Heart Rate Oscillations Research Articles

Vagal function indexed by respiratory sinus arrhythmia and cholinergic anti-inflammatory pathway

The autonomic nervous system, in particular vagal function, plays an important role in a wide range of somatic and mental disorders. Cardiac vagal function can be indexed by the respiratory sinus arrhythmia (RSA) – oscillations in heart rate linked to respiration mediated predominantly by fluctuations of vagus nerve efferent traffic originating in the nucleus ambiguus. Moreover, the neurocardiac vagal modulation has been shown to be related to physiological adaptability/flexibity and emotional regulation. Thus, greater vagal withdrawal during stressors and subsequent recovery should be indicative of a more flexible physiological response system.Importantly, the vagal inhibitory function plays a key role in the regulation of allostatic processes including the immune response (cholinergic anti-inflammatory pathway). Decreased cardiovagal function (lower RSA) was shown to be associated with increased proinflammatory markers and acute-phase proteins indicating increased allostatic load and poor health. Thus, the study of the vagal–immune interactions could help illuminate the pathway via which psychosocial factors may influence health and disease.

Why should one normalize heart rate variability with respect to average heart rate

Heart rate variability (HRV) is a recognized risk factor in many disease states (Bravi et al., 2011; Sacha et al., 2013a). However, HRV is significantly correlated with an average heart rate (HR), and this association is both physiologically and mathematically determined. The physiological determination comes from the autonomic nervous system activity (Task Force of the European Society of Cardiology, and the North American Society of Pacing and Electrophysiology, 1996), but the mathematical one is caused by the non-linear (inverse) relationship between R-R interval and HR (Sacha and Pluta, 2005a,b, 2008). HRV may be estimated by using R-R interval (the most frequent method) or HR signals, yet, they both do not yield the same results since they are inversely related with each other—indeed, the analyses are mathematically biased (Sacha and Pluta, 2005a,b). If one uses R-R intervals, the same changes of HR cause much higher fluctuations of R-R intervals for the slow average HR than for the fast one (Figure ​(Figure1A).1A). Conversely, if one employs HR signals, the same changes of R-R intervals cause much higher fluctuations of HR for the fast than slow average HR (Figure ​(Figure1B).1B). Consequently, due to these mathematical reasons, HRV estimated from R-R intervals should negatively correlate with average HR (or positively with average R-R interval), but HRV estimated from HR signals should be positively correlated with average HR (or negatively with average R-R interval) (Sacha and Pluta, 2005a,b). Moreover, due to the inverse relationship between R-R interval and HR, there is a possibility that a given patient may have higher HRV than another in terms of R-R intervals and lower HRV in terms of HRs—Figure 1C explains such a case (Sacha and Pluta, 2005a). Figure 1 (A)The non-linear (mathematical) relationship between R-R interval and heart rate is depicted. One can see that the oscillations of a slow average heart rate (x-axis, dark gray area) result in much greater oscillations of RR intervals (y-axis, dark gray ... Another mathematical problem concerning the association between HRV and HR is presented in Figure ​Figure1D.1D. One can see that the fluctuations of R-R intervals may be potentially very high for slow average HR, however, the same fluctuations are not possible for fast average HR, since the R-R intervals should have become negative. The same problem can be met if one calculates HRV from HR signals, i.e., the average HR of 80 bpm may potentially fluctuate between 30 and 130 bpm (i.e., the fluctuation amplitude equals 100 bpm), however, such fluctuations are not possible for the average HR of 40 bpm, since the heart rhythm must have fluctuated between −10 and 90 bpm. Due to the above facts, the standard HRV analysis is mathematically biased, particularly if patients differ in terms of their average HRs. The only way to overcome it is to calculate HRV with respect to the average value, i.e., to normalize the fluctuations with respect to the mean (Sacha and Pluta, 2005a,b, 2008). One can do that by division of the signal by the average R-R interval in the case of R-R interval signal, or by the average HR in the case of HR signal. Moreover, this way the same results are obtained no matter if one calculates HRV from R-R intervals or HRs (Sacha and Pluta, 2005a). Such an approach enables to explore the HR contribution to the physiological and clinical significance of HRV (Billman, 2013; Sacha et al., 2013a). Recently, this approach has been further developed to enhance or completely remove the HR influence (even physiological one) on HRV, what turned out to provide valuable information on cardiac and non-cardiac prognosis in patients after myocardial infarction—the details have been published elsewhere (Sacha et al., 2013a,b,c). To conclude, HRV is significantly associated with HR, which is caused by both physiological and mathematical phenomena, however, by a simple mathematical modification one may exclude mathematical bias and explore a real clinical value of HR and its variability.

