Ultra Low Frequency Power Research Articles

Heart rate variability measured early in patients with evolving acute coronary syndrome and 1-year outcomes of rehospitalization and mortality.

ObjectiveThis study sought to examine the prognostic value of heart rate variability (HRV) measurement initiated immediately after emergency department presentation for patients with acute coronary syndrome (ACS).BackgroundAltered HRV has been associated with adverse outcomes in heart disease, but the value of HRV measured during the earliest phases of ACS related to risk of 1-year rehospitalization and death has not been established.MethodsTwenty-four-hour Holter recordings of 279 patients with ACS were initiated within 45 minutes of emergency department arrival; recordings with ≥18 hours of sinus rhythm were selected for HRV analysis (number [N] =193). Time domain, frequency domain, and nonlinear HRV were examined. Survival analysis was performed.ResultsDuring the 1-year follow-up, 94 patients were event-free, 82 were readmitted, and 17 died. HRV was altered in relation to outcomes. Predictors of rehospitalization included increased normalized high frequency power, decreased normalized low frequency power, and decreased low/high frequency ratio. Normalized high frequency >42 ms2 predicted rehospitalization while controlling for clinical variables (hazard ratio [HR] =2.3; 95% confidence interval [CI] =1.4–3.8, P=0.001). Variables significantly associated with death included natural logs of total power and ultra low frequency power. A model with ultra low frequency power <8 ms2 (HR =3.8; 95% CI =1.5–10.1; P=0.007) and troponin >0.3 ng/mL (HR =4.0; 95% CI =1.3–12.1; P=0.016) revealed that each contributed independently in predicting mortality. Nonlinear HRV variables were significant predictors of both outcomes.ConclusionHRV measured close to the ACS onset may assist in risk stratification. HRV cut-points may provide additional, incremental prognostic information to established assessment guidelines, and may be worthy of additional study.

Estimates of the power per mode number of broadband ULF waves at geosynchronous orbit

AbstractIn studies of radial diffusion processes in the magnetosphere it is well known that ultralow frequency (ULF) waves of frequency mωd can resonantly interact with particles of drift frequency ωd, where m is the waves' azimuthal mode number. Due to difficulties in estimating m, an oversimplifying assumption is often made in simulations, namely that all ULF wave power is located at a single mode number. In this paper a technique is presented for extracting information on the distribution of ULF power in a range of azimuthal mode numbers. As a first step, the cross power and phase differences between time series from azimuthally aligned magnetometers are calculated. Subsequently, through integrating the ULF power at particular ranges of phase differences that correspond to particular mode numbers, estimates of the fraction of the total power at each phase difference range or mode number are provided. Albeit entwined with many ambiguities, this technique offers critical information that is currently missing when estimating radial diffusion of energetic particles. As proof‐of‐concept, the technique is first tested successfully for a well‐studied case of narrowband ULF Field Line Resonances (FLR) for which the mode number was calculated simultaneously through ground‐based and space measurements. Subsequently, the technique is demonstrated for the broadband ULF waves that accompanied the 2003 “Halloween” magnetospheric storms. The temporal evolution of power at each mode number gives insight into the evolution of ULF waves during a storm as well as more accurate characterization of broadband ULF waves that can be used in radial diffusion simulations.

Physical activity and heart rate variability in older adults: the Cardiovascular Health Study.

