Low High Frequency Ratio Research Articles

Isolation of the murine Glut1 deficient thalamocortical circuit: wavelet characterization and reverse glucose dependence of low and gamma frequency oscillations.

Glucose represents the principal brain energy source. Thus, not unexpectedly, genetic glucose transporter 1 (Glut1) deficiency (G1D) manifests with encephalopathy. G1D seizures, which constitute a prominent disease manifestation, often prove refractory to medications but may respond to therapeutic diets. These seizures are associated with aberrant thalamocortical oscillations as inferred from human electroencephalography and functional imaging. Mouse electrophysiological recordings indicate that inhibitory neuron failure in thalamus and cortex underlies these abnormalities. This provides the motivation to develop a neural circuit testbed to characterize the mechanisms of thalamocortical synchronization and the effects of known or novel interventions. To this end, we used mouse thalamocortical slices on multielectrode arrays and characterized spontaneous low frequency oscillations and less frequent 30-50 Hz or gamma oscillations under near-physiological bath glucose concentration. Using the cortical recordings from layer IV among other regions recorded, we quantified oscillation epochs via an automated wavelet-based algorithm. This method proved analytically superior to power spectral density, short-time Fourier transform or amplitude-threshold detection. As expected from human observations, increased bath glucose reduced the lower frequency oscillations while augmenting the gamma oscillations, likely reflecting strengthened inhibitory neuron activity, and thus decreasing the low:high frequency ratio (LHR). This approach provides an ex vivo method for the evaluation of mechanisms, fuels, and pharmacological agents in a crucial G1D epileptogenic circuit.

Physiologic Characteristics of Hyperosmolar Therapy After Pediatric Traumatic Brain Injury.

All work was performed at the Barrow Neurological Institute at Phoenix Children's Hospital.Objective: Investigate injury severity, neuroimaging, physiology, and outcomes with bolus hyperosmolar therapy (HT) of 3% hypertonic saline or mannitol.Methods: Retrospective cohort analysis was performed. Physiologic variables included intracranial pressure (ICP), arterial blood pressure (ABP), and heart rate (HR). Volume-pressure compensation (PVC) indices included ICP pulse amplitude (AMP) and correlation of AMP and ICP (RAP). Cerebrovascular pressure reactivity (CVPR) indices included pressure reactivity index (PRx), pulse amplitude index (PAx), wavelet PRx (wPRx), and correlation of AMP and cerebral perfusion pressure (RAC). Heart rate variability (HRV) indices included heart rate standard deviation (HRsd), heart rate root mean square of successive differences (HRrmssd) and low-high frequency ratio (LHF). Outcome was assessed using Glasgow Outcomes Scale Extended Pediatrics, 12-months post-injury. Generalized estimating equations was applied to investigate associations of physiologic changes and pre-treatment indices with HT efficacy. Repeated measures analysis of variance was applied to investigate changes after HT without intracranial hypertension (ICH). Wilcoxon rank-sum was applied to investigate HT responsiveness with age, injury severity, neuroimaging, and outcomes.Results: Thirty children received bolus HT. ICH reduction after HT was associated with reduced ICP (p = 0.0064), ABP (p = 0.0126), PRx (p = 0.0063), increased HRsd (p = 0.0408), and decreased pretreatment RAC (p = 0.0115) and wPRx (p = 0.0072). HT-responsive patients were older and had improved outcomes (p = 0.0394). HT without ICH was associated with increased ICP (P < 0.0001) and ABP (P < 0.0001), increases in all HRV indices and decreases in all PVC indices.Conclusion: After pediatric TBI, efficacious HT is associated with decreased ICP and ABP, pre-treatment indices suggesting efficient CVPR, and potentially improved outcomes.

Multimodal Assessment of Cerebral Autoregulation and Autonomic Function After Pediatric Cerebral Arteriovenous Malformation Rupture.