Physical therapy for airway clearance improves cardiac autonomic modulation in children with acute bronchiolitis

BackgroundThe effects of physical therapy on heart rate variability (HRV), especially in children, are still inconclusive. ObjectiveWe investigated the effects of conventional physical therapy (CPT) for airway clearance and nasotracheal suction on the HRV of pediatric patients with acute bronchiolitis. Method24 children were divided into two groups: control group (CG, n=12) without respiratory diseases and acute bronchiolitis group (BG, n=12). The heart rate was recorded in the BG at four different moments: basal recording (30 minutes), 5 minutes after the CPT (10 minutes), 5 minutes after nasotracheal suction (10 minutes), and 40 minutes after nasotracheal suction (30 minutes). The CG was subjected to the same protocol, except for nasotracheal suction. To assess the HRV, we used spectrum analysis, which decomposes the heart rate oscillations into frequency bands: low frequency (LF=0.04-0.15Hz), which corresponds mainly to sympathetic modulation; and high frequency (HF=0.15-1.2Hz), corresponding to vagal modulation. ResultsUnder baseline conditions, the BG showed higher values in LF oscillations, lower values in HF oscillations, and increased LF/HF ratio when compared to the CG. After CPT, the values for HRV in the BG were similar to those observed in the CG during basal recording. Five minutes after nasotracheal suction, the BG showed a decrease in LF and HF oscillations; however, after 40 minutes, the values were similar to those observed after application of CPT. ConclusionsThe CPT and nasotracheal suction, both used for airway clearance, promote improvement in autonomic modulation of HRV in children with acute bronchiolitis.

Abstract 9481: The Response of the Qt Interval and the T-wave Morphology to Sudden Tachycardia Provoked by Standing in Young Athletes

Background: the response of the QT interval to the sudden tachycardia provoked by standing can aid in the diagnosis of the long QT syndrome (LQTS). It is therefore important to know what is the normal response to this maneuver. The aim of this study was to characterise the response of the QT interval and the T-wave morphology following this provocation test in young healthy athletes. Methods: ECG was analysed as part of a prospective study about the impact of cardiovascular screening with ECG in young (14-35 years) athletes. ECG was performed after 5 minute of supine resting. Athletes without cardiac abnormalities, not taking drugs and with normal ECG (QTc for men < 450 msec, for women < 460 msec) were asked to stand up quickly with continuous ECG monitoring for 30”. Heart rate, QT, QTc (Bazett) and T-wave morphology [normal, biphasic, notched G1 (T2>T1), notched G2 (T2>>T1)] were analysed at baseline and at maximal tachycardia. Results: ECG of 289 athletes was analysed (76 % men, mean age 18.4 ± 5.6 years). Baseline parameters were following: heart rate 69 ± 11/min, QT 378 ± 27 msec, QTc 401 ± 21 msec. After standing, the maximal heart rate was 101 ± 13/min. QT was 361 ± 28 msec (shortening by 17 ±11 msec). In 4 % of athletes QT increased by 10-20 msec. QTc was 466 ± 30 msec (lengthening of 65 ± 24 msec). In 12 % of athletes QTc was ≥ 500 msec. T-wave morphology during tachycardia were notched G2 in 6% of athletes. During tachycardia, 15 % of athletes displayed a QTc ≥ 500 msec or QT lengthening or notched G2 morphology of T waves. Conclusions: During sudden tachycardia, a significant proportion of healthy young athletes demonstrated QTc interval and changes of T-wave morphology in the magnitude observed in patients with the LQTS. Caution should be applied in interpreting these parameters in ECG tracing and Holter monitoring displaying sudden oscillations of heart rate in this population.