Cardiac mortality and electrophysiological dysfunction both increase with age. Heart rate variability (HRV) provides indices of autonomic function and electrophysiology that are associated with cardiac risk. How habitual physical activity among older adults prospectively relates to HRV, including nonlinear indices of erratic sinus patterns, is not established. We hypothesized that increasing the levels of both total leisure-time activity and walking would be prospectively associated with more favorable time-domain, frequency-domain, and nonlinear HRV measures in older adults. We evaluated serial longitudinal measures of both physical activity and 24-hour Holter HRV over 5 years among 985 older US adults in the community-based Cardiovascular Health Study. After multivariable adjustment, greater total leisure-time activity, walking distance, and walking pace were each prospectively associated with specific, more favorable HRV indices, including higher 24-hour standard deviation of all normal-to-normal intervals (Ptrend=0.009, 0.02, 0.06, respectively) and ultralow-frequency power (Ptrend=0.02, 0.008, 0.16, respectively). Greater walking pace was also associated with a higher short-term fractal scaling exponent (Ptrend=0.003) and lower Poincaré ratio (Ptrend=0.02), markers of less erratic sinus patterns. Greater total leisure-time activity, and walking alone, as well, were prospectively associated with more favorable and specific indices of autonomic function in older adults, including several suggestive of more normal circadian fluctuations and less erratic sinoatrial firing. Our results suggest potential mechanisms that might contribute to lower cardiovascular mortality with habitual physical activity later in life.

Physical Activity and Aerobic Fitness are Positively Associated With Heart Rate Variability in Obese Adults

Autonomic nervous system (ANS) dysfunction and obesity are intrinsically related to each other. In normal-weight subjects physical activity (PA) and fitness are related to cardiovascular autonomic regulation, providing evidence that aerobic training may improve ANS functioning measured by heart rate variability (HRV). The goal of this study was to investigate the association between lifetime PA, aerobic fitness and HRV in obese adults. Participants included 107 (87 females) volunteers (mean age 44.5 years, median BMI 35.7) who completed health and lifestyle questionnaires and measurements of maximal aerobic performance, anthropometry and 24 h HRV. In the multivariate linear regression analyses, lifetime physical activity explained 40% of the variance in normal R-R intervals (SDNN). Each 1-category increase in the activity index increased SDNN by 15.4 (P = .009) and 24% of the variance in natural logarithmic value of ultra-low frequency power (P = .050). High measured VO2max explained 45% of the variance in natural logarithmic value of high-frequency power (P = .009) and 25% of the variance in low frequency/high frequency ratio (P < .001). Lifetime physical activity and aerobic fitness may reduce obesity-related health risks by improving the cardiac autonomic function measured by HRV in obese working-age subjects. This research supports the role of lifetime physical activity in weight management strategies and interventions to reduce obesity-related health risks.

Magnetic field and dynamic pressure ULF fluctuations in coronal-mass-ejection-driven sheath regions

Abstract. Compressed sheath regions form ahead of interplanetary coronal mass ejections (ICMEs) that are sufficiently faster than the preceding solar wind. The turbulent sheath regions are important drivers of magnetospheric activity, but due to their complex internal structure, relatively little is known on the distribution of the magnetic field and plasma variations in them. In this paper we investigate ultra low frequency (ULF) fluctuations in the interplanetary magnetic field (IMF) and in dynamic pressure (Pdyn) using a superposed epoch analysis of 41 sheath regions observed during solar cycle 23. We find strongest fluctuation power near the shock and in the vicinity of the ICME leading edge. The IMF and Pdyn ULF power have different profiles within the sheath; the former is enhanced in the leading part of the sheath, while the latter is increased in the trailing part of the sheath. We also find that the ICME properties affect the level and distribution of the ULF power in sheath regions. For example, sheath regions associated with strong or fast ICMEs, or those that are crossed at intermediate distances from the center, have strongest ULF power and large variation in the power throughout the sheath region. The weaker or slower ICMEs, or those that are crossed centrally, have in general considerably weaker ULF power with relatively smooth profiles. The strong and abrupt decrease of the IMF ULF power at the ICME leading edge could be used to distinguish the ICME from the preceding sheath plasma.

