-
[show abstract]
[hide abstract]
ABSTRACT: We applied a microdialysis technique to the left ventricular myocardium of anesthetized mice and tried to monitor acetylcholine (ACh) release from cardiac vagal nerves. Transection of bilateral cervical vagal nerves decreased dialysate ACh concentration. Electrical stimulation of the left cervical vagal nerve increased dialysate ACh concentration in proportion to the frequency of stimulation. Intravenous administration of hexamethonium, prevented the increase in dialysate ACh concentration during vagal nerve stimulation, indicating that ACh in the dialysate primarily reflects ACh released from post-ganglionic cardiac vagal nerves. Microdialysis permits monitoring of ACh release from post-ganglionic cardiac vagal nerves that are most likely to be innervating the left ventricle in mice.
Autonomic neuroscience: basic & clinical 03/2013; · 1.82 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: AIM: To examine whether dynamic characteristics of the peripheral vagal control of heart rate (HR) are altered in chronic heart failure (CHF). METHODS: The right vagal nerve was electrically stimulated according to a binary white noise signal, and the transfer function from vagal nerve stimulation (VNS) to HR was estimated in the frequency range from 0.01 to 1 Hz in five control rats and five CHF rats under anesthetized conditions. The rate of VNS was changed among 10, 20, and 40 Hz. RESULTS: A multiple linear regression analysis indicated that the increase in the VNS rate augmented the ratio of the high-frequency gain to the steady-state gain in the control group but not in the CHF group. As a result, the dynamic gain of the transfer function in the frequencies near 1 Hz decreased more in the CHF group than in the control group. CONCLUSION: Changes in the dynamic characteristics of the peripheral vagal control of HR may contribute to the manifestation of decreased high-frequency components of HR variability observed in CHF. © 2012 The Authors Acta Physiologica © 2012 Scandinavian Physiological Society.
Acta Physiologica 12/2012; · 3.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The dynamic characteristics of vagal heart rate control can be approximated by a first-order low-pass filter with pure dead time in rabbits. However, this model may not necessarily be the best approximation of the vagal transfer function of the heart rate control in rats, because a flatter portion exists in the gain plot above approximately 0.3 Hz. We developed a new model that includes a frequency-independent gain term to reproduce the flatter portion of the gain plot seen in the vagal transfer function in rats. The inclusion of the new term increased the coefficient of determination in an external validation of the linear regression relationship between measured and predicted heart rate responses to vagal stimulation, and made the slope of the regression line closer to unity. The parameters of mathematical transfer functions were determined in both the frequency and time domains. The frequency-domain fitting provided a set of parameters that was also able to reproduce the time-domain step response reasonably well. In contrast, the time-domain fitting provided a set of parameters that reproduced the frequency-domain transfer function only up to 0.2 Hz. Determination of proper model parameters was crucial for the development of a new model to describe the dynamic heart rate response to vagal stimulation in rats.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:3809-12.
-
[show abstract]
[hide abstract]
ABSTRACT: To elucidate the abnormality of vagal control in spontaneously hypertensive rats (SHR) by measuring left ventricular myocardial interstitial acetylcholine (ACh) release in response to α(2) -adrenergic stimulation as an index of in vivo vagal nerve activity.
A cardiac microdialysis technique was applied to the rat left ventricle in vivo, and the effect of α(2) -adrenergic stimulation by medetomidine or electrical vagal nerve stimulation on myocardial interstitial ACh levels was examined in normotensive Wistar-Kyoto rats (WKY) and SHR under anaesthetized conditions.
Intravenous medetomidine (0.1 mg kg(-1) ) significantly increased the ACh levels in WKY (from 2.4 ± 0.6 to 4.2 ± 1.3 nmol L(-1) , P < 0.05, n = 7) but not in SHR (from 2.5 ± 0.7 to 2.7 ± 0.7 nmol L(-1) , n = 7). In contrast, electrical vagal nerve stimulation increased the ACh levels in both WKY (from 1.0 ± 0.4 to 2.9 ± 0.9 nmol L(-1) , P < 0.001, n = 6) and SHR (from 0.9 ± 0.2 to 2.2 ± 0.4 nmol L(-1) , P < 0.001, n = 6). Intravenous administration of medetomidine (0.1 mg kg(-1) ) did not affect the vagal nerve stimulation-induced ACh release in either WKY or SHR.
