Heart rate variability and cardiac reflexes in small for gestational age infants.

To assess the influence of intrauterine growth retardation and postnatal development on heart rate variability (HRV) and cardiac reflexes, we studied 27 healthy small for gestational age (SGA) and 23 appropriate for gestational age (AGA) infants during a nap study. Resting HRV was assessed by point dispersion of Poincaré plots for overall (SDRR) and instantaneous beat-to-beat variability (SDDeltaRR) and the ratio (SDRR/SDDeltaRR). Heart rate reflex and arousal responses to a 60 degrees head-up tilt were determined. All tests/measures were repeated twice in quiet and active sleep and in prone and supine sleep positions at 1 and 3 mo of age. SGA infants exhibited higher resting sympathetic tone [SDRR/SDDeltaRR: 1.9 (95% confidence interval: 1.7, 2.0) and 1.7 (95% confidence interval: 1.5, 1.8) in SGA and AGA, respectively; P=0.046] and a tendency for a smaller tachycardic reflex response to the tilt [Deltaheart rate: 24 beats/min (95% confidence interval: 20, 28) and 30 (95% confidence interval: 25, 34)] in SGA and AGA, respectively; P=0.06]. HRV indexes were reduced in the prone compared with supine position (P<0.0001), but reflex tilt responses were unchanged with position. SGA/AGA differences were independent of sleep position. Gestational age weight status did not influence the likelihood of arousal, but prone sleeping per se reduced the odds 2.5-fold. The findings suggest reduced autonomic activity and cardiac reflexes in SGA infants. The finding that the sympathetic component of the control of HRV was higher in SGA infants could link with findings in adulthood of an association between being born SGA and a higher risk of cardiovascular disease.     

Acute effects of stretching exercise on the heart rate variability in subjects with low flexibility levels

The study investigated the heart rate (HR) and heart rate variability (HRV) before, during, and after stretching exercises performed by subjects with low flexibility levels. Ten men (age: 23 ± 2 years; weight: 82 ± 13 kg; height: 177 ± 5 cm; sit-and-reach: 23 ± 4 cm) had the HR and HRV assessed during 30 minutes at rest, during 3 stretching exercises for the trunk and hamstrings (3 sets of 30 seconds at maximum range of motion), and after 30 minutes postexercise. The HRV was analyzed in the time ('SD of normal NN intervals' [SDNN], 'root mean of the squared sum of successive differences' [RMSSD], 'number of pairs of adjacent RR intervals differing by >50 milliseconds divided by the total of all RR intervals' [PNN50]) and frequency domains ('low-frequency component' [LF], 'high-frequency component' [HF], LF/HF ratio). The HR and SDNN increased during exercise (p < 0.03) and decreased in the postexercise period (p = 0.02). The RMSSD decreased during stretching (p = 0.03) and increased along recovery (p = 0.03). At the end of recovery, HR was lower (p = 0.01), SDNN was higher (p = 0.02), and PNN50 was similar (p = 0.42) to pre-exercise values. The LF increased (p = 0.02) and HF decreased (p = 0.01) while stretching, but after recovery, their values were similar to pre-exercise (p = 0.09 and p = 0.3, respectively). The LF/HF ratio increased during exercise (p = 0.02) and declined during recovery (p = 0.02), albeit remaining higher than at rest (p = 0.03). In conclusion, the parasympathetic activity rapidly increased after stretching, whereas the sympathetic activity increased during exercise and had a slower postexercise reduction. Stretching sessions including multiple exercises and sets acutely changed the sympathovagal balance in subjects with low flexibility, especially enhancing the postexercise vagal modulation.     

