Low-frequency Component Of Heart Rate Variability Research Articles

Characterization of heart rate variability in end-stage renal disease patients after kidney transplantation with recurrence quantification analysis.

Heart rate variability (HRV) is a noninvasive approach to studying the autonomic modulation of heart rate in experimental settings, such as active standing sympathetic stimulation. It is known that patients with end-stage renal disease during active standing have few changes in HRV dynamics, which are improved after hemodialysis. However, it is unknown whether the response to active standing is recovered after definitive treatment with kidney transplantation. This work aims to assess the change in HRV dynamics in the supine position and active standing through time and frequency-based metrics, as well as recurrence plot quantitative analysis (RQA). We studied HRV dynamics by obtaining 5-minute electrocardiographic recordings from kidney transplant recipients who underwent an active standing test. The mean duration of heartbeats and their standard deviation diminished in active standing, compared with the supine position. Also, the low-frequency component of HRV and the presence of diagonal and vertical structures in RQA were predominant. A larger estimated glomerular filtration rate was significantly correlated with broader HRV in the supine position and during active standing. The narrower HRV during active standing may indicate a sympathetic response to external stimuli, which is expected in a functional cardiovascular system, and may be influenced by renal function.

Alterations in Heart Rate Variability and Electroencephalogram during20‐MinuteExtremely Low Frequency Electric Field Treatment in Healthy Men during theEyes‐OpenCondition

AbstractOur previous study examined the neural effects of extremely low frequency electric field (ELF‐EF) using electroencephalogram (EEG) and heart rate variability (HRV) measurement and revealed that the theta power of EEG increases during 1‐min EF treatment (30 kV and 50 Hz). In the present study, the effects of a longer treatment duration were assessed. EF was applied between two electrodes, one above the head and the other under the feet, for 20 min to 10 healthy men sitting on a chair. Occipital EEG and HRV were measured in the eyes‐open condition. Power spectrum analysis showed that during the EF treatment, the power of alpha and theta rhythms as well as the low frequency component of HRV increased, and the heart rate decreased. These effects did not persist after the end of EF treatment. It is suggested that ELF‐EF treatment alters not only the brain activity but also the autonomic activity reflected in HRV. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Hypoxic Respiratory Chemoreflex Control in Young Trained Swimmers.

During an apnea, changes in PaO2 activate peripheral chemoreceptors to increase respiratory drive. Athletes with continuous apnea, such as breath-hold divers, have shown a decrease in hypoxic ventilatory response (HVR), which could explain the long apnea times; however, this has not been studied in swimmers. We hypothesize that the long periods of voluntary apnea in swimmers is related to a decreased HVR. Therefore, we sought to determine the HVR and cardiovascular adjustments during a maximum voluntary apnea in young-trained swimmers. In fifteen trained swimmers and twenty-seven controls we studied minute ventilation (VE), arterial saturation (SpO2), heart rate (HR), and autonomic response [through heart rate variability (HRV) analysis], during acute chemoreflex activation (five inhalations of pure N2) and maximum voluntary apnea test. In apnea tests, the maximum voluntary apnea time and the end-apnea HR were higher in swimmers than in controls (p < 0.05), as well as a higher low frequency component of HRV (p < 0.05), than controls. Swimmers showed lower HVR than controls (p < 0.01) without differences in cardiac hypoxic response (CHR). We conclude that swimmers had a reduced HVR response and greater maximal voluntary apnea duration, probably due to decreased HVR.