Effect of copper and cadmium ions on heart function and calpain activity in blue mussel Mytilus edulis

The heart rate and calpain activity of blue mussels Mytilus edulis from the sublittoral zone, exposed to different levels of water-borne copper and cadmium, was investigated in a long-term experiment. The content of cadmium and copper in the blue mussel was determined using flame and graphite Atomic absorption spectroscopy. The observed concentrations ranged from 2.5 to 89.1 μg/g dry weight for cadmium and from 6.1 to 51.0 μg/g dry weight for copper in the control and highest concentration, respectively. Initially, increase in cardiac activity in response to copper and Cadmium exposure was observed under all pollutant concentrations (5–250 and 10–500 μg/L, respectively). The calpain-like activity in gills and hepatopancreas of the mussels treated with metals changed in dose- and time-dependent manner: from a sharp rise at the 250 μg/L concentration of copper on the first day to a significant decrease under the effect of Cadmium in the concentration of 500 μg/L on the third day of the experiment. These results suggest that: (i) heart rate oscillation may reflect active adaptation of blue mussels to contamination and (ii) animals have different sensitivity to copper and Cadmium according to the role of the metals in the mussels’ life activity.

Selection of optimal dose of beta-blocker treatment in myocardial infarction patients based on changes in synchronization between 0.1 Hz oscillations in heart rate and peripheral microcirculation

Selection of the optimal dose of beta-blocker treatment in myocardial infarction (MI) patients is problematic because of a lack of well-established guidelines. We evaluated changes in synchronization between 0.1 Hz oscillations in heart rate (HR) and plethysmographic peripheral microcirculation in response to a tilt-table test and to 3-month treatment with the highest tolerated beta-blocker (metoprolol) dose in 43 patients aged between 41 and 77 years with acute MI 6 months prior to the start of the study. Before the study the patients were treated with small doses of beta-blocker. Phase differences between HR and peripheral microcirculation oscillations were used to measure the degree of synchronization (S), and relative change in S from horizontal position was used to characterize the response to vertical tilt. Two groups of MI patients matched for clinical characteristics were identified on the basis of the results. The first group was composed of patients with decreased S as a response to vertical tilt at the beginning of the study. The patients with increased S during vertical tilt before treatment with the highest tolerated beta-blocker dose were attributed to the second group. The response to vertical tilt in the first group of patients was postulated to indicate the need to increase beta-blocker dose, and in turn, the response in the second group to indicate an already adequate beta-blocker dose. Assessment of synchronization of 0.1 Hz HR and peripheral microcirculation oscillations as a response to a tilt test can possibly be used as a guideline for selecting beta-blocker dose in post-MI patients.

Oscillations of Heart Rate and Respiration Synchronize During Affective Visual Stimulation

The objective of this study is to investigate the synchronization between breathing patterns and heart rate during emotional visual elicitation, that is, using sets of images gathered from the international affective picture system having five levels of arousal and five levels of valence, including a neutral reference level. Thirty-five healthy volunteers were emotionally elicited in agreement with a bidimensional spatial localization of affective states, i.e., arousal/valence plane, while two peripheral physiological signals, ECG and Respiration activity, were acquired simultaneously. The synchronization was then quantified by applying the concept of phase synchronization of chaotic oscillators, i.e., the cardio-respiratory synchrogram. This technique allowed us to estimate the synchronization ratio m:n as the attendance of n heartbeats in each m respiratory cycle, even for noisy and nonstationary data. We found a stronger evidence of cardiorespiratory synchronization during arousal than during neutral states.