Impact of gender on the cardiac autonomic response to angiotensin II in healthy humans

Premenopausal women have a lower risk of cardiovascular disease (CVD) compared with men of a similar age. Furthermore, the regulation of factors that influence CVD appears to differ between the sexes, including control of the autonomic nervous system (ANS) and the renin-angiotensin system. We examined the cardiac ANS response to angiotensin II (Ang II) challenge in healthy subjects to determine whether differences in women and men exist. Thirty-six healthy subjects (21 women, 15 men, age 38 ± 2 years) were studied in a high-salt balance. Heart-rate variability (HRV) was calculated by spectral power analysis [low-frequency (LF) sympathetic modulation, high-frequency (HF) parasympathetic/vagal modulation, and LF:HF as a measure of overall ANS balance]. HRV was assessed at baseline and in response to graded Ang II infusions (3 ng·kg(-1)·min(-1) × 30 min; 6 ng·kg(-1)·min(-1) × 30 min). Cardiac ANS tone did not change significantly in women after each Ang II dose [3 ng·kg(-1)·min(-1) mean change (Δ)LF:HF (mean ± SE) 0.5 ± 0.3, P = 0.8, vs. baseline; 6 ng·kg(-1)·min(-1) ΔLF:HF (mean ± SE) 0.5 ± 0.4, P = 0.4, vs. baseline], whereas men exhibited an unfavorable shift in overall cardiac ANS activity in response to Ang II (ΔLF:HF 2.6 ± 0.2, P = 0.01, vs. baseline; P = 0.02 vs. female response). This imbalance in sympathovagal tone appeared to be largely driven by a withdrawal in cardioprotective vagal activity in response to Ang II challenge [ΔHF normalized units (nu), -5.8 ± 2.9, P = 0.01, vs. baseline; P = 0.006 vs. women] rather than an increase in sympathetic activity (ΔLF nu, -4.5 ± 5.7, P = 0.3, vs. baseline; P = 0.5 vs. women). Premenopausal women maintain cardiac ANS tone in response to Ang II challenge, whereas similarly aged men exhibit an unfavorable shift in cardiovagal activity. Understanding the role of gender in ANS modulation may help guide risk-reduction strategies in high-risk CVD populations.     

Increased sympathetic and decreased parasympathetic cardiovascular modulation in normal humans with acute sleep deprivation.

Cardiovascular autonomic modulation during 36 h of total sleep deprivation (SD) was assessed in 18 normal subjects (16 men, 2 women, 26.0 +/- 4.6 yr old). ECG and continuous blood pressure (BP) from radial artery tonometry were obtained at 2100 on the first study night (baseline) and every subsequent 12 h of SD. Each measurement period included resting supine, seated, and seated performing computerized tasks and measured vigilance and executive function. Subjects were not supine in the periods between measurements. Spectral analysis of heart rate variability (HRV) and BP variability (BPV) was computed for cardiac parasympathetic modulation [high-frequency power (HF)], sympathetic modulation [low-frequency power (LF)], sympathovagal balance (LF/HF power of R-R variability), and BPV sympathetic modulation (at LF). All spectral data were expressed in normalized units [(total power of the components/total power-very LF) x 100]. Spontaneous baroreflex sensitivity (BRS), based on systolic BP and pulse interval powers, was also measured. Supine and sitting, BPV LF was significantly increased from baseline at 12, 24, and 36 h of SD. Sitting, HRV LF was increased at 12 and 24 h of SD, HRV HF was decreased at 12 h SD, and HRV LF/HF power of R-R variability was increased at 12 h of SD. BRS was decreased at 24 h of SD supine and seated. During the simple reaction time task (vigilance testing), the significantly increased sympathetic and decreased parasympathetic cardiac modulation and BRS extended through 36 h of SD. In summary, acute SD was associated with increased sympathetic and decreased parasympathetic cardiovascular modulation and decreased BRS, most consistently in the seated position and during simple reaction-time testing.     

Effects of recombinant human thyrotropin on heart rate variability and blood pressure in patients on l-thyroxine-suppressive therapy for differentiated thyroid carcinoma

