High Frequency Index Research Articles

The impact of regular physical training on the function of the autonomic nervous system in patients with inappropriate sinus tachycardia

Introduction: Sympathetic overactivity plays a crucial role in the pathogenesis of inappropriate sinus tachycardia (IST). It has been shown that regular physical activity positively affects the balance between the sympathetic and parasympathetic nervous systems, which may benefit patients with IST.Objective: This study aimed to assess the impact of regular physical training on the autonomic nervous system (ANS) function in patients with IST, focusing on heart rate variability (HRV) as an indicator of autonomic balance.Methods:The study included 32 female patients diagnosed with IST, with 16 in the study group (Group A) and 16 in the control group (Group B). The women in Group A participated in a structured physical training program lasting 12 weeks. HRV was analyzed based on 24-hour Holter monitoring recordings before and after the intervention. The statistical data obtained were presented as graphs illustrating changes in selected HRV parameters in response to physical training.Results:The study results indicate a significant improvement in heart rate variability (HRV) after 12 weeks of regular physical training in the study group. Notably, there was an increase in parameters associated with parasympathetic activity, such as the HF (High Frequency) index. Additionally, the SDNN index, which measures overall heart rate variability, also improved. These observations suggest that physical training contributed to an improvement in autonomic balance. The graphs in the study clearly depict changes in individual HRV parameters, confirming the positive impact of physical activity on the function of the autonomic nervous system in patients with IST.

Effect of olfactory stimulation from aromatherapy on the autonomic nervous activity during aerobic exercises

Variations in the autonomic nervous system activity during exercise therapy in patients with cardiovascular diseases may lead to adverse events. Aromatherapy may reduce these adverse events by enhancing parasympathetic nervous activity (PNA). However, the effects of aromatherapy during exercise remain relatively unknown. This study aimed to evaluate the effect of aromatherapy on autonomic nervous activity during exercise and recovery. This randomized crossover study included 20 healthy men subjected to both aroma and placebo conditions which involved rest and moderate-intensity aerobic exercise on a cycle ergometer, followed by recovery. Blood pressure, heart rate variability indices, and SpO2 were measured during the rest, exercise, and recovery phases. Moreover, aroma preferences and emotional changes in response to the aroma were assessed. Under the placebo condition, high frequency (HF), root mean square of successive differences indices, and heart rate showed delayed recovery (P < 0.05). Furthermore, a moderate positive correlation was identified between aroma preference, pleasant emotions induced by aromatherapy, and the HF index (P < 0.05). These results indicate that aromatherapy facilitates the recovery of PNA after exercise. Furthermore, these effects were more pronounced among individuals who exhibited a stronger preference for and more positive emotions toward aromas.

Heart rate fragmentation is impaired in type 2 diabetes mellitus patients

AimsTo evaluate the heart rate fragmentation (HRF) of type 2 diabetes mellitus (T2DM) patients and its relationship with heart rate variability (HRV) indices. MethodsOne hundred sixty-four men, aged 47–57 years were retrospectively analyzed from a database. Participants were T2DM (n = 82) and apparently healthy (n = 82). R-R interval time series recorded by electrocardiogram were collected at the supine position for 10 to 15 min. From HRF, the percentage of inflection points (PIP), percentage of words with zero, one, two, or three inflections points (W0, W1, W2, W3), and percentage with only type hard, soft, or mixed inflections points type (WH, WS, WM) were quantified. ResultsT2DM presented higher PIP, WS, WM and W3, while WH and W1 was lower compared with healthy (p < 0.05). Moreover, a positive moderate correlation was found between WH and root mean square of the successive R-R differences (RMSSD) and high frequency (HF) indices. In contrast, a negative moderate correlation was found between WS and WM with RMSSD and HF indices. ConclusionsT2DM have increased fragmentation patterns, and words grouped by inflection type are more closely related to HRV. The HRF approach might be useful to assess heart rate dynamic abnormalities in males with type 2 diabetes.