Medetomidine-induced central vagal activation was impaired in SHR, whereas peripheral vagal control of ACh release was preserved. In addition to abnormal sympathetic control, vagal control by the central nervous system may be impaired in SHR.
Acta Physiologica 03/2012; 206(1):72-9. · 3.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Intravenous leiomyomatosis is a benign smooth muscle tumor that sometimes spreads to the right heart via the inferior vena cava. A complete surgical resection is necessary to ensure its successful treatment. Surgical removal has been performed safely in middle-aged patients. Here we report a case of successful surgical removal in an elderly woman (age 81 years). The woman was admitted with palpitation and diagnosed as having an intravenous leiomyomatosis with cardiac extension. She underwent a one-stage surgical removal with cardiopulmonary bypass and circulatory arrest. We therefore recommend a one-stage operation, if possible, even in elderly patients.
General Thoracic and Cardiovascular Surgery 03/2012; 60(3):153-6.
-
Shuji Shimizu,
Tsuyoshi Akiyama,
Toru Kawada,
Yusuke Sata,
Masaki Mizuno,
Atsunori Kamiya,
Toshiaki Shishido,
Masashi Inagaki,
Mikiyasu Shirai,
Shunji Sano,
Masaru Sugimachi
[show abstract]
[hide abstract]
ABSTRACT: Although α(2)-adrenergic agonists have been reported to induce a vagal-dominant condition through suppression of sympathetic nerve activity, there is little direct evidence that they directly increase cardiac vagal nerve activity. Using a cardiac microdialysis technique, we investigated the effects of medetomidine, an α(2)-adrenergic agonist, on norepinephrine (NE) and acetylcholine (ACh) release from cardiac nerve endings.
A microdialysis probe was implanted into the right atrial wall near the sinoatrial node in anesthetized rabbits and perfused with Ringer's solution containing eserine. Dialysate NE and ACh concentrations were measured using high-performance liquid chromatography. Both 10 and 100µg/kg of intravenous medetomidine significantly decreased mean blood pressure (BP) and the dialysate NE concentration, but only 100µg/kg of medetomidine enhanced ACh release. Combined administration of medetomidine and phenylephrine maintained mean BP at baseline level, and augmented the medetomidine-induced ACh release. When we varied the mean BP using intravenous administration of phenylephrine, treatment with medetomidine significantly steepened the slope of the regression line between mean BP and log ACh concentration.
Medetomidine increased ACh release from cardiac vagal nerve endings and augmented baroreflex control of vagal nerve activity.
Circulation Journal 01/2012; 76(1):152-9. · 3.77 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: When the Norwood procedure is conducted for the hypoplastic left heart syndrome using a non-valved right ventricle (RV) to pulmonary artery (PA) shunt, diastolic regurgitation from PA to RV may have an adverse effect on postoperative hemodynamics. In this study, we examined the impact of the diastolic regurgitation on ventricular energetics by computational analysis using a combination of a time-varying elastance chamber model and a modified three-element Windkessel vascular model. This study revealed that use of the valved or non-valved RV-PA shunt eliminated pulmonary over-circulation which was observed when using the systemic to pulmonary artery shunt (modified Blalock-Taussig shunt). Although the valved RV-PA shunt improved pulmonary blood supply and consequently increased pulmonary artery flow and oxygen saturation compared to the non-valved RV-PA shunt, the non-valved RV-PA shunt improved ventricular energetics in spite of the presence of PA to RV regurgitation.
The Journal of Physiological Sciences 08/2011; 61(6):457-65. · 1.61 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To examine whether moderate efferent vagal nerve stimulation (VNS) attenuates the carotid sinus baroreflex-mediated arterial pressure (AP) regulation via its antagonism to the sympathetic system.
Carotid sinus baroreceptor regions were isolated from the systemic circulation in eight anesthetized and vagotomized rats. A staircase-wise input was imposed on carotid sinus pressure (CSP) with or without efferent VNS (20Hz, 2ms, 1-4V), while the responses in AP, heart rate (HR), and splanchnic sympathetic nerve activity (SNA) were measured.
