Differential effects of ketamine and midazolam on heart rate variability

The Use of Midazolam as an Antiseizure Medication in Neonatal Seizures: Single Center Experience and Literature Review

BACKGROUND

Existing therapeutic alternatives for neonatal crises have expanded in recent decades, but no consensus has been reached on protocols based on neonatal seizures. In particular, little is known about the use of midazolam in newborns.

AIM

The aim of our study is to evaluate the response to midazolam, the appearance of side effects, and their impact on therapeutic decisions.

METHODS

This is a STROBE-conformed retrospective observational study of 10 patients with neonatal seizures unresponsive to common antiseizure drugs, admitted to San Marco University Hospital's neonatal intensive care (Catania, Italy) from September 2015 to October 2022. In our database search, 36 newborns were treated with midazolam, but only ten children met the selection criteria for this study.

RESULTS

Response was assessed both clinically and electrographic. Only 4 patients at the end of the treatment showed a complete electroclinical response; they were full-term infants with a postnatal age greater than 7 days. Non-responders and partial responders are all premature (4/10) or full-term neonates who started therapy in the first days of life (< 7th day) (2/10).

CONCLUSION

Neonatal seizures in preterm show a lower response rate to midazolam than seizures in full-term infants, with poorer prognosis. Liver and renal function and central nervous system development are incomplete in premature infants and the first days of life. In this study, we show that midazolam, a short-acting benzodiazepine, appears to be most effective in full-term infants and after 7 days of life.

Time of day influences stress hormone response to ketamine

Over 50% of depressed patients show hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. Conventional therapy takes weeks to months to improve symptoms. Ketamine has rapid onset antidepressant effects. Yet its action on HPA axis activity is poorly understood. Here, we measured the corticosterone (CORT) response to ketamine administered at different times of day in the Wistar-Kyoto (WKY) rat. In male rats, blood was collected every 10 min for 28 h using an automated blood sampling system. Ketamine (5/10/25 mg · kg) was infused through a subcutaneous cannula at two time points-during the active and inactive period. CORT levels in blood were measured in response to ketamine using a radioimmunoassay. WKY rats displayed robust circadian secretion of corticosterone and was not overly different to Sprague Dawley rats. Ketamine (all doses) significantly increased CORT response at both infusion times. However, a dose dependent effect and marked increase over baseline was observed when ketamine was administered during the inactive phase. Ketamine has a robust and rapid effect on HPA axis function. The timing of ketamine injection may prove crucial for glucocorticoid-mediated action in depression.

Safety and feasibility of continuous ketamine infusion for analgosedation in medical and cardiac ICU patients who received mechanical ventilation support: A retrospective cohort study

Purpose

To assess the effect of continuous ketamine administration in patients admitted to medical and cardiac intensive care units (ICUs) and received mechanical ventilation support.

Methods

We conducted a retrospective cohort study between March 2012 and June 2020 at an academy-affiliated tertiary hospital. Adult patients who received mechanical ventilation support for over 24 h and continuous ketamine infusion for at least 8 h were included. The primary outcome was immediate hemodynamic safety after continuous ketamine infusion. The secondary outcomes included immediate delirium, pain, and use of sedation.

Results

Of all 12,534 medical and cardiac ICU patients, 564 were eligible for the analysis. Ketamine was used for 33.3 (19.0–67.5) h and the median continuous infusion dose was 0.11 (0.06–0.23) mcg/kg/h. Of all patients, 469 (83.2%) received continuous ketamine infusion concomitant with analgosedation. Blood pressure and vasopressor inotropic scores did not change after continuous ketamine infusion. Heart rate decreased significantly from 106.9 (91.4–120.9) at 8 h before ketamine initiation to 99.8% (83.9–114.4) at 24 h after ketamine initiation. In addition, the respiratory rate decreased from 21.7 (18.6–25.4) at 8 h before ketamine initiation to 20.1 (17.0–23.0) at 24 h after ketamine initiation. Overall opioid usage was significantly reduced: 3.0 (0.0–6.0) mcg/kg/h as fentanyl equivalent dose at 8 h before ketamine initiation to 1.0 (0.0–4.1) mcg/kg/h as fentanyl equivalent dose at 24 h post-ketamine initiation. However, the use of sedatives and antipsychotic medications did not decrease. In addition, ketamine did not increase the incidence of delirium within 24 h after ketamine infusion.

Conclusion

Ketamine may be a safe and feasible analgesic for medical and cardiac ICU patients who received mechanical ventilation support as an opioid-sparing agent without adverse hemodynamic effects.

Parasympathetic Tone Changes in Anesthetized Horses after Surgical Stimulation, and Morphine, Ketamine, and Dobutamine Administration

Simple Summary

A parasympathetic tone activity (PTA) monitor has been developed similar to the analgesia nociception index (ANI) used in human medicine to evaluate the changes in the autonomic nervous system based on heart rate variability. The autonomic nervous system acts unconsciously and regulates body functions (autonomic response). Examples of autonomic response are decreases of heart rate or/and blood pressure due to an increase of parasympathetic tone activity. It is important to know how stimuli and medication may affect the autonomic nervous system since they can modify heart rate and blood pressure. This study attempts to find how a surgical nociceptive stimulus, along with the administration of medication frequently used in horses, can affect mean parasympathetic tone activity (PTAm) (one of the values of the PTA monitor), heart rate and blood pressure in clinically anesthetized horses. Values of the PTAm, heart rate, and blood pressure were registered before and after surgical incision and after the administration of morphine, ketamine, and dobutamine at defined time points. No changes were found after the incision or the administration of morphine and dobutamine. It seems that only ketamine affects the autonomic nervous system by decreasing PTAm.

Abstract

Autonomic nervous system (ANS) activity can modify cardiovascular parameters in response to nociceptive stimuli or drugs in anesthetized animals. The aim of this study was to determine if a surgical nociceptive stimulus and morphine, ketamine, and dobutamine administration would modify ANS activity observed as a change in the mean parasympathetic tone activity (PTAm) in anesthetized horses. In 20 anesthetized horses, heart rate (HR), mean arterial pressure (MAP), and PTAm were monitored before and 1, 3, and 5 min after surgical incision, and before and 10 min after the administration of morphine (0.2 mg/kg IV). If nystagmus or spontaneous ventilation was observed, ketamine (0.5 mg/kg IV) was given, and the three variables were registered before and 3 and 5 min afterward. If MAP reached ≤62 mmHg, a dobutamine infusion was administered, and the three variables were recorded before and 5 min after starting/increasing the infusion (0.25 μg/kg/min IV every 5 min). The three variables were registered before and 1, 3, and 5 min after a PTAm decrease of ≥20%, HR increase of ≥10%, or MAP increase of ≥20%. The PTAm decreased 3 min after the administration of ketamine and 1 min after a PTA event. The surgical incision, dobutamine, and morphine did not modify PTAm. The absence of changes in ANS activity after the nociceptive stimulus and lack of correlation between PTAm and HR or MAP suggest that PTAm is a poor indicator of sympathetic activation under the study conditions. Ketamine seems to affect ANS activity by decreasing PTAm.