Spectral analysis of signals of autonomic regulation of blood circulation in patients with COVID-19 and arterial hypertension

The work aims to carry out a comparative analysis of the spectral indices of the photoplethysmogram signals and RR-intervals of healthy volunteers, patients with COVID-19, as well as patients with COVID-19 and chronic arterial hypertension of 1-2 degrees. The study included 45 records of pairs of electrocardiogram and photoplethysmogram signals. Each sample included 15 pairs of 20-minute experimental signals. The study revealed an increase in the integrated power of the low-frequency (LF) band over the integrated power of the high-frequency (HF) band in the photoplethysmogram signals in patients with COVID-19, burdened with hypertension. In the signals of the RR-intervals, the largest values of the ratio of the LF to HF indices are associated with patients without cardiovascular diseases. In turn, this may be an indicator of the different effects of viral infection and arterial hypertension on the loops of autonomic control of heart rate and vascular tone.

Increased afternoon step count increases heart rate variability in patients with cardiovascular risk factors.

The present study investigated whether morning or afternoon activity is more effective at increasing the high-frequency (HF) index, a parasympathetic index, in patients with cardiovascular risk factors. A decreased HF index, a heart rate variability (HRV) parameter, is a well-established marker of poor cardiovascular prognosis. Because blood pressure and sympathetic tone are higher in the morning, physical activity and exercise in the afternoon has been recommended for patients with cardiovascular diseases. However, there have been no reports concerning the superior effects of afternoon exercise on parasympathetic activity and sleep. This observational study was a post hoc comparison. Patients' physical activity was measured for 1month to determine their habits. Patients' HF index was measured by 24-h Holter electrocardiography. The study enrolled 56 patients. Each patient's morning step count (before lunch) and afternoon step count (between lunch and dinner) were compared. We adhered to the STROBE guidelines in the present study. Thirty-one patients took more steps in the morning, and 25 patients took more steps in the afternoon. The present study showed that those who took more steps in the afternoon had a significantly higher HF index during the first hour after sleep onset and during sleep than those who took more steps in the morning (p=.003, .047). The present study showed that those who took more steps in the afternoon had a significantly higher HF index during the first hour after sleep onset and a higher HF index during sleep than those who took more steps in the morning. Exercise in the afternoon may improve the prognosis in patients with cardiovascular disease by not only preventing excessive blood pressure, afterload, and sympathetic tone but also positively influencing the parasympathetic system and sleep.

Identification of the sleep-wake states in rats using the high-frequency activity of the electroencephalogram.

The electroencephalographic signal constitutes the main sign classically used for the identification of states of alertness. However, activities in the high frequency (>100Hz) range have not been properly studied despite their high potential for sleep scoring in rodents. In the present study, we designed a method for the identification of the sleep-wake states in rats by exclusively using high-frequency activities of the electroencephalogram. By calculating the ratio between the amplitude of the electroencephalographic signal from 110 to 200Hz and from 110 to 300Hz, we obtained an index that had values that were low during wakefulness, intermediate during non-REM sleep and high during REM sleep. This high-frequency index (HiFI) allowed the identification of each state without the need to study other signs such as muscle activity or eye movements. To evaluate the performance of the index, we compared it with the conventional scoring of the sleep-wake cycle based upon the study of the electromyogram and delta (0.5-4Hz), theta (6-9Hz) and sigma (10-14Hz) bands of the electroencephalogram. The index had an accuracy of 90.43±1.91% (Cohen's kappa value of 0.82), confirming that the study of the high-frequency activities of the electroencephalogram was sufficient to reliably identify alertness states in the rat. Compared to other sleep-scoring methods, the HiFI has several advantages. It only requires one electroencephalography electrode, thus reducing the severity of the surgical preparation of the experimental animal, and its calculation is very simple, so it can be easily implemented online to classify sleep-wake states in real time.

