Pulse arrival time: Measurement and clinical applications

Pulse arrival time is the time elapsed between the R-wave of electrocardiogram and systolic peak in peripheral pulse obtained by any of the plethysmographic methods. Similarly, differential pulse arrival time, also known as pulse transit time, is the time elapsed between systolic peaks of proximal and distal peripheral pulse recordings in an extremity. Distance between the proximal and distal site in the extremity (in meters) divided by differential pulse arrival time (in seconds) gives arterial pulse wave velocity in the limb segment. Differential pulse arrival time has been used to discriminate between an aortic or arterial block from generalized atherosclerosis in aortic and arterial occlusive diseases for nearly four decades. All along there have been efforts to monitor beat-to-beat blood pressure with the help of these time intervals and other pulse parameters. Encouraging correlation has been observed with that obtained by Finapres. Recently pulse arrival time has been explored for the prompt detection of sudden hypertensive episodes during laryngeal microsurgery, for detection of mental stress, monitoring of baroreflex sensitivity, and real-time monitoring of blood pressure. This paper briefly describes the measurement technique of pulse arrival time and an overview of its clinical applications.

Naringin and trimetazidine improve baroreflex sensitivity and nucleus tractus solitarius electrical activity in renal ischemia-reperfusion injury / Naringin and trimetazidine improve baroreflex sensitivity and nucleus tractus solitarius electrical activity in renal ischemia-reperfusion injury

Resumo Fundamento: O núcleo do trato solitário (NTS) é uma área do cérebro que desempenha um papel fundamental na regulação renal e cardiovascular através dos impulsos dos barorreceptores. Objetivos: O objetivo deste estudo foi avaliar o efeito da Naringina (NAR) e trimetazidina (TMZ), isoladamente e combinadas, na atividade elétrica do NTS e na sensibilidade barorreflexa (SBR) na lesão de isquemia e reperfusão (I/R) renal. Métodos: Foram utilizados quarenta ratos machos Sprague-Dawley (200-250 g), alocados em 5 grupos com 8 ratos cada. Grupos: 1) Sham; 2) I/R; 3) TMZ 5 mg/kg; 4) NAR 100 mg/kg; e 5) TMZ5 + NAR100. A veia femoral esquerda foi canulada para infundir a solução salina ou droga e avaliar a SBR. A I/R foi induzida por oclusão dos pedículos renais por 45 min, seguida de reperfusão de 4 horas. O eletroencefalograma local do NTS foi registrado antes, durante a isquemia e durante a reperfusão. A fenilefrina foi injetada por via intravenosa para avaliar a SBR ao final do tempo de reperfusão. Os dados foram analisados por ANOVA de duas vias com medidas repetidas seguida pelo teste post hoc de Tukey. Um valor de p<0,05 foi considerado como significativo. Resultados: As ondas elétricas do NTS não se alteraram durante o tempo de isquemia, mas diminuíram significativamente durante todos os tempos de reperfusão. A atividade elétrica do NTS e a SBR foram reduzidas drasticamente em ratos com lesão I/R; no entanto, a administração de NAR e TMZ, isoladamente e combinadas, melhorou significativamente essas alterações em ratos com lesão I/R. Conclusões: Os resultados mostraram que a lesão de I/R leva à redução da atividade elétrica da SBR e do NTS, e pode haver uma ligação entre a I/R e a diminuição da SBR. Além disso, a NAR e a TMZ são agentes promissores para tratar complicações de I/R.

Abstract Background: Nucleus tractus solitarius (NTS) is a brain area that plays a key role in kidney and cardiovascular regulation via baroreceptors impulses. Objectives: The aim of this study was to evaluate the effect of naringin (NAR) and trimetazidine (TMZ) alone and their combination on NTS electrical activity and baroreceptor sensitivity (BRS) in renal ischemia- reperfusion (I/R) injury. Methods: Forty male Sprague-Dawley rats (200- 250 g) were allocated into 5 groups with 8 in each. 1) Sham; 2) I/R; 3) TMZ 5 mg/kg; 4) NAR 100 mg/kg; and 5) TMZ5+ NAR100. The left femoral vein was cannulated to infuse saline solution or drug and the BRS was evaluated. I/R was induced by occlusion of renal pedicles for 45 min, followed by 4 hours of reperfusion. The NTS local electroencephalogram (EEG) was recorded before, during ischemia and throughout the reperfusion. Phenylephrine was injected intravenously to evaluate BRS at the end of reperfusion time. The data were analyzed by two-way repeated measurement ANOVA followed by Tukey's post hoc test. A p-value <0.05 was considered significant. Results: NTS electrical waves did not change during ischemia time, while they significantly decreased during the entire reperfusion time. NTS electrical activity and BRS dramatically reduced in rats with I/R injury; however, administration of NAR, TMZ alone or their combination significantly improved these changes in rats with I/R injury. Conclusions: The results showed that I/R injury leads to reduced BRS and NTS electrical activity and there may be an association between I/R and decreased BRS. In addition, NAR and TMZ are promising agents to treat I/R complications.

