Differences In Total Power Research Articles

Spectral Power Distribution of Heart Rate Variability in Contiguous Short-Term Intervals.

Heart rate variability (HRV) is determined by the variation of consecutive cardiac electrical excitations, usually from RR intervals of an EKG. The sequence of intervals is a time series that yields three HRV parameter categories: time domain, frequency domain, and nonlinear. Parameter estimates are based on widely different EKG sample times: short-term (~5-10 minutes), longer (24 hours), and ultra-short (<5 minutes). Five-minute intervals are useful to evaluate intervention effects that change HRV in a single session by comparing pre-to-post values. This approach relies on knowing the minimal detectible change (MDC) that indicates a real change in clinical and research studies. The specific aims of this pilot study were to (1) evaluate HRV power and its spectral distribution among contiguous five-minute intervals, (2) compare the power distribution in a five-minute interval with a full 45-minute assessment, and (3) provide data to aid estimation of the MDC between pre- and post-interventions during a single session. Methods: Twelve self-reported healthy young adults participated after signing an approved consent. Participation required subjects who had no history of cardiovascular disease or were taking vasoactive substances. Persons with diabetes were not eligible. While subjects were supine, EKG leads were placed, and EKG was recorded for 45 minutes at 1000 samples/sec. The 45 minutes were divided into nine five-minute contiguous intervals, and the spectral density in each was determined. Total power and spectral percentages within each interval were assessed in the very low (VLF, 0.003-0.04 Hz), low (LF, 0.04-0.15 Hz), and high (HF, 0.15-0.4 Hz) frequency bands. These were compared among intervals and to the full 45-minute sample. The MDC was determined by comparing powers in five-minute intervals separated by 10 minutes. The standard error of the measurement (SEME) for each pair was calculated from the square root of the mean square error (√MSE). MSE was based on a two-factor analysis of variance, and MDC was 2×√2×SEME. Differences in total power and spectral power distribution among intervals were not statistically significant. The total mean power±SD was 4561±1434 ms². The maximum difference in total power was 7.85%. The mean power for the VLF, LF, and HF bands wasrespectively1713±1736 ms², 1574±1072 ms², and 1257±1016 ms². The maximum percentage difference in spectral power across all intervals for VLF, LF, and HF wasrespectively3.75%, 8.5%, and 7.4%. The percentage of power in the VLF, LF, and HF bands wasrespectively37.9%, 36.1%, and 25.9%. The ratios of spectral to total power for VLF, LF, and HF bands were respectively 0.80±0.07, 1.20±0.11, and 1.22±0.10. MDC percentage values were 21.0±4.9% for the HF band, 25.7±1.4% for the LF band, and 30.4±5.5% for the VLF band. Results offer initial estimates of variations in HRV power in the VLF, LF, and HF bands in contiguous five-minute intervals and estimates of the minimum detectible "real" changes between intervals separated by 10 minutes. The pattern of variation and data are useful in experimental planning in which HRV spectral power changes are assessed subsequent to a short-duration intervention during a single session. MDC values (21.0% in the HF band to 30.4% in the VLF band) provide initial estimates useful for estimating the number of participants needed to evaluate the impact of an intervention on spectral components of HRV.

P006 The Impact of Growth Hormone Treatment on Cardiovascular Control in Children with Prader-Willi syndrome