Seismo-acoustic evidence for vent drying during shallow submarine eruptions at Bogoslof volcano, Alaska

Characterizing the state of the volcanic vent is key for interpreting observational datasets and accurately assessing volcanic hazards. This is particularly true for remote, complex eruptions such as the 2016–2017 Bogoslof volcano, Alaska eruption sequence. Bogoslof’s eruptions in this period were either shallow submarine or subaerial, or some combination of both. Our results demonstrate how low-frequency sound waves (infrasound), integrated with seismic and satellite data, can provide unique insight into shallow vent processes, otherwise not available. We use simple metrics, such as the infrasound frequency index (FI), event duration, and acoustic-seismic amplitude ratio, to look at changes in the elastic energy radiation and infer changes in seawater access to the vent. Satellite imagery before and after selected eruptions is used to ground-truth inferences on vent conditions. High FI and gradual increases in infrasound frequency content at Bogoslof correspond with transitions from submarine to subaerial vent conditions and a diminished or absent role of water, likely resulting in a drying out of the vent region. Event durations generally correlate with high FI and the range of FI values for each event, suggesting long duration events were more effective at drying out the vent region. A trend from low to high acoustic-seismic amplitude ratios for some long duration events also suggests an increase in acoustic efficiency as the vent dried out. We demonstrate that infrasound can serve as a robust indicator of seawater involvement for Bogoslof and other shallow submarine eruptions that may not be inferable from other datasets, particularly in near-real-time.

Increased Activity in Patients with Cardiovascular Risk Factors Increases Heart Rate Variability.

This study evaluated the effect of increased physical activity on high-frequency (HF) heart rate variability (HRV) during the first hour after sleep onset in patients with hypertension and/or stable angina pectoris. Physical activity and HF were measured using activity monitors and 24-hour Holter monitors at baseline and 6 months later. The physical activity increased in 28 patients (increase group) and decreased in 20 patients (decrease group) after 6 months. In this study, after 6 months, compared to the decreased physical activity group, the increased physical activity group showed a significant increase in the HF index during the first hour after sleep onset. Therefore, the increase in the HF index may have been due to the increase in physical activity. An increase in physical activity suggests that the quality of sleep early in the sleep cycle may be improved, which may affect the patient's prognosis.

Tonin Overexpression in Mice Diminishes Sympathetic Autonomic Modulation and Alters Angiotensin Type 1 Receptor Response.

Background: Tonin, a serine-protease that forms Angiotensin II (AngII) from angiotensinogen, is increased in failing human heart samples. Increased blood pressure (BP) and decreased heart rate (HR) variabilities are associated with higher risk of cardiovascular morbidity. Losartan has been used to reduce hypertension and, therefore, lowers the risk of fatal and non-fatal cardiovascular events. Determination of tonin's impact on BP and HR variabilities as well as the impact of losartan remain questions to be elucidated.Aim: Evaluation of cardiovascular autonomic profile in transgenic mice overexpressing the rat tonin enzyme TGM'(rton) and the impact of AT1 receptor blocker, losartan.Methods: Male C57BL/6 (WT) and TGM'(rTon) mice were cannulated for recording BP (Windaq, 4 MHz) for 30 min at baseline and 30 min after losartan injection (20 mg/kg). BP and HR variabilities were analyzed in time and frequency domain method. Low-frequency (LF) and high-frequency (HF) components were identified for sympathetic and parasympathetic modulations analysis. Ang I, AngII, and Ang1-7 were quantified by high performance liquid chromatography method. The total enzymatic activity for AngI, AngII, and Ang1-7 formation was evaluated in the heart and plasma by Liquid chromatography mass spectrometry (LC-MS/MS).Results: At the baseline TGM'(rTon) exhibited higher BP, lower cardiac LF, higher cardiac HF, lower LF/HF, and lower alpha index than wild type (WT). After losartan injection, TGM'(rTon) mice presented an additional decrease in cardiac LF and increase in HF in relation to baseline and WT. In the vasculature, losartan caused decreased in BP and LF of systolic BP in WT mice in relation to its baseline. A similar effect was observed in the BP of TGM'(rTon) mice; however, LF of systolic BP increased compared to baseline. Our data also indicates that AT1R receptor signaling has been altered in TGM’(rTon)mice. Interestingly, the dynamics of the renin-angiotensin system kinetics change, favoring production of Ang1-7.Conclusion: Autonomic evaluation of TGM’(rTon) mice indicates an unclear prognosis for diseases that affect the heart. HR variability in TGM’(rTon) mice indicates high risk of morbidity, and sympathetic and parasympathetic modulation indicate low risk of morbidity. The low risk of morbidity could be the biased production of Ang1-7 in the heart and circulation; however, the altered response of AT1R in the TGM’(rTon) remains to be elucidated, as well aswhether that signaling is pro-protection or pro-pathology.