The importance of highly effective lipid-lowering therapy with atorvastatin in the normalization of the autonomic regulation of heart rate in patients with STEMI

Abstract Purpose To assess the importance of highly effective lipid-lowering therapy with atorvastatin in the normalization of the autonomic regulation of cardiac activity in patients with myocardial infarction with ST segment elevation (STEMI). Methods The study included 130 patients with STEMI aged 51.3±8.9 years, the majority of males (91%). Inclusion criteria: age from 35 to 70 years, STEMI confirmed by ECG and the level of biomarkers (troponin I, CK-MB), the presence of hemodynamically significant stenosis of a culprit artery according to coronary angiography provided that other coronary arteries are occluded no more than 50%, left main coronary artery - not more than 30%. Exclusion criteria: a history of myocardial infarction, CHF III-IV NYHA, bundle branch block, atrial fibrillation, artificial pacemaker. All patients took atorvastatin at a dose of 40–80 mg/day for 48 weeks after STEMI. As part of a further study at the 7th-9th day and 48 weeks after STEMI, 24-hour ECG monitoring was performed with the Astrocard system. The spectral parameters of heart rate variability (HRV) were evaluated: TotP (ms2), ULF (ms2), VLF (ms2), LF (ms2), HF (ms2), LF / HF. By the 48th week of treatment, patients were divided into groups depending on the achievement of the target level of low density lipoproteins (LDL) of less than 1.4 mmol / l or less than 50% of the initial values: 64 people who reached target values of LDL and formed the group of high-effective lipid-lowering therapy “H”, the group of low effective treatment “L” included 66 patients whose LDL did not meet the recommended level. The groups were matched by gender, age, and anthropometric data. Results In the “H” group, by the 48th week, a pronounced power amplification of all spectral components was obtained. The TotP parameter increased from 13021 (95% CI 10967; 15076) ms2 to 20988 (95% CI 17617; 24358) ms2 (p=0.0001); HF - from 164 (95% CI 105; 222) ms2 to 249 (95% CI 178; 321) ms2 (p=0.003). An increase in the low-frequency components of HRV was observed: an increase in ULF from 10695 (95% CI 8985; 12406) ms2 to 20401 (95% CI 15099; 25703) ms2 (p=0.0001), VLF - from 1473 (95% CI 1212; 1734) ms2 to 1734 (95% CI 1478; 1990) ms2 (p=0.01), LF - from 761 (95% CI 573; 949) ms2 to 909 (95% CI 736; 1082) ms2 (p=0.02). Against the background of an increase in all parameters of the frequency spectrum, the sympathovagal balance coefficient LF / HF decreased from 6.6 (95% CI 5.7; 7.6) to 5.2 (95% CI 4.3; 6.1) ( p=0.004). An analysis of the HRV indicators dynamics in the L group revealed an increase in only the total spectrum power - TotP from 12740 (95% CI 10947; 14533) ms2 to 20195 (95% CI 16619; 23770) ms2. Conclusions Highly effective therapy with atorvastatin in STEMI patients helps to normalize the parameters of the autonomic regulation of heart rate in the post-infarction period due to the increased effects of parasympathetic activity. Funding Acknowledgement Type of funding source: None

Association between heart rate, heart rate variability, cortisol, glucose and electrolytes in healthy newborn calves

ABSTRACT This study aims at evaluating the effects of electrolytes, glucose and cortisol levels over heart rate (HR) and heart rate variability (HRV) in healthy newborn calves. Seventeen healthy Holstein calves were evaluated during their first month of life, and the plasma concentrations of glucose, cortisol, calcium, magnesium, inorganic phosphorus, sodium and potassium were analyzed. HRV indexes were determined in the time and frequency domains through the analysis of neonatal electrocardiogram recordings. In the first day, low blood levels of phosphorus presented a strong correlation with the HR and the increased high-frequency components of HRV. The plasma concentrations of magnesium decreased significantly throughout the 35 days, revealing a positive association with a decreasing low-frequency components of HRV at day 28. There was a strong correlation between HR, HRV indexes, some plasma electrolytes, glucose and cortisol during the studied period. Variations in the concentrations and correlations observed may be attributed to the adaptive neonatal period in calves.