BACKGROUND: Recombinant human thyrotropin (rhTSH) is now currently used for the follow-up of patients with differentiated thyroid carcinoma (DTC) after total thyroid ablation. Side effects after rhTSH could involve the autonomic system and TSH receptors are possibly expressed in the heart and coronary arteries. METHODS:Heart rate variability (HRV), studied by power spectral analysis of low (LF) and high frequency (HF) powers, blood pressure (BP) and their responses to orthostatism were investigated before and 3, 6, 9 days after the first of two administrations of rhTSH on alternate days in 11 patients on chronic l-thyroxine (l-T4) suppressive therapy for DTC and in 31 healthy controls. RESULTS: A transient asymptomatic decrease in systolic and mean BP was observed during the rhTSH test, but rhTSH did not modify sympathovagal control of HRV and the lying to standing responses. Decreased LF power and LF/(LF + HF) and LF/HF ratios in DTC patients versus healthy controls indicated a sympathetic failure ascribed to the TSH-suppressive therapy with l-T4 rather than to direct effects of rhTSH. CONCLUSIONS: These findings allowed us to confirm the cardiovascular safety of rhTSH and the absence of its effects on sympathovagal control of HRV when used in the follow-up of patients with normal heart function after thyroid ablation for DTC.     

Heart Rate Variability and Skin Conductance During Repetitive TMS Course in Children with Autism

Autism spectrum disorder (ASD) is a developmental disorder marked by difficulty in social interactions and communication. ASD also often present symptoms of autonomic nervous system (ANS) functioning abnormalities. In individuals with autism the sympathetic branch of the ANS presents an over-activation on a background of the parasympathetic activity deficits, creating an autonomic imbalance, evidenced by a faster heart rate with little variation and increased tonic electrodermal activity. The objective of this study was to explore the effect of 12 sessions of 0.5 Hz repetitive transcranial magnetic stimulation (rTMS) over dorsolateral prefrontal cortex (DLPFC) on autonomic activity in children with ASD. Electrocardiogram and skin conductance level (SCL) were recorded and analyzed during each session of rTMS. The measures of interest were time domain (i.e., R–R intervals, standard deviation of cardiac intervals, NN50-cardio-intervals >50 ms different from preceding interval) and frequency domain heart rate variability (HRV) indices [i.e., power of high frequency (HF) and low frequency (LF) components of HRV spectrum, LF/HF ratio]. Based on our prior pilot studies it was proposed that the course of 12 weekly inhibitory low-frequency rTMS bilaterally applied to the DLPFC will improve autonomic balance probably through improved frontal inhibition of the ANS activity, and will be manifested in an increased length of cardiointervals and their variability, and in higher frequency-domain HRV in a form of increased HF power, decreased LF power, resulting in decreased LF/HF ratio, and in decreased SCL. Our post-12 TMS results showed significant increases in cardiac intervals variability measures and decrease of tonic SCL indicative of increased cardiac vagal control and reduced sympathetic arousal. Behavioral evaluations showed decreased irritability, hyperactivity, stereotype behavior and compulsive behavior ratings that correlated with several autonomic variables.     

A circadian rhythm in heart rate variability contributes to the increased cardiac sympathovagal response to awakening in the morning

Morning hours are associated with a heightened risk of adverse cardiovascular events. Recent evidence suggests that the sleep-wake cycle and endogenous circadian system modulate cardiac function in humans and may contribute to these epidemiological findings. The aim of the present study was to investigate the interaction between circadian and sleep-wake-dependent processes on heart rate variability (HRV). Fifteen diurnally active healthy young adults underwent a 72-h ultradian sleep-wake cycle (USW) procedure (alternating 60-min wake episodes in dim light and 60-min nap opportunities in total darkness) in time isolation. The present study revealed a significant main effect of sleep-wake-dependent and circadian processes on cardiac rhythmicity, as well as a significant interaction between these processes. Turning the lights off was associated with a rapid increase in mean RR interval and cardiac parasympathetic modulation (high-frequency [HF] power), whereas low-frequency (LF) power and sympathovagal balance (LF:HF ratio) were reduced (p?≤?.001). A significant circadian rhythm in mean RR interval and HRV components was observed throughout the wake and nap episodes (p?≤?.001). Sleep-to-wake transitions occurring in the morning were associated with maximal shifts towards sympathetic autonomic activation as compared to those occurring during the rest of the day. Namely, peak LF:HF ratio was observed in the morning, coincidental with peak salivary cortisol levels. These results contribute to our understanding of the observed increase in cardiovascular vulnerability after awakening in the morning.     