Spectral analysis of dike‐induced earthquakes in Afar, Ethiopia

AbstractShallow dike intrusions may be accompanied by fault slip above the dikes, a superposition which complicates seismic and geodetic data analyses. The diverse volcano‐tectonic and low‐frequency local earthquakes accompanying the 2005–2010 large‐volume dike intrusions in the Dabbahu‐Manda Hararo rift (Afar), some with fault displacements of up to 3 m at the surface, provide an opportunity to examine the relations among the earthquakes, dike intrusions, and surface ruptures. We apply the frequency index (FI) method to characterize the spectra of swarm earthquakes from six of the dikes. These earthquakes often have broad spectra with multiple peaks, making the usual peak frequency classification method unreliable. Our results show a general bimodal character with high FI earthquakes associated with deeper dikes (top &gt; 3 km subsurface) and low FI earthquakes associated with shallow dikes, indicating that shallow dikes result in earthquakes with more low‐frequency content and larger‐amplitude surface waves. Low FI earthquakes are more common during dike emplacement, suggesting that interactions between the dike and faults may lead to lower FI. Taken together, likely source processes for low FI earthquakes are shallow hypocenters (&lt;3 km) possibly with surface rupture, slow rupture velocities, and interactions with dike fluids. Strong site effects also heavily influence the earthquake spectral content. Additionally, our results suggest a continuum of spectral responses, implying either that impulsive volcano‐tectonic earthquakes and the unusual, emergent earthquakes have similar source processes or that simple spectral analyses, such as FI, cannot distinguish different source processes.

Low intensity static stretching does not modulate heart rate variability in trained men

OBJECTIVE: To investigate the acute effect of static stretching on heart rate variability in trained men. METHODS: Eight subjects were randomly submitted to two situations, as follows: a static stretch protocol and 20 minutes at rest. The stretch protocol consisted of two sets of 30 seconds of static stretch of the chest muscles with a 40 second of interval between them. After 48 hours, the procedures were reversed so that all the subjects should were submitted to the two situations. The values of heart rate variability were measured before and after the experimental and control situation (stretch vs. rest). We registered the following cardiac variables: root mean square of standard deviation (rMSSD), the number of pairs of successive beats that differ by more than 50 ms (pNN50), low frequency (LF) and high frequency (HF). The Shapiro-Wilk and the paired Student's test were used for statistical analysis; a critical level of significance of p 0.05) were found (stretching vs. control) to the RMSSD, pNN50, LF and HF indices. However, although no statistical differences were observed, the figures show large changes on mean values, suggesting an unclear effect on the sympathetic-vagal modulation. CONCLUSION: The present results suggest that a low intensity (motion range until discomfort point) and volume (1 minute) of static stretching does not significantly affect the acute sympathetic-vagal control in trained men. Because the protocol did not show differences regarding the studied variables, we suggest that there is not a sufficient level of physiological basis to perform this type of exercise in a traditional pre-exercise setting, if the purpose is obtain gains in physical performance.

Cardiac autonomic activity has a circadian rhythm in summer but not in winter in non-lactating pregnant dairy cows