Emotion, Respiration, and Heart Rate Variability: A Mathematical Model and Simulation Analyses

Although the generation mechanism of the low-frequency (LF) component of heart rate variability (HRV) is controversial, HRV is a potential candidate in designing objective measurement methodologies for emotions. These methodologies could be valuable for several biosignal applications. Here, we have conducted a simulation analysis using a novel mathematical model that integrates emotion, respiration, the nervous system, and the cardiovascular system. Our model has well reproduced experimental results, specifically concerning HRV with respiratory sinus arrhythmia and LF, the relation between HRV total power and the respiration frequency, and the homeostatic maintenance by the baroreflex. Our model indicates the following possibilities: (i) The delay in the heart rate control process of the parasympathetic activity works as a low-pass filter and the HRV total power decreases with a higher respiration frequency; (ii) the LF component of HRV and the Mayer wave are generated as transient responses of the baroreflex feedback control to perturbations induced by an emotional stimulus; and (iii) concentration on breathing to reduce the respiration frequency can reduce LF/HF and the reduction can be fed back to the emotional status.

Very low frequency component of heart rate variability as a marker for therapeutic efficacy in patients with obstructive sleep apnea: Preliminary study.

Background:Although positive airway pressure (PAP) therapy is effective for treating obstructive sleep apnea (OSA), some patients with severe OSA are intolerable to this treatment, which may lead to an increase in the mortality and morbidity of cardiovascular diseases. We investigated the relationship between heart rate variability (HRV) and sleep parameters during natural sleep and treatment of patients with OSA.Materials and Methods:This was the cross-sectional observation study. Patients were 17 males with severe OSA who were unable to accept continuous PAP. Standard polysomnography was performed for two consecutive nights, i.e., during natural sleep and following night with bilevel PAP (BiPAP) treatment. Time-dependent responses of the amplitudes of low frequency (LF), very low frequency (VLF), and high frequency components of HRV were assessed with the technique of complex demodulation.Results:Apnea–hypopnea index, oxygen desaturation time, and percentage of stage 1 sleep were significantly reduced, whereas the percentages of rapid eye movement and stages 3 + 4 sleep were increased, by BiPAP treatment. Therapy also reduced the amplitudes of VLF and LF components of HRV. Difference in amplitudes of VLF during natural sleep and treatment with BiPAP was significantly correlated with difference in percentages of stage 1 and stages 3 + 4 sleep.Conclusion:Therapy-induced amelioration of OSA and sleep quality was accompanied by decrease in the amplitudes of VLF components of HRV. The VLF component may thus reflect physiological changes in both autonomic activity and sleep structure and serve as an objective marker for therapeutic efficacy in patients with severe OSA.

Analysis of Reproducibility of Noninvasive Measures of Sympathetic Autonomic Control Based on Electrodermal Activity and Heart Rate Variability

Heart rate variability (HRV) and electrodermal activity (EDA) are useful tools for assessing the central and peripheral dynamics of the sympathetic nervous system and detecting the effects of numerous systemic diseases and life-challenging situations. However, the indices of HRV and EDA are highly influenced by mental stress, environmental conditions, body position, and other physiological conditions that introduce variability. In this paper, we assessed the five-day reproducibility of HRV and EDA measures of sympathetic control, for N = 20 subjects undergoing 70° head-up tilt test (HUT) and Stroop task tests. We made the assessment in highly controlled conditions without environmental causes of variability, to have a good baseline understanding of the consistency of the various indices of HRV and EDA. Therefore, we assessed intra-subject variation (using the coefficient of variation, CV) and consistency (using the intra-class correlation coefficient, ICC) of the test-to-baseline differences produced by both tests on the studied measures. The low-frequency component of HRV (HRVLF), and its normalized variant was computed as HRV measures of sympathetic control. For EDA, the skin conductance level, frequency of non-specific skin conductance responses, spectral index (EDASympn), and time-varying index (TVSymp) were computed. TVSymp (ICC = 0.85) and HRV indices exhibited higher consistency during the HUT (ICC ≥ 0.8), compared to other EDA measures, and HRVLF was the least variable measure (CV = 85.4%). EDA indices exhibited higher consistency (except for the EDASympn) during the Stroop task (ICC ≥ 0.79) when compared to HRV, and TVSymp was the least variable measure (CV = 97.2%). Remarkably, TVSymp proved to be a reproducible measurement (low variation and high consistency) in both scenarios. These results are the necessary groundwork for studying the use of EDA and HRV in real-world conditions, as reproducibility of the indices has remarkable importance in clinical practice.

