The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform

Masaru Sugimachi - One of the best experts on this subject based on the ideXlab platform.

  • Sustained reduction in blood pressure from electrical activation of the baroreflex is mediated via the central pathway of unmyelinated baroreceptors.
    Life sciences, 2014
    Co-Authors: Michael J. Turner, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    This study aims to identify the contribution of myelinated (A-fiber) and unmyelinated (C-fiber) baroreceptor central pathways to the baroreflex control of sympathetic nerve activity and arterial pressure. Two binary white noise stimulation protocols were used to electrically stimulate the aortic depressor nerve and activate reflex responses from either A-fiber (3 V, 20-100 Hz) or C-fiber (20 V, 0-10 Hz) baroreceptor in anesthetized Sprague-Dawley rats (n=10). Transfer function analysis was performed between stimulation and sympathetic nerve activity (central Arc), sympathetic nerve activity and arterial pressure (peripheral Arc), and stimulation and arterial pressure (Stim-AP Arc). The central Arc Transfer function from nerve stimulation to splanchnic sympathetic nerve activity displayed derivative characteristics for both stimulation protocols. However, the modeled steady-state gain (0.28 ± 0.04 vs. 4.01 ± 0.2%·Hz(-1), P<0.001) and coherence at 0.01 Hz (0.44 ± 0.05 vs. 0.81 ± 0.03, P<0.05) were significantly lower for A-fiber stimulation compared with C-fiber stimulation. The slope of the dynamic gain was higher for A-fiber stimulation (14.82 ± 1.02 vs. 7.21 ± 0.79 dB·decade(-1), P<0.001). The steady-state gain of the Stim-AP Arc was also significantly lower for A-fiber stimulation compared with C-fiber stimulation (0.23 ± 0.05 vs. 3.05 ± 0.31 mmHg·Hz(-1), P<0.001). These data indicate that the A-fiber central pathway contributes to high frequency arterial pressure regulation and the C-fiber central pathway provides more sustained changes in sympathetic nerve activity and arterial pressure. A sustained reduction in arterial pressure from electrical stimulation of arterial baroreceptor afferents is likely mediated through the C-fiber central pathway. Copyright © 2014 Elsevier Inc. All rights reserved.

  • Sustained reduction in blood pressure from electrical activation of the baroreflex is mediated via the central pathway of unmyelinated baroreceptors
    Life Sciences, 2014
    Co-Authors: Michael J. Turner, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    Abstract Aims This study aims to identify the contribution of myelinated (A-fiber) and unmyelinated (C-fiber) baroreceptor central pathways to the baroreflex control of sympathetic nerve activity and arterial pressure. Main methods Two binary white noise stimulation protocols were used to electrically stimulate the aortic depressor nerve and activate reflex responses from either A-fiber (3 V, 20–100 Hz) or C-fiber (20 V, 0–10 Hz) baroreceptor in anesthetized Sprague-Dawley rats ( n  = 10). Transfer function analysis was performed between stimulation and sympathetic nerve activity (central Arc), sympathetic nerve activity and arterial pressure (peripheral Arc), and stimulation and arterial pressure (Stim-AP Arc). Key findings The central Arc Transfer function from nerve stimulation to splanchnic sympathetic nerve activity displayed derivative characteristics for both stimulation protocols. However, the modeled steady-state gain (0.28 ± 0.04 vs. 4.01 ± 0.2%·Hz − 1 , P P − 1 , P − 1 , P Significance These data indicate that the A-fiber central pathway contributes to high frequency arterial pressure regulation and the C-fiber central pathway provides more sustained changes in sympathetic nerve activity and arterial pressure. A sustained reduction in arterial pressure from electrical stimulation of arterial baroreceptor afferents is likely mediated through the C-fiber central pathway.

  • EMBC - Differential dynamic control of cardiac and splanchnic sympathetic nerve activity by the arterial baroreflex
    Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Inte, 2013
    Co-Authors: Michael J. Turner, Toru Kawada, Masaru Sugimachi
    Abstract:

    The arterial baroreflex is the primary negative feedback system involved in stabilizing arterial pressure from external disturbances. Determining the dynamic characteristics of the baroreflex is important for our understanding of the mechanisms involved in rapid restoration of arterial pressure. This study examined the differences in the dynamic baroreflex control of cardiac (CSNA) and splanchnic (SSNA) sympathetic nerve activity. The baroreceptor region of the right aortic depressor nerve was isolated from the systemic circulation to control baroreceptor region pressure (BRP) with a Gaussian white noise signal while simultaneously recording CSNA and SSNA in anesthetized Sprague-Dawley rats. SSNA was recorded from a postganglionic branch of the splanchnic sympathetic nerve and CSNA was recorded from a branch of the left stellate ganglion. Neural Arc Transfer functions from BRP to SSNA (HSSNA) and BRP to CSNA (HCSNA) displayed derivative characteristics. When dynamic gain below 0.03 Hz was normalized to unity, HSSNA had a higher gain at frequencies 0.1 and 1 Hz and increasing slope from 0.1 to 1 Hz relative to HCSNA. The peak decrease in the step response was higher for SSNA than CSNA. These data indicate differential dynamic baroreflex control of SSNA and CSNA. Rapid changes in baroreceptor pressure input would result in a larger response in SSNA compared with CSNA.

  • EMBC - Effects of L-type Ca 2+ channel blocker nifedipine on dynamic arterial blood pressure control
    Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Inte, 2013
    Co-Authors: Toru Kawada, Shuji Shimizu, Hiromi Yamamoto, Michael J. Turner, Masaru Sugimachi
    Abstract:

    Dynamic characteristics of arterial pressure (AP) regulation are important components in our understanding of rapid AP restoration by the arterial baroreflex system. The present study examined the effects of an L-type Ca2+ channel blocker nifedipine on baroreflex-mediated dynamic AP regulation. In anesthetized and vagotomized rats, carotid sinus pressure was externally perturbed using a Gaussian white noise signal, and the neural Arc Transfer function from pressure input to efferent sympathetic nerve activity (SNA) and the peripheral Arc Transfer function from SNA to AP were identified. The peripheral Arc Transfer function approximated a second-order low-pass filter with pure dead time. Intravenous administration of nifedipine significantly decreased the steady-state gain and increased the damping ratio of the peripheral Arc without affecting the dynamic characteristics of the neural Arc. When the step response of AP was calculated based on the peripheral Arc Transfer function alone, nifedipine prolonged 80% rise time by 26%. When the closed-loop AP response was simulated based on both the neural Arc and peripheral Arc Transfer functions and the dynamic gain of the baroreflex total loop was assumed to be 2.0, nifedipine prolonged 80% recovery time by 107%. In conclusion, L-type Ca2+ channel blockade may compromise the baroreflex-mediated AP control not only in the magnitude but also in the speed of AP restoration.