This investigation was conducted to examine circadian and seasonal rhythms of heart rate and heart rate variability (HRV) by means of hour-by-hour recordings over 24h in a large population of non-lactating Holstein–Friesian pregnant cows [N=56, summer (June–July); N=61, winter (November–December)]. Data were collected during a 5-day period from each animal. Besides parameters of cardiac autonomic function [the high-frequency (HF) component of HRV and the ratio between the low-frequency (LF) and the HF components (LF/HF ratio)], the RR triangular index and Lmax were calculated. A clear circadian profile was observed for every parameter in summer. Heart rate elevated gradually with the course of the day from 7:00 to 17:00 o'clock and then slightly decreased from 18:00 to 6:00. Sympathovagal balance shifted towards sympathetic dominance during the daytime (increased LF/HF ratio), whereas parasympathetic activity was predominant during the night (increased HF). Lmax reflected a chaotic behavior of heart rate fluctuations during the afternoon in summer. Decreased values of RR triangular index indicated a sensitive period for cows between 14:00 and 16:00 o'clock in summer. During winter, except for the RR triangular (RRtri) index reflecting a high overall variability in R–R intervals between 12:00 and 23:00 o'clock, heart rate and HRV showed no periodicity over the 24-h period. The results suggest an impaired cardiac autonomic function during daytime in summer. HF, Lmax and RRtri index showed seasonal differences for both daytime and nighttime. Heart rate was higher in summer than in winter during the daytime, whereas the LF/HF ratio was higher in winter during the nighttime. Circadian and seasonal rhythms of cardiovascular function are presumably related to the differing temperature, and animal activity associated with summer and winter. As all of the investigated parameters are commonly used in bovine HRV research, these findings have practical implications for behavioral, physiological and welfare studies on dairy cattle.

Resposta aguda do sistema nervoso autônomo a diferentes estímulos auditivos musicais em mulheres

Objective. To compare the acute response of the autonomic nervous system (ANS) before exposure to auditory stimuli of different musi­cal styles in women. Method. Cross-sectional study with 27 women aged between 18 and 30 years old, apparently healthy. Volunteers remained at rest for 10 minutes and were exposed to classical music (64-84 dB) and heavy metal (75-84 dB) for 10 minutes, via headset, and their heart rate variability (HRV) was recorded during the entire period. Statistical indices were analyzed in the time domain and in­dexes in the frequency domain: low frequency component (LF), high frequency (HF) and LF / HF ratio of HRV. Results. There was an increase in the LF index (p=0.04) and decrease in HF index (p=0.02) in comparing stimuli of heavy metal and classical music. There was also a difference in LF/HF ratio (p=0.007) when comparing classical and heavy metal music. Conclusion. The acute response to exposure of the SNA musical auditory stimuli through headphones attended incremental component of the sympathetic, parasympathetic with­drawal and increased sympathetic-vagal balance component in heavy metal style compared to classical music.

Response of cardiac autonomic modulation after a single exposure to musical auditory stimulation.

The acute effects after exposure to different styles of music on cardiac autonomic modulation assessed through heart rate variability (HRV) analysis have not yet been well elucidated. We aimed to investigate the recovery response of cardiac autonomic modulation in women after exposure to musical auditory stimulation of different styles. The study was conducted on 30 healthy women aged between 18 years and 30 years. We did not include subjects having previous experience with musical instruments and those who had an affinity for music styles. The volunteers remained at rest for 10 min and were exposed to classical baroque (64-84 dB) and heavy metal (75-84 dB) music for 10 min, and their HRV was evaluated for 30 min after music cessation. We analyzed the following HRV indices: Standard deviation of normal-to-normal (SDNN) intervals, root mean square of successive differences (RMSSD), percentage of normal-to-normal 50 (pNN50), low frequency (LF), high frequency (HF), and LF/HF ratio. SDNN, LF in absolute units (ms2) and normalized (nu), and LF/HF ratio increased while HF index (nu) decreased after exposure to classical baroque music. Regarding the heavy metal music style, it was observed that there were increases in SDNN, RMSSD, pNN50, and LF (ms2) after the musical stimulation. In conclusion, the recovery response of cardiac autonomic modulation after exposure to auditory stimulation with music featured an increased global activity of both systems for the two musical styles, with a cardiac sympathetic modulation for classical baroque music and a cardiac vagal tone for the heavy metal style.