Effects of exercise training on autonomic modulation and mood symptoms in patients with obstructive sleep apnea

We evaluated the effects of exercise training (ET) on the profile of mood states (POMS), heart rate variability, spontaneous baroreflex sensitivity (BRS), and sleep disturbance severity in patients with obstructive sleep apnea (OSA). Forty-four patients were randomized into 2 groups, 18 patients completed the untrained period and 16 patients completed the exercise training (ET). Beat-to-beat heart rate and blood pressure were simultaneously collected for 5 min at rest. Heart rate variability (RR interval) was assessed in time domain and frequency domain (FFT spectral analysis). BRS was analyzed with the sequence method, and POMS was analyzed across the 6 categories (tension, depression, hostility, vigor, fatigue, and confusion). ET consisted of 3 weekly sessions of aerobic exercise, local strengthening, and stretching exercises (72 sessions, achieved in 40±3.9 weeks). Baseline parameters were similar between groups. The comparisons between groups showed that the changes in apnea-hypopnea index, arousal index, and O2 desaturation in the exercise group were significantly greater than in the untrained group (P<0.05). The heart rate variability and BRS were significantly higher in the exercise group compared with the untrained group (P<0.05). ET increased peak oxygen uptake (P<0.05) and reduced POMS fatigue (P<0.05). A positive correlation (r=0.60, P<0.02) occurred between changes in the fatigue item and OSA severity. ET improved heart rate variability, BRS, fatigue, and sleep parameters in patients with OSA. These effects were associated with improved sleep parameters, fatigue, and cardiac autonomic modulation, with ET being a possible protective factor against the deleterious effects of hypoxia on these components in patients with OSA.

Resting spontaneous baroreflex sensitivity and cardiac autonomic control in anabolic androgenic steroid users

OBJECTIVES: Misuse of anabolic androgenic steroids in athletes is a strategy used to enhance strength and skeletal muscle hypertrophy. However, its abuse leads to an imbalance in muscle sympathetic nerve activity, increased vascular resistance, and increased blood pressure. However, the mechanisms underlying these alterations are still unknown. Therefore, we tested whether anabolic androgenic steroids could impair resting baroreflex sensitivity and cardiac sympathovagal control. In addition, we evaluate pulse wave velocity to ascertain the arterial stiffness of large vessels. METHODS: Fourteen male anabolic androgenic steroid users and 12 nonusers were studied. Heart rate, blood pressure, and respiratory rate were recorded. Baroreflex sensitivity was estimated by the sequence method, and cardiac autonomic control by analysis of the R-R interval. Pulse wave velocity was measured using a noninvasive automatic device. RESULTS: Mean spontaneous baroreflex sensitivity, baroreflex sensitivity to activation of the baroreceptors, and baroreflex sensitivity to deactivation of the baroreceptors were significantly lower in users than in nonusers. In the spectral analysis of heart rate variability, high frequency activity was lower, while low frequency activity was higher in users than in nonusers. Moreover, the sympathovagal balance was higher in users. Users showed higher pulse wave velocity than nonusers showing arterial stiffness of large vessels. Single linear regression analysis showed significant correlations between mean blood pressure and baroreflex sensitivity and pulse wave velocity. CONCLUSIONS: Our results provide evidence for lower baroreflex sensitivity and sympathovagal imbalance in anabolic androgenic steroid users. Moreover, anabolic androgenic steroid users showed arterial stiffness. Together, these alterations might be the mechanisms triggering the increased blood pressure in this population.