  • closed loop spontaneous baroreflex Transfer function is inappropriate for system identification of neural Arc but partly accurate for peripheral Arc predictability analysis
    The Journal of Physiology, 2011
    Co-Authors: Atsunori Kamiya, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    Non-technical summary  The arterial baroreflex is a closed-loop, negative feedback control system that senses baroreceptor pressure and controls systemic arterial pressure (AP) to attenuate perturbations in AP. The total Arc of the baroreflex consists of two subsystems: the neural (baroreceptor pressure input to sympathetic nerve activity (SNA)) and peripheral (SNA input to AP) Arcs. We show that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting condition, when compared with open-loop Transfer functions that have good predictabilities of time-series output dynamics from input signals. Our results indicate that in the spontaneous baroreflex system under closed-loop conditions, the peripheral Arc (feedforward) function predominates over the neural Arc (feedback) function, probably because of the SNA component that is independent of the baroreceptor pressure input. Abstract  Although the dynamic characteristics of the baroreflex system have been described by baroreflex Transfer functions obtained from open-loop analysis, the predictability of time-series output dynamics from input signals, which should confirm the accuracy of system identification, remains to be elucidated. Moreover, despite theoretical concerns over closed-loop system identification, the accuracy and the predictability of the closed-loop spontaneous baroreflex Transfer function have not been evaluated compared with the open-loop Transfer function. Using urethane and α-chloralose anaesthetized, vagotomized and aortic-denervated rabbits (n= 10), we identified open-loop baroreflex Transfer functions by recording renal sympathetic nerve activity (SNA) while varying the vascularly isolated intracarotid sinus pressure (CSP) according to a binary random (white-noise) sequence (operating pressure ± 20 mmHg), and using a simplified equation to calculate closed-loop-spontaneous baroreflex Transfer function while matching CSP with systemic arterial pressure (AP). Our results showed that the open-loop baroreflex Transfer functions for the neural and peripheral Arcs predicted the time-series SNA and AP outputs from measured CSP and SNA inputs, with r2 of 0.8 ± 0.1 and 0.8 ± 0.1, respectively. In contrast, the closed-loop-spontaneous baroreflex Transfer function for the neural Arc was markedly different from the open-loop Transfer function (enhanced gain increase and a phase lead), and did not predict the time-series SNA dynamics (r2; 0.1 ± 0.1). However, the closed-loop-spontaneous baroreflex Transfer function of the peripheral Arc partially matched the open-loop Transfer function in gain and phase functions, and had limited but reasonable predictability of the time-series AP dynamics (r2, 0.7 ± 0.1). A numerical simulation suggested that a noise predominantly in the neural Arc under resting conditions might be a possible mechanism responsible for our findings. Furthermore, the predictabilities of the neural Arc Transfer functions obtained in open-loop and closed-loop conditions were validated by closed-loop pharmacological (phenylephrine and nitroprusside infusions) pressure interventions. Time-series SNA responses to drug-induced AP changes predicted by the open-loop Transfer function matched closely the measured responses (r2, 0.9 ± 0.1), whereas SNA responses predicted by closed-loop-spontaneous Transfer function deviated greatly and were the inverse of measured responses (r, −0.8 ± 0.2). These results indicate that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting conditions, when compared with open-loop analysis.

Toru Kawada - One of the best experts on this subject based on the ideXlab platform.

  • Sustained reduction in blood pressure from electrical activation of the baroreflex is mediated via the central pathway of unmyelinated baroreceptors.
    Life sciences, 2014
    Co-Authors: Michael J. Turner, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    This study aims to identify the contribution of myelinated (A-fiber) and unmyelinated (C-fiber) baroreceptor central pathways to the baroreflex control of sympathetic nerve activity and arterial pressure. Two binary white noise stimulation protocols were used to electrically stimulate the aortic depressor nerve and activate reflex responses from either A-fiber (3 V, 20-100 Hz) or C-fiber (20 V, 0-10 Hz) baroreceptor in anesthetized Sprague-Dawley rats (n=10). Transfer function analysis was performed between stimulation and sympathetic nerve activity (central Arc), sympathetic nerve activity and arterial pressure (peripheral Arc), and stimulation and arterial pressure (Stim-AP Arc). The central Arc Transfer function from nerve stimulation to splanchnic sympathetic nerve activity displayed derivative characteristics for both stimulation protocols. However, the modeled steady-state gain (0.28 ± 0.04 vs. 4.01 ± 0.2%·Hz(-1), P<0.001) and coherence at 0.01 Hz (0.44 ± 0.05 vs. 0.81 ± 0.03, P<0.05) were significantly lower for A-fiber stimulation compared with C-fiber stimulation. The slope of the dynamic gain was higher for A-fiber stimulation (14.82 ± 1.02 vs. 7.21 ± 0.79 dB·decade(-1), P<0.001). The steady-state gain of the Stim-AP Arc was also significantly lower for A-fiber stimulation compared with C-fiber stimulation (0.23 ± 0.05 vs. 3.05 ± 0.31 mmHg·Hz(-1), P<0.001). These data indicate that the A-fiber central pathway contributes to high frequency arterial pressure regulation and the C-fiber central pathway provides more sustained changes in sympathetic nerve activity and arterial pressure. A sustained reduction in arterial pressure from electrical stimulation of arterial baroreceptor afferents is likely mediated through the C-fiber central pathway. Copyright © 2014 Elsevier Inc. All rights reserved.