A comparative study of pulse rate variability and heart rate variability in healthy subjects

Both heart rate variability (HRV) and pulse rate variability (PRV) are noninvasive means for the assessment of autonomic nervous control of the heart. However, it is not settled whether or not the PRV obtained from either hand can be the surrogate of HRV. The HRV measures obtained from electrocardiographic signals and the PRV measures obtained from the pulse waves recorded from the index fingers of both hands were compared in normal subjects by using linear regression analysis and Bland and Altman method. Highly significant correlations (P<0.001, 0.89<r<1.0) were found between all HRV measures and the corresponding PRV measures of both hands. However, there were insufficient agreements in some measures between pairwise comparisons among HRV, right PRV and left PRV except heart rate and ultra-low frequency power (ULFP). The PRV of either hand is close to, but not the same as the HRV in healthy subjects. The HRV, right PRV and left PRV are not surrogates of one another in normal subjects except heart rate and ULFP. Since HRV is generally accepted as the standard method for the assessment of the autonomic nervous modulation of a subject, the PRV of either hand may not be suitable for the assessment of the cardiac autonomic nervous modulation of the subject.

Possible evidence of virtual resonance in the dayside magnetosphere

On day 108, 2001, the Sub‐Auroral Magnetometer Network (SAMNET) and Magnetometers along the Eastern Atlantic Seaboard for Undergraduate Research and Education (MEASURE) magnetometer arrays detected dayside magnetic pulsations at a common frequency of ∼15 mHz at all locations below L = 4. This global pulsation event was associated with alignment of the interplanetary magnetic field with the Sun‐Earth axis, a condition known to generate ultralow‐frequency (ULF) waves in front of the bow shock. The event occurred during the early recovery phase of a geomagnetic storm. Magnetic field measured by the GOES 8 geostationary satellite on the dayside indicated elevated broadband (7–80 mHz) ULF power in the compressional component without a strong peak at 15 mHz. These observations suggest that the global pulsations originated from a compressional magnetohydrodynamic eigenmode oscillation of the inner magnetosphere stimulated by a broadband external disturbance. The equatorial Alfvén velocity corresponding to the toroidal frequencies that were determined with the cross‐phase analysis of SAMNET and MEASURE data showed a gradual decrease of the velocity with L without a clear signature of a plasmapause. The observed properties of the global pulsations are consistent with virtual resonance in the inner magnetosphere.

Ground-based Pc5 ULF wave power: Solar wind speed and MLT dependence

Using over 20 years of ground-based magnetometer data from the CANOPUS/CARISMA magnetometer array, we present a statistical characterisation of Pc5 ultra-low frequency (ULF) power in the 2–10 mHz band as a function of magnetic local time (MLT), L-shell, and solar wind speed. We examine the power across L-shells between 4.2 and 7.9, using data from the PINA, ISLL, GILL and FCHU stations, and demonstrate that there is a significant MLT dependence in both the H- and D-component median 2–10 mHz power during both fast (>500 km/s) and slow (<500 km/s) solar wind speeds. The H-component power consistently dominates over D-component power at all MLTs and during both fast and slow solar wind. At the higher- L stations ( L >5.4), there are strong MLT power peaks in the morning and midnight local time sectors; the morning sector dominating midnight during fast solar wind events. At lower L-shells, there is no evidence of the midnight peak and the 2–10 mHz power is more symmetric with respect to MLT except during the fastest solar wind speeds. There is little evidence in the ground-based power of a localised MLT peak in ULF power at dusk, except at the lowest L-shell station, predominantly in the H-component. The median 2–10 mHz power increases with an approximate power law dependence on solar wind speed, at all local times across the L-shell domain studied in both components. The H-component power peaks at the latitude of the GILL station, with significantly lower power at both higher and lower L-shells. Conversely, the D-component power increases monotonically. We believe that this is evidence for 2–10 mHz power accumulating at auroral latitudes in field line resonances. Finally, we discuss how such ULF wave power characterisation might be used to derive empirical radiation belt radial diffusion coefficients based on, and driven by, the solar wind speed dependence of ULF wave power.

