Effects of nicardipine and diltiazem on fractal features of short-term heart rate variability—application of coarse graining spectral analysis

Purpose. This study was designed to investigate the effects of nicardipine and diltiazem on the fractal features of short-term heart rate variability (HRV), using coarse graining spectral analysis (CGSA). Methods. Eighteen healthy volunteers participated in this study; they were divided into two groups according to the drug administered. Five-minute electrocardiogram and arterial pressure recordings were made during stepwise infusions of either nicardipine (0.4, 0.8, 1.6, and 3.2 μg·kg⁻¹·min⁻¹) or diltiazem (2, 4, 8, and 16 μg·kg⁻¹·min⁻¹) under rate-controlled breathing at 0.25 Hz. CGSA broke down the total power of the time series into harmonic (low frequency [0.0–0.15 Hz; LF] and high frequency [0.15–0.5 Hz; HF]) and nonharmonic (fractal) components. Cardiac sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) activity indicators were evaluated as the ratios LF/HF and HF/TP (total spectral power), respectively. Fractal components were evaluated as %fractal and the spectral exponent β of 1/f^β. Results. Compared with control measurements, the maximum dose of nicardipine infusion caused a significant decrease in systolic arterial pressure, a significant increase in the mean heart rate, and a significant increase in plasma norepinephrine level, findings that were associated with significant increases in %fractal and β values (54.2 ± 13.3 vs 75.6 ± 9.8, and 0.86 ± 0.22 vs 1.32 ± 0.46, respectively; P < 0.05). PNS and SNS indicators showed decreased and increased values, respectively. Diltiazem caused a reduction in arterial pressure; however, no other parameters, including the nonharmonic components of HRV, were affected by this drug. Conclusions. These findings strongly suggest that nicardipine suppresses vagal cardiac neural outflow and activate the SNS, an action which, subsequently, causes changes in the fractal features of HRV. Although diltiazem reduces arterial pressure, it preserves the basic neural balance of the autonomic nervous system in regard to heart rate control. Received: April 16, 2001 / Accepted: October 9, 2001     

Effects of surgically induced weight loss by Roux-en-Y gastric bypass on cardiovascular autonomic nerve function

BackgroundObesity is associated with autonomic imbalance. With respect to cardiovascular autonomic dysfunction, this is characterized by reduced heart rate variability (HRV). Our objective was to determine the effect of surgically induced weight loss on cardiovascular autonomic nerve fiber function in subjects with severe obesity and examine whether an association with reduced insulin resistance exists. The setting was a hospital and private practice in the United States.MethodsA total of 32 morbidly obese patients (body mass index 51 ± 11 kg/m²) underwent laparoscopic Roux-en-Y gastric bypass. Measures of HRV (e.g., power spectral analysis, RR variation during deep breathing) were used to evaluate autonomic function before and 6 months after surgery. The homeostasis model assessment of insulin resistance index (HOMA-IR) was used to assess insulin resistance.ResultsAt 6 months after bariatric surgery, the patients had lost 58% excess body mass index with improvement in the HOMA-IR (3.0 ± 1.4 versus 1.1 ± .7; P < .001). Measures of RR variation during deep breathing and total spectral power, low frequency (LF) power (influenced by sympathetic and parasympathetic activity), and high frequency (HF) power (parasympathetic activity) increased with weight loss. The LF/HF ratio was lower (1.5 ± 1.5 versus .9 ± .7, P < .05) with a reduction in weight. Spectral analysis of HRV combined with spectral analysis of respiratory activity generated the respiration frequency area (RFA) and low frequency area. The RFA was increased, and the LFA/RFA ratio was reduced with weight loss. HOMA-IR and HRV did not correlate.ConclusionSurgically induced weight loss has a favorable effect on autonomic function, but it does not appear to be directly attributable to reduced insulin resistance.     