Abstract Background Many children with Prader-Willi syndrome (PWS) are treated with growth hormone (GH), which may increase the risk of obstructive sleep apnoea. Children with PWS also have impaired cardiac autonomic control due to reduced parasympathetic activity, which may increase cardiovascular risk, however the impact of GH on autonomic control is yet to be elucidated. Methods Pre- and post-GH polysomnographic data in 38 children (aged 0-18 years) were retrospectively collected. Spectral analysis of heart rate variability (HRV) was used to determine total, low frequency (LF, sympathetic and parasympathetic activity), high frequency (HF, parasympathetic activity) power and LF/HF (sympathovagal balance). Data were compared with Wilcoxon Signed Rank Test and Spearman Rank Order Correlation analysis and are presented as median [interquartile range]. Results HRV data were significantly correlated with age so children were grouped into those &amp;lt;2 years (n=22) and &amp;gt;2 years (n=16). There were no significant differences in the obstructive or central apnoea-hypopnoea indexes between pre- and post-GH studies in either group. In children &amp;lt;2 years, there were no significant differences in total power, LF, HF and LF/HF between studies. In children &amp;gt;2 years, total power (1912.2 ms2, [920.2, 4916.1] vs 1010.2 ms2 [416.0, 2828.7), LF (434.0 ms2 [247.0, 1340.7] vs 278.9 ms2 [83.4, 676.0]) and HF (986.0 ms2 [321.8, 2400.6] vs 414.4 ms2 [146.2, 1152.7]) were lower (p&amp;lt; 0.01 for all) post-GH. Conclusions Our results demonstrate that GH decreases both sympathetic and parasympathetic activity during sleep in children &amp;gt;2 years, which could further increase cardiovascular risk.

Altered Joint Powers During Running After Tibial Bone Stress Injury

Background:Tibial bone stress injuries (tib-BSI) are common in adolescent runners. Previous research has examined running mechanics as possible risk factors for tib-BSI’s and implications have been observed for both kinematic and kinetic measures. Combining these measures to examine power absorption and production of the lower extremity can provide context on mechanical differences in individuals with a history of tib-BSI.Hypothesis/Purpose:The purpose of this study was to examine total limb power and percent joint contribution in healthy adolescent runners compared to peers with a history of tib-BSI. It was hypothesized that runners with a history of tib-BSI would have a greater contribution of power production and absorption at the ankle, and less at the hip and knee joints, with no difference in total power.Methods:Twenty-six runners were divided into groups: history of tib-BSI (n=14; male=10, female=4; age=16±2) and healthy controls (n=12; male=5, female=7; age=18±7). Data were collected using 3D motion capture with embedded force plates during overground running at self-selected pace. Total limb power and percent joint contribution were calculated from joint work. Positive and negative joint work was summed from the integrations of the joint power-time curve in each plane. Joint work was divided by step-time to obtain total joint power. Joint powers for the hip, knee, and ankle were summed to determine total limb power and percentage of limb power was calculated for each joint. Variables were grouped by control limb (CON), uninvolved limb (UNI), and involved limb (BSI). Both limbs in the healthy controls were averaged to generate the CON group. A one-way ANOVA was used to compare the variables of limb and joint power.Results:There were no significant differences between BSI and UNI limbs for any variables measured. The CON group exhibited significantly greater hip negative power compared to the BSI group (p=0.047), and significantly less ankle negative power compared to the BSI (p=0.001) and UNI groups (p=0.002). Despite a significant difference in total positive power between groups (p=0.04), there were no differences in joint positive power. Variables are presented in Table 1.Conclusion:This study is preliminary evidence that adolescent runners with a history of tib-BSI can present with adaptations in running mechanics that are not limited to the injured leg. Negative power may be more sensitive to change with the ankle increasing its contribution, comparatively. Clinicians and researchers should be aware of this adaptation after injury as it may influence treatment.

Relationship Between Heart Rate Variability and Pulse Rate Variability Measures in Patients After Coronary Artery Bypass Graft Surgery.