The Influence of the Call with a Mobile Phone on Heart Rate Variability Parameters in Healthy Volunteers

It is possible that electromagnetic field (EMF) generated by mobile phones (MP) may have an influence on the autonomic nervous system (ANS) and modulates the function of circulatory system. The aim of the study was to estimate the influence of the call with a mobile phone on heart rate variability (HRV) in young healthy people. The time and frequency domain HRV analyses were performed to assess the changes in sympathovagal balance in a group of 32 healthy students with normal electrocardiogram (ECG) and echocardiogram at rest. The frequency domain variables were computed: ultra low frequency (ULF) power, very low frequency (VLF) power, low frequency (LF) power, high frequency (HF) power and LF/HF ratio was determined. ECG Holter monitoring was recorded in standardized conditions: from 08:00 to 09:00 in the morning in a sitting position, within 20 min periods: before the telephone call (period I), during the call with use of mobile phone (period II), and after the telephone call (period III). During 20 min call with a mobile phone time domain parameters such as standard deviation of all normal sinus RR intervals (SDNN [ms]--period I: 73.94+/-25.02, period II: 91.63+/-35.99, period III: 75.06+/-27.62; I-II: p<0.05, II-III: p<0.05) and standard deviation of the averaged normal sinus RR intervals for all 5-mm segments (SDANN [ms]--period I: 47.78+/-22.69, period II: 60.72+/-27.55, period III: 47.12+/-23.21; I-II: p<0.05, II-III: p<0.05) were significantly increased. As well as very low frequency (VLF [ms2]--period I: 456.62+/-214.13, period II: 566.84+/-216.99, period III: 477.43+/-203.94; I-II: p<0.05), low frequency (LF [ms(2)]--period I: 607.97+/-201.33, period II: 758.28+/-307.90, period III: 627.09+/-220.33; I-II: p<0.01, II-III: p<0.05) and high frequency (HF [ms(2)]--period I: 538.44+/-290.63, period II: 730.31+/-445.78, period III: 590.94+/-301.64; I-II: p<0.05) components were the highest and the LF/HF ratio (period I: 1.48+/-0.38, period II: 1.16+/-0.35, period III: 1.46+/-0.40; I-II: p<0.05, II-III: p<0.05) was the lowest during a call with a mobile phone. The tone of the parasympathetic system measured indirectly by analysis of heart rate variability was increased while sympathetic tone was lowered during the call with use of a mobile phone. It was shown that the call with a mobile phone may change the autonomic balance in healthy subjects. Changes in heart rate variability during the call with a mobile phone could be affected by electromagnetic field but the influence of speaking cannot be excluded.

Cardiac Arrhythmias and Conduction Disturbances in Patients With Ankylosing Spondylitis

Conduction disturbances, aortic incompetence, and myocardial fibrosis are known complications in adult patients with ankylosing spondylitis (AS). Its incidence has been reported to be 10% to 30%; however, less attention has been paid to all cardiac arrhythmias. The aim of this study was to evaluate arrhythmias and conduction disturbances in patients with AS using electrocardiograms and Holter monitoring (including heart rate variability analysis) and to estimate its relationships with age, gender, clinical features, and duration of AS. Thirty-one patients with AS (20 to 69 years old, mean 50 +/- 14) and 22 healthy volunteers (26 to 69 years old, mean 49 +/- 13) underwent rheumatologic and cardiologic evaluations. Ventricular extrasystoles were present in 55% of AS patients and in 28% of controls. Supraventricular extrasystoles were present in 94% of AS patients and 100% of controls. The frequency of ventricular extrasystoles was found to be higher in the AS patients than in the control subjects. Significant differences were found in heart rate variability analyses: ultra low-frequency power and root mean square recessive difference (r-MSSD) were lower in the AS group. When the AS group was divided into subgroups (stages 3 and 4), significant differences were found between control subjects and stage 3 patients in PR interval, heart rate (HR), T-wave duration, ultra low frequency, and r-MSSD and between controls and stage 4 patients in HR, T-wave duration, and r-MSSD. QTc and QTd were not significantly different in groups and subgroups and were not correlated with any other clinical or electrocardiographic parameter. Cardiac arrhythmias were more frequent in patients with AS than in the healthy population. Simple electrocardiograms and Holter parameters do not correlate with the incidence of VESs, age, gender, clinical features, and duration of AS.