Management after cerebral arteriovenous malformation (AVM) rupture aims toward preventing hemorrhagic expansion while maintaining cerebral perfusion to avoid secondary injury. We investigated associations of model-based indices of cerebral autoregulation (CA) and autonomic function (AF) with outcomes after pediatric cerebral AVM rupture. Multimodal neurologic monitoring data from the initial 3days after cerebral AVM rupture were retrospectively analyzed in children (< 18years). AF indices included standard deviation of heart rate (HRsd), root-mean-square of successive differences in heart rate (HRrmssd), low-high frequency ratio (LHF), and baroreflex sensitivity (BRS). CA indices include pressure reactivity index (PRx), wavelet pressure reactivity indices (wPRx and wPRx-thr), pulse amplitude index (PAx), and correlation coefficient between intracranial pressure pulse amplitude and cerebral perfusion pressure (RAC). Percent time of cerebral perfusion pressure (CPP) below lower limits of autoregulation (LLA) was also computed for each CA index. Primary outcomes were determined using Pediatric Glasgow Outcome Score Extended-Pediatrics (GOSE-PEDs) at 12months and acquired epilepsy. Association of biomarkers with outcomes was investigated using linear regression, Wilcoxon signed-rank, or Chi-square. Fourteen children were analyzed. Lower AF indices were associated with poor outcomes (BRS [p = 0.04], HRsd [p = 0.04], and HRrmssd [p = 0.00]; and acquired epilepsy (LHF [p = 0.027]). Higher CA indices were associated with poor outcomes (PRx [p = 0.00], wPRx [p = 0.00], and wPRx-thr [p = 0.01]), and acquired epilepsy (PRx [p = 0.02] and wPRx [p = 0.00]). Increased time below LLA was associated with poor outcome (percent time below LLA based on PRx [p = 0.00], PAx [p = 0.04], wPRx-thr [p = 0.03], and RAC [p = 0.01]; and acquired epilepsy (PRx [p = 0.00], PAx [p = 0.00], wPRx-thr [p = 0.03], and RAC [p = 0.01]). After pediatric cerebral AVM rupture, poor outcomes are associated with AF and CA when applying various neurophysiologic model-based indices. Prospective work is needed to assess these indices of CA and AF in clinical decision support.

Arrhythmic Risk in Elderly Patients Candidates to Transcatheter Aortic Valve Replacement: Predictive Role of Repolarization Temporal Dispersion.

Background/AimDegenerative aortic valve stenosis (AS) is associated to ventricular arrhythmias and sudden cardiac death, as well as mental stress in specific patients. In such a context, substrate, autonomic imbalance as well as repolarization dispersion abnormalities play an undoubted role. Aim of the study was to evaluate the increase of premature ventricular contractions (PVC) and complex ventricular arrhythmias during mental stress in elderly patients candidate to the transcatheter aortic valve replacement (TAVR).MethodsIn eighty-one elderly patients with AS we calculated several short-period RR- and QT-derived variables at rest, during controlled breathing and during mild mental stress, the latter being represented by a mini-mental state evaluation (MMSE).ResultsAll the myocardial repolarization dispersion markers worsened during mental stress (p < 0.05). Furthermore, during MMSE, low frequency component of the RR variability increased significantly both as absolute power (LFRR) and normalized units (LFRRNU) (p < 0.05) as well as the low-high frequency ratio (LFRR/HFRR) (p < 0.05). Eventually, twenty-four (30%) and twelve (15%) patients increased significantly PVC and, respectively, complex ventricular arrhythmias during the MMSE administration. At multivariate logistic regression analysis, the standard deviation of QTend (QTesd), obtained at rest, was predictive of increased PVC (odd ratio: 1.54, 95% CI 1.14–2.08; p = 0.005) and complex ventricular arrhythmias (odd ratio: 2.31, 95% CI 1.40–3.83; p = 0.001) during MMSE. The QTesd showed the widest sensitive-specificity area under the curve for the increase of PVC (AUC: 0.699, 95% CI: 0.576–0.822, p < 0.05) and complex ventricular arrhythmias (AUC: 0.801, 95% CI: 0.648–0.954, p < 0.05).ConclusionIn elderly with AS ventricular arrhythmias worsened during a simple cognitive assessment, this events being a possible further burden on the outcome of TAVR. QTesd might be useful to identify those patients with the highest risk of ventricular arrhythmias. Whether the TAVR could led to a QTesd reduction and, hence, to a reduction of the arrhythmic burden in this setting of patients is worthy to be investigated.