  • Sustained reduction in blood pressure from electrical activation of the baroreflex is mediated via the central pathway of unmyelinated baroreceptors
    Life Sciences, 2014
    Co-Authors: Michael J. Turner, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    Abstract Aims This study aims to identify the contribution of myelinated (A-fiber) and unmyelinated (C-fiber) baroreceptor central pathways to the baroreflex control of sympathetic nerve activity and arterial pressure. Main methods Two binary white noise stimulation protocols were used to electrically stimulate the aortic depressor nerve and activate reflex responses from either A-fiber (3 V, 20–100 Hz) or C-fiber (20 V, 0–10 Hz) baroreceptor in anesthetized Sprague-Dawley rats ( n  = 10). Transfer function analysis was performed between stimulation and sympathetic nerve activity (central Arc), sympathetic nerve activity and arterial pressure (peripheral Arc), and stimulation and arterial pressure (Stim-AP Arc). Key findings The central Arc Transfer function from nerve stimulation to splanchnic sympathetic nerve activity displayed derivative characteristics for both stimulation protocols. However, the modeled steady-state gain (0.28 ± 0.04 vs. 4.01 ± 0.2%·Hz − 1 , P P − 1 , P − 1 , P Significance These data indicate that the A-fiber central pathway contributes to high frequency arterial pressure regulation and the C-fiber central pathway provides more sustained changes in sympathetic nerve activity and arterial pressure. A sustained reduction in arterial pressure from electrical stimulation of arterial baroreceptor afferents is likely mediated through the C-fiber central pathway.

  • EMBC - Differential dynamic control of cardiac and splanchnic sympathetic nerve activity by the arterial baroreflex
    Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Inte, 2013
    Co-Authors: Michael J. Turner, Toru Kawada, Masaru Sugimachi
    Abstract:

    The arterial baroreflex is the primary negative feedback system involved in stabilizing arterial pressure from external disturbances. Determining the dynamic characteristics of the baroreflex is important for our understanding of the mechanisms involved in rapid restoration of arterial pressure. This study examined the differences in the dynamic baroreflex control of cardiac (CSNA) and splanchnic (SSNA) sympathetic nerve activity. The baroreceptor region of the right aortic depressor nerve was isolated from the systemic circulation to control baroreceptor region pressure (BRP) with a Gaussian white noise signal while simultaneously recording CSNA and SSNA in anesthetized Sprague-Dawley rats. SSNA was recorded from a postganglionic branch of the splanchnic sympathetic nerve and CSNA was recorded from a branch of the left stellate ganglion. Neural Arc Transfer functions from BRP to SSNA (HSSNA) and BRP to CSNA (HCSNA) displayed derivative characteristics. When dynamic gain below 0.03 Hz was normalized to unity, HSSNA had a higher gain at frequencies 0.1 and 1 Hz and increasing slope from 0.1 to 1 Hz relative to HCSNA. The peak decrease in the step response was higher for SSNA than CSNA. These data indicate differential dynamic baroreflex control of SSNA and CSNA. Rapid changes in baroreceptor pressure input would result in a larger response in SSNA compared with CSNA.

  • EMBC - Effects of L-type Ca 2+ channel blocker nifedipine on dynamic arterial blood pressure control
    Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Inte, 2013
    Co-Authors: Toru Kawada, Shuji Shimizu, Hiromi Yamamoto, Michael J. Turner, Masaru Sugimachi
    Abstract:

    Dynamic characteristics of arterial pressure (AP) regulation are important components in our understanding of rapid AP restoration by the arterial baroreflex system. The present study examined the effects of an L-type Ca2+ channel blocker nifedipine on baroreflex-mediated dynamic AP regulation. In anesthetized and vagotomized rats, carotid sinus pressure was externally perturbed using a Gaussian white noise signal, and the neural Arc Transfer function from pressure input to efferent sympathetic nerve activity (SNA) and the peripheral Arc Transfer function from SNA to AP were identified. The peripheral Arc Transfer function approximated a second-order low-pass filter with pure dead time. Intravenous administration of nifedipine significantly decreased the steady-state gain and increased the damping ratio of the peripheral Arc without affecting the dynamic characteristics of the neural Arc. When the step response of AP was calculated based on the peripheral Arc Transfer function alone, nifedipine prolonged 80% rise time by 26%. When the closed-loop AP response was simulated based on both the neural Arc and peripheral Arc Transfer functions and the dynamic gain of the baroreflex total loop was assumed to be 2.0, nifedipine prolonged 80% recovery time by 107%. In conclusion, L-type Ca2+ channel blockade may compromise the baroreflex-mediated AP control not only in the magnitude but also in the speed of AP restoration.

  • closed loop spontaneous baroreflex Transfer function is inappropriate for system identification of neural Arc but partly accurate for peripheral Arc predictability analysis
    The Journal of Physiology, 2011
    Co-Authors: Atsunori Kamiya, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    Non-technical summary  The arterial baroreflex is a closed-loop, negative feedback control system that senses baroreceptor pressure and controls systemic arterial pressure (AP) to attenuate perturbations in AP. The total Arc of the baroreflex consists of two subsystems: the neural (baroreceptor pressure input to sympathetic nerve activity (SNA)) and peripheral (SNA input to AP) Arcs. We show that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting condition, when compared with open-loop Transfer functions that have good predictabilities of time-series output dynamics from input signals. Our results indicate that in the spontaneous baroreflex system under closed-loop conditions, the peripheral Arc (feedforward) function predominates over the neural Arc (feedback) function, probably because of the SNA component that is independent of the baroreceptor pressure input. Abstract  Although the dynamic characteristics of the baroreflex system have been described by baroreflex Transfer functions obtained from open-loop analysis, the predictability of time-series output dynamics from input signals, which should confirm the accuracy of system identification, remains to be elucidated. Moreover, despite theoretical concerns over closed-loop system identification, the accuracy and the predictability of the closed-loop spontaneous baroreflex Transfer function have not been evaluated compared with the open-loop Transfer function. Using urethane and α-chloralose anaesthetized, vagotomized and aortic-denervated rabbits (n= 10), we identified open-loop baroreflex Transfer functions by recording renal sympathetic nerve activity (SNA) while varying the vascularly isolated intracarotid sinus pressure (CSP) according to a binary random (white-noise) sequence (operating pressure ± 20 mmHg), and using a simplified equation to calculate closed-loop-spontaneous baroreflex Transfer function while matching CSP with systemic arterial pressure (AP). Our results showed that the open-loop baroreflex Transfer functions for the neural and peripheral Arcs predicted the time-series SNA and AP outputs from measured CSP and SNA inputs, with r2 of 0.8 ± 0.1 and 0.8 ± 0.1, respectively. In contrast, the closed-loop-spontaneous baroreflex Transfer function for the neural Arc was markedly different from the open-loop Transfer function (enhanced gain increase and a phase lead), and did not predict the time-series SNA dynamics (r2; 0.1 ± 0.1). However, the closed-loop-spontaneous baroreflex Transfer function of the peripheral Arc partially matched the open-loop Transfer function in gain and phase functions, and had limited but reasonable predictability of the time-series AP dynamics (r2, 0.7 ± 0.1). A numerical simulation suggested that a noise predominantly in the neural Arc under resting conditions might be a possible mechanism responsible for our findings. Furthermore, the predictabilities of the neural Arc Transfer functions obtained in open-loop and closed-loop conditions were validated by closed-loop pharmacological (phenylephrine and nitroprusside infusions) pressure interventions. Time-series SNA responses to drug-induced AP changes predicted by the open-loop Transfer function matched closely the measured responses (r2, 0.9 ± 0.1), whereas SNA responses predicted by closed-loop-spontaneous Transfer function deviated greatly and were the inverse of measured responses (r, −0.8 ± 0.2). These results indicate that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting conditions, when compared with open-loop analysis.