Heart Rate Variability in Acute Coronary Syndrome Patients With Major Depression

Major depressive disorder (MDD) associated with acute coronary syndrome (ACS) increases the risk of mortality. Decreased heart rate variability (HRV), also a predictor of mortality, is reduced in patients with MDD after ACS, and has been suggested to be a mediator of MDD mortality after ACS. Although selective serotonin reuptake inhibitors may reduce mortality post-ACS, little is known about their effects on HRV. To examine the influence of both sertraline and improvement in mood on HRV. The Sertraline Antidepressant Heart Attack Randomized Trial assessed HRV from 24-hour Holter electrocardiogram recordings at baseline in 290 patients and from a second recording in 258 of these patients 16 weeks after randomization to sertraline or placebo. Frequency domain measures of HRV included high-frequency power, low-frequency power, very low-frequency power, ultra low-frequency power, and total power. Depression severity was measured by the Hamilton Rating Scale for Depression. Clinical response was measured with the Clinical Global Impressions Improvement scale. At baseline, prior episodes of MDD were associated with lower HRV. Sertraline significantly increased ultra low-frequency power, while improvement in mood was associated with higher low-frequency power independent of treatment. However, the expected recovery in HRV following ACS was not observed in patients with MDD. Higher ultra low-frequency during sertraline treatment and higher low-frequency power in patients whose mood improved resulted primarily from these measures decreasing in their comparison groups. Heart rate variability recovery is impaired in depressed patients after ACS. Previously reported differences in baseline HRV between patients with and without depression after ACS grew larger in the 16 weeks following a coronary event. Both sertraline treatment and symptomatic recovery from depression were associated with increased HRV compared with placebo-treated and nonrecovered post-ACS control groups, respectively, but this results primarily from decreased HRV in the comparison groups.

Global profiles of compressional ultralow frequency wave power at geosynchronous orbit and their response to the solar wind

We investigate the global local‐time profiles of compressional wave power in three ultralow frequency (ULF) bands corresponding to Pc3, Pc4, and Pc5 pulsations using magnetic field data from the geosynchronous GOES satellites. The global power profiles of the three frequency bands are studied for low, moderate, and high levels of geomagnetic activity based on the Dst index. We also consider the seasonal variation of the ULF power profiles, as well as the effects of solar wind and interplanetary magnetic field (IMF) parameters. For high geomagnetic activity, we find that the greatest power is associated with compressional Pc5 pulsations in the afternoon sector; for low geomagnetic activity, ULF power levels are consistently highest in the tail region. A summer power minimum in all three frequency bands is observed in our study of seasonal variation, while higher power levels occur around local midnight throughout the year. The enhancement of ULF power by high solar wind velocity and pressure is greater for the lower‐frequency waves. Furthermore, solar wind plasma parameters have a significantly greater influence on ULF wave power than IMF parameters like cone angle and northward/southward orientation.

Effects of passive smoking on heart rate variability, heart rate and blood pressure: an observational study

Exposure to environmental tobacco smoke (ETS) has been shown to increase the risk for cardiovascular diseases and death, and autonomic dysfunction (specifically, reduced heart rate variability (HRV)) is a predictor of increased cardiac risk. This study tests the hypothesis that ETS exposure reduces HRV in the general population and discusses possible pathways. This cross-sectional study was conducted between 2001 and 2003 and is part of the SAPALDIA (Swiss Cohort Study on Air Pollution and Lung Diseases in Adults) study. The analysis included 1218 randomly selected non-smokers aged 50 and above who participated in 24-h electrocardiogram recordings. Other examinations included an interview, investigating health status (especially respiratory and cardiovascular health and health relevant behaviours and exposure to ETS) and measurements of blood pressure, body height and weight. Subjects exposed to ETS at home or at work for more than 2 h/day had a difference of -15% in total power (95%CI: -26 to -3%), low frequency power (-28 to -1%), low/high frequency ratio (-26 to -3%) and -18% (-29 to -4%) in ultralow frequency power of HRV compared with subjects not exposed to ETS at home or work. We also found a 2.7% (-0.01 to 5.34%) higher heart rate during the recording in exposed subjects. Exposure to ETS at home and work is associated with lower HRV and with higher heart rate in an ageing population. Our findings suggest that exposure to ETS increases cardiac risk through disturbances in the autonomic nervous system.