Assessing cross-partner associations in physiological responses via coupled oscillator models.

A host of theoretical frameworks suggest associations of physiological signals between two individuals within a romantic relationship. However, few studies have provided empirical evidence of such associations using physiological reactivity from both partners in the dyad. In this study we use measures of respiration and heart rate from romantic partners recorded across three laboratory tasks. We examine the interrelations of each measure between both dyad members using coupled linear oscillators (Boker & Nesselroade, 2002). These models were used to capture oscillations in respiration and heart rate, and to examine interdependence in the physiological signals between both partners. Results show that associations were detectable within all three tasks, with different patterns of coupling within each task. Discussion centers on ways to investigate the synchrony of physiological responses across within relationships, including the promises of and obstacles for doing so.

Autonomic regulation during quiet and active sleep states in very preterm neonates

The immature autonomic nervous system (ANS) in premature infants regulates heart rate (HR) and respiration different during quiet sleep (QS) and active sleep (AS). Little information is available about ANS regulation in these subjects. The aim of this study was to investigate changes in autonomic regulation and cardiorespiratory coupling during AS and QS in five very preterm neonates with gestational age (GA) 26–31 weeks, applying univariate and bivariate linear and non-linear dynamics methods to the recorded cardiorespiratory signals. During QS univariate linear indices revealed lower standard deviations and entropies, indicating decreased heart rate (HR) variability. More balanced sympatho-vagal behavior of the ANS was revealed by decreased low frequency (LF), increased high frequency (HF), and a trend toward lower ratio LF/HF in QS. Applied non-linear indices (probabilities, entropies, and fractal measures) quantifying the complexity and scaling behavior of HR regulation processes were significantly altered in QS in comparison to AS. This reflects a lower short-term variability, less complexity, and a loss of fractal-like correlation properties of HR dynamics in QS. One major finding is that cardiorespiratory coupling is not yet completely developed in very preterm neonates with 26–31 weeks GA. Significantly different regulation patterns in bivariate oscillations of HR and respiration during AS and QS could be recognized. These patterns were characterized on the one hand by predominant monotonous regulating sequences originating from respiration independently from HR time series in AS, and to a minor degree in QS, and on the other hand by some prominent HR regulation sequences in QS independent of respiratory regulation. We speculate that these findings might be suitable for monitoring preterm neonates and for detecting disorders in the developing cardiorespiratory system.

Individual approach to antihypertensive drug choice in hypertensive patients based on individual features of autonomic cardiovascular dysfunction

Objective. Development of differentiated method for selection of antihypertensive drugs in hypertensive patients based on assessment of individual features of autonomic cardiovascular dysfunction evaluated by spectral parameters of heart rate variability (HRV) and synchronization of 0.1 Hz oscillation in heart rate and microcirculation. Design and methods. 105 patients with arterial hypertension stage 1-2 aged 47 ± 8 years were examined. 0.1 Hz oscillations in heart rate and microcirculation were registered during passive tilt test under spontaneous breathing. The signals were recorded before and after three-week treatment by angiotensin-converting enzyme (ACE) inhibitors (fosinopril or enalapril) and β-blockers (atenolol or metoprolol). Phase differences between 0.1 Hz oscillations were used to measure the synchronization index S . Power of low- (LF) and high-frequency (HF) bands of HRV spectrum was also assessed. Results. ACE inhibitors are preferred for treatment of hypertensive patients with initially severe systemic autonomic dysfunction (index S is 250 ms 2 in supine position). β-blockers are recommended for patients with initially severe systemic autonomic dysfunction and dysfunction of autonomic heart regulation (index S 2 in vertical body position). If severe autonomic dysfunction (index S is > 25 % and power of LF band of HRV spectrum is > 250 ms 2 ) is not present the treatment by ACE inhibitors and β-blockers is not recommended. Conclusions. The type of antihypertensive drugs (ACE inhibitors or β-blockers) should be selected based on individual features of autonomic cardiovascular dysfunction. Sensitivity and specificity of this method was 65 and 73 %, respectively.