The Female Heart: Sex Differences in the Dynamics of ECG in Response to Stress.

Sex differences in the study of the human physiological response to mental stress are often erroneously ignored. To this end, we set out to show that our understanding of the stress response is fundamentally altered once sex differences are taken into account. This is achieved by comparing the heart rate variability (HRV) signals acquired during mental maths tests from ten females and ten males of similar maths ability; all females were in the follicular phase of their menstrual cycle. For rigor, the HRV signals from this pilot study were analyzed using temporal, spectral and nonlinear signal processing techniques, which all revealed significant statistical differences between the sexes, with the stress-induced increases in the heart rates from the males being significantly larger than those from the females (p-value = 4.4 × 10−4). In addition, mental stress produced an overall increase in the power of the low frequency component of HRV in the males, but caused an overall decrease in the females. The stress-induced changes in the power of the high frequency component were even more profound; it greatly decreased in the males, but increased in the females. We also show that mental stress was followed by the expected decrease in sample entropy, a nonlinear measure of signal regularity, computed from the males' HRV signals, while overall, stress manifested in an increase in the sample entropy computed from the females' HRV signals. This finding is significant, since mental stress is commonly understood to be manifested in the decreased entropy of HRV signals. The significant difference (p-value = 2.1 × 10−9) between the changes in the entropies from the males and females highlights the pitfalls in ignoring sex in the formation of a physiological hypothesis. Furthermore, it has been argued that estrogen attenuates the effect of catecholamine stress hormones; the findings from this investigation suggest for the first time that the conventionally cited cardiac changes, attributed to the fight-or-flight stress response, are not universally applicable to females. Instead, this pilot study provides an alternative interpretation of cardiac responses to stress in females, which indicates a closer alignment to the evolutionary tend-and-befriend response.

PERSONALIZED EXERCISE TRAINING PROGRAM AS A COUNTERMEASURE TO ORTHOSTATIC INTOLERANCE AFTER SPACE FLIGHTS.

PERSONALIZED EXERCISE TRAINING PROGRAM AS A COUNTERMEASURE TO ORTHOSTATIC INTOLERANCE AFTER SPACE FLIGHTS.

MECHANISMS OF INTERACTION BETWEEN THE CIRCADIAN SYSTEM, EEG RHYTHMS AND REGULATION OF VEGETATIVE PROCESSES

Aim - to investigate the dynamics of EEG rhythms and vegetative responses in human on a short-term exposure of the retina to the blue light in the spectrum of maximum sensitivity of circadian photoreceptors during daytime wake. Materials and methods. EEG parameters (BP-010302 BrainАmp Standart128), blood pressure and heart rate variability (HRV) were recorded at 22 volunteer students aged 18-20 years before, after and during the 2-5 minute stimulation of circadian retinal receptors by blue light with maximum wavelength of 480 nm. Results. The stimulation of the photoreceptors of the circadian system correlates with the dynamics of the following neurovegetative processes: desynchronization in beta2- and gamma EEG rhythms, synchronization in teta2- and alpha1-frequency bands; increase in the duration of RR interval and power of low-frequency component of HRV, decrease in the percentage of high-frequency oscillation spectrum of HRV and decrease in systolic blood pressure. Termination of the stimulation of circadian system photoreceptors causes the transformation of EEG rhythms response with predominance of synchronization in low (teta1, teta 2), medium (alpha 1, alpha 2, alfa 3) and high frequency (beta 2) bands. Conclusion. The paper shows the possibility of quick correction of human vegetative background by controlling the circadian system. The human circadian clock is likely to control functional brain activity involving beta 2- and gamma-quantization.

Postexercise hypotension after maximal short-term incremental exercise depends on exercise modality.