Kenji Sunagawa - One of the best experts on this subject based on the ideXlab platform.

  • Effects of neuronal norepinephrine uptake blockade on baroreflex neural and peripheral Arc Transfer characteristics
    American journal of physiology. Regulatory integrative and comparative physiology, 2004
    Co-Authors: Toru Kawada, Atsunori Kamiya, Masaru Sugimachi, Kazunori Uemura, Koji Kashihara, Tadayoshi Miyamoto, Kenji Sunagawa
    Abstract:

    Neuronal uptake is the most important mechanism by which norepinephrine (NE) is removed from the synaptic clefts at sympathetic nerve terminals. We examined the effects of neuronal NE uptake blocka...

  • A derivative-sigmoidal model reproduces operating point-dependent baroreflex neural Arc Transfer characteristics.
    American Journal of Physiology-heart and Circulatory Physiology, 2004
    Co-Authors: Toru Kawada, Atsunori Kamiya, Masaru Sugimachi, Kazunori Uemura, Koji Kashihara, Kenji Sunagawa
    Abstract:

    A cascade model comprised of a derivative filter followed by a nonlinear sigmoidal component reproduces the input size dependence of Transfer gain in the baroreflex neural Arc from baroreceptor pressure input to efferent sympathetic nerve activity (SNA). We examined whether the same model could predict the operating point dependence of the baroreflex neural Arc Transfer characteristics estimated by a binary white noise input. In eight anesthetized rabbits, we isolated bilateral carotid sinuses from the systemic circulation and controlled intracarotid sinus pressure (CSP). We estimated the linear Transfer function from CSP to SNA while varying mean CSP among 70, 100, 130, and 160 mmHg (P(70), P(100), P(130), and P(160), respectively). The Transfer gain at 0.01 Hz was significantly smaller at P(70) (0.61 +/- 0.26) and P(160) (0.60 +/- 0.25) than at P(100) (1.32 +/- 0.42) and P(130) (1.36 +/- 0.45) (in arbitrary units/mmHg; means +/- SD; P < 0.05). In contrast, Transfer gain values above 0.5 Hz were similar among the protocols. As a result, the slope of increasing gain between 0.1 and 0.5 Hz was significantly steeper at P(70) (17.6 +/- 3.6) and P(160) (14.1 +/- 4.3) than at P(100) (8.1 +/- 4.4) and P(130) (7.4 +/- 6.6) (in dB/decade; means +/- SD; P < 0.05). These results were consistent with those predicted by the derivative-sigmoidal model, where the deviation of mean input pressure from the center of the sigmoidal nonlinearity reduced the Transfer gain mainly in the low-frequency range. The derivative-sigmoidal model functionally reproduces the dynamic SNA regulation by the arterial baroreflex over a wide operating range.

  • Intravenous angiotensin II does not affect dynamic baroreflex characteristics of the neural or peripheral Arc.
    The Japanese journal of physiology, 2003
    Co-Authors: Koji Kashihara, Toru Kawada, Masaru Sugimachi, Can Zheng, Yousuke Takahashi, Kaori Chatani, Kenji Sunagawa
    Abstract:

    Although the elevation of angiotensin II (Ang II) associated with cardiovascular diseases has been considered to suppress the arterial baroreflex function, how Ang II affects dynamic arterial pressure (AP) regulation remains unknown. The aim of the present study was to elucidate the acute effects of Ang II on dynamic AP regulation by the arterial baroreflex. In seven anesthetized Japanese white rabbits, we randomly perturbed intra-carotid sinus pressure (CSP) according to a binary white noise sequence while recording renal sympathetic nerve activity (RSNA) and AP. We estimated the neural Arc Transfer function from CSP to RSNA and the peripheral Arc Transfer function from RSNA to AP before and after 30-min intravenous administration of Ang II (100 ng/kg/min). Ang II increased mean AP from 75.7 +/- 3.1 to 95.5 +/- 5.1 mmHg (p < 0.01), while it did not affect mean RSNA (from 5.9 +/- 1.3 to 5.7 +/- 1.2 a.u.). The neural Arc Transfer functions did not differ before or after Ang II administration (dynamic gain: -0.94 +/- 0.04 vs. -0.94 +/- 0.13, corner frequency: 0.06 +/- 0.01 vs.0.06 +/- 0.01 Hz, pure delay: 0.16 +/- 0.01 vs. 0.17 +/- 0.02 s). The peripheral Arc Transfer function did not differ before or after Ang II administration (dynamic gain: 1.18 +/- 0.05 vs. 1.06 +/- 0.11, natural frequency: 0.07 +/- 0.01 vs. 0.08 +/- 0.01 Hz, damping ratio: 1.19 +/- 0.06 vs. 1.24 +/- 0.19, pure delay: 0.83 +/- 0.06 vs. 0.78 +/- 0.05 s). Intravenous Ang II hardly affects the dynamic characteristics of neural and peripheral Arc around the physiological operating pressure.

