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

  • Acute Effects of Vagotomy on Baroreflex Equilibrium Diagram in Rats with Chronic Heart Failure.
    Clinical Medicine Insights. Cardiology, 2016
    Co-Authors: Toru Kawada, Can Zheng, Masaru Sugimachi
    Abstract:

    The arterial baroreflex system can be divided into the neural arc, from pressure input to efferent sympathetic nerve activity (SNA), and the peripheral arc, from SNA to arterial pressure (AP). Plotting the neural and peripheral arcs on a pressure–SNA plane yields a baroreflex Equilibrium Diagram. We examined the effects of vagotomy on the open-loop static characteristics of the carotid sinus baroreflex in normal control rats (NC, n = 10) and rats with heart failure after myocardial infarction (MI, n = 10). In the NC group, vagotomy shifted the neural arc toward higher SNA and decreased the slope of the peripheral arc. Consequently, the operating-point SNA increased without a significant change in the operating-point AP on the baroreflex Equilibrium Diagram. These vagotomy-induced effects were not observed in the MI group, suggesting a loss of vagal modulation of the carotid sinus baroreflex function in heart failure.

  • predominant role of neural arc in sympathetic baroreflex resetting of spontaneously hypertensive rats analysis of an open loop baroreflex Equilibrium Diagram
    Circulation, 2015
    Co-Authors: Yusuke Sata, Toru Kawada, Shuji Shimizu, Atsunori Kamiya, Tsuyoshi Akiyama, Masaru Sugimachi
    Abstract:

    BACKGROUND There is ongoing controversy over whether neural or peripheral factors are the predominant cause of hypertension. The closed-loop negative feedback operation of the arterial baroreflex hampers understanding of how arterial pressure (AP) is determined through the interaction between neural and peripheral factors. METHODS AND RESULTS: A novel analysis of an isolated open-loop baroreceptor preparation to examine sympathetic nervous activity (SNA) and AP responses to changes in carotid sinus pressure (CSP) in adult spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) was conducted. In the neural arc (CSP-SNA relationship), the midpoint pressure (128.9±3.8 vs. 157.9±8.1 mmHg, P<0.001) and the response range of SNA to CSP (90.5±3.7 vs. 115.4±7.6%/mmHg, P=0.011) were higher in SHR. In the peripheral arc (SNA-AP relationship), slope and intercept did not differ. A baroreflex Equilibrium Diagram was obtained by depicting neural and peripheral arcs in a pressure-SNA plane with rescaled SNA (% in WKY). The operating-point AP (111.3±4.4 vs. 145.9±5.2 mmHg, P<0.001) and SNA (90.8±3.2 vs. 125.1±6.9% in WKY, P<0.001) were shifted towards a higher level in SHR. CONCLUSIONS The shift of the neural arc towards a higher SNA range indicated a predominant contribution to baroreflex resetting in SHR. Notwithstanding the resetting, the carotid sinus baroreflex in SHR preserved an ability to reduce AP if activated with a high enough pressure.

  • Calibration of Baroreflex Equilibrium Diagram Based on Exogenous Pressor Agents in Chronic Heart Failure Rats
    Clinical Medicine Insights: Cardiology, 2015
    Co-Authors: Toru Kawada, Can Zheng, Yusuke Sata, Michael J. Turner, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    A baroreflex Equilibrium Diagram describes the relation between input pressure and sympathetic nerve activity (SNA) and that between SNA and arterial pressure (AP). To calibrate the SNA axis (abscissa) of the baroreflex Equilibrium Diagram, the AP response to intravenous bolus injections of phenylephrine (0.2-50 μg/kg) or norepinephrine (NE, 0.02-5 μg/kg) was examined in normal control rats (NC, n = 9) and rats with chronic heart failure (CHF, n = 6). The maximum slope of the dose–effect curve was significantly smaller in the CHF group than in the NC group (57.3 ± 5.2 vs 80.9 ± 6.3 mmHg/decade for phenylephrine, 60.2 ± 7.8 vs 80.4 ± 5.9 mmHg/decade for NE; P < 0.01). The CHF/NC ratio of the maximum slope was used to calibrate SNA. While the calibrated baroreflex Equilibrium Diagram showed increased maximum SNA and operating-point SNA in CHF rats compared with NC rats, the magnitude of increase was smaller than that expected from the excess plasma NE concentration in CHF rats. Plasma NE concentration in the CHF group could be disproportionally high relative to SNA.