Twenty-Four-Hour Heart Rate Is a Trait but Not State Marker for Depression in a Pilot Randomized Controlled Trial With a Single Infusion of Ketamine

Background: Abnormalities of heart rate (HR) and its variability are characteristic of major depressive disorder (MDD). However, circadian rhythm is rarely taken into account when statistically exploring state or trait markers for depression. Methods: A 4-day electrocardiogram was recorded for 16 treatment-resistant patients with MDD and 16 age- and sex-matched controls before, and for the patient group only, after a single treatment with the rapid-acting antidepressant ketamine or placebo (clinical trial registration available on https://www.clinicaltrialsregister.eu/ with EUDRACT number 2016-001715-21). Circadian rhythm differences of HR and the root mean square of successive differences (RMSSD) were compared between groups and were explored for classification purposes. Baseline HR/RMSSD were tested as predictors for treatment response, and physiological measures were assessed as state markers. Results: Patients showed higher HR and lower RMSSD alongside marked reductions in HR amplitude and RMSSD variation throughout the day. Excellent classification accuracy was achieved using HR during the night, particularly between 2 and 3 a.m. (90.6%). A positive association between baseline HR and treatment response (r = 0.55, p = 0.046) pointed toward better treatment outcome in patients with higher HR. Heart rate also decreased significantly following treatment but was not associated with improved mood after a single infusion of ketamine. Limitations: Our study had a limited sample size, and patients were treated with concomitant antidepressant medication. Conclusion: Patients with depression show a markedly reduced amplitude for HR and dysregulated RMSSD fluctuation. Higher HR and lower RMSSD in depression remain intact throughout a 24-h day, with the highest classification accuracy during the night. Baseline HR levels show potential for treatment response prediction but did not show potential as state markers in this study. Clinical trial registration: EUDRACT number 2016-001715-21.

Combination of syringaresinol-di-O-β-D-glucoside and chlorogenic acid shows behavioral pharmacological anxiolytic activity and activation of hippocampal BDNF-TrkB signaling

Mental stress, such as anxiety and conflict, causes physiological changes such as dysregulation of autonomic nervous activity, depression, and gastric ulcers. It also induces glucocorticoid production and changes in hippocampal brain-derived neurotrophic factor (BDNF) levels. We previously reported that Acanthopanax senticosus HARMS (ASH) exhibited anxiolytic activity. Thus, we attempted to identify the anxiolytic constituents of ASH and investigated its influence on hippocampal BDNF protein expression in male Sprague Dawley rats administered chlorogenic acid (CHA), ( +)-syringaresinol-di-O-β-D-glucoside (SYG), or a mixture of both (Mix) for 1 week using the open field test (OFT) and improved elevated beam walking (IEBW) test. As with ASH and the benzodiazepine anxiolytic cloxazolam (CLO), Mix treatment significantly increased locomotor activity in the OFT. CHA and Mix increased the time spent in the open arm in the IEBW test. SYG and Mix treatment inhibited the significant increase in normalized low-frequency power, indicative of sympathetic nervous activity, and significant decrease in normalized high-frequency power, indicative of parasympathetic nervous activity, as observed in the IEBW test. SYG and Mix treatment significantly increased hippocampal BDNF protein expression. The combination of CHA and SYG possibly induces anxiolytic behavior and modulates autonomic regulation, activates hippocampal BDNF signaling as with ASH.

The association between various characteristics of hypnotics and cardiac autonomic control in community-dwelling older adults: the Yilan Study, Taiwan

BACKGROUND

Alteration of cardiac autonomic function may underlie the link between hypnotics use and the risk for cardiovascular morbidity and mortality. This study aimed to examine the relationship between the various characteristics of benzodiazepine receptor agonists (BzRAs) and heart rate variability (HRV).

METHODS

A community-based survey using the cohort from the Yilan Study, Taiwan was conducted. Older adults aged 65 and older were randomly selected to participate from August 2013 to November 2016. Cardiac autonomic function was evaluated using HRV, and the lowest quartiles of HRV parameters were defined as unhealthy. Those who used BzRAs as a sleep aid were defined as BzRA hypnotic users. The characteristics of BzRA use were further detailed and included the half-life, drug compound, frequency of use, and cumulative daily equivalent dosage.

RESULTS

Of all participants, 379 (14.5%) were BzRA hypnotic users. After controlling for covariates, BzRA hypnotic users had a higher risk for unhealthier HRV than non-users. Among all BzRA hypnotic users, those who only used benzodiazepines (BZDs), used short half-life BzRAs, and used the middle tertile of daily cumulative BZD equivalent had a higher risk for poor total power (odds ratio [OR]: 2.11, 95% confidence interval [CI]: 1.07-4.16), high frequency (OR: 3.43, 95% CI: 1.07-10.97), and high frequency (OR: 2.94, 95% CI: 1.35-6.42), respectively, than their counterparts.

CONCLUSIONS

BzRA hypnotics are linked with poor cardiac autonomic function. Various characteristics of BzRA hypnotics showed an independent pattern of association with cardiac autonomic function.

Effects of continuous ketamine infusion on hemodynamics and mortality in critically ill children

We investigated the hemodynamic and mortality effects of continuous ketamine infusion in critically ill pediatric patients. We conducted a retrospective cohort study in a tertiary pediatric intensive care unit (PICU). Patients who used continuous sedative from 2015 to 2017 for 24 hours or more were included. We compared blood pressure, heart and respiratory rates, vasogenic medications, and sedation and pain scores for 12 hours before and after initiation of continuous ketamine. The mortality rates for continuous ketamine and Non-ketamine groups were compared by multivariate logistic regression. A total of 240 patients used continuous sedation, and 82 used continuous ketamine. The median infusion rate of ketamine was 8.1 mcg/kg/min, and the median duration was 6 days. Heart rates (138 vs. 135 beat/minute, P = .033) and respiratory rates (31 vs. 25 respiration/minute, P = .001) decreased, but blood pressure (99.9 vs. 101.1 mm Hg, P = .124) and vasogenic medications did not change after ketamine infusion. Continuous ketamine was not a significant risk factor for mortality (hazard ratio 1.352, confidence interval 0.458–3.996). Continous ketamine could be used in PICU without hemodynamic instability. Further studies in randomized controlled design about the effects of continuous ketamine infusion on hemodynamic changes, sedation, and mortality are required.

Ketamine effects on default mode network activity and vigilance: A randomized, placebo-controlled crossover simultaneous fMRI/EEG study

In resting‐state functional connectivity experiments, a steady state (of consciousness) is commonly supposed. However, recent research has shown that the resting state is a rather dynamic than a steady state. In particular, changes of vigilance appear to play a prominent role. Accordingly, it is critical to assess the state of vigilance when conducting pharmacodynamic studies with resting‐state functional magnetic resonance imaging (fMRI) using drugs that are known to affect vigilance such as (subanesthetic) ketamine. In this study, we sought to clarify whether the previously described ketamine‐induced prefrontal decrease of functional connectivity is related to diminished vigilance as assessed by electroencephalography (EEG). We conducted a randomized, double‐blind, placebo‐controlled crossover study with subanesthetic S‐Ketamine in N = 24 healthy, young subjects by simultaneous acquisition of resting‐state fMRI and EEG data. We conducted seed‐based default mode network functional connectivity and EEG power spectrum analyses. After ketamine administration, decreased functional connectivity was found in medial prefrontal cortex whereas increased connectivities were observed in intraparietal cortices. In EEG, a shift of energy to slow (delta, theta) and fast (gamma) wave frequencies was seen in the ketamine condition. Frontal connectivity is negatively related to EEG gamma and theta activity while a positive relationship is found for parietal connectivity and EEG delta power. Our results suggest a direct relationship between ketamine‐induced functional connectivity changes and the concomitant decrease of vigilance in EEG. The observed functional changes after ketamine administration may serve as surrogate end points and provide a neurophysiological framework, for example, for the antidepressant action of ketamine (trial name: 29JN1556, EudraCT Number: 2009‐012399‐28).