Depressed autonomic nervous system function in African Americans and individuals of lower social class: A potential mechanism of race- and class-related disparities in health outcomes

Both race and social class influence cardiovascular outcomes, through mechanisms not yet fully understood. Minority race and lower social class are sources of chronic stress, which can alter autonomic nervous system function. Heart rate variability (HRV), a measure of autonomic function, is also an important predictor of cardiovascular outcomes. To determine whether minority race/ethnicity and lower social class are associated with depressed HRV, we prospectively collected data on sociodemographic, clinical, psychological, and behavioral factors by survey in 360 outpatients undergoing ambulatory electrocardiographic monitoring. Heart rate variability (24-hour) was measured by frequency domain analysis. In unadjusted analysis, African Americans had lower HRV than whites, and individuals of lower social class as measured by education, occupation, and income had lower HRV than those of higher class. In multivariable analysis, both race and social class were independent predictors of ultralow frequency power after controlling for clinical and psychological factors. African Americans were 3.45 (95% CI 1.74-6.98, P = .0004) times as likely as whites to have depressed HRV (ultralow frequency power, lowest tertile), and non-college graduates 2.94 (95% CI, 1.71-5.14, P = .0001) times as likely as college graduates to have depressed HRV. Heart rate variability is lower in African Americans and individuals of lower social class, independent of the effects of measured clinical, psychological, or behavioral factors. This suggests that the adverse effects of minority race and lower social class on cardiovascular outcomes may be mediated by dysregulation of autonomic function.

A case study to determine the relationship of relativistic electron events to substorm injections and ULF power

We study the two storm events of 1997: one in May that was accompanied by a relativistic electron event (REE) and the other in September, with a more profound Dst decrease, but with no significant flux increase of relativistic electrons. We find that a larger amount of seed electrons was present in the May event compared to that of the September storm, whereas the ULF (ultra low frequency) power was more enhanced and the particle spectrum was harder in the September event. Hence, we demonstrate that a larger storm does not necessarily produce more seed electrons and that the amount of seed electrons is an important factor in an actual increase in REE flux levels. We note that whistler mode chorus was enhanced in the May event and could also contribute to the acceleration of electrons.

Significant and Morbid Changes in Heart Rate Variability Precedes and Complicates Symptomatic Hypotension in Peripheral Blood Stem Cell Apheresis.

Peripheral blood stem cell harvest (PBSCH) has been widely performed for rescue following high-dose chemotherapy or as an alternative to BMT for allogeneic stem cell transplantation. However, severe complications, which caused sudden death, were reported in PBSCH from healthy donors. Recent cumulative evidence shows that decrease in cardiovascular signal variability of the R-R period (heart rate variability, HRV) is strongly associated with sudden death and/or cardiac event after a myocardial infarction. Furthermore, usefulness of HRV as a clinical tool has been explored in numerous conditions such as hypertrophic cardiomyopathy, obstructive sleep apnea, diabetic neuropathy, and various neurological alterations. Two types, time domain and frequency domain, are included in HRV analysis. In this study, we investigated HRV during and after apheresis for PBSCH in 23 cases [8 autologous transplant patients, 15 allogeneic transplant donors; 8 men, 15 women; median age 47 years (27–55)]. Date from 24-hour ambulatory ECG recordings were analyzed with R-R data analysis software (MemCalc/CHIRAM version 1, Suwatrust, Tokyo, Japan). Acknowledged simple markers in time domain analysis are the standard deviation of all normal beats (SDNN) and the square root of the mean of the sum of squared differences between adjacent normal-to-normal intervals (r-MSSD). On the other hand, markers in frequency domain analysis include LH, low frequency power (0.04–0.15Hz); HF, high frequency power (0.15–0.4 Hz); LH/HF ratio; VLF, very low frequency power (0.003–0.04 Hz); and ULF, ultra low frequency power (<0.0033 Hz). These power spectrum analyses of HRV are used to investigate sympathovagal balance, autonomic cardiovascular control and/or target function impairment. Among frequency domain analysis markers, VLF or ULF reportedly have particular prognostic value in all causes of mortality after myocardial infarction. In our study, SDNN, r-MSSD, HF, VLF, and ULF significantly and markedly decreased to morbid levels during apheresis (all P<0.001). Of 23 harvest cases, symptomatic hypotension occurred during apheresis in 2 cases and after apheresis in one case. Notably, in these 3 cases, SDNN and VLF had already begun to decrease about 5–10 minutes before significant symptomatic hypotension occurred (P=0.03, P=0.04, respectively). Our results suggested that morbidly decreased HRV indicates serious cardiovascular load and suppression of the parasympathetic nervous system in apheresis for PBCSH. HRV analysis might be a useful tool to prevent donors from severe autonomic cardiovascular complications in PBCSH.