  • Integrated characterization of the human chemoreflex system controlling ventilation, using an Equilibrium Diagram.
    European journal of applied physiology, 2004
    Co-Authors: Tadayoshi Miyamoto, Toru Kawada, Masashi Inagaki, Yusuke Yanagiya, Masaru Sugimachi, Hiroshi Takaki, Kenji Sunagawa
    Abstract:

    The chemoreflex system controlling ventilation consists of two subsystems, i.e., the central controller (controlling element), and peripheral plant (controlled element). We developed an integral framework to quantitatively characterize individual ventilatory regulation by experimental determination of an Equilibrium Diagram using a modified metabolic hyperbola and the CO2 response curve. In 13 healthy males, the steady-state arterial CO2 pressure (PaCO2) and minute ventilation (V e ) were measured. To characterize the central controller, we changed fraction of inspired CO2 (0, 3.5, 5 and 6% CO2 in 80% oxygen with nitrogen balance) and measured the PaCO2–V e relation. To characterize the peripheral plant, we altered V e by hyper- or hypoventilation using a visual feedback method, which made it possible to control both tidal volume and breathing frequency, and measured the V e –PaCO2 relation. The intersection between the two relationship lines gives the operating point. The relationship between PaCO2 and V e for the central controller was reasonably linear in each subject (r2=0.808~0.995). The peripheral plant approximated a modified metabolic hyperbolic curve (r2=0.962~0.996). The operating points of the system estimated from the two relationship lines were in good agreement with those measured under the closed-loop condition. The gain of the central controller was 1.9 (1.0) l min−1 mmHg−1 and that of the peripheral plant was 3.0 (0.5) mmHg l−1 min−1. The total loop gain, the product of the two gains, was 5.3 (2.5). We conclude that human ventilatory regulation by the respiratory chemoreflex system can be quantitatively characterized using an Equilibrium Diagram. This framework should be useful for understanding the mechanisms responsible for abnormal ventilation under various pathophysiological conditions.

  • bezold jarisch reflex blunts arterial baroreflex via the shift of neural arc toward lower sympathetic nerve activity
    Japanese Journal of Physiology, 2004
    Co-Authors: Koji Kashihara, Toru Kawada, Masaru Sugimachi, Kenji Sunagawa
    Abstract:

    Although the Bezold-Jarisch (BJ) reflex is potentially evoked during acute myocardial ischemia or infarction, its effects on the static characteristics of the arterial baroreflex remain to be analyzed in terms of an Equilibrium Diagram between the neural and peripheral arcs. The neural arc represents the static input-output relationship between baroreceptor pressure input and efferent sympathetic nerve activity (SNA), whereas the peripheral arc represents that between SNA and arterial pressure (AP). In 8 anesthetized rabbits, we increased carotid sinus pressure stepwise from 40 to 160 mmHg in increments of 20 mmHg at one-minute intervals while measuring renal SNA and AP under control conditions and during the activation of the BJ reflex by intravenous administration of phenylbiguanide (PBG, 100 microg.kg(-1).min(-1)). The neural arc approximated a sigmoid curve whereas the peripheral arc approximated a straight line. PBG decreased AP at the operating point from -91.3 +/- 2.4 to -71.7 +/- 3.1 mmHg (P < 0.01), and attenuated the total loop gain at the operating point from -1.31 +/- 0.44 to -0.51 +/- 0.14 (P < 0.05). The Equilibrium Diagram indicated that PBG caused a parallel shift of the neural arc toward lower SNA such that the maximum SNA was reduced to approximately 60% of control. PBG decreased neural and peripheral arc gains at the operating point to approximately 43% and 77%, respectively. In conclusion, the BJ reflex blunts arterial baroreflex via the shift of the neural arc toward lower SNA.