Heart and soul: heart rate variability and major depression

There is a bidirectional relationship between affective disorders and cardiovascular abnormalities, often described as a downward spiral, whereas major depressive disorders (MDD, and anxiety disorders) significantly increase the risk of developing cardiovascular diseases (CVD); CVD are also associated with increased risk of developing MDD (and anxiety disorders). Moreover, the prognosis and progression of CVD is significantly worsened in the presence of MDD. Heart rate variability (HRV) has often been suggested as a potential mediator in this comorbidity. In this review, we discuss HRV alterations in MDD. However, we mainly focus on the direct relationship between HRV alterations and psychiatric symptoms, rather than its relationship with CVD, as this has been reviewed elsewhere. After a general introduction to HRV and how it can be measured, we review how HRV is altered in MDD. We subsequently describe how antidepressant drugs affect HRV, showing that some classes (such as tricyclics) generally worsen HRV, whereas others (most notably selective serotonin reuptake inhibitors) have a more positive influence. We also review the effects of several other treatments, with a special focus on vagal nerve stimulation, finishing with some further considerations and recommendation for further research, both in humans and animals.

Relation of Various Parameters Used to Estimate Cardiac Vagal Activity and Validity of pNN50 in Anesthetized Humans

Objectives Analysis of heart rate variability (HRV) has been used as a measure of cardiac autonomic function. According to the pNN50 statistic, the percentage of differences between successive normal RR intervals (RRI) that exceed 50 ms, has been known to reflect cardiac vagal modulation. Relatively little is known about the validity of pNN50 during general anesthesia (GA). Therefore, we evaluated the correlation of pNN50 with other variables such as HF, RMSSD, SD1 of HRV reflecting the vagal tone, and examined the validity of pNN50 in anesthetized patients. Methods: We assessed changes in RRI, pNN50, root mean square of successive differences of RRI (RMSSD), high frequency (HF) and standard deviation 1 (SD1) of Poincaré plots after GA using sevoflurane anesthesia. We also calculated the probability distributions for the family of pNNx statistics (x: 2-50 ms). Results All HRV variables were significantly decreased during GA. HF power was not correlated with pNN50 during GA (r = 0.096, P = 0.392). Less than pNN47 was shown to have a correlation with other variables. Conclusions These data suggest that pNN50 can not reflect the level of vagal tone during GA.

Effects of vagotomy on cardiovascular and heart rate variability alterations following chronic normobaric hypoxia in adult rabbits

BACKGROUND

chronic hypoxia increases basal ventilation and pulmonary vascular resistance, with variable changes in arterial blood pressure and heart rate, but it's impact on heart rate variability and autonomic regulation have been less well examined. We studied changes in arterial blood pressure, heart rate and heart rate variability (HRV) in rabbits subjected to chronic normobaric hypoxia (CNH; PB ~ 719 mmHg; F_IO₂ ~ 9.2%) for 14 days and assess the effect of autonomic control by acute bilateral vagal denervation.

RESULTS

exposure to CNH stalled animal weight gain and increased the hematocrit, without affecting heart rate or arterial blood pressure. Nevertheless, Poincaré plots of the electrocardiographic R-R intervals showed a reduced distribution parallel to the line of identity, which interpreted as reduced long-term HRV. In the frequency domain, CNH reduced the very-low- (< 0.2 Hz) and high-frequency components (> 0.8 Hz) of the R-R spectrograms and produced a prominent component in the low-frequency component (0.2-0.5 Hz) of the power spectrum. In control and CNH exposed rabbits, bilateral vagotomy had no apparent effect on the short- and long-term HRV in the Poincaré plots. However, bilateral vagotomy differentially affected higher-frequency components (> 0.8 Hz); reducing it in control animals without modifying it in CNH-exposed rabbits.

CONCLUSIONS

These results suggest that CNH exposure shifts the autonomic balance of heart rate towards a sympathetic predominance without modifying resting heart rate or arterial blood pressure.

Autonomic cardiac regulation after general anesthesia in children

BACKGROUND

General anesthesia dramatically decreases the activity of the autonomic nervous system. Most of the hypnotic agents used to induce anesthesia inhibit sympathetic cardiovascular regulation and baroreflex control in a dose-dependent manner, lowering cardiac adaptability during the operation. The consequence of this effect in children during and after surgery has never been studied to date.

AIM

The aim of this study was to follow the variations in autonomic cardiac indices in children younger than 8 years old after general anesthesia (6-24 hours) in programmed surgery.

METHOD

A prospective descriptive monocentric study of 44 children under 8 years old who underwent scheduled surgery at our hospital center (Saint-Étienne University Hospital, France) was performed between June 1, 2016 and November 1, 2016. Heart rate variability was monitored for 24 hours using Holter-ECG devices and the resulting data were interpreted using linear and nonlinear analyses.

RESULTS

Compared to baseline thresholds before surgery, all heart rate variability indices decreased dramatically during general anesthesia. After awakening, a slight reduction in sympathetic activity persisted 6 hours after surgery, but all measurements of sympathetic and parasympathetic activity had returned to baseline thresholds 12 hours after the operation. Twenty-four hours after surgery, some parameters had increased above the corresponding baseline levels.

CONCLUSION

Autonomic nervous function normalizes rapidly (within 12 hours) in prepubertal children. This study indicates that general anesthesia does not seem to increase the long-term risk of autonomic dysfunction in these patients.

Effects of Premedication on Heart Rate Variability at Induction of Anaesthesia: Comparison between Midazolam and Hydroxyzine

Objective

The present study was performed to compare the effects of midazolam premedication, which is useful for its anti-anxiety and amnesic effects, with antihistamine hydroxyzine on cardiac sympathetic and parasympathetic activities using heart rate variability (HRV) at induction of anaesthesia.

Methods

Eighty patients aged 40-60 years, with an American Society of Anaesthesiologists (ASA) physical status of I or II and undergoing general anaesthesia for neck and body surface surgery were randomised equally into midazolam and hydroxyzine groups. As a premedication, midazolam 0.06 mg kg^-1 with atropine 0.5 mg (midazolam group) or hydroxyzine 1 mg kg^-1 with atropine 0.5 mg (hydroxyzine group) were intramuscularly administered 15 min and 30 min before anaesthesia induction, respectively. Anaesthesia was induced with midazolam 0.1 mg kg^-1 and thiopental 3 mg kg^-1. Oro-tracheal intubation was facilitated with vecuronium 0.15 mg kg^-1. Blood pressure, heart rate and HRV were measured at predetermined time points for 10 min after intubation.

Results

Systolic blood pressure and heart rate significantly increased after intubation in both groups and the increase was greater in the hydroxyzine group. The high frequency (HF) component decreased significantly in both groups, and no difference was found between the two groups. The low frequency component/HF ratio significantly increased in the hydroxyzine group but did not change in the midazolam group.