Including patients with diabetes mellitus or coronary artery bypass grafting decreases the association between heart rate variability and mortality after myocardial infarction

Background Decreased heart rate variability (HRV) is often assumed to be associated with mortality in all patients after myocardial infarction (MI), independent of clinical factors or time after MI. Method HRV was determined from Holter tapes in the Cardiac Arrhythmia Suppression Trial (CAST). Patients were 71 ± 120 days after MI. A total of 735 pre-therapy tapes were analyzed in patients who had ventricular premature contractions (VPCs) suppressed on the first treatment. The period of follow-up was 362 ± 243 days (69 deaths). The association of clinical and demographic factors and 24-hour, daytime, and nighttime HRV to mortality in all patients, patients without coronary artery bypass graft (CABG) surgery between the qualifying MI and the Holter monitoring, and patients with neither CABG nor diabetes mellitus was determined with univariate Cox regression analysis. Results For the entire group and the subgroup without CABG, the strongest association was with increased daytime normalized high frequency power (NHF day). Further excluding patients with diabetes mellitus strengthened the association of HRV with mortality rate. Decreased natural logarithm (ln) 24-hour total and ultra low frequency (ULF) power were the strongest predictors of mortality. The best cutoff point for ln ULF for separating survivors and non-survivors was determined. After including a history of MI, congestive heart failure, or both as co-factors, ln ULF ≤7.85 identified patients at approximately 4-times the relative risk of mortality, but did not risk-stratify patients without prior MI or history of congestive heart failure. Conclusions HRV predicts mortality rate in a broad range of times after MI. Excluding patients with CABG after MI or with diabetes mellitus significantly strengthens the association of HRV with mortality. HRV measures beyond the peri-infarction period, with clinical factors, can identify subgroups at an elevated risk of mortality.

Correlations between ULF wave power, solar wind speed, and relativistic electron flux in the magnetosphere: solar cycle dependence

We present results from a rank order correlation coefficient (ROCC) analysis between ground-based 1– 10 mHz ultra-low frequency (ULF) wave power, upstream solar wind speed ( v SW), and MeV electron flux across the outer radiation belt. We use data spanning a complete solar cycle (1990–2001) from ground magnetometers from the SAMNET and IMAGE arrays, and MeV electron data from the Los Alamos spacecraft at geosynchronous orbit (GEO) and from a HEO spacecraft at L=5.5 and 4.5. We find a very high correlation between ULF wave power and v SW at all local times and on all L-shells between L=3.1 and 6.6. Very strong cross- L-shell ULF power coherence is maintained throughout the solar cycle, although the efficiency of v SW in driving a given ULF power response is solar cycle dependent. Peak ULF power and peak ROCC (∼0.75) are observed during the declining phase of the solar cycle around 1994–1995, with smaller localised peaks in these parameters occurring during slower average v SW conditions close to solar maximum in 2000. There is also a strong correlation of both v SW and ULF power with MeV electron flux, these correlations being more strongly dependent on solar cycle phase. The v SW and ULF power correlations with MeV electron flux peak during the late declining phase of the solar cycle, when the radiation belts are most intense. Our results confirm that radiation belt flux demonstrates extremely strong global cross- L-shell coherence throughout the solar cycle. The ROCC between v SW or ULF power and MeV electron flux demonstrate a clear and systematic time lag following the peak in either v SW or ULF power. Electron fluxes respond first at GEO (lag ∼2 days), before subsequently peaking at lower L-shells. Importantly, our results indicate that v SW-correlated MeV electron acceleration processes operate by inwards radial transport. The correlation between ULF power and MeV energy electron flux further suggests that ULF waves could be causally responsible via ULF wave enhanced radial diffusion.