Exercise training attenuates hypertension progression via activation of central ACE2-Ang(1-7)-Mas axis in prehypertensive rats / 中国病理生理杂志

AIM:To investigate the effects of exercise training on the progression from prehypertension to hy -pertension,blood pressure regulation and the angiotensin-converting enzyme 2(ACE2)-angiotensin(Ang)(1-7)-MAS axis activation in cardiovascular centers ,and to elucidate the central mechanisms of exercise training postponing hyperten -sion progression.METHODS:The male spontaneously hypertensive rats(SHR;n=20,5 weeks old)and normotensive Wistar Kyoto(WKY)rats(n=20)were randomly assigned to sedentary(Sed)group and exercise training(ExT)group. The trained rats run on a treadmill in moderate-intensity for 20 weeks.Systolic blood pressure(SBP)was measured by tail-cuff method.The baroreflex sensitivity(BRS)was assessed by intravenous injection of phenylephrine.The expression of ACE2 and MAS receptor at mRNA and protein levels in baroreflex centers were determined by real-time PCR and Western blot,respectively.Alterations of BRS were evaluated before and after intracerebroventricular injection of MAS receptor ago -nist Ang(1-7)and its antagonist A779,respectively.RESULTS:Compared with SHR +Sed group,exercise training since prehypertension significantly postponed the development of hypertension ,delayed the hypertension progression ,and decreased SBP in both SHR and WKY rats(P<0.05).Exercise training enhanced blood pressure regulation and improved the BRS in SHR(P<0.01).The expression of ACE2 and MAS receptor at mRNA and protein levels in the baroreflex cen-ters(rostral ventrolateral medulla ,nucleus tract solitarius and paraventricular nucleus )were up-regulated in SHR +ExT group(P<0.05).Central administration of A779 abolished the benefits of exercise-induced improvement of BRS in SHR +ExT group(P<0.01).In contrast,Ang(1-7)improved the BRS in both SHR +Sed group and SHR +ExT group(P<0.05).CONCLUSION:Exercise training postpones hypertension progression and improves blood pressure regula -tion,which may be associated with the activation of central ACE 2-Ang(1-7)-Mas axis.

Evaluación de la Presencia de Disautonomía en Pacientes con Parkinson mediante el Análisis de Señales Cardiovasculares / Assessment of the Dysautonomia Presence in Parkinson disease through Cardiovascular Signal Analysis

Resumen: En este trabajo se evalúa y compara la respuesta del sistema nervioso autónomo (SNA) en pacientes con enfermedad de Parkinson (EP) y sujetos sanos para detectar la posible presencia de disautonomía. Las señales de electrocardiograma y fotopletismografía fueron adquiridas durante las maniobras: reposo, cambio de postura (Post-CP), respiración controlada (RC) e hiperventilación (Hip.). El análisis de las señales incluyó índices de la variabilidad de la frecuencia cardiaca (VFC) lineales y no lineales, índices de la señal de tiempo de tránsito de pulso y la sensibilidad del barorreflejo (índice α). Los pacientes con Parkinson mostraron una alteración en la modulación simpática principalmente durante Post-CP y una deficiencia en la respuesta cardiovagal en RC. La entropía aproximada disminuyó significativamente en sujetos sanos respecto a pacientes con EP durante RC. El índice α fue menor en pacientes con EP con respecto a sujetos sanos durante todo el protocolo, lo cual sugiere una alteración en el control del barorreflejo en EP. Sin embargo, es necesario aumentar el número de sujetos con la finalidad de determinar grados de disautonomía. El protocolo diseñado para evaluar la presencia de disautonomía en mexicanos con EP a través de señales no invasivas aportó información sobre el comportamiento del SNA.

Abstract: The goal of this work is to assess and to compare the autonomic nervous system (SNA) response in Parkinson's disease (EP) patients and healthy subjects in order to evaluate the possible dysautonomia presence. Electrocardiogram and photoplethysmography signals were acquired during the following maneuvers: rest, orthostatic change (Post-CP), controlled breathing (RC) and hyperventilation (Hip.). The signal processing was carried out by means of linear and no linear indices of heart rate variability (VFC), indices of pulse transit time (PTT) and baroreflex sensitivity (α index). Parkinson disease patients showed an attenuated sympathetic modulation mainly during Post-CP and the cardiovagal response resulted blunted during RC. Approximate entropy was significantly decreased in healthy subjects with respect to EP subjects during RC. In addition, the index α resulted in lower values in EP patients with respect to healthy subjects during the complete protocol, this result suggests that the baroreflex control in EP patients is blunted. However, is necessary to increase the number of subjects with the objective of determining levels of dysautonomia. The protocol designed to evaluate the dysautonomia presence in mexicans with EP through non invasive signals provides information about the SNA behavior.