Heart Rate Variability and Autonomic Modulations in Preeclampsia

BackgroundAlthough the exact pathophysiology of preeclampsia is not well understood, autonomic nervous system imbalance is suggested as one of the main factors.AimsTo investigate heart rate variability (HRV) and autonomic modulations in Sudanese pregnant women with preeclampsia.ResultsPatients with preeclampsia achieved significantly higher LF Norm [49.80 (16.25) vs. 44.55 (19.15), P = 0.044] and LnLF/HF [0.04 (0.68) vs. -0.28 (0.91), P = 0.023] readings, but lower HF Norm [49.08 (15.29) vs. 55.87 (19.56), P = 0.012], compared with healthy pregnant women. Although all other HRV measurements were higher in the patients with preeclampsia compared with the controls, only LnVLF [4.50 (1.19) vs. 4.01 (1.06), P = 0.017] and LnLF [4.01 (1.58) vs. 3.49 (1.23), P = 0.040] reached statistical significance.ConclusionThe study adds further evidence for the dominant cardiac sympathetic modulations on patients with preeclampsia, probably secondary to parasympathetic withdrawal in this group. However, the higher LnVLF and LnLF readings achieved by preeclamptic women compared with the controls are unexpected in the view that augmented sympathetic modulations usually depresses all HRV parameters including these two measures.     

急性心肌梗死患者PCI治疗后抑郁对心率变异性、内皮功能及不良心血管事件发生率的影响

目的:探讨急性心肌梗死(AMI)患者经皮冠状动脉介入(PCI)治疗后抑郁对心率变异性(HRV)、内皮功能及不良心血管事件(MACE)发生率的影响。方法:选择2017年1月-2018年12月期间在本院接受PCI治疗的AMI患者117例作为研究对象,根据PCI术后出院当日的抑郁自评量表(SDS)评分值将其分为抑郁组(评分值≥53分)41例、非抑郁组(评分值<53分)76例。对比两组患者HRV相关指标[正常RR间期标准差(SDNN)、5 min内正常RR间期平均值标准差(SDANN)、相邻正常RR间期差值均方的平方根(RMSSD)、总功率(TP)、低频功率(LF)、高频功率(HF)、低频功率与高频功率比值(LF/HF)]、内皮功能指标[内皮依赖性血管舒张功能(FMD)、非内皮依赖性血管舒张功能(NMD)]水平差异,记录两组随访期内MACE发生情况。结果:PCI术后出院当日,抑郁组患者的HRV时域指标SDNN、SDANN、RMSSD水平低于非抑郁组患者;频域指标中LF、LF/HF的水平高于非抑郁组,HF的水平低于非抑郁组(P<0.05),两组患者TP水平的差异无统计学意义(P>0.05)。抑郁组患者的FMD、NMD水平均低于非抑郁组患者,差异有统计学意义(P<0.05)。随访期内,抑郁组患者的MACE总发生率、再发心肌梗死发生率高于非抑郁组,差异有统计学意义(P<0.05)。两组患者顽固性心绞痛、新发心肌梗死、心力衰竭、心源性死亡发生率的差异无统计学意义(P>0.05)。结论:AMI患者PCI后合并抑郁可能对心血管系统造成负面影响并最终增加MACE的发生风险。     

Heart rate variability changes in business process outsourcing employees working in shifts

Background and Objectives

Irregular and poor quality sleep is common in business process outsourcing (BPO) employees due to continuous shift working. The influence of this on the cardiac autonomic activity was investigated by the spectral analysis of heart rate variability (HRV).

Methods

36 night shift BPO employees (working from 22:00 to 06:00h) and 36 age and sex matched day shift BPO employees (working from 08:00 to 16:00h) were recruited for the study. Five minute electrocardiogram (ECG) was recorded in all the subjects. Heart rate variability was analyzed by fast Fourier transformation using RMS Vagus HRV software. The results were analyzed using Mann Whitney U test, Student t-test, Wilcoxon signed rank test and were expressed as mean ± SD.