Heart Rate Variability and Cardio-respiratory Coupling During Sleep in Patients Prior to Bariatric Surgery

Obesity is associated with increased cardiac risk of morbidly and mortality and for the development and progression of obstructive sleep apnea (OSA). Severity of obesity negatively affects the heart rate variability (HRV) in patients with indication for bariatric surgery (BS). The purpose of this study is to determine if the severity of obesity alters the autonomic cardiac regulation and the cardio-respiratory coupling during sleep using spectral analysis of HRV and respiration variability signals (RS) in patients prior to BS. Twenty-nine consecutive preoperative BS and ten subjects (controls) underwent polysomnography. The spectral and cross-spectral parameters of the HRV and RS were computed during different sleep stages (SS). Spectral analysis of the HRV and RV indicated lower respiration regularity during sleep and a lower HRV in obese patients (OP) during all SS when compared with controls (p < 0.05). Severely (SO) and super-obese patients (SOP) presented lower values of low frequency/high frequency (LF/HF) ratio and LF power during REM sleep and higher HF power (p < 0.05), while morbidly obese (MO) patients presented lower LF/HF ratio and LF power in SS-S2 and higher HF power when compared to controls (p < 0.05). The cross-spectral parameters showed that SOP presented lower percentage of tachogram power coherent with respiration in SS-S3 when compared to controls (p < 0.05). Patients prior to BS presented altered HRV and RV in all SS. SO, MO, and SOP presented altered cardio-respiratory coupling during sleep, and these alterations are related with severity of obesity and OSA parameters.     

Effect of fentanyl on heart rate variability during mechanical ventilation

Purpose This study was performed to investigate the effect of fentanyl alone on heart rate variability (HRV) during mechanical ventilation using power spectral analysis. Arterial baroreceptor reflex was also tested with pharmacological manipulation to assess the contribution of vagal baroreceptor reflex modulation of HRV during fentanyl anesthesia. Method Ten patients participated in this study. Electrocardiograms and arterial pressure were recorded prior to and during fentanyl (10 μg·kg⁻¹) and vecuronium (0.2 mg·kg⁻¹) anesthesia, with respiratory rate and tidal volume controlled ventilation. R-R intervals were analyzed by fast Fourier transformation, and changes in low-frequency (LF) and high-frequency (HF) power were compared. Arterial baroreceptor reflex regulation was also tested with administration of nitroglycerin (250 μg) or phenylephrine (250 μg). Results HF power was significantly reduced during anesthesia from 3.20±2.93 to 0.46±0.48 ms²·Hz⁻¹·10³ (mean±SD,P<0.05). However, LF power did not change despite increases in plasma catecholamine concentrations. The response to phenylephrine was reduced during fentanyl anesthesia from 16.6±5.7 to 9.5±5.4 ms·mmHg⁻¹ (P<0.05), whereas the response to nitroglycerin was not affected. Conclusion Our data indicate that fentanyl modulates the respiratory frequency fluctuation of HRV. This is partly caused by the effects of fentanyl on arterial baroreflex sensitivity.     

Heart Rate Variability During Hemodialysis and Following Renal Transplantation

Previous studies have shown awareness of uremic dysfunction in end-stage renal disease (ESRD) patients. Dysautonomia in ESRD patients may be reversible after renal transplantation. We used a power spectral analysis (PSA) of heart rate variability (HRV) to assess alterations of autonomic activity in 14 controls and 14 nondiabetic hemodialysis ESRD patients who had undergone renal transplantation. Compared with matched control subjects, the power frequency determinations of low frequency (LF; 3.42 ln(ms²) vs 6.38 ln(ms²); P < .05 high frequency (HF; 2.29 ln(ms²) vs 5.27 ln(ms²); P < .05)), and total power (TP; 5.39 ln(ms²) vs 7.53 ln(ms²); P < .05) were significantly suppressed in ESRD patients undergoing hemodialysis. ESRD patients showed significantly improved HRV after renal transplantation. After renal transplantation, there was no significant difference in the TP (6.82 ln(ms²) vs 7.53 ln(ms²); P = .15) component between measurements in both patient subgroups. We further divided the ESRD patients into 2 groups based on their pretransplantation HRV, observing alterations in HRV after renal transplantation. Patients with significantly improved HRV were those with more suppressed HRV before transplantation (HF <3 In(ms²). Autonomic dysfunction in ESRD patients was not irreversible even if severe, and recovery was observed as early as 6 months after transplantation.     