A multiple linear regression analysis indicated that VNS decreased the minimum HR in the CSP-HR relationship by 58.2±4.9 beats/min (P<0.01) from its reference value of 387.0±5.8 beats/min. Although VNS significantly decreased an intercept of the SNA-AP relationship, it did not affect parameters of the CSP-AP relationship or the CSP-SNA relationship significantly. The operating-point AP of the baroreflex was decreased by 2.8±1.0mmHg (P<0.01) during VNS, which was less than 3% of the reference value of 117.7±1.2mmHg.
VNS, at an intensity of decreasing HR by approximately 13%, does not acutely attenuate the baroreflex-mediated sympathetic AP regulation.
Life sciences 08/2011; 89(13-14):498-503. · 2.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The carotid sinus baroreflex is one of the most important negative feedback systems to stabilize arterial pressure. Although static characteristics of the carotid sinus baroreflex can be assessed by using a stepwise input protocol under baroreflex open-loop conditions, the step duration has been determined empirically. In the present study, we examined the effects of different time windows (5-10, 15-20, 25-30, 35-40, 45-50, and 55-60 s) on the static characteristics estimated by using a 60-s stepwise input protocol in 10 anesthetized rats. Based on the results, we compared the static characteristics between actual 60-s and 20-s stepwise input protocols. Most of the parameters of the static characteristics did not differ significantly between the 60-s and 20-s stepwise input protocols, suggesting that the open-loop baroreflex static characteristics can be estimated by using a stepwise input with the step duration as short as 20 s in normal rats.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2011; 2011:689-92.
-
Shuji Shimizu,
Tsuyoshi Akiyama,
Toru Kawada,
Takashi Sonobe,
Atsunori Kamiya,
Toshiaki Shishido,
Takeshi Tokudome,
Hiroshi Hosoda,
Mikiyasu Shirai,
Kenji Kangawa,
Masaru Sugimachi
[show abstract]
[hide abstract]
ABSTRACT: Although central ghrelin has cardioprotective effect through inhibiting sympathetic nerve activity, the effects of central ghrelin on cardiac vagal nerve remain unknown. We investigated the effects of centrally administered ghrelin on cardiac autonomic nerve activities using microdialysis technique. A microdialysis probe was implanted in the right atrial wall adjacent to the sinoatrial node of an anesthetized rabbit and was perfused with Ringer's solution containing a cholinesterase inhibitor, eserine. After injection of ghrelin (1 nmol) into the right lateral cerebral ventricle, norepinephrine (NE) and acetylcholine (ACh) concentrations in the dialysate samples were measured as indices of NE and ACh release from nerve endings to the sinoatrial node using high-performance liquid chromatography. Heart rate was 270±4 bpm at baseline and decreased gradually after ghrelin injection to 234±9 bpm (P<0.01) at 60-80 min, followed by gradual recovery. Dialysate ACh concentration was 5.5±0.8 nM at baseline and increased gradually after ghrelin injection to 8.8±1.2 nM (P<0.01) at 60-80 min; the concentration started to decrease gradually from 100 to 120 min after injection reaching 5.6±0.8 nM at 160-180 min. Central ghrelin did not change mean arterial pressure or dialysate NE concentration. The elevated dialysate ACh concentration declined rapidly after transection of cervical vagal nerves. These results indicate that centrally administered ghrelin activates cardiac vagal nerve.
Autonomic neuroscience: basic & clinical 07/2011; 162(1-2):60-5. · 1.82 Impact Factor
-
[show abstract]
[hide abstract]
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.
The Journal of Physiology 04/2011; 589(Pt 7):1769-90. · 4.72 Impact Factor
-
[show abstract]
[hide abstract]
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 anesthetized, 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 r(2) 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 (r(2); 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 (r(2); 0.7±0.1). A numerical simulation suggested that an internal noise predominantly in the neural arc under resting condition 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 (r(2); 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 condition, when compared with open-loop analysis.
The Journal of Physiology 02/2011; · 4.72 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Fibrous-type left ventricular (LV) diverticulum is usually discovered incidentally. Most fibrous diverticula are clinically silent; they may, however, cause several fatal complications, such as spontaneous rupture. Here, we report a case in which multiple cerebral thromboembolisms occurred while a patient with a fibrous LV diverticulum was awaiting surgery. An 81-year-old woman was diagnosed as having an LV diverticulum and was scheduled for open surgery. Following admission for correction, she complained of headache, and magnetic resonance imaging revealed multiple cerebral infarctions. We recommend surgical treatment for asymptomatic LV diverticula to prevent systemic thromboembolism.