This study investigated postexercise hypotension (PEH) after maximal cardiopulmonary exercise testing (CPET) performed using different exercise modalities. Twenty healthy men (aged 23 ± 3 years) performed 3 maximal CPETs (cycling, walking, and running), separated by 72 h in a randomized, counter-balanced order. Systolic (SBP) and diastolic blood pressure (DBP), heart rate, cardiac output, systemic vascular resistance (SVR), autonomic function (spontaneous baroreflex sensitivity (BRS) and heart rate variability (HRV)), and energy expenditure (EE) were assessed during a 60-min nonexercise control session and for 60 min immediately after each CPET. Total exercise volume (EE during CPET plus 60 min recovery) was significantly higher in running versus cycling and walking CPETs (P ≤ 0.001). Compared with control, only SBP after running CPET was significantly reduced (Δ = -6 ± 8 mm Hg; P < 0.001). Heart rate and cardiac output were significantly increased (P < 0.001) and SVR significantly decreased (P < 0.001) postexercise. BRS and HRV decreased after all CPETs (P < 0.001), whereas sympatho-vagal balance (low- and high-frequency (LF:HF) ratio) increased significantly after all exercise conditions, especially after running CPET (P < 0.001). Changes in SVR, BRS, sympathetic activity (low-frequency component of HRV), and LF:HF ratio were negatively correlated to variations in SBP (range -0.69 to -0.91; P < 0.001) and DBP (range -0.58 to -0.93; P ≤ 0.002). These findings suggest that exercise mode or the total exercise volume are major determinants of PEH magnitude in healthy men. Because of the running CPET, the PEH was primarily related to a decrease in SVR and to an increase in sympatho-vagal balance, which might be a reflex response to peripheral vasodilatation after exercise.

Synchronization analysis between heart rate variability and EEG activity before, during, and after epileptic seizure

Abstract An innovative concept for synchronization analysis between heart rate (HR) components and rhythms in EEG envelopes is represented; it applies time-variant analyses to heart rate variability (HRV) and EEG, and it was tested in children with temporal lobe epilepsy (TLE). After a removal of ocular and movement-related artifacts, EEG band activity was computed by means of the frequency-selective Hilbert transform providing envelopes of frequency bands. Synchronization between HRV and EEG envelopes was quantified by Morlet wavelet coherence. A surrogate data approach was adapted to test for statistical significance of time-variant coherences. Using this processing scheme, significant coherence values between a HRV low-frequency sub-band (0.08-0.12 Hz) and the EEG δ envelope (1.5-4 Hz) occurring both in the preictal and early postictal periods of a seizure can be shown. Investigations were performed for all electrodes at 20-s intervals and for selected electrode pairs (T3÷C3, T4÷C4) in a time-variant mode. Synchronization was more pronounced in the group of right hemispheric TLE patients than in the left hemispheric group. Such a group-specific augmentation of synchronization confirms the hypothesis of a right hemispheric lateralization of sympathetic cardiac control of the low-frequency HRV components.

Mental Work Stimulates Cardiovascular Responses through a Reduction in Cardiac Parasympathetic Modulation in Men and Women

Mental Work (MW) stimulates Cardiovascular (CV) functions in healthy adults and a reduction in cardiac parasympathetic modulation could be one mechanism involved in such a response. The influence of sex on these CV responses remains ambiguous. The aim of the study was to evaluate CV impacts of MW in healthy individuals and whether sex influences CV responses induced by MW. The impact of a 45-min reading and writing session vs. a control condition, on Blood Pressure (BP), Heart Rate (HR), and Heart Rate Variability (HRV), was evaluated in 44 healthy adults with the use of a randomized crossover design. The influence of sex on those variables was then evaluated. Diastolic BP (74 ± 1 vs. 69 ± 1 mm Hg; p < 0.05) and mean arterial pressure (MAP; 87 ± 7 vs. 83 ± 8 mmHg; p < 0.005), HR (68 ± 1 vs. 62 ± 1 bpm; p < 0.0001) and low frequency/high frequency ratio (2.8 ± 0.1 vs. 2.0 ± 0.1; p < 0.0001) were higher, while global HRV (SDNN: 84 ± 3 vs.104 ± 3 ms; p < 0.0001) and cardiac parasympathetic activity were lower during MW (p < 0.0001) vs. the control condition in the whole sample. During both experimental conditions, HR was higher (p < 0.0001), while BP, rMSSD, pNN50 and low frequency component of HRV were lower in women compared to men (all p < 0.05). The intensity of the cognitive demand and its influence on CV variables were comparable between men and women. These results support that MW increases BP and HR through decrement in cardiac parasympathetic modulation in healthy subjects and suggest that sex does not influence CV responses induced by cognitive demand of similar intensity.