Comparison of the effects of propofol and midazolam on the cardiovascular autonomic nervous system during combined spinal and epidural anesthesia

STUDY OBJECTIVE: To investigate the effect of propofol and midazolam on cardiac autonomic nervous system (CANS) activity during combined spinal-epidural anesthesia. DESIGN: Prospective, clinical study. SETTING: Operating room of a university hospital. PATIENTS: Forty ASA physical status I and II patients scheduled for knee surgery. INTERVENTION: Patients were randomized to receive sedation with either propofol or midazolam. MEASUREMENTS: Heart rate (HR), HR variability (HRV), systolic arterial pressure (SAP), and SAP variability (SAPV) were used for the analysis. These values were measured at the preanesthetic period, after intrathecal injection for spinal anesthesia, after sedation with propofol or midazolam, and just before the end of surgery with sedation. Cross-spectral analyses of the HR and SAP data were assessed to quantify the frequency-related coherence spectra and phase spectra. MAIN RESULTS: Spinal anesthesia itself had no effect on power spectral changes in both groups. After sedation, as for HRV, high-frequency (HF) power (HF, 0.15-0.40 Hz) did not change, whereas low-frequency (LF) power (LF, 0.04-0.15 Hz) and LF/HF, an indicator of CANS balance, significantly decreased with propofol. Further, coherence in cross-spectra presented depression in the LF band area after sedation with propofol. Before the end of surgery with sedation, LF and LF/HF in both HRV and SAPV were correlated with age in those with propofol; however, scarce relation was observed in those who received midazolam. CONCLUSIONS: Propofol was more potent than midazolam in causing CANS activity to be sympatholytic during combined spinal and epidural anesthesia and which was correlated with age only with propofol.     

Heart Rate Variability,Left Ventricular Functions,and Cardiac Autonomic Neuropathy in Patients Undergoing Chronic Hemodialysis

Objective.?Autonomic neuropathy and impairment of left ventricular functions (LVF) have been frequently encountered in chronic renal failure (CRF). The aim of the present study was to evaluate the relationship of cardiac autonomic modulation impairments, as assessed by means of heart rate variability (HRV), with clinical characteristics, and left ventricular function in the patients with CRF undergoing hemodialysis (HD). Methods.?Twenty control subjects (Group I) and 22 comparable by age and gender patients with CRF undergoing hemodialysis (Group II) were enrolled in the study. After routine clinical and biochemical evaluations, electrocardiography, and 2 Dimensional, M Mode echocardiography were performed in all participants. Frequency domain HRV analysis was studied by using Kardiosis System. The powers (P₁ and P₂) and the central frequencies (F₁ and F₂) of low and of high frequency spectral bands were recorded. Results.?End systolic (ESV) and end diastolic volumes (EDV) were significantly higher in Group II (59.3 ± 21.1 mL vs. 34.0 ± 14.3 mL and 131.5 ± 37.3 mL vs. 96.9 ± 18.9 mL, p<0.01, p<0.05, respectively) when compared to those of Group I. Ejection fraction (EF) and fractional shortening (FS) were significantly lower in Group II than in control subjects (52.3 ± 2.4% vs. 63.7 ± 10.1% and 0.29 ± 0.01 vs. 0.34 ± 0.07, p<0.001, p<0.05, respectively). P1 and P2 were decreased in Group II than in Group I (136.2 ± 173.9 m s² vs. 911.0 ± 685.5 and 96.5 ± 149.6 vs. 499.7 ± 679.5, p<0.001, p<0.01, respectively). Significant correlations were found between high frequency spectral power and dialysis duration (DD), ESV, EDV, EF, FS (r = 0.52 p<0.01, r = 0.68 p<0.001, r = 0.65 p<0.002, r = 0.66 p<0.02, and r = 0.69 p<0.01). Conclusion.?As a result, the dependence of cardiac autonomic neuropathy on the disease duration and degree of left ventricular function impairment was shown in the patients undergoing chronic hemodialysis.     