Conclusion

Midazolam but not hydroxyzine premedication inhibited sympathetic activation at induction of anaesthesia.

Heart rate variability: implications for perioperative anesthesia care

PURPOSE OF REVIEW

Heart rate variability (HRV) is a measure of the balance between both the parasympathetic and sympathetic nervous system and may provide useful information for anesthesia care providers. HRV may offer predictive information about critically ill and operative patients. Further, HRV collection provides real-time information of patient autonomic nervous system status and may allow tailoring of the analgesia for patients in the ICU and operating room.

RECENT FINDINGS

Reduced and abnormal resting HRV predict sudden and nonsudden cardiac death. Recent evidence shows that decreased HRV correlates with worsened outcomes in both trauma patients and patients with sepsis, as well as the risk of developing hypotension after induction of general anesthesia and placement of intrathecal local anesthesia. In addition, HRV appears to provide an accurate assessment of the nociception-analgesia balance in deeply sedated ICU patients and those under general anesthesia.

SUMMARY

No study has assessed the prognostic value of preoperative HRV in patients presenting for surgery. Use of HRV for patient risk stratification and intraoperative analgesia management may allow tailored perioperative care and improved outcomes. If intraoperative HRV data leads to decreased perioperative opioid use, opioid-related adverse events, a serious perioperative issue, may be decreased.

CLINICAL TRIALS REGISTRATION

Not applicable.

Effect of Low Dose Remifentanil on Postoperative Pain Relief and Heart Rate Variability in Post-Anaesthesia Care Unit

Objective

Several reports have shown the negligible adverse effects of low-dose remifentanil on the autonomic nervous system. We propose that the administration of low-dose remifentanil would be beneficial without adverse respiratory and hemodynamic effects. This study aimed to examine the effects of low-dose remifentanil on postoperative pain relief and heart rate variability (HRV) after surgery.

Methods

In total, 20 patients, who underwent breast cancer surgery, were analysed for HRV in the post-anaesthesia care unit (PACU). A sedative dose of remifentanil was continuously infused if patients experienced pain while in PACU. The remifentanil infusion dose was determined by achieving analgesia with no adverse effects on hemodynamics and/or respiration. Variables of low-frequency power, high-frequency power and low-frequency power/high-frequency power ratio were measured before and after the administration of remifentanil. Pain score was expressed as the numeric rating scale (NRS) from 0 to 10.

Results

The mean dosage of remifentanil administered as a continuous infusion was 0.029±0.0042 μg kg^-1 min^-1. After remifentanil administration, the value of the NRS decreased from 4.2±2.9 to 2.7±2.6. In addition, the value of high-frequency power increased from 35.6±14.3 to 49.4±3.0.

Conclusion

The continuous infusion of low-dose remifentanil may reduce post-operative pain scores and trigger the relative activation of the parasympathetic nervous system in post-surgical patients. This indicates that continuous infusion of low-dose remifentanil may be a useful option for postoperative pain relief in cases where postoperative pain control proves inadequate even with the application of regional block technique.

Pupillary reflex dilation in response to incremental nociceptive stimuli in patients receiving intravenous ketamine

Pupillometry is a non-invasive monitoring technique, which allows dynamic pupillary diameter measurement by an infrared camera. Pupillary diameter increases in response to nociceptive stimuli. In patients anesthetized with propofol or volatile agents, the magnitude of this pupillary dilation is related to the intensity of the stimulus. Pupillary response to nociceptive stimuli has never been studied under ketamine anesthesia. Our objective was to describe pupillary reflex dilation after calibrated tetanic stimulations in patients receiving intravenous ketamine. After written consent, 24 patients of our pediatric burn care unit were included. They received an oral morphine premedication (0.3 mg kg^-1) 1 h before their scheduled daily dressing change. Just before the procedure, they received 1 mg kg^-1 of intravenous ketamine. Two minutes after this bolus, tetanic stimulations of incremental intensities were performed on the arm of each patient (5-10-20-30-40-60 mA, 60 s interval between stimulations). Pupillary diameter, heart rate and movements were recorded before and after each stimulation. Tetanic stimulations were associated with changes in pupillary diameter and heart rate. The magnitude of these changes was significantly influenced by the intensity of stimulation (ANOVA for repeated measures, p < 0.001). Movement was associated with a 32% increase in diameter (ROC curves, AUC 0.758) with 65% sensitivity and 77% specificity. In children, pupillary reflex dilation to nociceptive stimuli persists under deep sedation obtained with 1 mg kg^-1 of intravenous ketamine combined with a 0.3 mg kg^-1 oral morphine premedication, and its magnitude depends on the intensity of the stimulation. Our results confirm that pupillometry could be a relevant way to monitor nociception in anaesthetised subjects, including those receiving ketamine. Trial registration clinicaltrials.gov, NCT 02648412.

Determinants of coronary blood flow in sandbar sharks, Carcharhinus plumbeus

The coronary circulation first appeared in the chordate lineage in cartilaginous fishes where, as in birds and mammals but unlike most teleost fishes, it supplies arterial blood to the entire myocardium. Despite the pivotal position of elasmobranch fishes in the evolution of the coronary circulation, the determinants of coronary blood flow have never been investigated in this group. Elasmobranch fishes are of special interest because of the morphological arrangement of their cardiomyocytes. Unlike teleosts, the majority of the ventricular myocardium in elasmobranch fishes is distant to the venous blood returning to the heart (i.e., the luminal blood). Also, the majority of the myocardium is in close association with the coronary circulation. To determine the relative contribution of the coronary and luminal blood supplies to cardiovascular function in sandbar sharks, Carcharhinus plumbeus, we measured coronary blood flow while manipulating cardiovascular status using acetylcholine and adrenaline. By exploring inter- and intra-individual variation in cardiovascular variables, we show that coronary blood flow is directly related to heart rate (R ² = 0.6; P < 0.001), as it is in mammalian hearts. Since coronary blood flow is inversely related to coronary resistance both in vivo and in vitro, we suggest that in elasmobranch fishes, changes in heart rate mediate changes in coronary vascular resistance, which adjust coronary blood flow appropriately.

A literature review of heart rate variability in depressive and bipolar disorders

OBJECTIVE

Autonomic nervous system dysfunction has the potential to adversely impact general medical health and is known to exist in a number of psychiatric disorders. It reflects alterations in the function of several regions of the central nervous system. Measurement of heart rate variability provides a non-invasive tool for studying autonomic function. While the literature relating to the technical process of heart rate variability and aspects of depressive disorders has been reviewed in the past, research relating to both depressive and bipolar disorders has not been comprehensively reviewed. This paper critically considers the published research in heart rate variability in both depressive and bipolar affective disorders.

METHOD

A literature search using Medline, EMBASE, PsycINFO, ProQuest Psychology and references included in published literature was conducted using the following keywords: 'heart rate variability and autonomic, combined with depression, depressive disorder, bipolar, mania and sleep'.

RESULTS

The evidence demonstrates that, using heart rate variability measures, significant distortions of autonomic function are evident in both depressive and bipolar disorders and from most of their pharmacological treatments.

CONCLUSION

The autonomic dysfunction evident in both unipolar and bipolar affective disorders, and many psychotropic medications, has significant implications for our understanding of the neurophysiology of these disorders, their treatment and associated general health.