  • Input-size dependence of the baroreflex neural Arc Transfer characteristics.
    American journal of physiology. Heart and circulatory physiology, 2002
    Co-Authors: Toru Kawada, Masaru Sugimachi, Kazunori Uemura, Yusuke Yanagiya, Can Zheng, Tadayoshi Miyamoto, Kenji Sunagawa
    Abstract:

    Static characteristics of the baroreflex neural Arc from pressure input to sympathetic nerve activity (SNA) show sigmoidal nonlinearity, whereas its dynamic characteristics approximate a derivative...

  • High-cut characteristics of the baroreflex neural Arc preserve baroreflex gain against pulsatile pressure.
    American journal of physiology. Heart and circulatory physiology, 2002
    Co-Authors: Toru Kawada, Masaru Sugimachi, Kazunori Uemura, Masashi Inagaki, Toshiaki Shishido, Yusuke Yanagiya, Can Zheng, Tadayoshi Miyamoto, Kenji Sunagawa
    Abstract:

    A Transfer function from baroreceptor pressure input to sympathetic nerve activity (SNA) shows derivative characteristics in the frequency range below 0.8 Hz in rabbits. These derivative characteristics contribute to a quick and stable arterial pressure (AP) regulation. However, if the derivative characteristics hold up to heart rate frequency, the pulsatile pressure input will yield a markedly augmented SNA signal. Such a signal would saturate the baroreflex signal transduction, thereby disabling the baroreflex regulation of AP. We hypothesized that the Transfer gain at heart rate frequency would be much smaller than that predicted from extrapolating the derivative characteristics. In anesthetized rabbits (n = 6), we estimated the neural Arc Transfer function in the frequency range up to 10 Hz. The Transfer gain was lost at a rate of -20 dB/decade when the input frequency exceeded 0.8 Hz. A numerical simulation indicated that the high-cut characteristics above 0.8 Hz were effective to attenuate the pulsatile signal and preserve the open-loop gain when the baroreflex dynamic range was finite.

Atsunori Kamiya - One of the best experts on this subject based on the ideXlab platform.

  • closed loop spontaneous baroreflex Transfer function is inappropriate for system identification of neural Arc but partly accurate for peripheral Arc predictability analysis
    The Journal of Physiology, 2011
    Co-Authors: Atsunori Kamiya, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    Non-technical summary  The arterial baroreflex is a closed-loop, negative feedback control system that senses baroreceptor pressure and controls systemic arterial pressure (AP) to attenuate perturbations in AP. The total Arc of the baroreflex consists of two subsystems: the neural (baroreceptor pressure input to sympathetic nerve activity (SNA)) and peripheral (SNA input to AP) Arcs. We show that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting condition, when compared with open-loop Transfer functions that have good predictabilities of time-series output dynamics from input signals. Our results indicate that in the spontaneous baroreflex system under closed-loop conditions, the peripheral Arc (feedforward) function predominates over the neural Arc (feedback) function, probably because of the SNA component that is independent of the baroreceptor pressure input. Abstract  Although the dynamic characteristics of the baroreflex system have been described by baroreflex Transfer functions obtained from open-loop analysis, the predictability of time-series output dynamics from input signals, which should confirm the accuracy of system identification, remains to be elucidated. Moreover, despite theoretical concerns over closed-loop system identification, the accuracy and the predictability of the closed-loop spontaneous baroreflex Transfer function have not been evaluated compared with the open-loop Transfer function. Using urethane and α-chloralose anaesthetized, vagotomized and aortic-denervated rabbits (n= 10), we identified open-loop baroreflex Transfer functions by recording renal sympathetic nerve activity (SNA) while varying the vascularly isolated intracarotid sinus pressure (CSP) according to a binary random (white-noise) sequence (operating pressure ± 20 mmHg), and using a simplified equation to calculate closed-loop-spontaneous baroreflex Transfer function while matching CSP with systemic arterial pressure (AP). Our results showed that the open-loop baroreflex Transfer functions for the neural and peripheral Arcs predicted the time-series SNA and AP outputs from measured CSP and SNA inputs, with r2 of 0.8 ± 0.1 and 0.8 ± 0.1, respectively. In contrast, the closed-loop-spontaneous baroreflex Transfer function for the neural Arc was markedly different from the open-loop Transfer function (enhanced gain increase and a phase lead), and did not predict the time-series SNA dynamics (r2; 0.1 ± 0.1). However, the closed-loop-spontaneous baroreflex Transfer function of the peripheral Arc partially matched the open-loop Transfer function in gain and phase functions, and had limited but reasonable predictability of the time-series AP dynamics (r2, 0.7 ± 0.1). A numerical simulation suggested that a noise predominantly in the neural Arc under resting conditions might be a possible mechanism responsible for our findings. Furthermore, the predictabilities of the neural Arc Transfer functions obtained in open-loop and closed-loop conditions were validated by closed-loop pharmacological (phenylephrine and nitroprusside infusions) pressure interventions. Time-series SNA responses to drug-induced AP changes predicted by the open-loop Transfer function matched closely the measured responses (r2, 0.9 ± 0.1), whereas SNA responses predicted by closed-loop-spontaneous Transfer function deviated greatly and were the inverse of measured responses (r, −0.8 ± 0.2). These results indicate that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting conditions, when compared with open-loop analysis.

  • Closed-loop spontaneous baroreflex Transfer function is inappropriate for system identification of neural Arc but partly accurate for peripheral Arc: predictability analysis.
    The Journal of physiology, 2011
    Co-Authors: Atsunori Kamiya, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    Although the dynamic characteristics of the baroreflex system have been described by baroreflex Transfer functions obtained from open-loop analysis, the predictability of time-series output dynamics from input signals, which should confirm the accuracy of system identification, remains to be elucidated. Moreover, despite theoretical concerns over closed-loop system identification, the accuracy and the predictability of the closed-loop spontaneous baroreflex Transfer function have not been evaluated compared with the open-loop Transfer function. Using urethane and α-chloralose anaesthetized, vagotomized and aortic-denervated rabbits (n = 10), we identified open-loop baroreflex Transfer functions by recording renal sympathetic nerve activity (SNA) while varying the vascularly isolated intracarotid sinus pressure (CSP) according to a binary random (white-noise) sequence (operating pressure ± 20 mmHg), and using a simplified equation to calculate closed-loop-spontaneous baroreflex Transfer function while matching CSP with systemic arterial pressure (AP). Our results showed that the open-loop baroreflex Transfer functions for the neural and peripheral Arcs predicted the time-series SNA and AP outputs from measured CSP and SNA inputs, with r2 of 0.8 ± 0.1 and 0.8 ± 0.1, respectively. In contrast, the closed-loop-spontaneous baroreflex Transfer function for the neural Arc was markedly different from the open-loop Transfer function (enhanced gain increase and a phase lead), and did not predict the time-series SNA dynamics (r2; 0.1 ± 0.1). However, the closed-loop-spontaneous baroreflex Transfer function of the peripheral Arc partially matched the open-loop Transfer function in gain and phase functions, and had limited but reasonable predictability of the time-series AP dynamics (r2, 0.7 ± 0.1). A numerical simulation suggested that a noise predominantly in the neural Arc under resting conditions might be a possible mechanism responsible for our findings. Furthermore, the predictabilities of the neural Arc Transfer functions obtained in open-loop and closed-loop conditions were validated by closed-loop pharmacological (phenylephrine and nitroprusside infusions) pressure interventions. Time-series SNA responses to drug-induced AP changes predicted by the open-loop Transfer function matched closely the measured responses (r2, 0.9 ± 0.1), whereas SNA responses predicted by closed-loop-spontaneous Transfer function deviated greatly and were the inverse of measured responses (r, −0.8 ± 0.2). These results indicate that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting conditions, when compared with open-loop analysis.

