’Connor¹,

Kett²,

Anderson³

et al. 2006

American Journal of Physiology-Renal Physiology

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. Renal medullary tissue oxygenation is dependent on both cortical and medullary blood flow. Am J Physiol Renal Physiol 290: F688 -F694, 2006. First published October 11, 2005 doi:10.1152/ajprenal.00275.2005The aim of the current study was to determine whether renal medullary oxygenation is independent of the level of cortical blood flow by testing responses to stimuli that selectively reduce blood flow in either the cortex or medulla. In anesthetized rabbits, renal arterial infusion of [Phe 2 ,Ile 3 ,Orn 8 ]-vasopressin selectively reduced medullary perfusion and PO 2 (Ϫ54 Ϯ 24 and Ϫ50 Ϯ 10%, respectively) but did not significantly affect cortical perfusion or tissue oxygenation. In contrast, stimulation of the renal nerves resulted in renal cortical ischemia with reductions in total renal blood flow (Ϫ76 Ϯ 3% at 4 Hz), cortical perfusion (Ϫ57 Ϯ 17%), and cortical PO 2 (Ϫ44 Ϯ 12%). Medullary tissue PO2 was reduced by Ϫ70 Ϯ 5% at 4 Hz, despite medullary perfusion being unaffected and distal tubular sodium reabsorption being reduced (by Ϫ83.3 Ϯ 1.2% from baseline). In anesthetized rats, in which renal perfusion pressure was maintained with an aortic constrictor, intravenous infusion of ANG II (0.5-5 g ⅐ kg Ϫ1 ⅐ min Ϫ1 ) dose dependently reduced cortical perfusion (up to Ϫ65 Ϯ 3%; P Ͻ 0.001) and cortical PO 2 (up to Ϫ57 Ϯ 4%; P Ͻ 0.05). However, medullary perfusion was only significantly reduced at the highest dose (5 g ⅐ kg Ϫ1 ⅐ min Ϫ1 ; by 29 Ϯ 6%). Medullary perfusion was not reduced by 1 g ⅐ kg Ϫ1 ⅐ min Ϫ1ANG II, but medullary PO2 was significantly reduced (Ϫ12 Ϯ 4%). Thus, although cortical and medullary blood flow may be independently regulated, medullary oxygenation may be compromised during moderate to severe cortical ischemia even when medullary blood flow is maintained.acute renal failure; acute tubular necrosis; hypoxia; ischemia; laserDoppler flowmetry; fluorescence oximetry; oxygen; rabbits; rats; renal circulation THE UNIQUE VASCULAR architecture of the kidney allows differential regulation of cortical and medullary blood flow (7,10,14). Indeed, many vasoconstrictor factors that profoundly reduce total renal blood flow (TRBF) and cortical blood flow appear to have considerably less impact on medullary blood flow (6). Thus the renal medulla may be at least partially protected from hypoxic insults during periods of reduced overall (total) renal blood flow, if medullary blood flow, and so presumably oxygen delivery to this region, is maintained. However, this hypothesis is predicated on renal cortical and medullary oxygenation being relatively independent. Changes in glomerular filtration, tubular sodium reabsorption, and/or the possibility of oxygen loss from preglomerular arterial blood (27) may render medullary oxygenation dependent on the level of cortical blood flow.The aim of the current study was to examine the relationship between tissue oxygenation and perfusion in the cortex and medulla. We tested the hypothesis that medullary oxygenation is independent of cortical blood flow. To achieve this...

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Contribution of renal nerves to renal blood flow variability during hemorrhage

Cited by 58 publications

References 28 publications

Slow oscillations in blood pressure via a nonlinear feedback model

Slow oscillations in blood pressure via a nonlinear feedback model

A model for the genesis of arterial pressure Mayer waves from heart rate and sympathetic activity

Renal medullary tissue oxygenation is dependent on both cortical and medullary blood flow

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