Analyse der Herzfrequenzvariabilität Grundlagen,Methodik und mögliche Anwendungen in der Anästhesie

Background and methods. Small, periodic fluctuations in heart rate are well known to physicians, the respiratory sinus arrhythmia (RSA) being the most easily detectable form of this heart rate variability (HRV). Since it is caused by changing activity of the autonomic nervous system (ANS) controlling heart rate, HRV is investigated to gain information on the functional states of the ANS. Recent developments have led to computer-aided processing of EKG signals based on time and frequency domain methods – the latter using power spectral analysis by fast Fourier or autoregressive algorithms – to exactly describe and quantify HRV. Three major regions in the frequency spectrum between 0.03 and 0.5?Hz (the suitable range for short-term recordings) have been established: (1) a region around the respiratory rate, usually between 0.2 and 0.35?Hz, called high frequency (HF), (2) a region around 0.1?Hz attributed to vasomotor activity feedback, called low (or mid-) frequency (LF), (3) a peak around 0.04–0.05?Hz correlated to thermoregulation, called very low (or low)frequency (VLF). Power spectral density of HRV is now commonly accetped as a measure of autonomic cardiovascular control activity. By studies on vagal or sympathetic blockade, the HF (or RSA) region has been attributed solely to vagal activity, while both parts of the ANS may contribute to the other two, with, however, the vagal part predominating the resting, healthy individuals. Clinical applications/anaesthesia. Thus, spectral analysis of HRV provides a measure for quantifying sympatho-vagal balance in its physiological range. Additionally, reduction of HRV along with cardiovascular disease, including hypertension, myocardial infarction, heart failure and sudden cardiac death, as well as with autonomic dysregulation, has been reported. Since is also a striking reduction produced by most anaesthetic agents, RSA and HRV are investigated as measures of anaesthetic depth. There are contradictory data on the influence of ventilation, medication, and co-existing disease on the spectrum, and thus validation of the method is still to be achieved. It has, however, been proven useful in some studies as a parameter for risk assessment of perioperative or post-infarction cardiovascular complications.     

Perioperative myocardial ischemia is associated with a prolonged cardiac vagal dysfunction after non–cardiac surgery

Background : Heart rate variability (HRV), a measure of cardiac autonomic balance seems to be linked to coronary artery disease (CAD). Impaired vagal input facilitates the generation of fatal arrhythmias and has a great impact on morbidity and mortality. The purpose of this study was to determine the relationship between perioperative HRV and the incidence of silent myocardial ischemia (SMI) and ventricular dysrhythmias in CAD–patients undergoing non–cardiac surgery.
Methods : 31 patients were studied by continuous Holter electrocardiography preoperatively and again on the evening before surgery until postoperative day 3. Three frequency and one time domain measures of HRV (TP, 0.01–1.00 Hz: total power of the amplitude spectral plot; LF, 0.04–0.15 Hz: low–frequency power; HF, 0.15–0.40 Hz: high–frequency power; MeanRR: mean of all coupling RR–intervals between normal beats) as well as ischemic events and ventricular couplets and runs were computed.
Results : Depending on the presence of ischemic episodes, each patient was assigned to either the no SMI–group (13 pts) or the SMI–group (18 pts). MeanRR, TP and LF significantly declined in both groups over time. The parasympathetically dominated index HF, however, only decreased in the SMI–group. Normalized HF power (HF/TP) even increased in the no SMI–group resulting in a postoperative decrease in LF/HF ratio. TP, LF, and HF inversely correlated with ischemia parameters whereas HF/ TP and HF/LF ratio correlated with the number of ventricular couplets. Incidence and severity of SMI significantly increased after surgery.
Conclusion : Postoperatively, a prolonged vagal withdrawal occurred in CAD–patients exhibiting perioperative SMI. Whether the increased incidence of SMI after surgery in conjunction with the observed parasympathetic derangement contributes to adverse cardiac outcome still has to be determined.     