Background: Heart rate variability (HRV) and pulse rate variability (PRV) measures are two kinds of physiological indices that can be used to evaluate the autonomic nervous function of healthy subjects and patients with various kinds of illness.Purpose: In this study, we compared the agreement and linear relationship between electrocardiographic signals (ECG)-derived HRV and photoplethysmographic signals (PPG)-derived right hand PRV (R-PRV) and left hand PRV (L-PRV) measures in 14 patients over 1 year after coronary artery bypass graft (CABG) surgery.Method: The ECG and PPG signals of the patient were recorded simultaneously for 10 min in a supine position. The last 512 stationary RR intervals (RRI) and peak-to peak intervals (PPI) of pulse wave were derived for data analysis. Bland-Altman plot was used to assess the agreement among HRV and both hand PRV measures, while linear regression analysis was used to examine the relationship among corresponding measures of HRV, R-PRV, and L-PRV.Result: The results revealed significant differences in total power (TP), very low-frequency power (VLF), low-frequency power (LF), high-frequency power (HF), and normalized VLF (VLFnorm) among HRV, R-PRV, and L-PRV. Bland-Altman plot analysis showed good agreements in almost all measures between R-PRV and L-PRV, except insufficient agreement was found in LF/HF. Insufficient agreements were found in root mean square successive difference (RMSSD), normalized HF (HFnorm), and LF/HF indices between HRV and L-PRV, and in VLFnorm, HFnorm, and LF/HF indices between HRV and R-PRV. Linear regression analysis showed that the HRV, R-PRV, and L-PRV measures were all highly correlated with one another (r = 0.94 ~ 1; p < 0.001).Conclusion: Though PRV measures of either hand are not surrogates of HRV measures, they might still be used to evaluate the autonomic nervous functions of CABG patients due to the moderate to good agreements in most time-domain and frequency-domain HRV measures and the strong and positive correlations among HRV and both hands PRV measures in CABG patients.

Impact of ocean waves on offshore wind farm power production

Offshore wind energy has seen a steady increase in the latest years as it serves as an ideal alternative energy source to meet our renewable energy goals. Due to this increase in interest and in installations of offshore wind farms a better understanding of the impact of waves on the power production of wind farms in necessary. This wave-wind farm power production interaction has scarcely been examined, however, some exceptions of small scale large-eddy-simulations exist. Unfortunately, these studies are not able to take multiple wind farms under real weather conditions into account. Here, we show the power production and wake lengths of 1250 offshore wind turbines located in the German Bight simulated by a stand-alone atmospheric (WRF) model and a coupled atmosphere-wave (WRF-SWAN) model. The coupled atmosphere-wave model estimates larger (smaller) power production in case of waves and wind traveling in the same (opposed) direction compared to the stand-alone atmospheric model. The relative difference between the two models can be as much as 20% for the two-week averaged grid power production, while the difference in total power over this two-week period is equal to 9%. Moreover, the wind farm wake lengths of waves and wind traveling in the same (opposed) direction are longer (shorter) for the coupled atmosphere-wave model compared to the stand-alone atmospheric model. Here, the relative difference of the mean wake length between the two models can be up to 25%. This shows the importance of waves as a part of the offshore wind environment and can be an important factor in future wind assessment or power production estimation studies.

Reduced-Order Modeling of Nuclear Reactor Kinetics Using Proper Generalized Decomposition

In this work, we attempt to overcome the “curse of dimensionality” inherent to neutron diffusion kinetics problems by employing a novel reduced-order modeling technique known as proper generalized decomposition (PGD). The novelty of this work is that it represents the first attempt at applying PGD reduced-order modeling to time-dependent multigroup neutron diffusion kinetics. The performance of PGD reduced-order models (ROMs) will be quantified by comparing PGD ROMs to reference high-fidelity solutions using Rattlesnake for the TWIGL problem, a standard reactor kinetics benchmark. We show that for problems that exhibit sufficient spatial regularity, our proposed PGD algorithm computes accurate ROMs in less time than the reference high-fidelity calculation. By considering a variation of the TWIGL benchmark that maintains an analogous delayed supercritical behavior but has a smooth spatial solution, we compute PGD ROMs with a maximum relative difference in total power of less than 2.2% using 103 fewer degrees of freedom and a speedup of nearly 13× when compared to reference solutions. However, when introducing the stronger spatial irregularities of the reference benchmark, the accuracy and timing of the proposed PGD algorithm diminishes. We show that by using continuous finite elements, PGD ROMs are subject to undesirable numerical oscillations. In this paper, we motivate the use of PGD in neutron diffusion kinetics, discuss the adopted mathematical framework, and using our results, discuss the challenges and unique aspects of our implementation.

Correlations between change in neural respiratory drive and heart rate variability in patients submitted to open-heart surgery.