Improvement of Heart Rate Variability by Eurythmy Therapy After a 6-Week Eurythmy Therapy Training

Eurythmy therapy (EYT) is a mind-body therapy used in anthroposophic medicine. Recently, the authors were able to show that at comparable workloads, EYT stimulated heart rate variability (HRV) whereas conventional ergometer training attenuated HRV. Furthermore, a long-term improvement of quality of life (QoL) and stress coping strategies by EYT could be shown. This study aimed to evaluate the long-term effects of EYT training on HRV. A total of 23 healthy women (mean age = 44.57 ± 8.04 years) performed 10 hours of EYT over a period of 6 weeks. Electrocardiograms were recorded before and after the EYT trial. HRV was quantified by the extent of high (HF), low (LF), very low (VLF), and ultra low frequency (ULF) oscillations of heart rate. Autonomic regulation was significantly changed following the EYT training compared with baseline. Especially the proportion referring to the total power (P) of HF/P and LF/P increased, whereas ULF/P and (ULF+VLF)/P decreased after the training period. EYT shifted the autonomic regulation proportionally referring to the total power mainly caused by changes of ULF and VLF components of HRV. The LF and HF spectral components were also decreased following EYT while their proportion in relation to the total variance of the power spectrum was increased. The proportional enhancement of the higher frequency and the decrease of the ULF and VLF components are probably an indicator of an improvement of autonomic regulation processes by more relaxed physical activity after the EYT training, thus supporting the plausibility of the improved QoL and better stress coping strategies.

Low-frequency fluctuations in heart rate, cardiac output and mean arterial pressure in humans: what are the physiological relationships?

Cardiovascular variability is a complex physiological phenomenon associated with the outcome of cardiovascular diseases. Blood pressure oscillations may cause cardiovascular complications, which, however, are also claimed to have antihypertensive effects. The physiological understanding is limited. This study evaluates whether oscillations in heart rate (HR) and cardiac output (CO) buffer fluctuations at approximately 0.1 Hz in arterial blood pressure (Mayer waves). We recorded mean arterial pressure (MAP), left cardiac stroke volume (SV), and HR in 10 healthy humans during autonomic blockade in supine and tilted (30 degrees) position. Variability in the cardiovascular variables at 0.04-0.15 Hz and phase angles (time lags) between the variables were calculated by spectral analysis. Fluctuations in cardiovascular variables at 0.1 Hz decreased after removal of HR variability (HRV) by propranolol and atropine in the supine position. Tilting from supine did not change fluctuations in MAP or total peripheral resistance (TPR), whereas variations in CO decreased. Variations in CO remained decreased in tilt after atropine compared to supine control, whereas variations in MAP and in TPR were unchanged. HRV were in phase with oscillations in CO. Variations in CO were in inverse phase with variations in TPR. TPR oscillations produce fluctuations in MAP at 0.1 Hz. HRV produces CO variations, but CO variations do not efficiently buffer MAP variations during supine rest and mild ortostasis. Both feedback and feedforward mechanisms are responsible for the interaction between HR and MAP.

Clustering Heart Rate Dynamics Is Associated with β-Adrenergic Receptor Polymorphisms: Analysis by Information-Based Similarity Index