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

  • Acute Effects of Vagotomy on Baroreflex Equilibrium Diagram in Rats with Chronic Heart Failure.
    Clinical Medicine Insights. Cardiology, 2016
    Co-Authors: Toru Kawada, Can Zheng, Masaru Sugimachi
    Abstract:

    The arterial baroreflex system can be divided into the neural arc, from pressure input to efferent sympathetic nerve activity (SNA), and the peripheral arc, from SNA to arterial pressure (AP). Plotting the neural and peripheral arcs on a pressure–SNA plane yields a baroreflex Equilibrium Diagram. We examined the effects of vagotomy on the open-loop static characteristics of the carotid sinus baroreflex in normal control rats (NC, n = 10) and rats with heart failure after myocardial infarction (MI, n = 10). In the NC group, vagotomy shifted the neural arc toward higher SNA and decreased the slope of the peripheral arc. Consequently, the operating-point SNA increased without a significant change in the operating-point AP on the baroreflex Equilibrium Diagram. These vagotomy-induced effects were not observed in the MI group, suggesting a loss of vagal modulation of the carotid sinus baroreflex function in heart failure.

  • predominant role of neural arc in sympathetic baroreflex resetting of spontaneously hypertensive rats analysis of an open loop baroreflex Equilibrium Diagram
    Circulation, 2015
    Co-Authors: Yusuke Sata, Toru Kawada, Shuji Shimizu, Atsunori Kamiya, Tsuyoshi Akiyama, Masaru Sugimachi
    Abstract:

    BACKGROUND There is ongoing controversy over whether neural or peripheral factors are the predominant cause of hypertension. The closed-loop negative feedback operation of the arterial baroreflex hampers understanding of how arterial pressure (AP) is determined through the interaction between neural and peripheral factors. METHODS AND RESULTS: A novel analysis of an isolated open-loop baroreceptor preparation to examine sympathetic nervous activity (SNA) and AP responses to changes in carotid sinus pressure (CSP) in adult spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) was conducted. In the neural arc (CSP-SNA relationship), the midpoint pressure (128.9±3.8 vs. 157.9±8.1 mmHg, P<0.001) and the response range of SNA to CSP (90.5±3.7 vs. 115.4±7.6%/mmHg, P=0.011) were higher in SHR. In the peripheral arc (SNA-AP relationship), slope and intercept did not differ. A baroreflex Equilibrium Diagram was obtained by depicting neural and peripheral arcs in a pressure-SNA plane with rescaled SNA (% in WKY). The operating-point AP (111.3±4.4 vs. 145.9±5.2 mmHg, P<0.001) and SNA (90.8±3.2 vs. 125.1±6.9% in WKY, P<0.001) were shifted towards a higher level in SHR. CONCLUSIONS The shift of the neural arc towards a higher SNA range indicated a predominant contribution to baroreflex resetting in SHR. Notwithstanding the resetting, the carotid sinus baroreflex in SHR preserved an ability to reduce AP if activated with a high enough pressure.

  • Calibration of Baroreflex Equilibrium Diagram Based on Exogenous Pressor Agents in Chronic Heart Failure Rats
    Clinical Medicine Insights: Cardiology, 2015
    Co-Authors: Toru Kawada, Can Zheng, Yusuke Sata, Michael J. Turner, Shuji Shimizu, Masaru Sugimachi
    Abstract:

    A baroreflex Equilibrium Diagram describes the relation between input pressure and sympathetic nerve activity (SNA) and that between SNA and arterial pressure (AP). To calibrate the SNA axis (abscissa) of the baroreflex Equilibrium Diagram, the AP response to intravenous bolus injections of phenylephrine (0.2-50 μg/kg) or norepinephrine (NE, 0.02-5 μg/kg) was examined in normal control rats (NC, n = 9) and rats with chronic heart failure (CHF, n = 6). The maximum slope of the dose–effect curve was significantly smaller in the CHF group than in the NC group (57.3 ± 5.2 vs 80.9 ± 6.3 mmHg/decade for phenylephrine, 60.2 ± 7.8 vs 80.4 ± 5.9 mmHg/decade for NE; P < 0.01). The CHF/NC ratio of the maximum slope was used to calibrate SNA. While the calibrated baroreflex Equilibrium Diagram showed increased maximum SNA and operating-point SNA in CHF rats compared with NC rats, the magnitude of increase was smaller than that expected from the excess plasma NE concentration in CHF rats. Plasma NE concentration in the CHF group could be disproportionally high relative to SNA.

  • Integrated characterization of the human chemoreflex system controlling ventilation, using an Equilibrium Diagram.
    European journal of applied physiology, 2004
    Co-Authors: Tadayoshi Miyamoto, Toru Kawada, Masashi Inagaki, Yusuke Yanagiya, Masaru Sugimachi, Hiroshi Takaki, Kenji Sunagawa
    Abstract:

    The chemoreflex system controlling ventilation consists of two subsystems, i.e., the central controller (controlling element), and peripheral plant (controlled element). We developed an integral framework to quantitatively characterize individual ventilatory regulation by experimental determination of an Equilibrium Diagram using a modified metabolic hyperbola and the CO2 response curve. In 13 healthy males, the steady-state arterial CO2 pressure (PaCO2) and minute ventilation (V e ) were measured. To characterize the central controller, we changed fraction of inspired CO2 (0, 3.5, 5 and 6% CO2 in 80% oxygen with nitrogen balance) and measured the PaCO2–V e relation. To characterize the peripheral plant, we altered V e by hyper- or hypoventilation using a visual feedback method, which made it possible to control both tidal volume and breathing frequency, and measured the V e –PaCO2 relation. The intersection between the two relationship lines gives the operating point. The relationship between PaCO2 and V e for the central controller was reasonably linear in each subject (r2=0.808~0.995). The peripheral plant approximated a modified metabolic hyperbolic curve (r2=0.962~0.996). The operating points of the system estimated from the two relationship lines were in good agreement with those measured under the closed-loop condition. The gain of the central controller was 1.9 (1.0) l min−1 mmHg−1 and that of the peripheral plant was 3.0 (0.5) mmHg l−1 min−1. The total loop gain, the product of the two gains, was 5.3 (2.5). We conclude that human ventilatory regulation by the respiratory chemoreflex system can be quantitatively characterized using an Equilibrium Diagram. This framework should be useful for understanding the mechanisms responsible for abnormal ventilation under various pathophysiological conditions.

  • bezold jarisch reflex blunts arterial baroreflex via the shift of neural arc toward lower sympathetic nerve activity
    Japanese Journal of Physiology, 2004
    Co-Authors: Koji Kashihara, Toru Kawada, Masaru Sugimachi, Kenji Sunagawa
    Abstract:

    Although the Bezold-Jarisch (BJ) reflex is potentially evoked during acute myocardial ischemia or infarction, its effects on the static characteristics of the arterial baroreflex remain to be analyzed in terms of an Equilibrium Diagram between the neural and peripheral arcs. The neural arc represents the static input-output relationship between baroreceptor pressure input and efferent sympathetic nerve activity (SNA), whereas the peripheral arc represents that between SNA and arterial pressure (AP). In 8 anesthetized rabbits, we increased carotid sinus pressure stepwise from 40 to 160 mmHg in increments of 20 mmHg at one-minute intervals while measuring renal SNA and AP under control conditions and during the activation of the BJ reflex by intravenous administration of phenylbiguanide (PBG, 100 microg.kg(-1).min(-1)). The neural arc approximated a sigmoid curve whereas the peripheral arc approximated a straight line. PBG decreased AP at the operating point from -91.3 +/- 2.4 to -71.7 +/- 3.1 mmHg (P < 0.01), and attenuated the total loop gain at the operating point from -1.31 +/- 0.44 to -0.51 +/- 0.14 (P < 0.05). The Equilibrium Diagram indicated that PBG caused a parallel shift of the neural arc toward lower SNA such that the maximum SNA was reduced to approximately 60% of control. PBG decreased neural and peripheral arc gains at the operating point to approximately 43% and 77%, respectively. In conclusion, the BJ reflex blunts arterial baroreflex via the shift of the neural arc toward lower SNA.