Respiratory muscle dysfunction after open-heart surgery may influence the cardiopulmonary interactions. The purpose of this study was to examine the correlation between change in the neural respiratory drive (NRD) and change in heart rate variability (HRV) in patients submitted to open-heart surgery. An observational cross-sectional study was conducted among 32 participants. NRD was assessed via a surface electromyogram of the parasternal intercostal muscle (sEMGpara). Polar heart rate monitor was used to measure HRV during the deep breathing maneuver. Evaluations were performed on the day of admission and discharge. There were statistically significant differences in NRD and HRV indices between admission and discharge periods (P<0.05). The difference in peak root mean square of sEMGpara recorded during resting (ΔRMS sEMGpara tidal), during maximal inspiratory maneuver (ΔsEMGpara max), and its normalized values (ΔRMS sEMGpara%max) were significantly correlated with the difference in total power (ΔTotal power), mean of heart rate (ΔMeanHR), and mean of R to R intervals (ΔMeanRR) (r=−0.844, P=0.004, r=−0.835, P=0.005, and r=0.643, P=0.043, respectively). It can be concluded that NRD correlated well with HRV in patients who had undergone open-heart surgery.

Testing the vagal withdrawal hypothesis during light exercise under autonomic blockade: a heart rate variability study.

We performed the first analysis of heart rate variability (HRV) at rest and during exercise under full autonomic blockade on the same subjects, to test the conjecture that vagal tone withdrawal occurs at exercise onset. We hypothesized that between rest and exercise there would be 1) no differences in total power (PTOT) under parasympathetic blockade, 2) a PTOT fall under β1-sympathetic blockade, and 3) no differences in PTOT under blockade of both autonomic nervous system branches. Seven men [24 (3) yr, mean (SD)] performed 5-min cycling (80 W) supine, preceded by 5-min rest during control and with administration of atropine, metoprolol, and atropine + metoprolol (double blockade). Heart rate and arterial blood pressure were continuously recorded. HRV and blood pressure variability were determined by power spectral analysis, and baroreflex sensitivity was determined by the sequence method. At rest, PTOT and the powers of low- and high-frequency components of HRV (LF and HF, respectively) were dramatically decreased with atropine and double blockade compared with control and metoprolol, with no effects on LF-to-HF ratio and on the normalized LF (LFnu) and HF (HFnu). During exercise, patterns were the same as at rest. Comparing exercise with rest, PTOT varied as hypothesized. For systolic and diastolic blood pressure, resting PTOT was the same in all conditions. During exercise, in all conditions, PTOT was lower than in control. Baroreflex sensitivity decreased under atropine and double blockade at rest and under control and metoprolol during exercise. The results support the hypothesis that vagal suppression determined disappearance of HRV during exercise.NEW & NOTEWORTHY This study provides the first demonstration, by systematic analysis of heart rate variability at rest and during exercise under full autonomic blockade on the same subjects, that suppression of vagal activity is responsible for the disappearance of spontaneous heart rate variability during exercise. This finding supports previous hypotheses on the role of vagal withdrawal in the control of the rapid cardiovascular response at exercise onset.

Effect of chewing or compressing food on autonomic nervous activity in older adults

To determine if autonomic nervous activity increases in older people during mastication and how this activity is related to the softness of food. We hypothesised that the coefficient of variation of R-R intervals (CVRR), high-frequency (HF) power, low-frequency (LF) power, LF/HF ratio and total power increase during chewing foods within the range of softness from moderate food to extremely soft food in older adults. Participants were 20 older volunteers (71-90year old). CVRR and HF on the electrocardiogram (ECG) were used as indices of parasympathetic nervous activity. LF and the LF/HF ratio on the ECG were used as indices of sympathetic nervous activity. Total power, reflecting the level of autonomic nervous activity, was also measured. Participants were asked to chew gum with three different degrees of softness, or to compress extremely soft gum between their palate and tongue. There were significant differences in HF between at resting and all chewing/compressing conditions, but no significant differences relating to food softness. There were significant differences in total power between at resting and all chewing/compressing conditions, but no significant differences relating to food softness. There were no significant differences in LF, LF/HF and CVRR among all conditions. Autonomic nervous activity, especially parasympathetic activity in older adults, increased during chewing and compressing food when compared to activity while at rest. Within the range of food's softness from moderate to extreme soft, food's softness had no measurable effect on autonomic nervous activity.