Results

Sleepiness was significantly higher among night shift workers as measured by Epworth Sleepiness Scale (p<0.001). Night shift BPO employees were found to have a trend towards lower values of vagal parameters - HF power (ms²), and higher values of sympathovagal parameters like LF Power (ms²) and the LF/HF power (%) suggesting decreased vagal activity and sympathetic over activity, when compared to day shift employees. However, HRV parameters did not vary significantly between the day shift employees and night shift workers baseline values, and also within the night shift group.

Interpretation and Conclusion

Night shift working increased the heart rate and shifted the sympathovagal balance towards sympathetic dominance and decreased vagal parameters of HRV. This is an indicator of unfavorable change in the myocardial system, and thus shows increased risk of cardiovascular disease among the night shift employees.     

Heart rate variability responses to hypoxic and hypercapnic exposures in different mouse strains.

Heart rate variability (HRV) is a well-characterized, noninvasive means of assessing cardiac autonomic nervous system activity. This study examines the basic cardiac responses to hypoxic and hypercapnic challenges in seven strains of commonly used inbred mice (A/J, BALB/cJ, C3H/HeJ, C57BL/6J, CBA/J, DBA/2J, and FVB/J). Adult male mice, 8-12 wk of age, were chronically instrumented to a femoral artery catheter for the continuous measurement of systemic arterial blood pressure and heart rate. Mice were exposed to multiple 4-min periods of hypoxia (10% O2), hypercapnia (5% CO2), and combined hypoxia/hypercapnia (10% O2 + 5% CO2). HRV was derived from pulse intervals of the blood pressure tracings. Hypoxia induced increases in high-frequency HRV power and decreased low-frequency (LF) HRV power in most strains. Hypercapnia led to decreased high-frequency HRV power and increased LF HRV power in most strains. Strain differences were most notable in regard to the concomitant exposures of hypoxia and hypercapnia, with FVB/J mice mirroring their own response to hypercapnia alone, whereas CBA/J mice mirrored their own responses to hypoxia. As blood pressure is most likely the driving factor for heart rate changes via the baroreflex pathway, it is interesting that LF, considered to reflect cardiac sympathetic activity, was negatively correlated with heart rate, suggesting that LF changes are driven by baroreflex oscillation and not necessarily by absolute sympathetic or parasympathetic activity to the heart. These findings suggest that genetic background can influence the centrally mediated cardiovascular responses to basic hypoxic and hypercapnic challenges.     

Effect of targeted deletions of beta1- and beta2-adrenergic-receptor subtypes on heart rate variability

Beta-adrenergic receptors (beta-ARs) play a major role in regulating heart rate (HR) and contractility in the intact cardiovascular system. Three subtypes (beta1, beta2, and beta3) are expressed in heart tissue, and the role of each subtype in regulating cardiac function has previously been determined by using both pharmacological and gene-targeting approaches. However, previous studies have only examined the role of beta-ARs in the macrolevel regulation of HR. We employed three knockout (KO) mouse lines, beta1-KO, beta2-KO, and beta1/beta2 double KO (DL-KO), to examine the role that beta-AR subtypes play in HR variability (HRV) and in the sympathetic and parasympathetic inputs into HR control. Fast Fourier transformation (FFT) in frequency domain methods of ECG spectral analysis was used to resolve HRV into high- and low-frequency (HF and LF) powers. Resting HR (in beats/min) was decreased in beta1-KO [488 (SD 27)] and DL-KO [495 (SD 12)] mice compared with wild-type [WT; 638 (SD 30)] or beta2-KO [656 (SD 51)] (P < 0.0005) mice. Mice lacking beta1-ARs (beta1-KO and DL-KO) had increased HRV (as illustrated by the standard deviation of normal R-R intervals) and increased normalized HF and LF powers compared with mice with intact beta1-ARs (WT and beta2-KO). These results demonstrate the differential role of beta-AR subtypes in regulating autonomic signaling.     

