Dynamic relationship between sympathetic nerve activity and renal blood flow: a frequency domain approach

Guild, Sarah-Jane; Austin, P.C.; Navakatikyan, Michael A.; Ringwood, John V.; Malpas, Simon C.

doi:10.1152/ajpregu.2001.281.1.r206

Cited by 43 publications

(57 citation statements)

References 12 publications

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“…An example of this is the renal vasculature, as quantified by [23] and Guild et al [24]. It can be seen that the block representing the dynamics of the vasculature in Fig.…”

Section: B Validity Of Df Approximationmentioning

confidence: 95%

A Simple Soft Limiter Describing Function for Biomedical Applications

Paor

Ringwood

2006

IEEE Trans. Biomed. Eng.

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Abstract-This paper suggests an arctangent function as a suitable parameterisation for the soft-limiting gain characteristic frequently encountered in models of biomedical systems. This function is shown, as an example, to fit the neural arc component of the baroreflex with the main contribution of the paper being the development of a simple describing function (DF) characteristic for the arctangent. The simple form of the DF allows transparency of the physiological parameters in, for example, stability analysis. For illustration, the derived DF is used to examine low-frequency limit cycles in blood pressure, sometimes termed Mayer waves.

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“…An example of this is the renal vasculature, as quantified by [23] and Guild et al [24]. It can be seen that the block representing the dynamics of the vasculature in Fig.…”

Section: B Validity Of Df Approximationmentioning

confidence: 95%

A Simple Soft Limiter Describing Function for Biomedical Applications

Paor

Ringwood

2006

IEEE Trans. Biomed. Eng.

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“…However, it was not clear whether the transfer function should be modeled with a first-order or second-order filter, because the average decay in the magnitude response was 30 Ϯ 1.2 dB per decade and thus halfway between the theoretical 20 dB (first order) and 40 dB (second order). Both models were therefore fitted to the experimental magnitude and phase responses using an optimizationbased strategy as given in Guild et al (13), using a cost function of the form where J is the total cost (error) to be minimized, G i and Ĝ i are the measured and modeled frequency response, respectively, and is the phase error weighting relative to the gain error weighting. This is similar to least squares fitting, but, because the cost function is not linear in the parameters (as required in least squares), an alternative optimization technique is required, such as the Simplex method used here.…”

Section: Baseline Cardiovascular Variablesmentioning

confidence: 99%

Dynamic baroreflex control of blood pressure: influence of the heart vs. peripheral resistance

Liu

Guild

Ringwood

et al. 2002

American Journal of Physiology-Regulatory, Integrative and Comp

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. Dynamic baroreflex control of blood pressure: influence of the heart vs. peripheral resistance. Am J Physiol Regulatory Integrative Comp Physiol 283: R533-R542, 2002; 10.1152/ajpregu.00489.2001The aim in the present experiments was to assess the dynamic baroreflex control of blood pressure, to develop an accurate mathematical model that represented this relationship, and to assess the role of dynamic changes in heart rate and stroke volume in giving rise to components of this response. Patterned electrical stimulation [pseudo-random binary sequence (PRBS)] was applied to the aortic depressor nerve (ADN) to produce changes in blood pressure under open-loop conditions in anesthetized rabbits. The stimulus provided constant power over the frequency range 0-0.5 Hz and revealed that the composite systems represented by the central nervous system, sympathetic activity, and vascular resistance responded as a second-order low-pass filter (corner frequency Ϸ0.047 Hz) with a time delay (1.01 s). The gain between ADN and mean arterial pressure was reasonably constant before the corner frequency and then decreased with increasing frequency of stimulus. Although the heart rate was altered in response to the PRBS stimuli, we found that removal of the heart's ability to contribute to blood pressure variability by vagotomy and ␤ 1-receptor blockade did not significantly alter the frequency response. We conclude that the contribution of the heart to the dynamic regulation of blood pressure is negligible in the rabbit. The consequences of this finding are examined with respect to low-frequency oscillations in blood pressure. sympathetic nerve activity; modeling; transfer function; vasculature; rabbit THE ABILITY OF THE ARTERIAL baroreflex pathway to regulate blood pressure under steady-state conditions is well understood (25). However, there is a paucity of information regarding its dynamic ability over the frequency range 0.001-0.5 Hz. This is particularly relevant when trying to understand the mechanisms that give rise to oscillations between 0.1 and 0.4 Hz. Although there is general acceptance that this oscillation seen in humans at 0.1 Hz involves an action of the sympathetic nervous system on the vasculature, it is a matter of debate as to the origin of the oscillation. It has been suggested that the oscillation results either as a by-product of the central generation of sympathetic nerve activity (SNA) (8,24) or from the time delay between the arterial baroreceptors sensing blood pressure and the subsequent reflex effect on the vasculature (3,6,9,22,29). Certainly the available evidence suggests that the oscillation requires the presence of each of the components of the baroreflex pathway, with baroreceptor denervation or sympathectomy abolishing the oscillation in blood pressure (7,16,19). Clearly, if measurement of the strength of such oscillations is to develop into a clinically useful tool, it is imperative to understand factors from which cardiovascular variability is derived (23).Although it is clear that SNA to t...