静脉注射利多卡因对老年冠心病非心脏手术围插管期心率变异性的影响

目的：研究静脉注射利多卡因在全麻诱导气管插管期间对老年冠心病自主神经系统功能的影响。方法：选择90例择期腹部手术老年冠心病患者．随机分成利多卡因组（L组n=45）和安慰剂组（P组n=45）．分别于麻醉前（T0）,麻醉诱导后（T1）及气管插管后（T2）用心率变异功率谱分析（HRPSA）技术观察患者的心率变异性（HRV）改变。结果：麻醉诱导后．两组HRV总功率频段（TP）和其中低频段（LF）,高频段（HF）．LF／HF（低频／高频比）均显著降低（P〈0．05）．组间比较L组LF低于C组（P〈0．05）;气管插管后,两组LF、HF、LF／HF及TP均显著升高（P〈0．05）．组间比较L组LF与LF／HF升高程度显著低于P组（P〈0．05）,HF组间差异无统计意义。结论：静注利多卡因能明显抑制插管操作引起植物神经功能的干扰．有利于维护老年冠心病患围插管期心脏自主神经调节功能。     

Analysis of Oscillatory Components of Short-Term Heart Rate Variability in Hemodynamically Stable and Unstable Patients During Hemodialysis

Short period oscillatory components embedded in heart rate variability (HRV) were studied during hemodialysis induced hypovolemia in 15 hypotension-resistant (stable) and 15 hypotension-prone (unstable) patients. Hemodialysis was undertaken so that a similar blood volume reduction was induced in all patients (p > 0.05) without causing acute hypotension events. Autoregressive HRV power spectrums were calculated using an eigenanalysis-based approach. The frequencies of the main HRV rhythmic components were estimated through the Pisarenko harmonic decomposition. Percent changes during the hemodialysis in both heart rate and arterial pressure were similar in the stable and unstable groups (p > 0.05). The HRV spectral density showed markedly different power distributions. In the stable patients, power was mainly in the low frequency band (74 ± 7 nU in the low frequency [LF] band vs. 21 ± 6 nU in the high frequency [HF] band) whereas in stable patients, it was mainly in the high frequency band (39 ± 10 nU in the LF band vs. 47 ± 7 nU in the HF band). The frequency of the main oscillation was 0.1 ± 0.02 Hz in stable patients and 0.18 ± 0.04 Hz in unstable ones (p < 0.01). These HRV spectral parameters have a clear diagnostic value in discriminating between stable and unstable patients when their hemodynamic behaviors are similar.     

Effect of high-frequency jet ventilation on heart rate variability

We investigated the effects of high-frequency jet ventilation (HFJV) on heart rate variability in nine patients during fentanyl (10μg·kg⁻¹) anesthesia using power spectral density analysis. ECG and arterial pressure were recorded during intermittent positive pressure ventilation (IPPV) (tidal volume 8 ml·kg⁻¹, respiratory rate 0.25 Hz) and during HFJV [5 Hz, 2.5 kg·(cm²)⁻¹]. The R-R interval time series obtained were analyzed by the autoregressive method, and low-frequency (LF) (0.05–0.15 Hz) power and high-frequency (HF) (0.20–0.50 Hz) power from R-R interval spectra were used for statistical comparison. LF power did not change during IPPV and HFJV (108.8±41.6 ms² vs 105.8±22.4 ms², mean±SE). HF power was detected during IPPV (65.1±14.3 ms²); however, it was not detected during HFJV. Plasma levels of norepinephrine and epinephrine were significantly higher during HFJV than during IPPV. The mean R-R interval, arterial pressure, and arterial blood gas data did not differ between IPPV and HFJV. These data indicate that, during fentanyl anesthesia, HFJV influences mainly the respiratory frequency fluctuation of heart rate variability, and they suggest that alteration of breathing patterns caused by HFJV might be involved, as well as elevated sympathetic neural outflow to the heart.     