Sex differences in baroreflex sensitivity, heart rate variability, and end organ damage in the TGR(mRen2)27 rat

The aim of this investigation was to evaluate sex differences in baroreflex and heart rate variability (HRV) dysfunction and indexes of end-organ damage in the TG(mRen2)27 (Ren2) rat, a model of renin overexpression and tissue renin-angiotensin-aldosterone system overactivation. Blood pressure (via telemetric monitoring), blood pressure variability [BPV; SD of systolic blood pressure (SBP)], spontaneous baroreflex sensitivity, HRV [HRV Triangular Index (HRV-TI), standard deviation of the average NN interval (SDNN), low and high frequency power (LF and HF, respectively), and Poincaré plot analysis (SD1, SD2)], and cardiovascular function (pressure-volume loop analysis and proteinuria) were evaluated in male and female 10-wk-old Ren2 and Sprague Dawley rats. The severity of hypertension was greater in Ren2 males (R2-M) than in Ren2 females (R2-F). Increased BPV, suppression of baroreflex gain, decreased HRV, and associated end-organ damage manifested as cardiac dysfunction, myocardial remodeling, elevated proteinuria, and tissue oxidative stress were more pronounced in R2-M compared with R2-F. During the dark cycle, HRV-TI and SDNN were negatively correlated with SBP within R2-M and positively correlated within R2-F; within R2-M, these indexes were also negatively correlated with end-organ damage [left ventricular hypertrophy (LVH)]. Furthermore, within R2-M only, LVH was strongly correlated with indexes of HRV representing predominantly vagal (HF, SD1), but not sympathetic (LF, SD2), variability. These data demonstrated relative protection in females from autonomic dysfunction and end-organ damage associated with elevated blood pressure in the Ren2 model of hypertension.     

Wavelet analysis of instantaneous heart rate: a study of autonomic control during thrombolysis

Myocardial infarction (MI) is known to elicit activation of the autonomic nervous system. Reperfusion, induced by thrombolysis, is thus expected to bring about a shift in the balance between the sympathetic and vagal systems, according to the infarct location. In this study, we explored the correlation between reperfusion and the spectral components of heart rate (HR) variability (HRV), which are associated with autonomic cardiac control. We analyzed the HR of patients during thrombolysis: nine anterior wall MI (AW-MI) and eight inferoposterior wall MI (IW-MI). Reperfusion was determined from changes in ST levels and reported pain. Reocclusion was detected in four patients. HRV was analyzed using a modified continuous wavelet transform, which provided time-dependent versions of the typically used low-frequency (LF) and high-frequency (HF) peaks and of their ratio, LF/HF. Marked alterations in at least one of the HRV parameters was found in all 18 reperfusion events. Patterns of HRV, compatible with a shift toward relative sympathetic enhancement, were found in all of the nine reperfusion events in IW-MI patients and in three AW-MI patients. Patterns of HRV compatible with relative vagal enhancement were found in six AW-MI patients (P < 0.001). Significant changes in HRV parameters were also found after reocclusion. Time-dependent spectral analysis of HRV using the wavelet transform was found to be valuable for explaining the patterns of cardiac rate control during reperfusion. In addition, examination of the entire record revealed epochs of markedly diminished HRV in two patients, which we attribute to vagal saturation.     

Aortic Intima-Media Thickness and Aortic Diameter in Small for Gestational Age and Growth Restricted Fetuses

ObjectiveThe objective of this study is to measure aortic intima-media thickness (aIMT) and aortic diameter (AD) in appropriate for gestational age (AGA) fetuses, small for gestational age (SGA) fetuses, and intrauterine growth restricted (IUGR) fetuses.MethodsCase-control study performed between June 2011 and June 2012. Forty-nine AGA fetuses, 40 SGA fetuses, and 35 IUGR fetuses underwent concomitant measurement of aIMT and AD at a mean gestational age of 34.4 weeks.ResultsMedian aIMT was higher in fetuses with IUGR (0.504 mm [95%CI: 0.477-0.530 mm]), than in SGA fetuses (0.466 mm [95% CI: 0.447–0.485 mm]), and AGA fetuses (0.471 mm [95% CI: 0.454-0.488 mm]) (p = 0.023). Mean AD was significantly lower in fetuses with IUGR (4.451 mm [95% CI: 4.258–4.655 mm]), than in AGA fetuses (4.74 mm [95% CI: 4.63-4.843 mm]) (p = 0.028).ConclusionsGrowth restricted fetuses have a thicker aortic wall than AGA and SGA fetuses, which possibly represents preclinical atherosclerosis and a predisposition to later cardiovascular disease.     