Quantitative EEG Metrics Differ Between Outcome Groups and Change Over the First 72h in Comatose Cardiac Arrest Patients.

Forty to sixty-six percent of patients resuscitated from cardiac arrest remain comatose, and historic outcome predictors are unreliable. Quantitative spectral analysis of continuous electroencephalography (cEEG) may differ between patients with good and poor outcomes. Consecutive patients with post-cardiac arrest hypoxic-ischemic coma undergoing cEEG were enrolled. Spectral analysis was conducted on artifact-free contiguous 5-min cEEG epochs from each hour. Whole band (1-30Hz), delta (δ, 1-4Hz), theta (θ, 4-8Hz), alpha (α, 8-13Hz), beta (β, 13-30Hz), α/δ power ratio, percent suppression, and variability were calculated and correlated with outcome. Graphical patterns of quantitative EEG (qEEG) were described and categorized as correlating with outcome. Clinical outcome was dichotomized, with good neurologic outcome being consciousness recovery. Ten subjects with a mean age =50yrs (range=18-65) were analyzed. There were significant differences in total power (3.50 [3.30-4.06] vs. 0.68 [0.52-1.02], p=0.01), alpha power (1.39 [0.66-1.79] vs 0.27 [0.17-0.48], p<0.05), delta power (2.78 [2.21-3.01] vs 0.55 [0.38-0.83], p=0.01), percent suppression (0.66 [0.02-2.42] vs 73.4 [48.0-97.5], p=0.01), and multiple measures of variability between good and poor outcome patients (all values median [IQR], good vs. poor). qEEG patterns with high or increasing power or large power variability were associated with good outcome (n=6). Patterns with consistently low or decreasing power or minimal power variability were associated with poor outcome (n=4). These preliminary results suggest qEEG metrics correlate with outcome. In some patients, qEEG patterns change over the first three days post-arrest.

Alterations in sociability and functional brain connectivity caused by early-life seizures are prevented by bumetanide

There is a well-described association between infantile epilepsy and pervasive cognitive and behavioral deficits, including a high incidence of autism spectrum disorders. Despite the robustness of the relationship between early-life seizures and the development of autism, the pathophysiological mechanism by which this occurs has not been explored. As a result of increasing evidence that autism is a disorder of brain connectivity we hypothesized that early-life seizures would interrupt normal brain connectivity during brain maturation and result in an autistic phenotype. Normal rat pups underwent recurrent flurothyl-induced seizures from postnatal (P)days 5–14 and then tested, along with controls, for developmental alterations of development brain oscillatory activity from P18–P25. Specifically we wished to understand how normal changes in rhythmicity in and between brain regions change as a function of age and if this rhythmicity is altered or interrupted by early life seizures.In rat pups with early-life seizures, field recordings from dorsal and ventral hippocampus and prefrontal cortex demonstrated marked increase in coherence as well as a decrease in voltage correlation at all bandwidths compared to controls while there were minimal differences in total power and relative power spectral densities. Rats with early-life seizures had resulting impairment in the sociability and social novelty tests but demonstrated no evidence of increased activity or generalized anxiety as measured in the open field. In addition, rats with early-life seizures had lower seizure thresholds than controls, indicating long-standing alterations in the excitatory/inhibition balance. Bumetanide, a pharmacological agent that blocks the activity of NKCC1 and induces a significant shift of ECl toward more hyperpolarized values, administration at the time of the seizures precluded the subsequent abnormalities in coherence and voltage correlation and resulted in normal sociability and seizure threshold. Taken together these findings indicate that early-life seizures alter the development of oscillations and result in autistic-like behaviors. The altered communication between these brain regions could reflect the physiological underpinnings underlying social cognitive deficits seen in autism spectrum disorders.