Interactive cardiovascular and thoracic surgery 02/2011; 12(2):319-20.
-
[show abstract]
[hide abstract]
ABSTRACT: In contrast to high mortality of open surgery for thoracic aortic catastrophes including ruptured thoracic aortic aneurysm (RTAA) and traumatic aortic injury (TAI), excellent short-term outcomes of thoracic endovascular aortic repair (TEVAR) have recently been reported. We report our single-center experiences with TEVAR for aortic catastrophes. Thirteen patients with thoracic aortic catastrophes (RTAA in 7 patients, TAI in 6 patients) have received TEVAR from February 2004 to June 2010. In cases of RTAA, 5 descending aortic aneurysm ruptures and 2 aortic arch aneurysm ruptures were included. In patients with arch aneurysm ruptures, fenestrated stent grafting (SG) and SG combined with arch debranching were performed. In all cases of TAI, aortic injuries occurred near the isthmus and 5 patients received fenestrated SG. The initial success rate was 100% and there was no perioperative death. Mean duration of observation was 24 months, which revealed 4 late deaths. The causes of late death were liver failure, cerebral contusion, senility and unknown. A patient with RTAA experienced a type III endoleak as an aorta-related event 24 months after operation. There was no enlargement of aneurysm in any patient. TEVAR for aortic catastrophes seems to be performed safely with acceptable outcomes. Although morphological incompatibility, unstable preoperative haemodynamics and longer time for preparation may become impediments to perform TEVAR, we believe that TEVAR should be the 1st choice for life-threatening aortic catastrophes. However, a careful follow-up is necessary because TEVAR has several unique late complications.
Kyobu geka. The Japanese journal of thoracic surgery 01/2011; 64(1):69-73.
-
[show abstract]
[hide abstract]
ABSTRACT: We examined the transfer function of autonomic heart rate (HR) control in anesthetized sedentary and exercise-trained (16 wk, treadmill for 1 h, 5 times/wk at 15 m/min and 15-degree grade) rats for comparison to HR variability assessed in the conscious resting state. The transfer function from sympathetic stimulation to HR response was similar between groups (gain, 4.2 ± 1.5 vs. 4.5 ± 1.5 beats·min(-1)·Hz(-1); natural frequency, 0.07 ± 0.01 vs. 0.08 ± 0.01 Hz; damping coefficient, 1.96 ± 0.55 vs. 1.69 ± 0.15; and lag time, 0.7 ± 0.1 vs. 0.6 ± 0.1 s; sedentary vs. exercise trained, respectively, means ± SD). The transfer gain from vagal stimulation to HR response was 6.1 ± 3.0 in the sedentary and 9.7 ± 5.1 beats·min(-1)·Hz(-1) in the exercise-trained group (P = 0.06). The corner frequency (0.11 ± 0.05 vs. 0.17 ± 0.09 Hz) and lag time (0.1 ± 0.1 vs. 0.2 ± 0.1 s) did not differ between groups. When the sympathetic transfer gain was averaged for very-low-frequency and low-frequency bands, no significant group effect was observed. In contrast, when the vagal transfer gain was averaged for very-low-frequency, low-frequency, and high-frequency bands, exercise training produced a significant group effect (P < 0.05 by two-way, repeated-measures ANOVA). These findings suggest that, in the frequency domain, exercise training augments the dynamic HR response to vagal stimulation but not sympathetic stimulation, regardless of the frequency bands.