Recent advance in patient monitoring

Recent advance in technology has developed a lot of new aspects of clinical monitoring. We can monitor sedation levels during anesthesia using various electroencephalographic (EEG) indices, while it is still not useful for anesthesia depth monitoring. Some attempts are made to monitor the changes in sympathetic nerve activity as one of the indicators of stress, pain/analgesia, or anesthesia. To know the balance of sympathetic and parasympathetic activity, heart rate or blood pressure variability is investigated. For trend of cardiac output, low invasive monitors have been investigated. Improvement of ultrasound enables us to see cardiac structure and function continuously and clearer, increases success rate and decreases complication of central venous puncture and various kinds of nerve blocks. Without inserting an arterial catheter, trends of arterial oxygen tension or carbon dioxide tension can be monitored. Indirect visualization of the airway decreases difficult intubation and makes it easier to teach tracheal intubation. The changes in blood volume can be speculated non-invasively. Cerebral perfusion and metabolism are not ordinary monitored yet, but some studies show their usefulness in management of critically ill. This review introduces recent advances in various monitors used in anesthesia and critical care including some studies of the author, especially focused on EEG and cardiac output. However, the most important is that these new monitors are not almighty but should be used adequately in a limited situation where their meaning is confirmed.

Predominant effects of midazolam for conscious sedation: benefits beyond the early postoperative period

PURPOSE

Conscious sedation with intravenous sedative-hypnotic drugs has the advantage of relaxing patients before invasive procedures. Preoperative anxiety has been suggested to correlate with postoperative comfortableness. In this study, we chose midazolam and droperidol as well-established intravenous sedative-hypnotic drugs. We evaluated the preoperative anxiolytic effect on postoperative memories and emotions up to the first postoperative morning.

METHODS

In a prospective, double blind study, 120 patients requiring epidural anesthesia were randomly assigned to one of three groups to receive saline, midazolam (0.04 mg/kg), or droperidol (0.1 mg/kg). Cardiovascular and respiratory measurements, observer's assessment of alertness/sedation scale, level of anxiety and discomfort of the patients, pain during the infiltration of local anesthetics, and incidence of adverse effects were recorded. Amnesia, anxiety, and discomfort during the epidural procedure were re-assessed between 12 and 20 h postsurgery.

RESULTS

Patients who received sedatives were significantly more sedated (P < 0.0001), but the pain score was significantly higher in the droperidol group (P = 0.0007) at epidural catheterization. On the first postoperative morning, patients receiving midazolam had a significantly lower pain score (P < 0.0001) with less anxiety and discomfort. Patients in both the midazolam and droperidol groups showed a significant decrease in blood pressure (P < 0.0167), but no respiratory impairment. No adverse effects were experienced throughout the study period.

CONCLUSION

Conscious sedation with intravenous midazolam 0.04 mg/kg significantly decreased the anxiety and discomfort scores of the patients on the day following surgery but had no effect on these immediately following the epidural catheterization procedure.

Modulation of brain dead induced inflammation by vagus nerve stimulation

Because the vagus nerve is implicated in control of inflammation, we investigated if brain death (BD) causes impairment of the parasympathetic nervous system, thereby contributing to inflammation. BD was induced in rats. Anaesthetised ventilated rats (NBD) served as control. Heart rate variability (HRV) was assessed by ECG. The vagus nerve was electrically stimulated (BD + STIM) during BD. Intestine, kidney, heart and liver were recovered after 6 hours. Affymetrix chip-analysis was performed on intestinal RNA. Quantitative PCR was performed on all organs. Serum was collected to assess TNFalpha concentrations. Renal transplantations were performed to address the influence of vagus nerve stimulation on graft outcome. HRV was significantly lower in BD animals. Vagus nerve stimulation inhibited the increase in serum TNFalpha concentrations and resulted in down-regulation of a multiplicity of pro-inflammatory genes in intestinal tissue. In renal tissue vagal stimulation significantly decreased the expression of E-selectin, IL1beta and ITGA6. Renal function was significantly better in recipients that received a graft from a BD + STIM donor. Our study demonstrates impairment of the parasympathetic nervous system during BD and inhibition of serum TNFalpha through vagal stimulation. Vagus nerve stimulation variably affected gene expression in donor organs and improved renal function in recipients.

Midazolam more effectively suppresses sympathetic activations and reduces stress feelings during mental arithmetic task than propofol

PURPOSE

The aim of the present study was to examine the effect of intravenous midazolam and propofol sedation on autonomic nervous activities during psychological stress, and whether these results are associated with changes in subjective stress feelings.

MATERIALS AND METHODS

Seven healthy male volunteers were included in a randomized crossover manner. The heart rate (HR), HR variability, arterial oxygen saturation, and bispectral index value were continuously monitored. A mental arithmetic task for 7 minutes was given with or without intravenous sedation with midazolam or propofol. A bispectral index value of 75 to 85 and an Observer's Assessment of Alertness/Sedation score of 4 were the targeted sedation level in both groups. HR variability was assessed using the power spectral analysis (low-frequency [LF] and high-frequency [HF] components and LF/HF ratio). The faces anxiety scale was used to grade their stress feelings after each mental arithmetic task.

RESULTS

During the mental arithmetic task with intravenous sedation, no differences were found in the bispectral index values, arterial oxygen saturation, or the results of the mental arithmetic task between the 2 groups. The HR, LF/HF ratio, and normalized unit LF increased, and the normalized unit HF decreased in both groups. However, the percentage of changes in LF/HF ratio, normalized unit LF, and normalized unit HF were smaller in the midazolam group. In addition, the reduction in faces anxiety scale was greater in the midazolam group.

CONCLUSIONS

These results suggest that midazolam more effectively suppresses sympathetic nervous activation and reduces subjective stress feelings during a mental arithmetic task than propofol.

Cardiac autonomic regulation during gastroscopy

BACKGROUND

Gastroscopy is sometimes associated with adverse cardiovascular events.

AIMS

We evaluated the effects of sedation and pharyngeal anaesthesia on cardiac autonomic regulation during gastroscopy.

PATIENTS

Two hundred thirteen outpatients undergoing gastroscopy.

METHODS

The patients were assigned to 4 groups: (1) sedation with intravenous midazolam and placebo throat spray (midazolam group), (2) placebo sedation and pharyngeal anaesthesia with lidocaine (lidocaine group), (3) placebo sedation and placebo throat spray (placebo group), and (4) no intravenous cannula nor throat spray (control group). Continuous electrocardiogram was recorded. Heart rate variability was assessed; the powers of low frequency (0.04-0.15 Hz) and high frequency (0.15-0.40 Hz) components as well as total power (0.0-0.4 Hz) were calculated.

RESULTS

Gastroscopy was associated with a decrease in high frequency normalized units, increases in low frequency normalized units and low frequency/high frequency ratio indicating activation of sympathetic and withdrawal of vagal modulation. Sympathetic activation resulted in a decrease in total power and all components of heart rate variability. The decrease was most prominent in the midazolam treated patients (p<0.001 vs the lidocaine group and p<0.01 vs placebo and control groups during the postendoscopy phase).

CONCLUSION

Gastroscopy induces a shift towards dominance of the sympathetic modulation of the heart. Premedication with midazolam potentiates this shift.