BackgroundGenetic polymorphisms in the gene encoding the β-adrenergic receptors (β-AR) have a pivotal role in the functions of the autonomic nervous system. Using heart rate variability (HRV) as an indicator of autonomic function, we present a bottom-up genotype–phenotype analysis to investigate the association between β-AR gene polymorphisms and heart rate dynamics.MethodsA total of 221 healthy Han Chinese adults (59 males and 162 females, aged 33.6±10.8 years, range 19 to 63 years) were recruited and genotyped for three common β-AR polymorphisms: β1-AR Ser49Gly, β2-AR Arg16Gly and β2-AR Gln27Glu. Each subject underwent two hours of electrocardiogram monitoring at rest. We applied an information-based similarity (IBS) index to measure the pairwise dissimilarity of heart rate dynamics among study subjects.ResultsWith the aid of agglomerative hierarchical cluster analysis, we categorized subjects into major clusters, which were found to have significantly different distributions of β2-AR Arg16Gly genotype. Furthermore, the non-randomness index, a nonlinear HRV measure derived from the IBS method, was significantly lower in Arg16 homozygotes than in Gly16 carriers. The non-randomness index was negatively correlated with parasympathetic-related HRV variables and positively correlated with those HRV indices reflecting a sympathovagal shift toward sympathetic activity.ConclusionsWe demonstrate a bottom-up categorization approach combining the IBS method and hierarchical cluster analysis to detect subgroups of subjects with HRV phenotypes associated with β-AR polymorphisms. Our results provide evidence that β2-AR polymorphisms are significantly associated with the acceleration/deceleration pattern of heart rate oscillation, reflecting the underlying mode of autonomic nervous system control.

A Novel Index of Sympathovagal Balance From Independent Component Analysis of Heart Rate and Blood Pressure Variability: Performance in Patients With Carotid Stenting and in the EuroBavar Data Set

The authors applied independent component analysis to oscillations of heart rate and blood pressure and obtained a new index of sympathovagal balance. The performance of this index was tested in patients with carotid artery stenting and in the EuroBavar data set according to the following criteria: (1) the index should vary similarly among subjects in response to different autonomic conditions; (2) the variability in the index among subjects exposed to the same autonomic conditions should be small; and (3) the response of the index to various autonomic conditions should reflect the underlying changes in the physiological state and have a meaningful interpretation. The new index from independent component analysis better fulfilled the criteria than the commonly used sympathovagal index, the ratio of low-to-high frequency spectra power of heart rate variability, and had higher discrimination power in distinguishing the autonomic status of the patients who had undergone carotid artery stenting from that of the control subjects.

Quantification of Nonlinear Features in Cardiovascular Signals

Quantification of Nonlinear Features in Cardiovascular Signals The analysis of spontaneous heart rate and blood pressure oscillations under standardized conditions is a rapid, sensitive, noninvasive and reproducible tool for the assessment of cardiovascular autonomic dysfunction. Since the heart and vessels are controlled by a nonlinear deterministic system, measures derived from nonlinear systems theory are increasingly used in cardiovascular variability analysis. New nonlinear methods with applicability to real biological signals are continuously developed to quantify new aspects of cardiovascular signals with the potential to reveal subtle changes in the cardiovascular control system. Nonlinear measures provide complementary information about qualitative features of the analyzed signal. Since the analysis of variability magnitude and signal nonlinear characteristics (complexity, recurrences, time irreversibility, etc.) can provide independent information on cardiovascular system control, we suggest that simultaneous use of both groups of measures can increase the information value and thus improve the sensitivity and reliability of the detection and monitoring of the cardiovascular system dysregulation during various pathological conditions.