Associations between Heart Rate Variability Parameters and Housing- and Individual-Related Variables in Dairy Cows Using Canonical Correspondence Analysis

We investigated the associations between heart rate variability (HRV) parameters and some housing- and individual-related variables using the canonical correspondence analysis (CCOA) method in lactating Holstein-Friesian dairy cows. We collected a total of 5200 5-min interbeat interval (IBI) samples from 260 animals on five commercial dairy farms [smaller-scale farms with 70 (Farm 1, n = 50) and 80 cows per farm (Farm 2, n = 40), and larger-scale farms with 850 (Farm 3, n = 66), 1900 (Farm 4, n = 60) and 1200 (Farm 5, n = 45) cows. Dependent variables included HRV parameters, which reflect the activity of the autonomic nervous system: heart rate (HR), the root mean square of successive differences (RMSSD) in IBIs, the standard deviation 1 (SD1), the high frequency (HF) component of HRV and the ratio between the low frequency (LF) and the HF parameter (LF/HF). Explanatory variables were group size, space allowance, milking frequency, parity, daily milk yield, body condition score, locomotion score, farm, season and physical activity (lying, lying and rumination, standing, standing and rumination and feeding). Physical activity involved in standing, feeding and in rumination was associated with HRV parameters, indicating a decreasing sympathetic and an increasing vagal tone in the following order: feeding, standing, standing and rumination, lying and rumination, lying. Objects representing summer positioned close to HR and LF and far from SD1, RMSSD and HF indicate a higher sympathetic and a lower vagal activity. Objects representing autumn, spring and winter associated with increasing vagal activity, in this order. Time-domain measures of HRV were associated with most of the housing- and individual-related explanatory variables. Higher HR and lower RMSSD and SD1 were associated with higher group size, milking frequency, parity and milk yield, and low space allowance. Higher parity and milk yield were associated with higher sympathetic activity as well (higher LF/HF), while individuals with lower locomotion scores (lower degree of lameness) were characterized with a higher sympathetic and a lower vagal tone (higher HR and LF/HF and lower RMSSD and SD1). Our findings indicate that the CCOA method is useful in demonstrating associations between HRV and selected explanatory variables. We consider physical activity, space allowance, group size, milking frequency, parity, daily milk yield, locomotion score and season to be the most important variables in further HRV studies on dairy cows.     

Preeclamptic pregnancy is associated with increased sympathetic and decreased parasympathetic control of HR

Previous work from our laboratory using heart rate variability (HRV) has demonstrated that women before menopause have a more dominant parasympathetic and less effective sympathetic regulations of heart rate compared with men. Because it is still not clear whether normal or preeclamptic pregnancy coincides with alternations in the autonomic functions, we evaluated the changes of HRV in 17 nonpregnant, 17 normotensive pregnant, and 11 preeclamptic women who were clinically diagnosed without history of diabetic neuropathy, cardiac arrhythmia, and other cardiovascular diseases. Frequency-domain analysis of short-term, stationary R-R intervals was performed to evaluate the total variance, low-frequency power (LF; 0.04-0.15 Hz), high-frequency power (HF; 0.15-0.40 Hz), ratio of LF to HF (LF/HF), and LF in normalized units (LF%). Natural logarithm transformation was applied to variance, LF, HF, and LF/HF for the adjustment of the skewness of distribution. We found that the normal pregnant group had a lower R-R value and HF but had a higher LF/HF and LF% compared with the nonpregnant group. The preeclamptic group had lower HF but higher LF/HF compared with either the normal pregnant or nonpregnant group. Our results suggest that normal pregnancy is associated with a facilitation of sympathetic regulation and an attenuation of parasympathetic influence of heart rate, and such alterations are enhanced in preeclamptic pregnancy.     