Haemodynamic changes and heart rate variability during midazolam-propofol co-induction

In a prospective, blind, randomised study, we examined the effects of midazolam-propofol co-induction on haemodynamic (blood pressure, heart rate and stroke volume) and heart rate variability. The latter was measured by spectral analysis using the maximum-entropy method to calculate the following: the low frequency component (LF), which reflects both the cardiac sympathetic and parasympathetic activity, the high frequency component (HF) and entropy, which reflects the cardiac parasympathetic activity, the total power (TP), calculated by the addition of LF and HF, and the LF/HF ratio, which reflects the balance between the cardiac sympathetic and parasympathetic nervous activity. Forty patients were randomly allocated to the propofol group and the midazolam-propofol group, and the parameters described above were calculated at baseline (T1), post induction (T2), after tracheal intubation (T3), and 3 min (T4) and 5 min after intubation (T5). Propofol was administered at 2.5 mg.kg(-1) in the propofol group and midazolam at 0.1 mg.kg(-1) followed by propofol at 1.5 mg.kg(-1) in the midazolam-propofol group for anaesthesia induction. Then, propofol was administered at 4-6 mg.kg(-1)propofol for maintenance in both groups. The midazolam-propofol group showed compensated haemodynamic changes, which were related to significant increases in the LF/HF ratio at T2, T4 and T5 (p = 0.011, 0.038 and 0.034). These results suggest that the midazolam-propofol combination yielded compensated modulatory effects on the cardiovascular system, including preserved baroreflex activity.

Loss of complexity characterizes the heart rate response to experimental hemorrhagic shock in swine

OBJECTIVE

To improve our ability to identify physiologic deterioration caused by critical illness, we applied nonlinear and frequency-domain analytical methods to R-to-R interval (RRI) and systolic arterial pressure (SAP) time series during hemorrhagic shock.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Animal laboratory of a government research institute.

SUBJECTS

Twenty swine (weight 36.4+/-0.11 kg).

INTERVENTIONS

Fixed-volume hemorrhage followed by resuscitation; off-line analysis of RRI and SAP data.

MEASUREMENTS AND MAIN RESULTS

Anesthetized swine (shock group, n=12) underwent withdrawal of 30 mL/kg blood in 10 mL/kg decrements. A control group (n=8) received maintenance fluids only. Electrocardiogram and arterial pressure waveforms were acquired at 500 Hz. Eight hundred-beat data sets were analyzed at six time points: at baseline, after each blood withdrawal, after lactated Ringer's resuscitation, and after infusion of shed blood. Nonlinear methods were used to estimate the complexity (approximate entropy, sample entropy, Lempel-Ziv entropy, normalized entropy of symbol dynamics), RRI bits per word, and fractal dimension by curve lengths and by dispersion analysis of the RRI and SAP time series. Fast Fourier transformation was used to measure the high-frequency and low-frequency powers of RRI and SAP. Baroreflex sensitivity was assessed in the time domain with the sequence method. Hemorrhagic shock caused decreases in RRI complexity as quantified by approximate entropy, sample entropy, and symbol dynamics; these changes were reversed by resuscitation. Similar but statistically insignificant changes in fractal dimension by curve lengths were seen. RRI high-frequency power decreased with hemorrhagic shock-indicating withdrawal of vagal cardiac input-and was restored by resuscitation. Similar changes in baroreflex sensitivity were seen. Hemorrhagic shock did not affect SAP complexity.

CONCLUSIONS

Hemorrhagic shock caused a reversible decrease in RRI complexity; these changes may be mediated by changes in vagal cardiac control. Assessment of RRI complexity may permit identification of casualties with hemorrhagic shock.

Peripheral circulation monitored by surface temperature and autonomic nervous function in hypobaric hypoxic environment: effects of submaximal exercise

Hypothermia and frostbite are frequently seen in accidents in remote wilderness environment, especially in hypobaric hypoxic conditions. The aim of this study was to clarify how hypobaric hypoxic conditions affects peripheral circulation. Peripheral skin temperature and autonomic nervous functions were assessed in two 1000-m ascent exercises. Subjects (n = 15) ascended from 1000 m above sea level in Study 1, and ascended from 2400 m in Study 2. Conditions other than environmental oxygen pressure were mostly identical in both studies. The autonomic nervous activities were decreased solely in Study 2. The relative sympathetic activity was significantly increased in the lower barometric pressure in Study 2 (p < 0.01). Peripheral skin temperature was significantly decreased after the exercise in Study 2 (p < 0.01). In conclusion, hypobaric hypoxia itself induced peripheral low temperature during exercise at high altitudes. Relative sympathetic hyperactivity may be responsible for the compromised peripheral circulation.

Modulation of Cardiac Autonomic Nervous Activity Early after Cardioversion of Atrial Fibrillation by Biphasic Waveform

BACKGROUND

Imbalance of cardiac autonomic nervous modulation might prominently contribute to early relapses of atrial fibrillation (AF) after cardioversion (CV). The biphasic (Bi) waveform is more effective than the monophasic (Mo) waveform in CV of AF. Whether these waveforms have different effects on autonomic modulation early after CV is unknown.

METHODS

We investigated 171 consecutive patients after successful electrical CV (mean age 65.4 years, 82% male, 80% structural heart disease). Bi waveform was used in 89, Mo waveform in 82. Heart rate variability (HRV) was analyzed from 24-hour Holter recordings, started directly after CV.

RESULTS

Mean delivered total energy was significantly lower in the Bi group (Bi 223 +/- 163 W, Mo 355 +/- 211 W, P < 0.001). Mean RR interval decreased within 5 hours after CV and increased again within the remaining hours, without significant differences between Bi and Mo groups. Time courses of time domain parameters of HRV revealed Bi profiles with the lowest levels 6 hours after CV in both groups. However, the hourly values of HRV were significantly higher in the Bi subgroup.

CONCLUSION

Our study indicates that waveform and total delivered energy significantly influence autonomic modulation of the sinus node in the early phase after CV of AF. In contrast to Bi CV, Mo CV is characterized by a significant decrease of cardiac vagal modulation, which may have an arrhythmic effect by increasing the degree of early electrical stunning after CV of AF.

The Different Effects of Intravenous Propofol and Midazolam Sedation on Hemodynamic and Heart Rate Variability

Heart rate (HR) and arterial blood pressure (BP) changes have been reported during conscious sedation with propofol and midazolam. One potential mechanism to explain these changes is that propofol and midazolam affect HR and BP via changes in the cardiac autonomic nervous system. Two specific hypotheses were tested by HR variability analysis: 1) propofol induces predominance of parasympathetic activity, leading to decreased HR and BP, and 2) midazolam induces predominance of sympathetic activity, leading to increased HR and decreased BP. Thirty dental patients were included in a prospective, randomized study. HR, BP, low frequency (LF), high frequency (HF), and entropy were monitored during the awake, sedation, and recovery periods and depth of sedation was assessed using the Observer's Assessment of Alertness/Sedation score. Propofol induced a significant decrease in total power (503 +/- 209 ms(2)/Hz versus 162 +/- 92 ms(2)/Hz) and LF/HF ratio (2.5 +/- 1.2 versus 1.0 +/- 0.4), despite the absence of any change in HR during the sedation period compared with baseline. Midazolam decreased normalized HF (34 +/- 10% versus 10 +/- 4%) but did not significantly change LF/HF ratio (2.3 +/- 1.1 versus 2.2 +/- 1.4) and increased HR in the sedation period. Compared with baseline, propofol was associated with a significant increase in normalized HF in the recovery period (34 +/- 11% versus 44 +/- 12%) and a significant decrease in HR, whereas midazolam was associated with an increase in LF/HF ratio (2.3 +/- 1.1 versus 3.7 +/- 1.8) with no change in HR. These results indicated a dominant parasympathetic effect of propofol and a dominant sympathetic effect of midazolam in both periods. These results should be considered during conscious sedation, especially in patients at risk of cardiovascular complications.