Synergistic effects of exposure to concentrated ambient fine pollution particles and nitrogen dioxide in humans

Context: Exposure to single pollutants e.g. particulate matter (PM) is associated with adverse health effects, but it does not represent a real world scenario that usually involves multiple pollutants.Objectives: Determine if simultaneous exposure to PM and NO2 results in synergistic interactions.Materials and methods: Healthy young volunteers were exposed to clean air, nitrogen dioxide (NO2, 0.5 ppm), concentrated fine particles from Chapel Hill air (PM2.5CAPs, 89.5 ± 10.7 µg/m3), or NO2+PM2.5CAPs for 2 h. Each subject performed intermittent exercise during the exposure. Parameters of heart rate variability (HRV), changes in repolarization, peripheral blood endpoints and lung function were measured before and 1 and 18 h after exposure. Bronchoalveolar lavage (BAL) was performed 18 h after exposure.Results: NO2 exposure alone increased cholesterol and HDL 18 h after exposure, decreased high frequency component of HRV one and 18 h after exposure, decreased QT variability index 1 h after exposure, and increased LDH in BAL fluid. The only significant change with PM2.5CAPs was an increase in HDL 1 h after exposure, likely due to the low concentrations of PM2.5CAPs in the exposure chamber. Exposure to both NO2 and PM2.5CAPs increased BAL α1-antitrypsin, mean t wave amplitude, the low frequency components of HRV and the LF/HF ratio. These changes were not observed following exposure to NO2 or PM2.5CAPs alone, suggesting possible interactions between the two pollutants.Discussion and conclusions: NO2 exposure may produce and enhance acute cardiovascular effects of PM2.5CAPs. Assessment of health effects by ambient PM should consider its interactions with gaseous copollutants.

Autonomic Cardiac Regulation During Spontaneous Nocturnal Hypoglycemia in Patients With Type 1 Diabetes

OBJECTIVEExperimental clamp studies have suggested that hypoglycemia evokes a reduction of cardiac vagal control in patients with type 1 diabetes. However, there are limited data on the influence of spontaneous nocturnal hypoglycemia on cardiac autonomic regulation.RESEARCH DESIGN AND METHODSAdults with type 1 diabetes (n = 37) underwent continuous glucose monitoring via a subcutaneous sensor as well as recording of R-R interval or electrocardiogram for 3 nights. Heart rate (HR) variability was analyzed during periods of hypoglycemia (glucose <3.5 mmol/L) (minimum length of 20 min) and a control nonhypoglycemic period (glucose >3.9 mmol/L) of equal duration and at the same time of night.RESULTSThe duration of hypoglycemic and control episodes (n = 18) ranged from 20 to 190 min (mean 71 min). HR (62 ± 7 vs. 63 ± 9 beats per min; P = 0.30) or the high-frequency component of HR power spectrum (2,002 ± 1,965 vs. 1,336 ± 1,506 ms2; P = 0.26) did not change during hypoglycemia. Hypoglycemia resulted in a significant decrease in the low-frequency component of HR variability (2,134 ± 1,635 vs. 1,169 ± 1,029 ms2, respectively; P = 0.006). The decline in the glucose concentration displayed a significant positive correlation with the decrease of the low-frequency component of HR variability (r = 0.48; P = 0.04). The latter was closely related to an increase in muscle sympathetic nerve activity recorded in 10 subjects during controlled sympathetic activation.CONCLUSIONSSpontaneous nocturnal hypoglycemia in patients with type 1 diabetes results in a reduction of the low-frequency component of HR, which is best explained by excessive sympathetic activation without a concomitant withdrawal of vagal outflow.