Ketamina frente a midazolam como adyuvante para el bloqueo peribulbar utilizando una única inyección inferonasal en los pacientes sometidos a vitrectomía: ensayo controlado aleatorizado

Introduction and objectivesThis study aimed to assess the safety and efficacy of midazolam and ketamine as adjuvants to the peribulbar block in vitreoretinal surgeries.Patients and methodsThis randomized controlled trial included 93 adult patients undergoing vitreoretinal surgeries performed with peribulbar anaesthesia. Patients were randomly allocated to 3 groups (31 participants each): control (standard anaesthetic mixture), midazolam (standard mixture + midazolam), and ketamine (standard mixture + ketamine). The primary outcomes were onset of globe akinesia and duration of analgesia. Secondary outcomes were duration of motor blockade, onset of corneal anaesthesia and lid akinesia, and changes in vital data (blood pressure, oxygen saturation, and pulse rate).ResultsThe ketamine group vs. the control and midazolam groups showed the most rapid onset of lid and globe akinesia (p < 0.001) and corneal anaesthesia (0.7 ± 0.2 vs. 1.5 ± 0.5 and 1.2 ± 0.4, respectively; p < 0.001) and the longest duration of both analgesia (3.7 ± 0.6 vs. 2.3 ± 0.4 and 3.1 ± 0.6, respectively; p < 0.001) and akinesia (3.8 ± 0.5 vs. 3.0 ± 0.4, and 3.7 ± 0.5, respectively; p < 0.001). The midazolam group showed better outcomes than controls, but the drug was less effective than ketamine. There were no significant differences in vital data among groups (p > 0.05).ConclusionsKetamine is an effective adjuvant for peribulbar blockade. It enhances both motor and sensory blockade by hastening onset and prolonging duration. These effects are desirable in lengthier ophthalmic procedures such as vitreoretinal surgeries. The effects of ketamine were superior to those of midazolam.     

Periodic cardiovascular and ventilatory activity during midazolam sedation

We have examined the effects of sedation with midazolam 0.1 mg kg-1 and reversal with flumazenil 0.5 mg on beat-to-beat heart rate (HR) variability (HRV), systolic arterial pressure (SAP), finger photoplethysmograph amplitude (PLA) and impedence pneumography in eight volunteers. With the onset of sedation there was a small decrease in SAP and increase in HR (ns). Spectral analysis of the HR time series showed reductions in the proportion of power in the high (> 0.15 Hz) frequency "ventilatory" band consistent with midazolam causing vagolysis. During sedation, low frequency (< 0.05 Hz) oscillations of PLA, HR, SAP and ventilation were observed. These were thought to be secondary to activity of coupled cardiorespiratory neurones within the brain stem and the ventilatory periodicity appeared similar to that observed during the early stages of sleep. The diminished high frequency and increased low frequency oscillations induced by midazolam sedation were reversed by administration of flumazenil.      

Effects of nitroglycerin on fractal features of short-term heart rate and blood pressure variability

Purpose. We investigated the effect of nitroglycerin(NTG) on fractal features of short-term heart rate variability (HRV) and blood pressure variability (BPV) using coarse-graining spectral analysis (CGSA). Method. Nine healthy young volunteers participated in this study. Five-minute recordings of electrocardiogram and blood pressure estimated by photoplethysmograph were made during stepwise NTG infusions of 0.2, 0.4, 0.8, and 1.6 μg·kg⁻¹·min⁻¹ under rate-controlled breathing at 0.25 Hz. CGSA broke down the total power of the time series into harmonic (low- and high-frequency) and nonharmonic (β of 1/f^β and %fractal) components. Results. A statistically significant difference from the control period was observed during the maximum dose of NTG infusion, with decrease in mean blood pressure, shortening of mean R-R interval, and increase in plasma norepinephrine and epinephrine. The β in HRV increased significantly (0.89 ± 0.06 vs. 1.27 ± 0.13, P < 0.05). However, %fractal was not affected (47.9 ± 6.7 vs. 50.1 ± 4.0). Indicators of parasympathetic and sympathetic nervous system activity showed reduced and increased values, respectively. No change in BPV was observed for any measurement. Conclusion. The data suggest that NTG significantly affected fractal features, as well as harmonic components, of short-term HRV. NTG had no effect on BPV, suggesting a different mechanism for genesis of 1/f^β fluctuation in BPV and HRV. Received for publication on March 31, 1998; accepted on October 14, 1998     