Ketamine for paediatric sedation/analgesia in the emergency department

This review investigates the use of ketamine for paediatric sedation and analgesia in the emergency department.

Relationship between arterial oxygen saturation and heart rate variability at high altitudes

Autonomic nervous systems have important roles for survival of victims under hypobaric hypoxic condition. In the present study, we assessed the correlation between arterial oxygen saturation (Sp O 2 ) and heart rate variability (HRV) to identify the autonomic nervous responsiveness among trekkers at high altitude (n = 21). HRV was analyzed by the maximum entropy method. Sp O 2 among subjects at 3456 m (495 mm Hg) was 80% +/- 5% (mean +/- SD; range, 69%-93%). Sp O 2 and percentile entropy, and Sp O 2 and low-frequency variability, had positive correlation ( r = 0.455 and 0.518, respectively). Sp O 2 value among subjects with mountain sickness symptoms was not different from that among subjects without the symptoms. In conclusion, autonomic responses among high-altitude trekkers may be blunted under hypobaric hypoxic conditions. Deterioration of autonomic function measured by HRV might be more sensitive to hypoxia than clinical symptoms at high altitudes.

[To understand blood pressure and heart rate variability]

OBJECTIVES

To review current data on the heart rate and blood pressure variability.

DATA SOURCES

Search through Medline databases of articles in french or english.

DATA SELECTION

Original articles and case reports were selected according to their quality and main advances. The articles were analysed in order to obtain current data about the methods of study and clinical application of blood pressure and heart rate variability.

DATA SYNTHESIS

Various regulatory systems in the cardiovascular system play crucial roles in controlling and assuring adequate perfusion of the peripheral tissues. Among them the baroreceptor reflex is the most important regulatory mechanism in the short-term control of the heart rate and blood pressure, and operates through the autonomic nervous system. The gain of the cardiac baroreflex further referred to, as baroreflex sensitivity is an interesting way to study this system. Unfortunately, with our current knowledge, it is not possible to predict the instantaneous output of the baroreceptor in response to instantaneous changes in input within a frequency range of physiological importance. The fast Fourier transform can describe variables as the sum of elementary oscillatory components and it has been established as practical clinical methods for detecting abnormalities in cardiovascular control. A time-frequency distribution provides an indication of how the spectral energy distribution varies with time and it is an interesting tool in non-stationary data. One of the major motivations behind spectral analysis is the hope that the combination of time-domain and frequency-domain analyses will provide dynamical informations about the relation between blood pressure and heart rate.

Effects of combining midazolam and barbiturate on the response to tracheal intubation: changes in autonomic nervous system

STUDY OBJECTIVE

To investigate the effects on the autonomic nervous system of anesthesia induction with a combination of midazolam and barbiturate using plasma catecholamine concentration and heart rate (HR) variability in comparison with the induction with barbiturate alone.

DESIGN

Prospective study.

SETTING

Operating room of a university hospital.

PATIENTS

40 ASA physical status I and II patients aged 30 to 70 years, who were scheduled for general anesthesia.

INTERVENTIONS

Anesthesia was induced with 0.1 mg/kg midazolam followed by 3 mg/kg thiopental sodium (Midazolam-Barbiturate group) or thiopental 5 mg/kg (Barbiturate group) with 6 L/min oxygen.

MEASUREMENTS

Arterial blood pressure (BP), HR, HR variability, and plasma concentrations of epinephrine and norepinephrine were measured.

MAIN RESULTS

Blood pressure and HR increased in response to tracheal intubation in both groups, but the increase was significantly larger in the Barbiturate group. In the Barbiturate group, the high-frequency component (HF) in HR variability increased significantly during intubation, whereas in the Midazolam-Barbiturate group, HF decreased continuously. The low-frequency component (LF)/HF ratio increased in both groups, with significantly higher values noted in the Barbiturate group. Plasma epinephrine concentrations decreased before intubation and increased in response to tracheal intubation in the Barbiturate group. Finally, plasma norepinephrine concentrations increased in response to tracheal intubation only in the Barbiturate group.

CONCLUSIONS

Anesthesia induction with a combination of midazolam-thiopental was effective in reducing hemodynamic and cardiac autonomic nervous system responses to tracheal intubation in comparison with the conventional induction with thiopental alone.

Rapid inhalation induction with 7% sevoflurane combined with intravenous midazolam

STUDY OBJECTIVE

To identify an improved rapid inhalation induction (RII) technique by investigating hemodynamics and heart rate variability of induction with midazolam and RII with 7% sevoflurane in comparison with RII alone.

DESIGN

Prospective, randomized study.

SETTING

Operating room of a university hospitals.

PATIENTS

40 patients scheduled for gastrectomy without complications.

INTERVENTIONS

In the sevoflurane (Sev) group, anesthesia was induced with tidal volume breathing of 7% sevoflurane with 50% nitrous oxide (N(2)O) in oxygen (O(2)) for 3 minutes. In the midazolam-sevoflurane group (Mid-Sev) intravenous midazolam 0.1 mg/kg was given, followed by 7% sevoflurane with 50% N(2)O. In both groups, endotracheal intubation was facilitated with vecuronium 0.15 mg/kg, which was administered at loss of consciousness.

MEASUREMENTS

Blood pressure, heart rate, heart rate variability, time to loss of response to verbal command (sleep time), rate of body movement or cough during induction, and patient satisfaction were monitored.

MAIN RESULTS

Blood pressure and heart rate increased significantly in the Sev group but not in the Mid-Sev group. Heart rate was significantly higher in the Sev group at 1 minute after intubation. High-frequency component (cardiac parasympathetic activity) in heart rate variability increased before intubation, with a higher value seen in the Sev group than the Mid-Sev group. The ratio of low-frequency component to high-frequency component (cardiac sympathetic activity) did not change in either group. Sleep time did not differ between the two groups. The numbers of patients with body movement and cough, and patients who were not satisfied with the induction method were, respectively, four, three, and eight in the Sev group; and one, zero, and two in the Mid-Sev group. The last value was significantly higher in the Sev group (p = 0.0285).

CONCLUSIONS

The addition of intravenous midazolam 0.1 mg/kg provides more stable hemodynamics, cardiac autonomic nervous system activity, and patient satisfaction in RII with 7% sevoflurane.