Cardiovagal Baroreflex Sensitivity in Parkinson's Disease and Multiple-System Atrophy

BACKGROUND AND PURPOSE: Parkinson's disease (PD) and multiple-system atrophy of the parkinsonian type (MSA-P) are progressive neurodegenerative disorders that in addition to dysfunction of the motor system also present with features of dysautonomia, frequently manifesting as orthostatic hypotension (OH). The pathophysiology of OH has been proposed to differ between these two disorders. This study investigated the spontaneous and cardiovagal baroreflex sensitivity (BRS) in Parkinson's disease patients with orthostatic hypotension (PD(OH)) and multiple system atrophy of Parkinsonian type with orthostatic hypotension in an attempt to differentiate the two disorders. METHODS: Two methods were used for determining the BRS: a spontaneous method (spontaneous BRS) and the reflexive baroreflex gain (cardiovagal BRS) from phases II and IV of the Valsalva maneuver (VM) in PD(OH) and MSA-P(OH). RESULTS: The spontaneous BRS (5.04±0.66 ms/mm Hg vs. 4.78±0.64 ms/mm Hg, p=0.54) and the cardiovagal BRS from phase II of the VM (0.96±0.75 ms/mm Hg vs. 1.34±1.51 ms/mm Hg, p=0.76) did not differ between PD(OH) and MSA-P(OH), but the cardiovagal BRS from phase IV of the VM (0.03±0.07 ms/mm Hg vs. 2.86±2.39 ms/mm Hg, p=0.004) was significantly lower in PD(OH). CONCLUSIONS: The cardiovagal BRS from phase IV of the VM has potential for differentiating PD(OH) and MSA-P(OH), indicating a difference in the pathophysiological mechanisms underlying the autonomic dysfunction in the two disorders.

Role of Baroreflex Sensitivity in Predicting Tilt Training Response in Patients with Neurally Mediated Syncope

PURPOSE: An association between baroreflex sensitivity (BRS) and the response to tilt training has not been reported in patients with neurally mediated syncope (NMS). This study sought to investigate the role of BRS in predicting the response to tilt training in patients with NMS. MATERIALS AND METHODS: We analyzed 57 patients who underwent tilt training at our hospital. A responder to tilt training was defined as a patient with three consecutive negative responses to the head-up tilt test (HUT) during tilt training. RESULTS: After tilt training, 52 patients (91.2%) achieved three consecutive negative responses to the HUT. In the supine position before upright posture during the first session of tilt training for responders and non-responders, the mean BRS was 18.17+/-10.09 ms/mm Hg and 7.99+/-5.84 ms/mm Hg (p=0.008), respectively, and the frequency of BRS > or =8.945 ms/mm Hg was 45 (86.5%) and 1 (20.0%; p=0.004), respectively. Age, male gender, frequency of syncopal events before HUT, type of NMS, phase of positive HUT, total number of tilt training sessions, and mean time of tilt training did not differ between the study groups. In the multivariate analysis, BRS <8.945 ms/mm Hg in the supine position (odds ratio 23.10; 95% CI 1.20-443.59; p=0.037) was significantly and independently associated with non-response to tilt training. CONCLUSION: The BRS value in the supine position could be a predictor for determining the response to tilt training in patients with NMS who are being considered for inpatient tilt training.

Static Magnetic Field Effect on Cardiovascular Regulation: A Review.

Mounting evidence suggests that environmental and occupational magnetic fields affect cardiovascular system. In this review, supported by original hemodynamic recordings - direct experimental evidence of the effect - static magnetic field (SMF) effects on arterial baroreflex cardiovascular control mechanism have been summarized. Local exposure of 120 - 350 mT SMF to sinocarotid baroreceptors in rabbits and healthy volunteers exerted a stimulatory effect on arterial baroreflex - normalized arterial blood pressure in hypertensive and hypotensive conditions, significantly increased microcirculation, heart rate variability, arterial baroreflex sensitivity and sodium nitroprusside (spontaneous nitric oxide donor) microcirculatory vasodilatory effect. The improvement of the vasodilator responsiveness to nitric oxide by baroreceptor stimulation suggested to be a new mechanism in baroreflex physiology with potential implementation in a spectrum of cardiovascular diseases where endothelial dysfunction and sympathovagal imbalance that results from a loss of baroreflex control over autonomic activity increases the risk of morbidity and mortality substantially. The modulation of the baroreflex-mediated autonomic cardiovascular control is a new concept for understanding environmental magnetic fields effect on cardiovascular system and an effective strategy to prevent their potential public health hazards.