Peripheral vascular response to inspiratory breath hold in paediatric homozygous sickle cell disease

New Findings• What is the central question of this study?Autonomic nervous dysfunction is implicated in complications of sickle cell anaemia (SCA). In healthy adults, a deep inspiratory breath hold (IBH) elicits rapid transient SNS- mediated vasoconstriction detectable using Laser Doppler Flux (LDF) assessment of the finger-tip cutaneous micovasculature.• What is the main finding and its importance?We demonstrate significantly increased resting peripheral blood flow and sympathetic activity in African children with SCA compared to sibling controls and increased sympathetic stimulation in response to vasoprovocation with DIG.This study is the first to observe an inverse association between resting peripheral blood flow and haemoglobin oxygen saturation (SpO2). These phenomena may be an adaptive response to the hypoxic exposure in SCA.There is increasing evidence that autonomic dysfunction in adults with homozygous sickle cell (haemoglobin SS) disease is associated with enhanced autonomic nervous system-mediated control of microvascular perfusion. However, it is unclear whether such differences are detectable in children with SS disease. We studied 65 children with SS disease [38 boys; median age 7.2 (interquartile range 5.1–10.6) years] and 20 control children without symptoms of SS disease [8 boys; 8.7 (5.5–10.8) years] and recorded mean arterial blood pressure (ABP) and daytime haemoglobin oxygen saturation (). Cutaneous blood flux at rest (RBF) and during the sympathetically activated vasoconstrictor response to inspiratory breath hold (IBH) were measured in the finger pulp of the non-dominant hand using laser Doppler fluximetry. Local factors mediating flow motion were assessed by power spectral density analysis of the oscillatory components of the laser Doppler signal. The RBF measured across the two study groups was negatively associated with age (r=−0.25, P < 0.0001), ABP (r=−0.27, P= 0.02) and daytime (r=−0.30, P= 0.005). Children with SS disease had a higher RBF (P= 0.005) and enhanced vasoconstrictor response to IBH (P= 0.002) compared with control children. In children with SS disease, higher RBF was associated with an increase in the sympathetic interval (r=−0.28, P= 0.022). The SS disease status, daytime and age explained 22% of the variance in vasoconstrictor response to IBH (P < 0.0001). Our findings suggest that blood flow and blood flow responses in the skin of young African children with SS disease differ from those of healthy control children, with increased resting peripheral blood flow and increased sympathetic stimulation from a young age in SS disease. They further suggest that the laser Doppler flowmetry technique with inspiratory breath hold manoeuvre appears to be robust for use in young children with SS disease, to explore interactions between , ABP and autonomic function with clinical complications, e.g. skin ulceration.

Effects of Intermittent Hypoxia on Heart Rate Variability during Rest and Exercise

Changes in heart rate variability induced by an intermittent exposure to hypoxia were evaluated in athletes unacclimatized to altitude. Twenty national elite athletes trained for 13 days at 1200 m and either lived and slept at 1200 m (live low, train low, LLTL) or between 2500 and 3000 m (live high, train low, LHTL). Subjects were investigated at 1200 m prior to and at the end of the 13-day training camp. Exposure to acute hypoxia (11.5% O(2)) during exercise resulted in a significant decrease in spectral components of heart rate variability in comparison with exercise in normoxia: total power (p < 0.001), low-frequency component. LF (p < 0.001), high-frequency component, HF (p < 0.05). Following acclimatization, the LHTL group increased its LF component (p < 0.01) and LF/HF ratio during exercise in hypoxia after the training period. In parallel, exposure to intermittent hypoxia caused an increased ventilatory response to hypoxia. Acclimatization modified the correlation between the ventilatory response to hypoxia at rest and the difference in total power between normoxia and hypoxia (r (2) = 0.65, p < 0.001). The increase in total power, LF component, and LF/HF ratio suggests that intermittent hypoxic training increased the response of the autonomic nervous system mainly through increased sympathetic activity.

Aging and spectral characteristics of the nonharmonic component of 24-h heart rate variability.