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“…Because it has been shown that changes in renal sympathetic nerve activity can alter RBF (1,10) and modulate P LL (18), the kidney used for RBF recording was denervated.…”

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confidence: 99%

Spontaneous renal blood flow autoregulation curves in conscious sinoaortic baroreceptor-denervated rats

Pires

Julien

Chapuis

et al. 2002

American Journal of Physiology-Renal Physiology

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Pires, Silene L. S., Claude Julien, Bruno Chapuis, Jean Sassard, and Christian Barrè s. Spontaneous renal blood flow autoregulation curves in conscious sinoaortic baroreceptor-denervated rats. Am J Physiol Renal Physiol 282: F51-F58, 2002. First published August 8, 2001 10.1152/ajprenal.00186.2001.-These experiments examined whether the conscious sinoaortic baroreceptor-denervated (SAD) rat, owing to its high spontaneous arterial pressure (AP) variability, might represent a model for renal blood flow (RBF) autoregulation studies. In eight SAD and six baroreceptor-intact rats, AP and RBF were recorded (1-h periods) before and after furosemide (10 mg/kg followed by 10 mg ⅐ kg Ϫ1 ⅐ h Ϫ1 iv) administration. In control conditions, AP variability was markedly enhanced in SAD rats (coefficient of variation: 16.0 Ϯ 1.2 vs. 5.4 Ϯ 0.5% in intact rats), whereas RBF variability was only slightly increased (8.7 Ϯ 0.6 vs. 6.1 Ϯ 0.5% in intact rats), suggesting buffering by autoregulatory mechanisms. In SAD rats, but not in intact rats, the AP-RBF relationships could be modeled with a four-parameter sigmoid Weibull equation (r 2 ϭ 0.24 Ϯ 0.07, 3,600 data pairs/rat), allowing for estimation of an autoregulatory plateau (10.1 Ϯ 0.7 ml/min) and a lower limit of RBF autoregulation (PLL ϭ 93 Ϯ 6 mmHg, defined as AP at RBF 5% below the plateau). After furosemide treatment, autoregulation curves (r 2 ϭ 0.49 Ϯ 0.07) in SAD rats were shifted downward (plateau ϭ 8.6 Ϯ 0.8 ml/min) and rightward (PLL ϭ 102 Ϯ 5 mmHg). In five of six intact rats, PLL became measurable (104 Ϯ 1 mmHg), albeit with limited accuracy (r 2 ϭ 0.09 Ϯ 0.03). In conclusion, the conscious SAD rat offers the possibility of describing RBF autoregulation curves under dynamic, unforced conditions. The tubuloglomerular feedback and myogenic mechanisms cooperate in setting PLL and thus in stabilizing RBF during spontaneous depressor episodes.arterial pressure variability; furosemide; modeling AUTOREGULATION OF TOTAL RENAL blood flow (RBF) is usually explored by measuring RBF responses to externally induced stepwise reductions of arterial pressure (AP) in both anesthetized (6,8,11,13,17,21,22) and conscious (2,4,16,18,(24)(25)(26) animals. Steady-state levels of RBF are plotted as a function of AP, which allows the drawing of autoregulation curves from which the plateau and lower pressure limit of RBF autoregulation (P LL ) are estimated. It is not known whether such information can be gained under spontaneous unforced conditions, i.e., using RBF responses to naturally occurring AP fluctuations.The conscious sinoaortic baroreceptor-denervated (SAD) rat is a well-recognized model of exaggerated AP variability, which is characterized by the spontaneous occurrence of pressor and depressor episodes of occasionally large amplitude (3,28). Recently, we have investigated in conscious SAD rats the relationships between AP variability and RBF variability (20). Although AP variability was markedly increased, RBF variability was only slightly increased, suggesting a powerful participa...

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Dynamic relationship between sympathetic nerve activity and renal blood flow: a frequency domain approach

Cited by 43 publications

References 12 publications

A Simple Soft Limiter Describing Function for Biomedical Applications

A Simple Soft Limiter Describing Function for Biomedical Applications

Dynamic baroreflex control of blood pressure: influence of the heart vs. peripheral resistance

Spontaneous renal blood flow autoregulation curves in conscious sinoaortic baroreceptor-denervated rats

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