Relation between preoperative autonomic function and blood pressure change after tourniquet deflation during total knee replacement arthroplasty / 대한마취과학회지

BACKGROUND: Tourniquets are used to provide a bloodless surgical field for extremities. Hypotension due to vasodilation and bleeding after tourniquet deflation is a common event. Hemodynamic stability is modulated by the autonomic nervous system (ANS). Heart rate variability (HRV) is a sensitive method for detecting individuals who may be at risk of hemodynamic instability during general anesthesia. The purpose of this study was to investigate ANS function to predict hypotension after tourniquet deflation. METHODS: Eighty-six patients who underwent total knee replacement arthroplasty (TKRA) were studied. HRV, systolic blood pressure variability (SBPV) and baroreflex sensitivity (BRS) were analyzed. We assigned two groups depending on the lowest systolic blood pressure (SBP) or mean BP (MBP) after tourniquet release (Group H; SBP 80 mmHg and MBP > 60 mmHg). RESULTS: Fifteen patients developed severe hypotension and ten patients were treated with ephedrine. Of the parameters of HRV, SBPV, and BRS, only BRSSEQ was significant being low in Group H. BRS and high-frequency SBPV were correlated with the degree of MBP change after tourniquet deflation. CONCLUSIONS: Preoperative low BRS is associated with hypotension after tourniquet deflation, suggesting the importance of baroreflex regulation for intraoperative hemodynamic stability.

The effect of carbon dioxide pneumoperitoneum on baroreflex sensitivity / 대한마취과학회지

BACKGROUND: To determine if positive pressure pneumoperitoneum has adverse effects on autonomic nervous system function, we examined baroreflex sensitivity (BRS) during carbon dioxide pneumoperitoneum in patients undergoing laparoscopic surgery. METHODS: Twenty adult patients scheduled for laparoscopic gynecologic surgery were selected for the study. After general anesthesia was induced with sevoflurane, continuous electrocardiography and blood pressure were monitored. Spontaneous BRS was achieved using sequence method immediately before, and 5 minutes after, pneumoperitoneum. Heart rate variability (HRV) was also determined. RESULTS: After pneumoperitoneum, BRS decreased from 12.9 +/- 1.8 ms/mmHg to 8.1 +/- 1.1 ms/mmHg (P < 0.05), and the power of the high frequency band decreased from 237.8 ms2/Hz to 49.6 ms2/Hz (P < 0.05). CONCLUSIONS: Compared to recordings obtained before pneumoperitoneum, BRS was decreased during pneumoperitoneum. This may predispose patients undergoing laparoscopic surgery to hemodynamic instability in addition to pneumoperitoneum itself.

Anesthesia and autonomic nervous system: is measurement of heart rate variability, blood pressure variability and baroreflex sensitivity useful in anesthesiology specialty? / 대한마취과학회지

The autonomic nervous system (ANS) contributes importantly to the short-term regulation of blood pressure and cardiovascular variability. Evidence from numerous studies indicates a strong association among compromised ANS, sudden cardiac death, blood pressure instability and adverse postoperative cardiac events. Heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS) have been studied for years as tools for assessing ANS. In this review, physiological origin and measurement principle of cardiovascular fluctuations are described and changes in indices of HRV, BPV and BRS observed in various situations of anesthesia are discussed. Anesthesiologists need to consider estimation of ANS function to predict hypertension/hypotension after anesthesia induction and to improve short-term outcome and long-term cardiac morbidity and mortality.

Autonomic modulation of arterial pressure and heart rate variability in hypertensive diabetic rats

OBJECTIVE: The aim of the present study was to evaluate the autonomic modulation of the cardiovascular system in streptozotocin (STZ)-induced diabetic spontaneously hypertensive rats (SHR), evaluating baroreflex sensitivity and arterial pressure and heart rate variability. METHODS: Male SHR were divided in control (SHR) and diabetic (SHR+DM, 5 days after STZ) groups. Arterial pressure (AP) and baroreflex sensitivity (evaluated by tachycardic and bradycardic responses to changes in AP) were monitored. Autoregressive spectral estimation was performed for systolic AP (SAP) and pulse interval (PI) with oscillatory components quantified as low (LF:0.2-0.6Hz) and high (HF:0.6-3.0Hz) frequency ranges. RESULTS: Mean AP and heart rate in SHR+DM (131±3 mmHg and 276±6 bpm) were lower than in SHR (160±7 mmHg and 330±8 bpm). Baroreflex bradycardia was lower in SHR+DM as compared to SHR (0.55±0.1 vs. 0.97±0.1 bpm/mmHg). Overall SAP variability in the time domain (standard deviation of beat-by-beat time series of SAP) was lower in SHR+DM (3.1±0.2 mmHg) than in SHR (5.7±0.6 mmHg). The standard deviation of the PI was similar between groups. Diabetes reduced the LF of SAP (3.3±0.8 vs. 28.7±7.6 mmHg2 in SHR), while HF of SAP were unchanged. The power of oscillatory components of PI did not differ between groups. CONCLUSIONS: These results show that the association of hypertension and diabetes causes an impairment of the peripheral cardiovascular sympathetic modulation that could be, at least in part, responsible for the reduction in AP levels. Moreover, this study demonstrates that diabetes might actually impair the reduced buffer function of the baroreceptors while reducing blood pressure.