  • Closed‐loop spontaneous baroreflex Transfer function is inappropriate for system identification of neural Arc but partly accurate for peripheral Arc: predictability analysis
    The Journal of Physiology, 2011
    Co-Authors: Atsunori Kamiya, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    Non-technical summary  The arterial baroreflex is a closed-loop, negative feedback control system that senses baroreceptor pressure and controls systemic arterial pressure (AP) to attenuate perturbations in AP. The total Arc of the baroreflex consists of two subsystems: the neural (baroreceptor pressure input to sympathetic nerve activity (SNA)) and peripheral (SNA input to AP) Arcs. We show that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting condition, when compared with open-loop Transfer functions that have good predictabilities of time-series output dynamics from input signals. Our results indicate that in the spontaneous baroreflex system under closed-loop conditions, the peripheral Arc (feedforward) function predominates over the neural Arc (feedback) function, probably because of the SNA component that is independent of the baroreceptor pressure input. Abstract  Although the dynamic characteristics of the baroreflex system have been described by baroreflex Transfer functions obtained from open-loop analysis, the predictability of time-series output dynamics from input signals, which should confirm the accuracy of system identification, remains to be elucidated. Moreover, despite theoretical concerns over closed-loop system identification, the accuracy and the predictability of the closed-loop spontaneous baroreflex Transfer function have not been evaluated compared with the open-loop Transfer function. Using urethane and α-chloralose anaesthetized, vagotomized and aortic-denervated rabbits (n= 10), we identified open-loop baroreflex Transfer functions by recording renal sympathetic nerve activity (SNA) while varying the vascularly isolated intracarotid sinus pressure (CSP) according to a binary random (white-noise) sequence (operating pressure ± 20 mmHg), and using a simplified equation to calculate closed-loop-spontaneous baroreflex Transfer function while matching CSP with systemic arterial pressure (AP). Our results showed that the open-loop baroreflex Transfer functions for the neural and peripheral Arcs predicted the time-series SNA and AP outputs from measured CSP and SNA inputs, with r2 of 0.8 ± 0.1 and 0.8 ± 0.1, respectively. In contrast, the closed-loop-spontaneous baroreflex Transfer function for the neural Arc was markedly different from the open-loop Transfer function (enhanced gain increase and a phase lead), and did not predict the time-series SNA dynamics (r2; 0.1 ± 0.1). However, the closed-loop-spontaneous baroreflex Transfer function of the peripheral Arc partially matched the open-loop Transfer function in gain and phase functions, and had limited but reasonable predictability of the time-series AP dynamics (r2, 0.7 ± 0.1). A numerical simulation suggested that a noise predominantly in the neural Arc under resting conditions might be a possible mechanism responsible for our findings. Furthermore, the predictabilities of the neural Arc Transfer functions obtained in open-loop and closed-loop conditions were validated by closed-loop pharmacological (phenylephrine and nitroprusside infusions) pressure interventions. Time-series SNA responses to drug-induced AP changes predicted by the open-loop Transfer function matched closely the measured responses (r2, 0.9 ± 0.1), whereas SNA responses predicted by closed-loop-spontaneous Transfer function deviated greatly and were the inverse of measured responses (r, −0.8 ± 0.2). These results indicate that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting conditions, when compared with open-loop analysis.

  • Open-loop dynamic and static characteristics of the carotid sinus baroreflex in rats with chronic heart failure after myocardial infArction
    The Journal of Physiological Sciences, 2010
    Co-Authors: Toru Kawada, Atsunori Kamiya, Shuji Shimizu, Kazunori Uemura, Hiromi Yamamoto, Masaru Sugimachi
    Abstract:

    We estimated open-loop dynamic characteristics of the carotid sinus baroreflex in normal control rats and chronic heart failure (CHF) rats after myocardial infArction. First, the neural Arc Transfer function from carotid sinus pressure to splanchnic sympathetic nerve activity (SNA) and its corresponding step response were examined. Although the steady-state response was attenuated in CHF, the negative peak response and the time to peak did not change significantly, suggesting preserved neural Arc dynamic characteristics. Next, the peripheral Arc Transfer function from SNA to arterial pressure (AP) and its corresponding step response were examined. The steady-state response and the initial slope were reduced in CHF, suggesting impaired end-organ responses. In a simulation study based on the dynamic and static characteristics, the percent recovery of AP was reduced progressively as the size of disturbance increased in CHF, suggesting that a reserve for AP buffering is lost in CHF despite relatively maintained baseline AP.