Time Irreversibility of Heart Rate Oscillations During Orthostasis

Time Irreversibility of Heart Rate Oscillations During Orthostasis Introduction: Time irreversibility is a characteristic feature of non-equilibrium, complex systems involving cardiovascular control mediated by autonomic nervous system. Its analysis in heart rate variability (HRV) signal represents a new approach to assess cardiovascular regulatory mechanisms. The purpose of this paper was to assess the changes in various time irreversibility indices during the orthostatic test (a balance of autonomic nervous system shifted towards sympathetic predominance). In addition, we tested the behaviour of the selected irreversibility indices in relation to different lengths of analysed data and their mutual dependence. Methods: We examined the irreversibility of HRV time series obtained from 28 healthy young subjects recorded during 20 minutes in the supine position followed by 15 minutes in the standing position. We used three different time irreversibility indices - Porta's, Guzik's and Costa's indices (P%, G% and A, respectively). The proposed irreversibility indices were derived from data segments containing 300, 600 and 1000 beat-to-beat intervals. Results: Two of three time irreversibility indices (P% and A) were sensitive to the shift in sympathovagal balance during the orthostatic challenge even when calculated from the shortest data length. Indices were relatively insensitive to data length - there were no significant differences in relation to data length. Despite the difference in algorithms for the calculation of indices P% and A, these are closely mathematically related and do not provide mutually independent information. Conclusion: We conclude that heart rate irreversibility indices are sensitive to the changes in autonomic tone after the orthostatic challenge even when derived from the 300 interbeat intervals. Porta's index seems to be more sensitive to autonomic nervous balance shift compared to Guzik's index. Costa's index is closely related to P% and do not provide any additional information compared to other indices.

Link between heart rate and blood pressure Mayer wave during general anesthesia

Mayer wave (~10 s) blood pressure (BP) oscillations may represent rhythmic vasomotor activity. However, it remains unclear if volatile anesthetics disturb the coherence between heart rate (HR) and BP rhythms in this region, which may result in improperly affecting BP-HR modulation by the baroreflex, especially when sympathetic stimulation is evoked during general anesthesia using sevoflurane-nitrous oxide (Sev-N2O). Twenty-seven patients were anesthetized with Sev-N2O, followed by surgical incision which induces Mayer wave augmentation. Baseline status before surgical incision was compared with that of 19 awake volunteers, and with status after surgical incision. Baroreflex function was assessed by gain and coherence by transfer function analysis, and the baroreflex effectiveness index (BEI). BP Mayer waves were measured by BP variability at a low frequency (LF) of ~0.1 Hz, and spontaneous baroreflex sensitivity (BRS) was obtained by assessing transfer function gain at LF (BRSLF), and the sequence technique (BRSSEQ). Sev-N2O anesthesia markedly reduced Mayer waves by 93%, BRSLF by 42%, BRSSEQ by 81%, BEI by 37%, coherence by 42%, and the number of coherent segments by 73%, compared with awake controls. During sympathetic stimulation by surgical incision, however, augmentation of Mayer waves (-1.57±0.72 vs. -0.60±1.00, ln mmHg2 P<0.001) did not improve depressed coherence above 0.5 (0.37±0.09 vs. 0.43±0.11) or BEI (0.17±0.13 vs. 0.13±0.05). Sev-N2O anesthesia alters the link between HR and BP Mayer wave oscillation even during sympathetic stimulation, indicating weak spontaneous baroreceptor-HR modulation during general anesthesia.

Post-weaning social isolation induces abnormal forms of aggression in conjunction with increased glucocorticoid and autonomic stress responses

We showed earlier that social isolation from weaning (a paradigm frequently used to model social neglect in children) induces abnormal forms of attack in rats, and assumed that these are associated with hyperarousal. To investigate this hypothesis, we deprived rats of social contacts from weaning and studied their behavior, glucocorticoid and autonomic stress responses in the resident-intruder paradigm at the age of 82 days. Social isolation resulted in abnormal attack patterns characterized by attacks on vulnerable targets, deficient social communication and increased defensive behaviors (defensive upright, flight, freezing). During aggressive encounters, socially deprived rats rapidly switched from one behavior to another, i.e. showed an increased number of behavioral transitions as compared to controls. We tentatively term this behavioral feature “behavioral fragmentation” and considered it a form of behavioral arousal. Basal levels of plasma corticosterone regularly assessed by radioimmunoassay between 27 and 78 days of age were not affected. In contrast, aggression-induced glucocorticoid responses were approximately doubled by socially isolation. Diurnal oscillations in heart rate assessed by in vivo biotelemetry were not affected by social isolation. In contrast, the aggression-induced increase in heart rate was higher in socially isolated than in socially housed rats. Thus, post-weaning social isolation induced abnormal forms of aggression that developed on the background of increased behavioral, endocrine and autonomic arousal. We suggest that this paradigm may be used to model aggression-related psychopathologies associated with hyperarousal, particularly those that are triggered by adverse rearing conditions.