Autonomic functioning in irritable bowel syndrome measured by heart rate variability: A meta‐analysis

To analyze autonomic functioning which presented as the high frequency (HF) component of heart rate variability, a measurement of vagal tone, and the ratio of low frequency (LF) to HF (LF : HF), an indicator of sympathovagal balance in irritable bowel syndrome (IBS) patients. We identified relevant studies by performing a literature search of MEDLINE, EMBASE and the ISI Web of Knowledge to 31 March 2013. Pooled effect sizes with 95% confidence interval (CI) were calculated using a random effects model. Between-study heterogeneity was assessed using the Q test and I(2) statistic. In all, 11 articles including 392 IBS patients and 263 controls met the inclusion criteria of the analysis. IBS patients had lower HF band power (Hedges's g = -0.38, 95% CI -0.68 to -0.09) than the controls (I(2) = 63.6%, P = 0.003). Moreover, IBS patients showed a higher LF : HF (Hedges's g = 0.43, 95% CI 0.13-0.74), with no significant heterogeneity. A subgroup analysis of the HF index according to the recording time yielded different results for the IBS patients and controls. Additionally, constipation-predominant IBS (IBS-C) patients had decreased HF band power, whereas no significant difference was found in LF : HF. Impaired parasympathetic functioning and abnormal sympathovagal balance may be involved in the pathogenesis of IBS. Vagal dysfunction is more obvious in the IBS-C subgroup.

Spikes in Mammalian Bipolar Cells Support Temporal Layering of the Inner Retina

In the mammalian retina, 10-12 different cone bipolar cell (BC) types decompose the photoreceptor signal into parallel channels, providing the basis for the functional diversity of retinal ganglion cells (RGCs). BCs differing in their temporal properties appear to project to different strata of the retina's inner synaptic layer, based on somatic recordings of BCs and excitatory synaptic currents measured in RGCs. However, postsynaptic currents in RGCs are influenced by dendritic morphology and receptor types, and the BC signal can be transformed at the axon terminals both through interactions with amacrine cells and through the generation of all-or-nothing spikes. Therefore, the temporal properties of the BC output have not been analyzed systematically across different types of mammalian BCs. We recorded calcium signals directly within axon terminals using two-photon imaging and show that BCs can be divided into ≥eight functional clusters. The temporal properties of the BC output were directly reflected in their anatomical organization within the retina's inner synaptic layer: faster cells stratified closer to the border between ON and OFF sublamina. Moreover, ≥three fastest groups generated clear all-or-nothing spikes. Therefore, the systematic projection pattern of BCs provides distinct temporal "building blocks" for the feature extracting circuits of the inner retina.

Spionidae (Annelida: Polychaeta) from the Aegean Sea (eastern Mediterranean)

The present paper deals with spionid species (Spionidae) collected from various depths (4–183 m) and biotopes at 100 stations along the eastern part of the Aegean Sea in June–September 2000. A total of 35 species and 16 genera were identified, of which two species (Laonice norgensis and Spiophanes algidus) are new to the Mediterranean fauna, two species (Laonice bahusiensis and Polydora agassizi) are new to the eastern Mediterranean fauna, three species (Prionospio (Prionospio) saccifera, P. (P.) depauperata and Spiophanes afer) are new to the fauna of the Aegean Sea and four species are new to the fauna of Turkey. Prionospio (Prionospio) fallax and P. (P.) steenstrupi were represented by the highest dominance values, and Laonice cirrata and P. (M.) cf. multibranchiata by the highest frequency index values. The maximum number of species (28) were found on muddy bottom at 5–25 m. Nine species [Laonice norgensis, Paraprionospio coora, Polydora cornuta, Prionospio (Prionospio) depauperata, P. (P.) saccifera, P. (Minuspio) pulchra, Pseudopolydora paucibranchiata, Spiophanes algidus and Streblospio gynobranchiata] can be classified as alien.