  • A derivative-sigmoidal model reproduces operating point-dependent baroreflex neural Arc Transfer characteristics.
    American Journal of Physiology-heart and Circulatory Physiology, 2004
    Co-Authors: Toru Kawada, Atsunori Kamiya, Masaru Sugimachi, Kazunori Uemura, Koji Kashihara, Kenji Sunagawa
    Abstract:

    A cascade model comprised of a derivative filter followed by a nonlinear sigmoidal component reproduces the input size dependence of Transfer gain in the baroreflex neural Arc from baroreceptor pressure input to efferent sympathetic nerve activity (SNA). We examined whether the same model could predict the operating point dependence of the baroreflex neural Arc Transfer characteristics estimated by a binary white noise input. In eight anesthetized rabbits, we isolated bilateral carotid sinuses from the systemic circulation and controlled intracarotid sinus pressure (CSP). We estimated the linear Transfer function from CSP to SNA while varying mean CSP among 70, 100, 130, and 160 mmHg (P(70), P(100), P(130), and P(160), respectively). The Transfer gain at 0.01 Hz was significantly smaller at P(70) (0.61 +/- 0.26) and P(160) (0.60 +/- 0.25) than at P(100) (1.32 +/- 0.42) and P(130) (1.36 +/- 0.45) (in arbitrary units/mmHg; means +/- SD; P < 0.05). In contrast, Transfer gain values above 0.5 Hz were similar among the protocols. As a result, the slope of increasing gain between 0.1 and 0.5 Hz was significantly steeper at P(70) (17.6 +/- 3.6) and P(160) (14.1 +/- 4.3) than at P(100) (8.1 +/- 4.4) and P(130) (7.4 +/- 6.6) (in dB/decade; means +/- SD; P < 0.05). These results were consistent with those predicted by the derivative-sigmoidal model, where the deviation of mean input pressure from the center of the sigmoidal nonlinearity reduced the Transfer gain mainly in the low-frequency range. The derivative-sigmoidal model functionally reproduces the dynamic SNA regulation by the arterial baroreflex over a wide operating range.

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  • Sustained reduction in blood pressure from electrical activation of the baroreflex is mediated via the central pathway of unmyelinated baroreceptors
    Life Sciences, 2014
    Co-Authors: Michael J. Turner, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    Abstract Aims This study aims to identify the contribution of myelinated (A-fiber) and unmyelinated (C-fiber) baroreceptor central pathways to the baroreflex control of sympathetic nerve activity and arterial pressure. Main methods Two binary white noise stimulation protocols were used to electrically stimulate the aortic depressor nerve and activate reflex responses from either A-fiber (3 V, 20–100 Hz) or C-fiber (20 V, 0–10 Hz) baroreceptor in anesthetized Sprague-Dawley rats ( n  = 10). Transfer function analysis was performed between stimulation and sympathetic nerve activity (central Arc), sympathetic nerve activity and arterial pressure (peripheral Arc), and stimulation and arterial pressure (Stim-AP Arc). Key findings The central Arc Transfer function from nerve stimulation to splanchnic sympathetic nerve activity displayed derivative characteristics for both stimulation protocols. However, the modeled steady-state gain (0.28 ± 0.04 vs. 4.01 ± 0.2%·Hz − 1 , P P − 1 , P − 1 , P Significance These data indicate that the A-fiber central pathway contributes to high frequency arterial pressure regulation and the C-fiber central pathway provides more sustained changes in sympathetic nerve activity and arterial pressure. A sustained reduction in arterial pressure from electrical stimulation of arterial baroreceptor afferents is likely mediated through the C-fiber central pathway.

  • Sustained reduction in blood pressure from electrical activation of the baroreflex is mediated via the central pathway of unmyelinated baroreceptors.
    Life sciences, 2014
    Co-Authors: Michael J. Turner, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    This study aims to identify the contribution of myelinated (A-fiber) and unmyelinated (C-fiber) baroreceptor central pathways to the baroreflex control of sympathetic nerve activity and arterial pressure. Two binary white noise stimulation protocols were used to electrically stimulate the aortic depressor nerve and activate reflex responses from either A-fiber (3 V, 20-100 Hz) or C-fiber (20 V, 0-10 Hz) baroreceptor in anesthetized Sprague-Dawley rats (n=10). Transfer function analysis was performed between stimulation and sympathetic nerve activity (central Arc), sympathetic nerve activity and arterial pressure (peripheral Arc), and stimulation and arterial pressure (Stim-AP Arc). The central Arc Transfer function from nerve stimulation to splanchnic sympathetic nerve activity displayed derivative characteristics for both stimulation protocols. However, the modeled steady-state gain (0.28 ± 0.04 vs. 4.01 ± 0.2%·Hz(-1), P<0.001) and coherence at 0.01 Hz (0.44 ± 0.05 vs. 0.81 ± 0.03, P<0.05) were significantly lower for A-fiber stimulation compared with C-fiber stimulation. The slope of the dynamic gain was higher for A-fiber stimulation (14.82 ± 1.02 vs. 7.21 ± 0.79 dB·decade(-1), P<0.001). The steady-state gain of the Stim-AP Arc was also significantly lower for A-fiber stimulation compared with C-fiber stimulation (0.23 ± 0.05 vs. 3.05 ± 0.31 mmHg·Hz(-1), P<0.001). These data indicate that the A-fiber central pathway contributes to high frequency arterial pressure regulation and the C-fiber central pathway provides more sustained changes in sympathetic nerve activity and arterial pressure. A sustained reduction in arterial pressure from electrical stimulation of arterial baroreceptor afferents is likely mediated through the C-fiber central pathway. Copyright © 2014 Elsevier Inc. All rights reserved.

  • EMBC - Effects of L-type Ca 2+ channel blocker nifedipine on dynamic arterial blood pressure control
    Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Inte, 2013
    Co-Authors: Toru Kawada, Shuji Shimizu, Hiromi Yamamoto, Michael J. Turner, Masaru Sugimachi
    Abstract:

    Dynamic characteristics of arterial pressure (AP) regulation are important components in our understanding of rapid AP restoration by the arterial baroreflex system. The present study examined the effects of an L-type Ca2+ channel blocker nifedipine on baroreflex-mediated dynamic AP regulation. In anesthetized and vagotomized rats, carotid sinus pressure was externally perturbed using a Gaussian white noise signal, and the neural Arc Transfer function from pressure input to efferent sympathetic nerve activity (SNA) and the peripheral Arc Transfer function from SNA to AP were identified. The peripheral Arc Transfer function approximated a second-order low-pass filter with pure dead time. Intravenous administration of nifedipine significantly decreased the steady-state gain and increased the damping ratio of the peripheral Arc without affecting the dynamic characteristics of the neural Arc. When the step response of AP was calculated based on the peripheral Arc Transfer function alone, nifedipine prolonged 80% rise time by 26%. When the closed-loop AP response was simulated based on both the neural Arc and peripheral Arc Transfer functions and the dynamic gain of the baroreflex total loop was assumed to be 2.0, nifedipine prolonged 80% recovery time by 107%. In conclusion, L-type Ca2+ channel blockade may compromise the baroreflex-mediated AP control not only in the magnitude but also in the speed of AP restoration.