Cardiac autonomic balance in rats submitted to protein restriction after weaning

1. In the present study, we evaluated the autonomic balance of the heart in protein/energy-undernourished rats. 2. Rats were divided into two groups according to the diet they received after weaning: (i) the control group (n=16), given a 15% protein diet, and (ii) the malnourished group (n=14), fed a 6% protein diet. Cardiovascular recordings were made and, through selective autonomic blockade, the tonic autonomic balance, cardiac autonomic index and the power spectrum of heart rate (HR) variability were determined. 3. Muscarinic receptor blockade with methylatropine (5.0 mg/kg, i.v.) increased HR in the control group (371 ± 6 vs 427 ± 15 b.p.m. before and after drug administration, respectively), but not the malnourished group (438 ± 24 vs 472 ± 38 b.p.m. before and after drug administration, respectively). Inhibition of β(1)-adrenoceptors with metoprolol (2.0 mg/kg, i.v.) reduced HR in malnourished rats (428 ± 24 vs 355 ± 16 b.p.m. before and after drug administration, respectively), but had no effect on the HR of the control group (363 ± 8 vs 362 ± 7 b.p.m. before and after drug administration, respectively). Double autonomic blockade by inhibiting both muscarinic cholinoceptors and β(1)-adrenoceptors reduced HR in the malnourished group (428 ± 24 vs 342 ± 14 b.p.m.) but had no effect on HR in the control group (371 ± 6 vs 382 ± 6 b.p.m.). 4. Sympathetic tone was augmented in malnourished compared with control rats (131 ± 17 vs 41 ± 11 b.p.m., respectively), whereas parasympathetic tone was reduced in malnourished compared with control rats (-4 ± 4 vs 22 ± 9 b.p.m., respectively). 5. The ratio of oscillations in HR induced by sympathetic and parasympathetic activity was higher in malnourished compared with control rats (0.43 ± 0.03 vs 0.34 ± 0.02, respectively). 6. The results of the present study indicate that protein malnutrition after weaning increases sympathetic activity and reduces vagal activity to the heart in rats. These data provide a new perspective on the pathophysiology of metabolic and cardiovascular diseases associated with protein malnutrition, especially with regard to autonomic modulation.

Automatic detection and quantification of sleep apnea using heart rate variability

Detection of sleep apnea using electrocardiographic (ECG) parameters is noninvasive and inexpensive. Our approach is based on the hypothesis that the patient's sleep-wake cycle during episodes of sleep apnea modulates heart rate (HR) oscillations. These HR oscillations appear as low-frequency fluctuations of instantaneous HR (IHR) and can be detected using HR variability analysis in the frequency domain. The purpose of this study was to evaluate the efficacy of our ECG-based algorithm for sleep apnea detection and quantification. The algorithm first detects normal QRS complexes and R-R intervals used to derive IHR and to estimate its spectral power in several frequency ranges. A quadratic classifier, trained on the learning set, uses 2 parameters to classify the 1-minute epoch in the middle of each 6-minute window as either apneic or normal. The windows are advanced by 1-minute steps, and the classification process is repeated. As a measure of quantification, the algorithm correctly classified 84.7% of all the 1-minute epochs in the evaluation database; and as a measure of the accuracy of apnea classification, the algorithm correctly classified all 30 test recordings in the evaluation database either as apneic or normal. Our sleep apnea detection algorithm based on analysis of a single-lead ECG provides accurate apnea detection and quantification. Because of its noninvasive and low-cost nature, this algorithm has the potential for numerous applications in sleep medicine.