Fractal correlation of heart rate variability in obese children

Background The loss of variability and fractal properties in the heart rate is related to greater morbidity and mortality rates. Objective The aim of the present study was to analyze heart rate dynamics in obese children by measuring short and long-term fractal exponents and heart rate variability (HRV) indices. Materials and methods 112 male and female children aged 8 to 12 years were divided into two groups based on body mass index: obese ( n = 51) and normal weight range ( n = 61). Heart rate was monitored beat-to-beat in the dorsal decubitus position for 20 min, analyzing the low frequency (LF) and high frequency (HF) spectral indices in normalized units and ms² as well as short and long-term fractal exponents (alpha-1 and alpha-2) of the detrended fluctuation analysis (DFA). The non-paired Student's t-test and Mann–Whitney test were used for the statistical analysis, with the level of significance set at P ≤ 0.05. Results The following were lower in the obese children: alpha-1 exponent value (0.930 ± 0.14 vs. 0.992 ± 0.11; P = 0.012), LF index (219.0 vs. 361.0; P = 0.001) and HF index (175.0 vs. 227.0; P = 0.019) in ms 2. No significant differences between groups were found for the alpha-2 exponent, LF and HF indices in normalized units or LF/HF ratio. Conclusion The obese children exhibited a reduction in short-term fractal correlation properties in heart frequency dynamics associated to a reduction in both sympathetic and parasympathetic activities, thereby demonstrating a need for early treatment for these children in order to avoid future complications.

The Health Effects of Mercury on the Cardiac Autonomic Activity According to the Heart Rate Variability

Objectives: The effect of mercury on the cardiovascular system has recently been reported on, but the mechanisms as well as its nature of this effect still need to be confirmed. In this study, the mercury in the hair of a community population was analyzed in relation to the cardiac autonomic activity. Methods: A hair sample was obtained from the occiput area and the mercury in the hair was analyzed by using a Direct Mercury Analyzer. We measured the cardiovascular risk factors, including total cholesterol, triglyceride, blood pressure, and the body mass index (BMI). Heart rate variability was assessed for 5 minutes, in the time and frequency domain, by using SA-3000P from the Medi-core ® company. The association between the mercury in the hair and heart rate variability was assessed after controlling for the other cardiovascular risk factors. Results: The mean age of the 671 total subjects was 36 years. The geometric mean of the hair mercury was 0.90 ppm. The hair mercury level was elevated in males, adults, smokers and drinkers. Hair mercury and age, the systolic and diastolic blood pressure, total cholesterol, triglyceride, LDL cholesterol and BMI were all positively correlated. However, hair mercury and heart rate, HDL cholesterol, standard deviation of the NN intervals (SDNN), total power (TP), low-frequency (LF), high- frequency (HF) were negatively correlated. In the higher mercury group, heart rate, SDNN, LF and HF indices were significantly lower compared with those of the lower mercury group. Heart rate was decreased 2.6 beats/min, Ln (HF) was decreased 0.131 msec2 and HF norm was decreased 2.550 with a 1 ppm increase of Ln (Hg), according to multiple linear regression analysis after controlling for age, gender and other cardiovascular risk factors. Conclusion: This cross-sectional study showed that mercury may affect the cardiac autonomic activity through parasympathetic dysfunction.

Estimation of spontaneous baroreflex sensitivity using transfer function analysis: effects of positive pressure ventilation

To determine the short-term effects of non-invasive positive pressure ventilation (PPV) on spontaneous baroreflex sensitivity, we acquired time series of RR interval and beat-to-beat blood pressure in 55 healthy volunteers (mean age 46.5+/-10.5 years), who performed breathing tests on four occasions at frequencies of 12 and 15/min, with application of PPV of 5 mbar, and without positive pressure (control). Using spectral and transfer function analysis, we estimated RR interval variability (HRV) and systolic blood pressure variability (SBPV), as well as the gain (alpha-index) and phase shift (Phi) of the baroreceptor reflex for low- (LF) and high-frequency (HF) bands. Compared to control breathing, PPV at 12 and 15/min led to an increase in mean RR (p<0.001) and blood pressure (p<0.05). The alpha-index in the HF band increased significantly due to PPV for both respiratory frequencies (p<0.05). Phase shifts did not show significant changes in response to pressure ventilation. These results indicate that short-term administration of PPV in normal subjects elicits significant enhancement in the HF index of baroreflex gain. These findings may contribute to understanding the mechanisms, indications, and effectiveness of positive pressure breathing strategies in treating cardiorespiratory and other disease conditions.