盐酸右美托咪定对老年冠心患者全麻气管插管期心率变异性的影响

目的：研究盐酸右美托咪定（dexmedetomidine．Dex）在全麻诱导气管插管期间对老年冠心病患者自主神经系统功能的影响。方法：98例择期腹部手术老年冠心病患者．随机分成盐酸右美托咪定（D组n=49,诱导前给予负荷剂量右美托咪定0．7ug,／0g．注射泵缓慢静脉注射．输注时间超过10rain．维持剂量以0．4ug/（kg·h）持续静脉注射）和安慰剂组（P组n=49．诱导前静脉注射等容量氯化钠溶液）．分别于麻醉前（To）．麻醉诱导后（T1）及气管插管后（T2）用心率变异功率谱分析（heart rate Power spectrum analysis．HRPSA）技术观察患者的心率变异性（heart rate variability．HRV）改变。结果：麻醉诱导后．两组HRV总功率频段（TP）和其中低频段（LF）、高频段（HF）．LF／HF（低频／高频比）均显著降低（P〈O．05）．组问比较D组LF低于P组（P〈O．05）;气管插管后,两组LF、HF及TP均显著升高（P〈O．05）,而D组的LF／HF较麻醉前（T0）差异无统计意义,P组的LF／HF较麻醉前（T0）显著升高（P〈O．05）：组间比较D组LF、TP升高程度显著低于P组（P〈0．05）．HF组间差异无统计学意义。结论：盐酸右美托咪定能明显抑制插管操作引起的对植物神经功能的干扰,有利于维护老年冠心病患者围插管期心脏的自主神经调节功能。     

The Study of Spectral Analysis of Heart Rate Variability in Different Blood Pressure Types in Euvolemic Peritoneal Dialysis Patients

Background: Heart rate variability (HRV) is an useful noninvasive tool to assess autonomic nervous system (ANS) function and may provide an insight into the understanding of the role of ANS in the pathogenesis of blood pressure (BP) abnormality in euvolemic continuous ambulatory peritoneal dialysis (CAPD) patients. Methods: In this cross-sectional study, 62 CAPD patients with normal hydration values (assessed by a bioimpedance spectroscopy device) were enrolled from our peritoneal dialysis (PD) unit. Patients were divided into three groups according to their BP: normotension (NT), hypertension (HT), and hypotension (HyT). Spectral analysis of HRV was measured by examination of the average heart rate using standard electrocardiogram in 5 min. Results: The HyT group had the lowest serum urea nitrogen among the three groups (all p < 0.05), and a lower serum potassium and albumin as compared with the NT group (p < 0.05). The HyT group also had the highest total power (TP) and highest frequency power (HF) among the three groups (all p < 0.05), and a lower normalized low frequency power (LF), LF/HF ratio, and a higher normalized HF as compared with the HT group (all p < 0.05). Conclusion: Our study suggested that autonomic insufficiency was present in euvolemic PD patients, and hypotensives had a relatively higher parasympathetic activity and blunted sympathetic activity.     

Heart Rate Variability Predicts Severe Hypotension after Spinal Anesthesia for Elective Cesarean Delivery

Background: Hypotension due to vasodilation during subarachnoid block (SAB) for elective cesarean delivery may be harmful. Heart rate variability (HRV), reflecting autonomic control, may identify patients at risk of hypotension.

Methods: Retrospectively, HRV was analyzed in 41 patients who were classified into one of three groups depending on the decrease in systolic blood pressure (SBP): mild (SBP > 100 mmHg), moderate (100 > SBP > 80 mmHg), or severe (SBP < 80 mmHg). Prospectively, HRV and hemodynamic data of 19 patients were studied. Relative low frequency (LF), relative high frequency (HF), and LF/HF ratio were analyzed.