Age alters cardiac autonomic modulations during and following exercise-induced heat stress in females

ABSTRACTThe aim of this study was to examine the effect of natural ageing on heart rate variability during and following exercise-induced heat stress in females. Eleven young (∼24 years) and 13 older (∼51 years), habitually active females completed an experimental session consisting of baseline rest, moderate intensity intermittent exercise (four 15-min bouts separated by 15-min recovery) and 1-hour of final recovery in a hot and dry (35°C, 20% relative humidity) environment. Respiratory and heart rate recordings were continuously logged with 10-min periods analysed at the end of: baseline rest; each of the exercise and recovery bouts; and during the 1-hour final recovery period. Comparisons over time during exercise and recovery, and between groups were conducted via two-way repeated-measures ANCOVAs with rest values as the covariate. During baseline rest, older females exhibited lower heart rate variability compared to young females with similar levels of respiration and most (∼71-79%) heart rate variability measures during repeated exercise and recovery. However, older females exhibited heart rate variability metrics suggestive of greater parasympathetic modulation (greater long axis of Poincare plot, cardiac vagal index; lower low-high frequency ratio) during repeated exercise with lower indices during the latter stage of prolonged recovery (less very low frequency component, Largest Lyapunov Exponent; greater cardiac sympathetic index). The current study documented several unique, age-dependent differences in heart rate variability, independent of respiration, during and following exercise-induced heat stress for females that may assist in the detection of normal heat-induced adaptations as well as individuals vulnerable to heat stress.

The Use of Heart Rate Variability Technique for Differential Diagnostics of Peptic Ulcer and Idiopathic Duodenal Ulcers

The aim of the investigation was to study the peculiarities of autonomic regulation using spectral analysis of heart rate variability for differential diagnostics of peptic ulcer and idiopathic duodenal ulcer. Materials and Methods. A stress level was assessed by vagosympathetic balance rate. Low-high frequency ratio in a frequency spectrum of heart rate was used as a marker of vagosympathetic balance of stress. Endoscopic findings were compared with Helicobacter pylori test, and autonomic status was studied using spectral analysis of heart rate variability. Results. We found significant differences in low/high frequency ratio in the spectrum of heart rate of patients with Hp-positive and Hpnegative duodenal ulcers. The result proved stress nature of idiopathic ulcers. Idiopathic ulcers are characterized by significant increase of LF /HF that can serve as a differential diagnostic criterion for different types of duodenal ulcers. Conclusion. Spectral analysis of heart rate variability can be used in differential diagnostics of peptic ulcers and idiopathic ulcers.

The Use of Heart Rate Variability in Assessing Precompetitive Stress in High-Standard Judo Athletes

The objective of this study is to examine the sensitivity to and changes in heart rate variability (HRV) in stressful situations before judo competitions and to observe the differences among judo athletes according to their competitive standards in both official and unofficial competitions. 24 (10 male and 14 female) national- and international-standard athletes were evaluated. Each participant answered the Revised Competitive State Anxiety Inventory (CSAI-2R) and their HRV was recorded both during an official and unofficial competition. The MANOVA showed significant main effects of the athlete's standard and the type of competition in CSAI-2R, in HRV time domain, in HRV frequency domain and in HRV nonlinear analysis (p<0.05). International-standard judo athletes have lower somatic anxiety, cognitive anxiety, heart rate and low-high frequency ratio than national-standard athletes (p<0.05). International-standard athletes have a higher confidence, mean RR interval, standard deviation of RR, square root of the mean squared difference of successive RR intervals, number of consecutive RR that differ by more than 5 ms, short-term variability, long-term variability, long-range scaling exponents and short-range scaling exponent than national-standard judo athletes. In conclusion, international-standard athletes show less pre-competitive anxiety than the national-standard athletes and HRV analysis is sensitive to changes in pre-competitive anxiety.

Repeated sudden falls in heart rate in a diabetic patient during sevoflurane anesthesia

Repeated sudden falls in heart rate were experienced in a diabetic patient during general anesthesia. During each fall in heart rate, analysis of heart rate variability showed a rapid increase in entropy and normalized power of high frequency. Simultaneously, a decrease was also shown in the power of the low-high frequency ratio, preceded by a trivial transient increase. These data indicated the excitation of vagal activity and the inhibition of sympathetic activity just after trivial sympathetic activation.