OBJETIVO: O objetivo do presente estudo foi investigar a modulação autonômica do sistema cardiovascular em ratos espontâneamente hipertensos (SHR) e diabéticos por estreptozotocina (STZ), avaliando a sensibilidade do reflexo barorreceptor e a variabilidade da pressão arterial e da freqüência cardíaca. MÉTODOS: Ratos SHR machos foram divididos em grupos controle (SHR) e diabéticos (SHR+DM, 5 dias após STZ). A pressão arterial (PA) e a sensibilidade dos barorreceptores (avaliada pelas respostas taquicárdicas e bradicárdicas a alterações da PA) foram monitoradas. Os sinais de pressão arterial sistólica (PAS) e o intervalo de pulso (IP) foram analisados no domínio do tempo e da freqüência pelo método autoregressivo sendo quantificados os componentes oscilatórios de baixa (BF: 0,2-0,6Hz) e alta (AF:0,6-3,0Hz) freqüência. RESULTADOS: A PA média e a freqüência cardíaca estavam reduzidas no grupo SHR+DM (131±3 mmHg e 276±6 bpm) em relação ao grupo SHR (160±7 mmHg e 330±8 bpm). A bradicardia reflexa a aumentos de PA estava atenuada no grupo SHR+DM quando comparada ao grupo SHR (0,55±0,1 vs 0,97±0,1 bpm/mmHg). A variabilidade da PAS no domínio do tempo (desvio padrão batimento-a-batimento da série temporal da PAS) foi menor no grupo SHR+DM (3,1±0,2 mmHg) quando comparada ao grupo SHR (5,7±0,6 mmHg). O desvio padrão do IP foi semelhante entre os grupos. O diabetes reduziu o componente BF da PAS (3,3±0,8 vs 28,7±7,6 mmHg² no SHR), mas não alterou o componente AF da PAS. Em relação aos componentes oscilatórios do IP não houve diferença entre os grupos. CONCLUSÕES: Estes resultados sugerem que a associação de hipertensão e diabetes causa uma importante diminuição da modulação simpática cardiovascular periférica que poderia, pelo menos em parte, ser responsável pela redução da PA. Além disso, este estudo demonstra que o diabetes pode, de fato, piorar a já reduzida função de tamponamento dos barorreceptores ao mesmo tempo em que reduz a pressão arterial.

The Influence of Sevoflurane Anesthesia on Various Kinds of Spontaneous Baroreflex Sensitivities / 대한마취과학회지

BACKGROUND: In contrast to classic drug injection method, various types of noninvasive spontaneous baroreflex sensitivity (SBRS) methods have been developed using the computer analysis of the spontaneous fluctuation of heart rate and arterial blood pressure for baroreflex evaluation. In this study, we evaluated the effects of sevoflurane anesthesia on SBRS by comparing various SBRS estimates and their correlations before and after sevoflurane anesthesia. METHODS: Radial arterial pressure and electrocardiography were recorded in 50 patients before and after sevoflurane anesthesia. We derived six SBRS indices from the methods including sequence, alpha-index, transfer function analysis and impulse response function. The sequence method measured an average of baroreflex sequences. The alpha-index used the average of the square roots of the ratios between the RRI and SBP spectral power. The transfer function index used RRI and SBP cross-spectral magnitude for this index. The impulse response function method employed an inverse Fourier transform. RESULTS: All SBRS and accompanying correlations were reduced after sevoflurane anesthesia. Low (44%) and high (4%) frequency transfer function gain and sequence SBRS (4%) failed to be computed out of some patients after sevoflurane anesthesia due to poor coherence and absence of a valid sequence. CONCLUSIONS: Sevoflurane anesthesia caused marked depression of SBRS and weakened their correlations. Therefore, it is necessary to understand the characteristics of each SBRS method for selecting an appropriate method during anesthesia.