To examine whether heart rate variability (HRV) during daily life shows power law behavior independently of age and interindividual difference in the total power, log-log scaled coarse-graining spectra of the nonharmonic component of 24-h HRV were studied in 62 healthy men (age 21-79 yr). The spectra declined with increasing frequency in all subjects, but they appeared as broken lines slightly bending downward, particularly in young subjects with a large total power. Regression of the spectrum by a broken line with a single break point revealed that the spectral exponent (beta) was greater in the region below than above the break point (1.63 +/- 0. 23 vs. 0.96 +/- 0.21, P < 0.001). The break point frequency increased with age (r = 0.51, P < 0.001) and beta correlated with age negatively below the break point (r = 0.39) and positively above the break point (r = 0.70). The contribution to interindividual difference in total power was greater from the differences in the power spectral density at frequencies closer to both ends of the frequency axis and minimal from that at -3.25 log(Hz), suggesting hingelike movement of the spectral shape at this frequency with the difference in total power. These characteristics of the 24-h HRV spectrum were simulated by an artificial signal generated by adding two noises with different beta values. Given that the power law assumption is fundamental to the analysis of dynamics through the log-log scaled spectrum, our observations are substantial for physiological and clinical studies of the heartbeat dynamic during daily life and suggest that the nonharmonic component of HRV in normal subjects during daily life may include at least two 1/fbeta fluctuations that differ in dynamics and age dependency.

The association between Trp64Arg polymorphism of the beta3-adrenergic receptor and autonomic nervous system activity.

The beta3-adrenergic receptor plays a significant role in the control of lipolysis and thermogenesis in brown adipose tissue through autonomic nervous system (ANS) activity. As the Trp64Arg polymorphism of the beta3-adrenergic receptor gene might affect ANS activity, we investigated the association of the polymorphism with ANS activity. The prevalence of the polymorphism was determined in 204 subjects. Ten normal homozygous, 10 heterozygous, and 1 variant homozygous subjects were examined for ANS activity during supine rest and standing by electrocardiogram R-R interval power spectral analysis. Subjects with the variant did not differ from subjects without the variant in body mass index, plasma glucose, plasma insulin, or family history of diabetes or obesity. The total power of heterozygotes at supine rest was lower than that of normal subjects (1124.6 +/- 191.6 vs. 3029.8 +/- 758.8 ms2; mean +/- SE). With a postural change to standing, the parasympathetic and sympathetic nervous system activity indexes of heterozygotes showed a higher response than those of normal subjects (parasympathetic nervous system index, 0.10 +/- 0.02 vs. 0.17 +/- 0.02; sympathetic nervous system index, 10.55 +/- 1.47 vs. 6.26 +/- 1.09), and the difference in total power disappeared. These findings show that subjects with the variant, even the heterozygotes, had lower resting ANS activity than normal subjects.

Spectral Analysis of Blood Pressure Variability in Heart Transplant Patients

The cardiac transplant patient provides a unique model for the study of blood pressure variability in the absence of heart rate variability. We examined the harmonic and fractal components of blood pressure variability in 14 heart transplant patients (12 men, 2 women; 21 to 62 years of age) and in age-and sex-matched control subjects during seated rest, supine rest, and supine rest with fixed-pace breathing (12 respirations per minute). Heart rate was faster in transplant patients than in control subjects, with much less heart rate variability (P < .0001). Spectral analysis of blood pressure variability revealed no difference in total power for either systolic or diastolic pressure, but transplant patients had less low-frequency (0 to 0.15 Hz) harmonic spectral power in both systolic (P < .01) and diastolic (P < .03) pressure and more high-frequency power (0.15 to 0.5 Hz) in diastolic pressure than control subjects. The ratio of high-frequency power in diastolic relative to systolic pressure was consistently higher (P < .0001) in the transplant patients (0.29 to 0.51) than in control subjects (0.11 to 0.13). The slope of the fractal component of systolic pressure was approximately 1.8 in both transplant patients and control subjects. This was greater than the slope for heart rate variability (approximately 1.1 in control subjects). These data provide clear evidence of independence of the fractal component of heart rate and blood pressure variabilities in both transplant patients and control subjects. The heart rate component of the arterial baroreflex minimized high-frequency diastolic pressure changes while contributing to low-frequency variations in both systolic and diastolic pressures.