AJP Regulatory Integrative and Comparative Physiology 01/2011; 300(4):R969-77. · 3.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Although baroreceptors are known to reset to operate in a higher pressure range in spontaneously hypertensive rats (SHR), the total profile of dynamic arterial pressure (AP) regulation remains to be clarified. We estimated open-loop transfer functions of the carotid sinus baroreflex in SHR and Wistar Kyoto (WKY) rats. Mean input pressures were set at 120 (WKY₁₂₀ and SHR₁₂₀) and 160 mmHg (SHR₁₆₀). The neural arc transfer function from carotid sinus pressure to efferent splanchnic sympathetic nerve activity (SNA) revealed derivative characteristics in both WKY and SHR. The slope of dynamic gain (in decibels per decade) between 0.1 and 1 Hz was not different between WKY₁₂₀ (10.1 ± 1.0) and SHR₁₂₀ (10.4 ± 1.1) but was significantly greater in SHR₁₆₀ (13.2 ± 0.8, P < 0.05 with Bonferroni correction) than in SHR₁₂₀. The peripheral arc transfer function from SNA to AP showed low-pass characteristics. The slope of dynamic gain (in decibels per decade) did not differ between WKY₁₂₀ (-34.0 ± 1.2) and SHR₁₂₀ (-31.4 ± 1.0) or between SHR₁₂₀ and SHR₁₆₀ (-32.8 ± 1.3). The total baroreflex showed low-pass characteristics and the dynamic gain at 0.01 Hz did not differ between WKY₁₂₀ (0.91 ± 0.08) and SHR₁₂₀ (0.84 ± 0.13) or between SHR₁₂₀ and SHR₁₆₀ (0.83 ± 0.11). In both WKY and SHR, the declining slope of dynamic gain was significantly gentler for the total baroreflex than for the peripheral arc, suggesting improved dynamic AP response in the total baroreflex. In conclusion, the dynamic characteristics of AP regulation by the carotid sinus baroreflex were well preserved in SHR despite significantly higher mean AP.
AJP Regulatory Integrative and Comparative Physiology 11/2010; 300(1):R155-65. · 3.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The internal thoracic artery (ITA) is harvested by either the pedicled or the skeletonized technique in coronary artery bypass grafting (CABG), with no clear advantage of one technique over the other. We compared graft flow between the pedicled and skeletonized ITA grafts while varying myocardial oxygen demand. CABG was performed to the left anterior descending artery in five anesthetized dogs using a pedicled ITA graft and the graft was subsequently skeletonized. Graft flow was measured during stepwise electrical stimulation of the stellate ganglion. The baseline graft flow before sympathetic stimulation was higher in skeletonized (27.8 ± 1.9 ml/min) than that in pedicled ITA grafts (22.6 ± 2.7 ml/min) (P < 0.05). In both ITA grafts, however, graft flow increased to a similar level during sympathetic stimulation that doubled the double product, correlating with the double product. Based on these results, we conclude that metabolic demand can override the potential difference in sympathetic vasoconstriction in both pedicled and skeletonized ITA grafts.
The Journal of Physiological Sciences 11/2010; 60(6):407-13. · 1.61 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We estimated the transfer function of autonomic heart rate (HR) control by using random binary sympathetic or vagal nerve stimulation in anaesthetized rats. The transfer function from sympathetic stimulation to HR response approximated a second-order, low-pass filter with a lag time (gain, 4.29 +/- 1.55 beats min(1) Hz(1); natural frequency, 0.07 +/- 0.03 Hz; damping coefficient, 1.96 +/- 0.64; and lag time, 0.73 +/- 0.12 s). The transfer function from vagal stimulation to HR response approximated a first-order, low-pass filter with a lag time (gain, 8.84 +/- 4.51 beats min(1) Hz(1); corner frequency, 0.12 +/- 0.06 Hz; and lag time, 0.12 +/- 0.08 s). These results suggest that the dynamic characteristics of HR control by the autonomic nervous system in rats are similar to those of larger mammals.
Experimental physiology 09/2010; 95(9):919-25. · 3.17 Impact Factor
-
[show abstract]
[hide abstract]
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.
The Journal of Physiological Sciences 07/2010; 60(4):283-98. · 1.61 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: One and a half ventricle repair (1.5VR) is a surgical option for hypoplastic right ventricle (RV). The benefits of this procedure compared to biventricular repair (2VR) or Fontan operation remain unsettled. To compare postoperative hemodynamics, we performed a theoretical analysis using a computational model based on lumped-parameter state-variable equations. We varied the RV stiffness constant (B (RV)) to simulate the various RV hypoplasia, and estimated hemodynamics for a given B (RV). With B (RV) < 150% of normal, cardiac output was the largest in 2VR. With B (RV) > 150%, cardiac output became larger in 1.5VR than in 2VR. With B (RV) > 250%, RV end-diastolic volume was almost the same between 1.5VR and 2VR, and a rapid increase in atrial pressure precluded the use of 1.5VR. These results indicate that the beneficial effect of 1.5VR depends on the RV stiffness constant. Determination of management strategy should not only be based on the morphologic parameters but also on the physiological properties of RV.
The Journal of Physiological Sciences 05/2010; 60(3):205-12. · 1.61 Impact Factor