Appropriate Thresholds of Systolic Blood Pressure and R-R Interval for Assessment of Baroreflex Sensitivity by the Sequence Method during Sevoflurane Anesthesia / 대한마취과학회지

BACKGROUND: The sequence method of determining baroreflex sensitivity (BRSSEQ) has been reported to correlate poorly with the phenylephrine method of determining BRS in individuals with attenuated BRS. Inhalation anesthetics are also known to decrease BRS. We therefore assessed the effect of varying the systolic blood pressure (SBP) and R-R interval (RRI) thresholds on BRSSEQ values and compared these results with the BRS obtained by the modified Oxford technique (BRSMODOX). METHODS: The average number of valid sequences and BRSSEQ values were derived by varying the SBP threshold from 0.5 to 2.5 mmHg and the RRI threshold from 1 to 6 ms, and the relation of BRSSEQ values to BRSMODOX values using sequential administration of nitroprusside and phenylephrine was assessed in 40 healthy individuals during sevoflurane anesthesia. RESULTS: Increasing either the SBP thresholds or RRI thresholds resulted in a decrease in the number of valid sequences. As the SBP thresholds were decreased and the RRI thresholds were increased, BRSSEQ values increased. When the SBP threshold exceeded 1 mmHg, no significant correlations were observed between BRSSEQ and BRSMODOX values. Significant correlations between the two methods were observed for an SBP threshold of 0.5 mmHg and RRI thresholds of 1, 2, 3 and 4 ms. Biases between the two methods were 2.1, 2.1, 0.4, and 0.4 ms/mmHg for 0.5 mmHg and 1, 2, 3 and 4 ms. CONCLUSIONS: These findings suggest that adjusting the SBP threshold to 0.5 mmHg and the RRI threshold to 3 or 4 ms may improve BRSSEQ validity during sevoflurane anesthesia, when compared to BRSMODOX.

Influence of Anesthesia Induction with Ketamine on Baroreflex Control of Heart Rate / 대한마취과학회지

BACKGROUND: It is reported that ketamine increases central sympathetic activity as well as catecholamine reuptake inhibition. However, little has been known about baroreflex control of heart rate in ketamine anesthetized humans. Thus, the aim of this study was to analyze the effect of ketamine on spontaneous baroreflex sensitivity (BRS) during ketamine induction of anesthesia. METHODS: Beat-by-beat arterial blood pressure and electrocardiogram at 5 min before and 10 min after ketamine administration (2 mg/kg) were recorded in twenty healthy living liver transplant donors. Spontaneous BRS was assessed by sequence method and transfer function analysis method. RESULTS: Spontaneous BRS assessed by sequence method, BRSsequence, decreased from 13.7 +/- 6.3 to 7.8 +/- 4.5 ms/mmHg (P < 0.001). Spontaneous BRS assessed by low frequency transfer function method decreased from 10.9 +/- 5.4 to 7.0 +/- 4.1 ms/mmHg and by high frequency transfer function method from 14.8 +/- 9.2 to 8.7 +/- 8.8 ms/mmHg, respectively (P < 0.05). CONCLUSIONS: The spontaneous BRS was decreased during ketamine induction of general anesthesia. These results suggest that anesthesia induction with ketamine impairs baroreflex control of heart rate, which may provoke hemodynamic instability.

Assessment of Cardiovascular Autonomic Function in Patients with Liver Cirrhosis Using Heart Rate Variability, Blood Pressure Variability and Baroreflex Sensitivity / 대한마취과학회지

BACKGROUND: Liver cirrhosis is associated with several hemodynamic abnormalities, including an impairment of autonomic nervous system reflexes, but very few have compared the disease severity with cardiovascular autonomic dysfunction assessed by spectral analysis of blood pressure and electrocardiogram. The aim of this study was to investigate the relationship between Child-Turcotte-Pugh (CTP) score and autonomic indices in patients with liver cirrhosis using the heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS). METHODS: Fifty patients scheduled for liver transplantation recipients under general anesthesia were enrolled in the study. Beat-to-beat blood pressure and RR interval were measured for five minutes before anesthesia induction. HRV and BPV were estimated by power spectral analysis of RR interval and systolic blood pressure. BRS was estimated by both the sequence method (Sequence BRS) and high frequency (HF) gain of transfer function analysis (HF BRS). RESULTS: Significant inverse correlations between CTP score and Sequence BRS (r = -0.61), HF BRS (r = -0.59), low frequency (LF) and HF power of HRV (r = -0.57, r = -0.46), LF power of BPV (r = -0.37) were found. However, no significant correlations were observed between CTP score and LF/HF ratio of HRV (r = -0.02) and HF power of BPV (r = 0.27). CONCLUSIONS: These results showed that autonomic dysfunction assessed by spectral analysis was associated with increasing severity of liver cirrhosis. Further study will be needed to clarify relationship between our findings and hemodynamic fluctuations during anesthesia for liver transplantation.