Assessment of Cardiac Autonomic Modulation during Adolescent Obesity

Objective: To investigate the cardiovascular autonomic function in pediatric obesity of different duration by using standard time domain, spectral heart rate variability (HRV), and nonlinear methods. Research Methods and Procedures: Fifty obese children (13.9 ± 1.7 years) were compared with 12 lean subjects (12.9 ± 1.6 years). Obese children were classified as recent obese (ROB) (<4 years), intermediate obese (IOB) (4 to 7 years), and long‐term obese (OB) (>7 years). In all participants, we performed blood pressure (BP) measurements, laboratory tests, and 24‐hour electrocardiogram/ambulatory BP monitoring. The spectral power was quantified in total power, very low‐frequency (LF) power, high‐frequency (HF) power, and LF to HF ratio. Total, long‐term, and short‐term time domain HRV were calculated. Poincaré plot and quadrant methods were used as nonlinear techniques. Results: All obese groups had higher casual and ambulatory BP and higher glucose, homeostasis model assessment, and triglyceride levels. All parameters reflecting parasympathetic tone (HF band, root mean square successive difference, proportion of successive normal‐to‐normal intervals, and scatterplot width) were significantly and persistently reduced in all obese groups in comparison with lean controls. LF normalized units, LF/HF, and cardiac acceleration (reflecting sympathetic activation) were significantly increased in the ROB group. In IOB and OB groups, LF, but not nonlinear, measures were similar to lean controls, suggesting biphasic behavior of sympathetic tone, whereas nonlinear analysis showed a decreasing trend with the duration of obesity. Long‐term HRV measures were significantly reduced in ROB and IOB. Discussion: Autonomic nervous system changes in adolescent obesity seem to be related to its duration. Nonlinear methods of scatterplot and quadrant analysis permit assessment of autonomic balance, despite measuring different aspects of HRV.     

Sleep-related sympathovagal imbalance in SHR

The role of the autonomic nervous system in spontaneous hypertension during each stage of the sleep-wake cycle remains unclear. The present study attempted to evaluate the differences in cardiac autonomic modulations among spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY), and Sprague-Dawley rats (SD) across sleep-wake cycles. Continuous power spectral analysis of electroencephalogram, electromyogram, and heart rate variability was performed in unanesthetized free moving rats during daytime sleep. Frequency-domain analysis of the stationary R-R intervals (RR) was performed to quantify the high-frequency power (HF), low-frequency power (LF)-to-HF ratio (LF/HF), and normalized LF (LF%) of heart rate variability. WKY and SD had similar mean arterial pressure, which is significantly lower than that of SHR during active waking, quiet sleep, and paradoxical sleep. Compared with WKY and SD, SHR had lower HF but similar RR, LF/HF, and LF% during active waking. During quiet sleep, SHR developed higher LF/HF and LF% in addition to lower HF. SHR ultimately exhibited significantly lower RR accompanied with higher LF/HF and LF% and lower HF during paradoxical sleep compared with WKY. We concluded that significant cardiac sympathovagal imbalance with an increased sympathetic modulation occurred in SHR during sleep, although it was less evident during waking.     

Identification of development and autonomic nerve activity from heart rate variability in preterm infants

Heartbeat intervals, which are determined basically by regular excitations of the sinoatrial node, show significant fluctuation referred to as the heart rate variability (HRV). The HRV is mostly due to nerve activities through the sympathetic and parasympathetic branches of the autonomic nervous system (ANS). In recent years, it has been recognized that the HRV shows a greater complexity than ever expected, suggesting that it includes much information about ANS activities. In this study, we investigated relationship between HRV and development in preterm infants. To this end, heartbeat intervals were continuously recorded from 11 preterm infants in NICU. The recording periods were ranging from several days to weeks depending on the individuals. The HRV at various ages was then characterized by several indices. They include power spectrum as well as the mean and standard deviation of the series. For the power spectrum, the low-frequency band power (LF), high-frequency band power (HF), LF/HF (the ratio between LF and HF), beta (scaling exponent of the spectrum) were estimated. The detrended fluctuation analysis (DFA) was also employed to obtain short- and long-range scaling exponents. Each of these indices showed a correlation with the age. We showed that the long-range scaling exponent, derived from the DFA, was most significantly correlated with the age, suggesting that it could be a robust index to characterize the development of preterm infants.