Failed heart rate recovery at a critical age in 5-HT-deficient mice exposed to episodic anoxia: implications for SIDS

Mice deficient in the transcription factor Pet-1⁻/⁻ have a ∼70% deficiency of brainstem serotonin [5-hydroxytryptamine (5-HT)] neurons and exhibit spontaneous bradycardias in room air at postnatal day (P)5 and P12 and delayed gasping in response to a single episode of anoxia at P4.5 and P9.5 (Cummings KJ, Li A, Deneris ES, Nattie EE. Am J Physiol Regul Integr Comp Physiol 298: R1333-R1342, 2010; and Erickson JT, Sposato BC. J Appl Physiol 106: 1785-1792, 2009). We hypothesized that at a critical age Pet-1⁻/⁻ mice will fail to autoresuscitate during episodic anoxia, ultimately dying from a failure of gasping to restore heart rate (HR). We exposed P5, P8, and P12 Pet-1⁻/⁻ mice and wild-type littermates (WT) to four 30-s episodes of anoxia (97% N₂-3% CO₂), separated by 5 min of room air. We observed excess mortality in Pet-1⁻/⁻ only at P8: 43% of Pet-1⁻/⁻ animals survived past the third episode of anoxia while ∼95% of WT survived all four episodes (P = 0.004). No deaths occurred at P5 and at P12, and one of six Pet-1⁻/⁻ mice died after the fourth episode, while all WT animals survived. At P8, dying Pet-1⁻/⁻ animals had delayed gasping, recovery of HR, and eupnea after the first two episodes of anoxia (P < 0.001 for each); death ultimately occurred when gasping failed to restore HR. Both high- and low-frequency components of HR variability were abnormally elevated in dying Pet-1⁻/⁻ animals following the first episode of anoxia. Dying P8 Pet-1⁻/⁻ animals had significantly fewer 5-HT neurons in the raphe magnus than surviving animals (P < 0.001). Our data indicate a critical developmental window at which a brainstem 5-HT deficiency increases the risk of death during episodes of anoxia. They may apply to the sudden infant death syndrome, which occurs at a critical age and is associated with 5-HT deficiency.

CORRELATION BETWEEN FASTING PLASMA GLUCOSE AND AUTONOMIC DYSFUNCTION IN HEALTHY SUBJECTS WITH NORMOGLYCEMIA: AN EARLY IMPAIRMENT IN CARDIOVASCULAR ADAPTATION: PP.17.144

Objective: Autonomic neuropathy associated with the higher risk of cardiovascular mortality. It is known, that the autonomic dysfunction appears in the early phases of the disturbances of the carbohydrate metabolism already. The aim of this study was to determine the correlations between autonomic dysfunction and the fasting plasma glucose in healthy subjects with a normal carbohydrate metabolism according to the WHO criteria, normal body weight and blood pressure. Design and Method: 14 healthy subjects were included. Autonomic function was investigated by means of the five standard cardiovascular reflex tests, heart rate variability (HRV) and the spontaneous baroreflex sensitivity (BRS). The blood pressure was measured continuously with the Finapres 2300. The ECG signal was detected continuously by means of a Siemens Sirecust 730 ECG. The signals were fed through an analog-digital converter into a computer and analysed off-line. The oscillation amplitude of R-R intervals were analysed as well as the time and frequency domain indexes of HRV. The spontaneous BRS was calculated in the supine position and after standing up and based on the analysis of the spontaneous fluctuations of blood pressure and interbeat intervals. Statistical analysis was performed by SPSS program. Results: There were statistical significant negative relationships between the fasting plasma glucose and the heart rate response to deep breathing (r = -0.58, p < 0.05), the heart rate response to standing up (r = -0.56, p < 0.05), standard deviation of all RR intervals (r = -0.59, p < 0.05), root mean square of successive RR differences (r = -0.57, p < 0.05), power of low frequency component of HRV (r = -0.56, p < 0.05), power of high frequency component of HRV (r = -0.57, p < 0.05) and the BRS after standing up (r = -0.56, p < 0.05). There were no statistical differences between the fasting plasma glucose and the another cardiovascular reflex tests. Conclusions: Our results suggest the existence of a close relationship between the increase of the normal range for fasting plasma glucose in healthy subjects and the autonomic dysfunction which may forecast the early cardiovascular adaptation damage.