Toshiaki Yoshioka - One of the best experts on this subject based on the ideXlab platform.

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

  • Integrated characterization of the human chemoreflex system controlling ventilation, using an Equilibrium Diagram.
    European journal of applied physiology, 2004
    Co-Authors: Tadayoshi Miyamoto, Toru Kawada, Masashi Inagaki, Yusuke Yanagiya, Masaru Sugimachi, Hiroshi Takaki, Kenji Sunagawa
    Abstract:

    The chemoreflex system controlling ventilation consists of two subsystems, i.e., the central controller (controlling element), and peripheral plant (controlled element). We developed an integral framework to quantitatively characterize individual ventilatory regulation by experimental determination of an Equilibrium Diagram using a modified metabolic hyperbola and the CO2 response curve. In 13 healthy males, the steady-state arterial CO2 pressure (PaCO2) and minute ventilation (V e ) were measured. To characterize the central controller, we changed fraction of inspired CO2 (0, 3.5, 5 and 6% CO2 in 80% oxygen with nitrogen balance) and measured the PaCO2–V e relation. To characterize the peripheral plant, we altered V e by hyper- or hypoventilation using a visual feedback method, which made it possible to control both tidal volume and breathing frequency, and measured the V e –PaCO2 relation. The intersection between the two relationship lines gives the operating point. The relationship between PaCO2 and V e for the central controller was reasonably linear in each subject (r2=0.808~0.995). The peripheral plant approximated a modified metabolic hyperbolic curve (r2=0.962~0.996). The operating points of the system estimated from the two relationship lines were in good agreement with those measured under the closed-loop condition. The gain of the central controller was 1.9 (1.0) l min−1 mmHg−1 and that of the peripheral plant was 3.0 (0.5) mmHg l−1 min−1. The total loop gain, the product of the two gains, was 5.3 (2.5). We conclude that human ventilatory regulation by the respiratory chemoreflex system can be quantitatively characterized using an Equilibrium Diagram. This framework should be useful for understanding the mechanisms responsible for abnormal ventilation under various pathophysiological conditions.

  • bezold jarisch reflex blunts arterial baroreflex via the shift of neural arc toward lower sympathetic nerve activity
    Japanese Journal of Physiology, 2004
    Co-Authors: Koji Kashihara, Toru Kawada, Masaru Sugimachi, Kenji Sunagawa
    Abstract:

    Although the Bezold-Jarisch (BJ) reflex is potentially evoked during acute myocardial ischemia or infarction, its effects on the static characteristics of the arterial baroreflex remain to be analyzed in terms of an Equilibrium Diagram between the neural and peripheral arcs. The neural arc represents the static input-output relationship between baroreceptor pressure input and efferent sympathetic nerve activity (SNA), whereas the peripheral arc represents that between SNA and arterial pressure (AP). In 8 anesthetized rabbits, we increased carotid sinus pressure stepwise from 40 to 160 mmHg in increments of 20 mmHg at one-minute intervals while measuring renal SNA and AP under control conditions and during the activation of the BJ reflex by intravenous administration of phenylbiguanide (PBG, 100 microg.kg(-1).min(-1)). The neural arc approximated a sigmoid curve whereas the peripheral arc approximated a straight line. PBG decreased AP at the operating point from -91.3 +/- 2.4 to -71.7 +/- 3.1 mmHg (P < 0.01), and attenuated the total loop gain at the operating point from -1.31 +/- 0.44 to -0.51 +/- 0.14 (P < 0.05). The Equilibrium Diagram indicated that PBG caused a parallel shift of the neural arc toward lower SNA such that the maximum SNA was reduced to approximately 60% of control. PBG decreased neural and peripheral arc gains at the operating point to approximately 43% and 77%, respectively. In conclusion, the BJ reflex blunts arterial baroreflex via the shift of the neural arc toward lower SNA.