Effects of amlodipine and lacidipine on heart rate variability in hypertensive patients with stable angina pectoris and isolated left ventricular diastolic dysfunction

Objective To estimate the influence of therapy with amlodipine (A) or lacidipine (L) on heart rate variability (HRV) time and frequency domain parameters in hypertensive patients with stable angina pectoris and isolated left ventricular diastolic dysfunction. Methods After a 1-week washout period, the patients were randomized to receive amlodipine 10 mg (30 patients) or lacidipine 6 mg (30 patients) once-daily for 4 weeks. HRV parameters were determined over a period of 24 h, echocardiography and exercise test were performed before and after treatment. Results All HRV time domain parameters after applying amlodipine did not change significantly. A reliable decrease only of the root mean square of differences between adjacent normal-to-normal intervals (RMSSD)—32.9±13 vs. 27.5±9—was noticed after treatment with lacidipine. In the lacidipine group, the change of RMSSD negatively correlated with the extent of ST segment depression during exercise testing ( R=−0.43; P<0.05). Both drugs reduced total power (A, 2234±1270 vs. 1813±889; L, 2205±1151 vs. 1825±896; P<0.01), very low (A, 1451±733 vs. 1143±534; L, 1413±759 vs. 1213±616; P<0.05), and low frequency power (A, 610±459 vs. 447±321; L, 569±323 vs. 442±241; P<0.01). After amlodipine, high frequency power remained unchanged, whereas low–high frequency ratio decreased (4.54±1.72 vs. 3.77±1.73; P<0.05). After lacidipine, high frequency power decreased (178.8±153.2 vs. 132.1±79.3; P<0.05), whereas the ratio of low frequency to high frequency did not change. Conclusions Amlodipine and lacidipine reduce the influence of humoral control and sympathetic autonomic nervous system activity. The autonomic balance becomes shifted toward the increased vagal activity only by amlodipine.

Obesity and cardiac autonomic nerve activity in healthy children: Results of the toyama birth cohort study

To determine the relationship between obesity and cardiac autonomic nerve activity in healthy children. 16 healthy male children comprising of 9 nonobese and 7 obese subjects (body mass index > 19.1 kg/m(2)) aged 8-9 years were selected. Electrocardiograms were measured for 10 min. under controlled ventilation (0.25 Hz) in the supine position. Consecutive 256-second RR interval data were transformed by the Fast Fourier Transform method into power spectral data. Very low frequency (VLF; 0.003-0.04 Hz), low frequency (LF; 0.04-0.15Hz), high frequency (HF; 0.15-0.40Hz), and total power (TP; 0.003-0.40Hz) were calculated and transformed into a natural logarithm (In). Normalized units (nu) were also calculated as follows: LFnu=LF/(TP-VLF)x100. HFnu=HF/(TP-VLF)x100. Low/high-frequency ratio (LHR) was calculated as LF divided by HF. Unpaired t test was performed to compare the 2 groups. TP In and HFnu, reflecting cardiac parasympathetic nerve activity, in obese children were significantly lower than those in nonobese children. In contrast, LFnu and LHF, reflecting cardiac sympathetic nerve activity, in obese children were significantly higher than those in nonobese children. These findings suggest that obese children have higher sympathetic nerve activity and lower parasympathetic nerve activity than nonobese children.

Heart rate variability in hypertensive subjects

Hypertension is often associated with findings of sympathetic hyperactivity. Evidence shows that adrenergic receptor stimulation can induce left ventricular hypertrophy. Using an autoregressive algorithm in a power spectrum analysis of heart-rate variability in 14 subjects with mild hypertension (mean age 41 ± 9.0 years) and 9 age-matched normotensives we compared autonomic nervous system function at baseline (rest) and during sympathetic stress (passive head-up tilt). The spectrum comprised four spectral frequency-domains: total power (0.0033–0.40 Hz), high-frequency power (0.16–0.40 Hz), low-frequency power (0.04–0.15 Hz) and very-low-frequency power (0.0033–0.04). The high-frequency spectral component predominantly reflects vagal activity, the low-frequency component sympathetic nervous system activity. The ratio between low- and high-frequency power expresses the sympathovagal balance. Results were expressed as natural logarithms of power and normalized units. In addition, we compared spectral densities obtained, with the left ventricular mass index evaluated by M-mode echocardiography. Hypertensive subjects had greater low-frequency and low-high frequency ratio values ( P < 0.001) than normotensive controls. They also had a low capacity for increase after tilt. Multiple regression analysis showed that the left-ventricular mass index was independently associated with the body mass index ( P < 0.0027), very-low frequency ( P < 0.043), and low frequency ( P < 0.0138) expressed as the natural logarithm, low-high frequency ratio ( P < 0.0172) and systolic blood pressure ( P < 0.0353). Our findings confirm enhanced sympathetic activity in hypertensive subjects. They also indicate a close association between the left-ventricular mass index and spectral indices of sympathetic activation.