Autonomic impairment after myocardial infarction: Role in cardiac remodelling and mortality

1. Impairmant of baroreflex sensitivity (BRS) has been implicated in the reduction of heart rate variability (HRV) and in the increased risk of death after myocardial infarction (MI). In the present study, we investigated whether the additional impairment in BRS induced by sinoaortic baroreceptor denervation (SAD) in MI rats is associated with changes in the low-frequency (LF) component of HRV and increased mortality rate. 2. Rats were randomly divided into four groups: control, MI, denervated (SAD) and SAD + MI rats. Left ventricular (LV) function was evaluated by echocardiography. Autonomic components were assessed by power spectral analysis and BRS. 3. Myocardial infarction (90 days) reduced ejection fraction (by approximately 42%) in both the MI and SAD + MI groups; however, an increase in LV mass and diastolic dysfunction were observed only in the SAD + MI group. Furthermore, BRS, HRV and the LF power of HRV were reduced after MI, with an exacerbated reduction seen in SAD + MI rats. The LF component of blood pressure variability (BPV) was increased in the MI, SAD and SAD + MI groups compared with the control group. Mortality was higher in the MI groups compared with the non-infarcted groups, with an additional increase in mortality in the SAD + MI group compared with the MI group. Correlations were obtained between BRS and the LF component of HRV and between LV mass and the LF component of BPV. 4. Together, the results indicate that the abolishment of BRS induced by SAD in MI rats further reduces the LF band of HRV, resulting in a worse cardiac remodelling and increased mortality in these rats. These data highlight the importance of this mechanism in the prognosis of patients after an ischaemic event.

Effect of acute sleep deprivation on vascular function in healthy subjects

Sleep disorders are associated with inflammation and sympathetic activation, which are suspected to induce endothelial dysfunction, a key factor in the increased risk of cardiovascular disease. Less is known about the early effects of acute sleep deprivation on vascular function. We evaluated microvascular reactivity and biological markers of endothelial activation during continuous 40 h of total sleep deprivation (TSD) in 12 healthy men (29 +/- 3 yr). The days before [day 1 (D1)] and during TSD (D3), at 1200 and 1800, endothelium-dependent and -independent cutaneous vascular conductance was assessed by iontophoresis of acetylcholine and sodium nitroprusside, respectively, coupled to laser-Doppler flowmetry. At 0900, 1200, 1500, and 1800, heart rate (HR) and instantaneous blood pressure (BP) were recorded in the supine position. At D1, D3, and the day after one night of sleep recovery (D4), markers of vascular endothelial cell activation, including soluble intercellular adhesion molecule-1, vascular cell adhesion molecule-1, E-selectin, and interleukin-6 were measured from blood samples at 0800. Compared with D1, plasma levels of E-selectin were raised at D3, whereas intercellular adhesion molecule-1 and interleukin-6 were raised at D4 (P < 0.05). The endothelium-dependent and -independent CVC were significantly decreased after 29 h of TSD (P < 0.05). By contrast, HR, systolic BP, and the normalized low-frequency component of HR variability (0.04-0.15 Hz), a marker of the sympathetic activity, increased significantly within 32 h of TSD (P < 0.05). In conclusion, acute exposure to 40 h of TSD appears to cause vascular dysfunction before the increase in sympathetic activity and systolic BP.