Measures of heart period variability as predictors of mortality in hospitalized patients with decompensated congestive heart failure

Depressed heart rate variability (HRV) is a powerful independent predictor of a poor outcome in patients with chronic and stable congestive heart failure (CHF). However, the prognostic value of HRV analysis in patients hospitalized for decompensated CHF is not known. The aim of this study was to investigate whether HRV parameters obtained during admission for decompensated CHF could predict survival after hospital discharge. We studied 199 patients (131 men, aged 60 ± 14 years) with a previous diagnosis of New York Heart Association class III or IV CHF who were admitted to the hospital for decompensated CHF. Twenty-four–hour Holter recordings were obtained on admission, and measures of HRV were calculated in the time and frequency domain. During a mean follow-up of 312 ± 150 days, 40 patients (21.1%) died. Kaplan-Meier analysis indicated that patients with SD of the RR intervals over a 24-hour period (p = 0.027), SD of all 5-minute mean RR intervals (p = 0.043), total power (p = 0.022), and ultra–low-frequency power (p = 0.008) in the lower tertile were at a higher risk of death. In a multivariate Cox regression model, the same indexes in the lower tertile were independent predictors of mortality: SD of the RR intervals over a 24-hour period (risk ratio [RR] 2.2, 95% confidence interval [CI] 1.05 to 4.3, p = 0.036), SD of all 5-minute mean RR intervals (RR 2.1, 95% CI 1.05 to 4.2, p = 0.04), total power (RR 2.2, 95% CI 1.08 to 4.2, p = 0.03), and ultra–low-frequency power (RR 2.6, 95% CI 1.3 to 5.3, p = 0.007). Therefore, the severity of autonomic perturbations during hospital admission for CHF decompensation, as reflected by measures of overall HRV, can predict survival after hospital discharge. Together with previous studies, our findings suggest that indexes of overall HRV provide useful prognostic information in the full spectrum of CHF severity.

Prognostic value of nonlinear heart rate dynamics in hemodialysis patients with coronary artery disease

Although altered nonlinear heart rate dynamics predicts death in patients with coronary artery disease (CAD), its prognostic value in chronic hemodialysis patients with CAD is unknown. We analyzed 24-hour electrocardiogram for nonlinear heart rate dynamics and heart rate variability in a retrospective cohort of 81 chronic hemodialysis patients with CAD. During a follow-up period of 31 +/- 20 months, 19 cardiac and 8 noncardiac deaths were observed. Cox hazards model, including diabetes, left ventricular ejection fraction, and the number of diseased coronary arteries, revealed that abnormal alpha2 (defined as both increase and decrease in alpha2 because of its J curve relationship with cardiac mortality), decreased approximate entropy and decreased heart rate variability (triangular index and ultra-low frequency power) were significant and independent predictors of cardiac death. No significant and independent predictive power for noncardiac death was observed in either the heart rate dynamics or the heart rate variability measures. The predictive power of alpha2 and approximate entropy was independent of that of triangular index and ultra-low frequency power. Combinations of two categories of measures improved the predictive accuracy; overall accuracy of approximate entropy + ultra-low frequency power for cardiac death was 87%. Altered nonlinear heart rate dynamics are independent predictors of cardiac death in chronic hemodialysis patients with CAD and their combinations with decreased heart rate variability provide clinically useful markers for risk stratification.