  • closed loop spontaneous baroreflex Transfer function is inappropriate for system identification of neural Arc but partly accurate for peripheral Arc predictability analysis
    The Journal of Physiology, 2011
    Co-Authors: Atsunori Kamiya, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    Non-technical summary  The arterial baroreflex is a closed-loop, negative feedback control system that senses baroreceptor pressure and controls systemic arterial pressure (AP) to attenuate perturbations in AP. The total Arc of the baroreflex consists of two subsystems: the neural (baroreceptor pressure input to sympathetic nerve activity (SNA)) and peripheral (SNA input to AP) Arcs. We show that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting condition, when compared with open-loop Transfer functions that have good predictabilities of time-series output dynamics from input signals. Our results indicate that in the spontaneous baroreflex system under closed-loop conditions, the peripheral Arc (feedforward) function predominates over the neural Arc (feedback) function, probably because of the SNA component that is independent of the baroreceptor pressure input. Abstract  Although the dynamic characteristics of the baroreflex system have been described by baroreflex Transfer functions obtained from open-loop analysis, the predictability of time-series output dynamics from input signals, which should confirm the accuracy of system identification, remains to be elucidated. Moreover, despite theoretical concerns over closed-loop system identification, the accuracy and the predictability of the closed-loop spontaneous baroreflex Transfer function have not been evaluated compared with the open-loop Transfer function. Using urethane and α-chloralose anaesthetized, vagotomized and aortic-denervated rabbits (n= 10), we identified open-loop baroreflex Transfer functions by recording renal sympathetic nerve activity (SNA) while varying the vascularly isolated intracarotid sinus pressure (CSP) according to a binary random (white-noise) sequence (operating pressure ± 20 mmHg), and using a simplified equation to calculate closed-loop-spontaneous baroreflex Transfer function while matching CSP with systemic arterial pressure (AP). Our results showed that the open-loop baroreflex Transfer functions for the neural and peripheral Arcs predicted the time-series SNA and AP outputs from measured CSP and SNA inputs, with r2 of 0.8 ± 0.1 and 0.8 ± 0.1, respectively. In contrast, the closed-loop-spontaneous baroreflex Transfer function for the neural Arc was markedly different from the open-loop Transfer function (enhanced gain increase and a phase lead), and did not predict the time-series SNA dynamics (r2; 0.1 ± 0.1). However, the closed-loop-spontaneous baroreflex Transfer function of the peripheral Arc partially matched the open-loop Transfer function in gain and phase functions, and had limited but reasonable predictability of the time-series AP dynamics (r2, 0.7 ± 0.1). A numerical simulation suggested that a noise predominantly in the neural Arc under resting conditions might be a possible mechanism responsible for our findings. Furthermore, the predictabilities of the neural Arc Transfer functions obtained in open-loop and closed-loop conditions were validated by closed-loop pharmacological (phenylephrine and nitroprusside infusions) pressure interventions. Time-series SNA responses to drug-induced AP changes predicted by the open-loop Transfer function matched closely the measured responses (r2, 0.9 ± 0.1), whereas SNA responses predicted by closed-loop-spontaneous Transfer function deviated greatly and were the inverse of measured responses (r, −0.8 ± 0.2). These results indicate that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting conditions, when compared with open-loop analysis.

  • Closed-loop spontaneous baroreflex Transfer function is inappropriate for system identification of neural Arc but partly accurate for peripheral Arc: predictability analysis.
    The Journal of physiology, 2011
    Co-Authors: Atsunori Kamiya, Toru Kawada, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    Although the dynamic characteristics of the baroreflex system have been described by baroreflex Transfer functions obtained from open-loop analysis, the predictability of time-series output dynamics from input signals, which should confirm the accuracy of system identification, remains to be elucidated. Moreover, despite theoretical concerns over closed-loop system identification, the accuracy and the predictability of the closed-loop spontaneous baroreflex Transfer function have not been evaluated compared with the open-loop Transfer function. Using urethane and α-chloralose anaesthetized, vagotomized and aortic-denervated rabbits (n = 10), we identified open-loop baroreflex Transfer functions by recording renal sympathetic nerve activity (SNA) while varying the vascularly isolated intracarotid sinus pressure (CSP) according to a binary random (white-noise) sequence (operating pressure ± 20 mmHg), and using a simplified equation to calculate closed-loop-spontaneous baroreflex Transfer function while matching CSP with systemic arterial pressure (AP). Our results showed that the open-loop baroreflex Transfer functions for the neural and peripheral Arcs predicted the time-series SNA and AP outputs from measured CSP and SNA inputs, with r2 of 0.8 ± 0.1 and 0.8 ± 0.1, respectively. In contrast, the closed-loop-spontaneous baroreflex Transfer function for the neural Arc was markedly different from the open-loop Transfer function (enhanced gain increase and a phase lead), and did not predict the time-series SNA dynamics (r2; 0.1 ± 0.1). However, the closed-loop-spontaneous baroreflex Transfer function of the peripheral Arc partially matched the open-loop Transfer function in gain and phase functions, and had limited but reasonable predictability of the time-series AP dynamics (r2, 0.7 ± 0.1). A numerical simulation suggested that a noise predominantly in the neural Arc under resting conditions might be a possible mechanism responsible for our findings. Furthermore, the predictabilities of the neural Arc Transfer functions obtained in open-loop and closed-loop conditions were validated by closed-loop pharmacological (phenylephrine and nitroprusside infusions) pressure interventions. Time-series SNA responses to drug-induced AP changes predicted by the open-loop Transfer function matched closely the measured responses (r2, 0.9 ± 0.1), whereas SNA responses predicted by closed-loop-spontaneous Transfer function deviated greatly and were the inverse of measured responses (r, −0.8 ± 0.2). These results indicate that although the spontaneous baroreflex Transfer function obtained by closed-loop analysis has been believed to represent the neural Arc function, it is inappropriate for system identification of the neural Arc but is essentially appropriate for the peripheral Arc under resting conditions, when compared with open-loop analysis.