Heart rate variability and arterial blood pressure variability show different characteristic changes during hemorrhage in isoflurane-anesthetized, mechanically ventilated dogs

We assessed the changes in heart rate variability (HRV) and blood pressure variability (BPV) as indices of autonomic nervous system and volume status during hemorrhage in isoflurane-anesthetized, mechanically ventilated dogs. Nine dogs were used. They were sequentially subjected to withdrawal of 30% estimated blood volume and graded isoflurane inhalation of 1% and 2% followed by discontinuation of isoflurane and retransfusion. The power spectra of HRV and BPV were computed using the fast Fourier transformation, and were quantified by determining the areas of the spectrum in two component widths: low-frequency component (LF) (0.04-0.15 Hz) and high-frequency component (HF) (0.15-0.4 Hz). During hemorrhage and isoflurane anesthesia, both HRV-LF and HRV-HF were decreased and plateaued at the smaller concentration of isoflurane, whereas BPV-LF decreased concentration-dependently. BPV-HF showed a completely different response and increased significantly during 2% isoflurane. We speculate that HRV and BPV-LF would be affected by the autonomic nervous activity, whereas BPV-HF would depend on relative/absolute change in circulating blood volume.

IMPLICATIONS

Power spectra of heart rate variability (HRV) and blood pressure variability (BPV) were computed using the fast Fourier transformation. The HRV and BPV showed their differential characteristics during hemorrhage, isoflurane anesthesia, and retransfusion, and would help to assess changes in autonomic nervous system and preload under mechanical ventilation.

Alterations in autonomic nervous control of heart rate among tourists at 2700 and 3700 m above sea level

OBJECTIVES

Many travelers who are not specially trained for activities at high altitude are at risk of physical problems, including cardiovascular disorders, when exposed to high-altitude environments. In the present study, we investigated how actual acute exposure to altitudes of 2700 and 3700 m affected the autonomic nervous control of heart rate in untrained office workers.

METHODS

Physiological parameters (heart rate, respiratory rate, arterial blood oxygen saturation, and end-expiratory carbon dioxide tension) were measured at sea level, 2700 m, and 3700 m. The power of heart rate variability was quantified by determining the areas of the spectrum in 2 component widths: low frequency (LF; 0.04-0.15 Hz) and high frequency (HF; 0.15-0.5 Hz). The ratio of LF power to HF power (LF:HF), which is considered to be an index of cardiac sympathetic tone, was also assessed.

RESULTS

Both HF and LF heart rate variability decreased according to the elevation of altitude. High- and low-frequency powers at 3700 m were significantly lower than those at sea level (P < .01 for HF, P < .05 for LF). The LF:HF ratio at 2700 m was not significantly different from that at sea level. However, it was significantly increased at 3700 m (P < .01).

CONCLUSIONS

At 2700 and 3700 m, the activity of the autonomic nervous system measured by heart rate variability was decreased in untrained office workers. The sympathetic nervous system was dominant to the parasympathetic at 3700 m. These alterations in the autonomic nervous system might play some role in physical fitness at high altitudes.

Effect of conscious sedation on cardiac autonomic regulation during colonoscopy

BACKGROUND

Colonoscopy is associated with cardiovascular events including hypotension, hypertension, and myocardial ischemia. The pathogenetic mechanisms of these cardiovascular events are unknown, but there is evidence that the autonomic nervous system may play a role. Conscious sedation is often used to relieve the inconvenience caused by the procedure. In this study, we evaluated the effects of sedation on cardiac autonomic regulation during colonoscopy.

METHODS

One hundred and eighty patients undergoing elective colonoscopy were prospectively randomized into three groups: (i) sedation with intravenous midazolam (midazolam group); (ii) sedation with intravenous saline (placebo group); and (iii) no intravenous cannula (control group). Continuous electrocardiogram was recorded prior to, during, and after the colonoscopic procedure. Heart rate variability (HRV) was assessed by means of the power spectral analysis; the powers of low-frequency (LF 0.04-0.15 Hz) and high-frequency (HF 0.15-0.40 Hz) components were calculated.

RESULTS

Intubation of the colonoscope increased the LF component of HRV and decreased HF power in all study groups compared to baseline recording. Furthermore, compared to baseline, the LF/HF ratio--a marker of cardiac sympathetic regulation--increased during intubation in the midazolam (P < 0.001) and placebo (P < 0.05) groups, with no change in the control group. During intubation the midazolam group presented with higher LF and lower HF power than placebo (P < 0.001) and control groups (P < 0.01). Accordingly, the LF/HF ratio was higher in the midazolam group than in the placebo (P < 0.05) or control groups (P < 0.05).

CONCLUSIONS

Midazolam potentiates the dominance of the sympathetic nervous system induced by colonoscopy. Therefore, conscious sedation with midazolam may contribute to the occurrence of cardiovascular events during colonoscopy.

Heart rate variability during massive hemorrhage and progressive hemorrhagic shock in dogs

PURPOSE

To investigate the sequential changes in heart rate (HR), autonomic nervous activity presented by the spectral analysis of heart rate variability (HRV), hemodynamics and metabolism during massive hemorrhage and progressive hemorrhagic shock in dogs.

METHODS

Twelve dogs were subjected to acute massive hemorrhage until mean arterial pressure (MAP) reached 50 mm Hg. Then bleeding was stopped and they were allowed to reach a plateau phase. They were divided, post hoc, into bradycardic or tachycardic groups according to their HR response to the acute massive hemorrhage. After reaching a plateau phase, the dogs were further bled to keep their MAP around 50 mmHg (progressive hemorrhagic shock). Their heart rate power spectra were quantified into low-frequency (LF) (0.04-0.15 Hz) and high-frequency (HF) (0.15-0.4 Hz) components.

RESULTS

In the bradycardic group, both LF and HF increased after massive hemorrhage, but during progressive hemorrhagic shock these components decreased while HR increased. In the tachycardic group, LF increased after massive hemorrhage, but during progressive hemorrhagic shock LF decreased with continuous suppression of HF CONCLUSION: Massive hemorrhage caused two types of HR response: bradycardia and tachycardia. The HRV profile showed differential autonomic characteristics, and could be a valuable tool in assessing various degrees of hemorrhagic shock.

Recovery of heart rate variability profile in patients after coronary artery surgery

We examined the different characteristics of heart rate variability (HRV) to define the time course of HRV profile after coronary artery surgery (CAS). Spectral analysis of HRV was performed on a 512-s segment of R-R intervals of the electrocardiogram on the preoperative day and on Postoperative Days 1, 2, 3, 4, 5, 6, 7, 14, 21, and 28. Power spectral area was divided into low (0.04-0.15 Hz; LF)- and high (0.15-0.5 Hz; HF)-frequency components. Fractal slope and sympathovagal slope of 1/f characteristics of HRV were determined in two different frequency ranges (from 0.01 to 0.15 Hz and from 0.01 to 0.5 Hz, respectively). Three recovery profiles of HRV were identified. Early HRV recovery profiles (Postoperative Days 1-6) included reduction in LF, HF, and sympathovagal slope, as well as an increase in fractal slope. Subsequent HRV recovery profiles (Postoperative Days 7-21) revealed reductions in LF, HF, and sympathovagal slope. Fractal slope became normal. Later HRV recovery profiles (Postoperative Day 28) demonstrated that all spectral components of HRV remained reduced, but sympathovagal and fractal slopes became normal. These changes in the HRV profile after CAS suggest significant postoperative alterations in cardiovascular homeostasis with significant but incomplete recovery during the first 28 postoperative days.

IMPLICATIONS

Heart rate variability reflects normal neural regulation of cardiac function. This variability remains depressed as long as 28 days after coronary artery bypass surgery, but can recover as early as 1 wk postoperatively. Despite implied loss of normal neural regulation of cardiac function, a specific correlation between depressed heart rate variability and outcomes was not performed.