Results: Retrospective analysis of HRV showed a significantly higher sympathetic and lower parasympathetic drive in the groups with moderate and severe compared with mild hypotension before SAB (median, 25th/75th percentiles): LF/HF: mild: 1.2 (0.9/1.8), moderate: 2.8 (1.8/4.6), P < 0.05 versus mild; severe: 2.7 (2.0/3.5), P < 0.05 versus mild. Results were confirmed by findings of LF and HF. Prospectively, patients were grouped according to LF/HF before SAB: low-LF/HF: 1.5 (1.1/2.0) versus high-LF/HF: 4.0 (2.8/4.7), P < 0.05; low-LF: 58 +/- 9% versus high-LF: 75 +/- 10%, P < 0.05; low-HF: 41 +/- 10% versus high-HF: 25 +/- 10%, P < 0.05. High-risk patients had a significantly lower SBP after SAB (76 +/- 21 vs. 111 +/- 12 mmHg; P < 0.05).     

Low-dose midazolam antagonizes cerebral metabolic stimulation by ketamine in the pig

In order to test the hypothesis that low-dose midazolam reduces excitatory cerebral symptoms by attenuating ketamine-induced increases in the cerebral metabolic rate for oxygen (CMRo₂), we compared the cerebral effects of a combination of an anaesthetic dose of ketamine hydrochloride (10.0 mg-kg¹ i.v.) and a subanaesthetic dose of midazolam maleate (0.25 mg- kg^-1 i.v., n = 6; or 0.10 mg-kg^-1 i.v., n = 6) with results recently obtained with ketamine (10.0 mg-kg^-1 i.v.) in normoventilated pigs anaesthetized with fentanyl, nitrous oxide and pancuronium. Cerebral blood flow (CBF) was measured with the intra-arterial ¹³³Xe clearance technique, and CMRo₂ was calculated from CBF and the cerebral arteriovenous oxygen content difference (Cavo₂). The CMRo₂ did not increase significantly. In contrast, the maximal increase in cerebral Cavo₂ (by 56–59% at 10 min; P < 0.01) was similar to that induced by ketamine, since CBF was more depressed (by 35–45% at 1 min: P < 0.001) by ketamine-midazolam than by ketamine only. Midazolam was found to increase CVR (P < 0.01) and further depress CBF (P < 0.01), and to antagonize the ketamineinduced increase in CMRo₂ (P < 0.05). Ketamine-induced effects on mean arterial pressure (MAP) and spectral electroencephalographic (EEG) voltage were not significantly altered by midazolam. The pharmacokinetics of ketamine, as measured during an 80-min period, were not affected by the concomitant administration of midazolam. We propose that a ketamine-midazolam combination comprising a low-dose fraction (1/ 100-1/40) of midazolam is superior to ketamine alone for anaesthetic use.     

Antinociceptive effects of epidural and intravenous ketamine to somatic and visceral stimuli in rats

Purpose

To evaluate the antinociceptive effect of epidural and intravenous ketamine on somatic and visceral stimuli and to address the emergency reaction.

Methods

Rats were randomly allocated into nine groups (n = 6); five groups with chronically implanted epidural catheters received saline or 0.5, 1, 2 and 4 mg · kg^?1 ketamine epidurally, four groups received saline, or 1, 5 and 10 mg · kg^?1 ketamine iv. To assess somatic and visceral antinociceptive effects, tail flick (TF) test and colorectal distension (CD) test were carried out, respectively. Emergence reactions were graded. Maximal possible effects (% MPE) were calculated.

Results

Epidural ketamine increased % MPE in both tests in a dose-dependent fashion for 30 min (vs saline group, P < 0.05). Epidural ketamine 0.5 mg · kg^?1 produced an increase in % MPE in the CD test (P < 0.05) but failed in the TF test. Intravenous ketamine, 10 mg · kg^?1, produced 100 ± 0 (mean ± SE) % MPE in the CD test but 36 ± 15 % MPE in the TF test. Dose response curves indicated greater visceral antinociception than somatic. All rats showed emergence reactions following intravenous ketamine 10 and 5 mg · kg^?1.

Conclusion

Both epidural and intravenous ketamine produce greater antinociceptive effects to visceral than to somatic stimulation, and that epidural ketamine has a low incidence of emergence reactions.