The Effect of Rilmenidine Pretreatment on the Cardiovascular Toxicity Caused by Intravenous Bupivacaine by Autonomic Nervous System Analysis in Anesthetized Cats / 대한마취과학회지

BACKGROUND: This study was designed to assess the effects of rilmenidine on the autonomic nervous system, and to evaluate whether it prevents bupivacaine-induced cardiovascular toxicity during intravenous bupivacaine infusion in anesthetized cats. METHODS: Thirty male cats were randomly divided into a control group (n = 15) and a rilmenidine group (n = 15). Following the injection of rilmenidine (10microgram/kg), systolic blood pressures (SBP) and R-R intervals (RRI) were recorded for 5 minutes. Then power spectral analyses of the SBP and RRI, and transfer function analysis were conducted to evaluate the autonomic nervous system. During the infusion of bupivacaine (0.5 mg/kg/min), blood pressures, heart rates, times to reach each events, and bupivacaine doses were measured at the first QRS modification, the first dysrhythmia, at 25% (HR25) and 50% reductions in baseline heart rate, and at 25% and 50% reductions in baseline mean arterial pressure and at final systole. RESULTS: The high frequency (HF) power of heart rate variability (HRV) was significantly elevated in the rilmenidine group versus the control group. Magnitude HF was significantly higher in the rilmenidine group than in the control group. The onset of dysrhythmia correlated significantly with the HFs of HRV and baroreflex sensitivity (BRS). Except for HR25, the rilmenidine group showed significantly higher bupivacaine doses and delayed event onsets versus the control group. CONCLUSIONS: We suggest that pretreatment with rilmenidine delays the onset of dysrhythmia by increasing vagal tone and BRS and by reducing cardiovascular toxicity when bupivacaine is infused continuously to isoflurane anesthetized cats.

Comparison of METHODS Assessing Spontaneous Baroreflex Sensitivity during Sevoflurane Anesthesia: Sequence versus Transfer Function Analysis / 대한마취과학회지

BACKGROUND: The arterial baroreflex is a key mechanism involved in blood pressure (BP) homeostasis and serves as a pressure buffer system against increase and decrease in BP. In contrast to awake patients, little has been known about correlations among METHODS assessing spontaneous baroreflex sensitivity (SBRS) during general anesthesia. The aim of present study was to compare SBRS obtained from sequence method and transfer function analysis (TFA), and examined their relationship to vagal cardiac function in patients during sevoflurane general anesthesia. METHODS: 20 patients were anesthetized with 1 MAC sevoflurane with 50% N2O and mechanically ventilated at 0.25 Hz. 5 min beat-to-beat BP and electrocardiogram were recorded to assess sequence BRS and TFA BRS from spontaneous RR interval and systolic BP fluctuation. We derived 4 proposed indices (Sequence BRS, low frequency (LF) BRS, high frequency (HF) BRS, and average BRS). RESULTS: The indices were correlated with each other significantly and the Bland-Altman method demonstrated that sequence BRS was in close agreement with each other except LF BRS. The indices were also correlated highly with HF heart rate variability representing vagal cardiac function. CONCLUSIONS: SBRS was related to vagal cardic function. Because of the correlations and agreements between these two METHODS, it may employ them except for LF BRS during sevoflurane general anesthesia.

Assessment of Autonomic Response before and after Total Spinal Anesthesia in Rats: Power Spectral Analysis / 대한마취과학회지

BACKGROUND: Total spinal anesthesia (TSA) after injections of local anesthetics into the intrathecal space during epidural anesthesia is not rare. TSA anesthetizes cranial nerves and peripheral nerves, causes specific circulatory disturbances related to autonomic imbalance. Spectral analysis of heart rate variability (HRV) and blood pressure variability (BPV) provide a dynamic assessment of sympathetic and parasympathetic tone. Cross-spectral analysis has been used to emphasize this dynamic baroreflex control of HR as a frequency-dependent phenomenon and allows an assessment of baroreflex function. To examine the effects of TSA on the autonomic nervous system, we used spectral and cross-spectral analytic METHODS. METHODS: We investigated 14 rats before and after TSA. Power spectral densities of blood pressure (BP) and heart rate (HR) were estimated by fast Fourier transform. To evaluate the effect of TSA on baroreflex function, the cross spectral gain, phase, and coherence between beat-to-beat BP and HR signals were calculated by using transfer function analysis. RESULTS: With the onset of TSA, BP and HR significantly decreased. TSA significantly decreased the low frequency (LF) and high frequency (HF) components of HRV and BPV. Baroreflex sensitivity (BRS) obtained from transfer function gain between these variables was significantly decreased. CONCLUSIONS: TSA reduces the LF and HF components of HRV and BPV. These suggest that TSA in rats decreases both parasympathetic and sympathetic drive. Moreover, the decrease in BRS suggests impairment of cardiac baroreflex buffering function during TSA.