  • Estimation of baroreflex gain using a baroreflex Equilibrium Diagram
    The Japanese journal of physiology, 2002
    Co-Authors: Toru Kawada, Toshiaki Shishido, Masashi Inagaki, Can Zheng, Yusuke Yanagiya, Kazunori Uemura, Masaru Sugimachi, Kenji Sunagawa
    Abstract:

    Two types of closed-loop perturbations can be applied to the arterial baroreflex system. The first (P D 1 ) is introduced into the baroreceptors without a direct effect on arterial pressure (AP), whereas the second (P D 2 )initially affects AP. Neck suction and hemorrhage are examples of P D 1 and P D 2 , respectively. To estimate the baroreflex open-loop gain (G B a r o ) without knowing the absolute magnitudes of P D 1 and P D 2 , we explored a new strategy to estimate G B a r o by combining P D 1 and P D 2 in a baroreflex Equilibrium Diagram. In this Diagram, the neural arc presents the input-output relationship between baroreceptor pressure input and sympathetic nerve activity (SNA). The peripheral arc presents the input-output relationship between SNA and AP. In 8 anesthetized rabbits, we estimated G B a r o by multiplying the slopes of the peripheral arc determined from P D 1 and the neural arc determined from P D 2 . We also estimated G B a r o by a conventional open-loop analysis. The G B a r o values estimated by the Equilibrium Diagram and the open-loop analysis showed a positive correlation (y=0.80x+0.22, r 2 =0.95) and a standard error of estimate of 0.21 across the animals. We conclude that G B a r o was estimated well by combining P D 1 and P D 2 in the Equilibrium Diagram.

  • Estimation of total baroreflex gain using an Equilibrium Diagram between sympathetic nerve activity and arterial pressure
    2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 1
    Co-Authors: Toru Kawada, Masaru Sugimachi, Kenji Sunagawa
    Abstract:

    The arterial baroreflex system may be divided into the mechano-neural arc from pressure input to sympathetic nerve activity (SNA) and the neuro-mechanical arc from SNA to arterial pressure (AP). We explored a new strategy to estimate total baroreflex gain (G/sub baro/) using an Equilibrium Diagram between the mechano-neural and neuro-mechanical arcs. In 8 anesthetized rabbits, a neck suction procedure (NS) was simulated by shifting isolated carotid sinus pressure above AP by 30 mmHg. NS shifted the mechano-neural arc alone, yielding the slope of the neuro-mechanical arc around the operating point. A lower body negative pressure procedure (LBNP) was simulated by 5 ml/kg hemorrhage. LBNP shifted the neuro-mechanical arc alone, yielding the slope of the mechano-neural arc around the operating point. By multiplying the slopes of the neuro-mechanical and mechano-neural arcs, we obtained G/sub baro/ under baroreflex closed-loop conditions. We also estimated G/sub baro/ from the relationship between isolated carotid sinus pressure and AP under baroreflex open-loop conditions. G.. estimated by the Equilibrium Diagram matched reasonably well with that estimated by the open-loop method (y=1.06/spl times/-0.09, r/sup 2/=0.96, SEE=0.15). In conclusion, G/sub baro/ could be estimated using the Equilibrium Diagram without opening the baroreflex negative feedback loop when data obtained from NS and LBNP were combined in a given subject.

Tomohito Kameda - One of the best experts on this subject based on the ideXlab platform.