Transfer of Heart Rate Feedback Training to Reduce Heart Rate Response to Laboratory Tasks

To examine whether transfer of heart rate (HR) feedback training to tasks not used during training could be improved by using multiple tasks during training, a modified multiple baseline across tasks, single subject design study was conducted using six high HR-reactive young adults. Participants received HR feedback training during the presentation of a videogame, and transfer of training was assessed to a mental arithmetic challenge and handgrip task. Transfer of training was next assessed following training with the mental arithmetic challenge and handgrip task. HR responses to each training task with no HR feedback were assessed during a pre-treatment session, an immediate post-training period following training on each task, a short delay (1–2 days) post-training session, and a long delay (1–2 weeks) post-training session. HR response to a novel speech task was assessed at pre-treatment and during short delay and long delay post-training sessions. Results revealed that participants reduced HR during training and generally maintained this reduction in HR during the immediate post-training assessment when HR feedback was not present. Participants were not able to reduce HR responses to tasks during short delay and long delay post-training sessions, and they were unable to transfer HR reduction skills to the speech task. Transfer of HR feedback training to new tasks was limited in nature and efforts to train across multiple stressors did not appear to improve transfer of training.     

Heart Rate Variability during Performance of Various Resultive Tasks

Heart rate variability was studied in 30 subjects before and after the assembling of a single-type color mosaic. The heart rate analysis was performed by evaluating its statistical structure (variation curves, scatter plots, and standard deviation). The wave structure of a series of cardiointervals was assessed by calculating and plotting the autocorrelation function. Certain heart rate parameters in different subjects reflected to various extents their success in achieving the useful end result of the visuomotor design task.     

Differences in Lower Extremity and Trunk Kinematics between Single Leg Squat and Step Down Tasks

The single leg squat and single leg step down are two commonly used functional tasks to assess movement patterns. It is unknown how kinematics compare between these tasks. The purpose of this study was to identify kinematic differences in the lower extremity, pelvis and trunk between the single leg squat and the step down. Fourteen healthy individuals participated in this research and performed the functional tasks while kinematic data were collected for the trunk, pelvis, and lower extremities using a motion capture system. For the single leg squat task, the participant was instructed to squat as low as possible. For the step down task, the participant was instructed to stand on top of a box, slowly lower him/herself until the non-stance heel touched the ground, and return to standing. This was done from two different heights (16cm and 24cm). The kinematics were evaluated at peak knee flexion as well as at 60° of knee flexion. Pearson correlation coefficients (r) between the angles at those two time points were also calculated to better understand the relationship between each task. The tasks resulted in kinematics differences at the knee, hip, pelvis, and trunk at both time points. The single leg squat was performed with less hip adduction (p ≤ 0.003), but more hip external rotation and knee abduction (p ≤ 0.030), than the step down tasks at 60° of knee flexion. These differences were maintained at peak knee flexion except hip external rotation was only significant in the 24cm step down task (p ≤ 0.029). While there were multiple differences between the two step heights at peak knee flexion, the only difference at 60° of knee flexion was in trunk flexion (p < 0.001). Angles at the knee and hip had a moderate to excellent correlation (r = 0.51–0.98), but less consistently so at the pelvis and trunk (r = 0.21–0.96). The differences in movement patterns between the single leg squat and the step down should be considered when selecting a single leg task for evaluation or treatment. The high correlation of knee and hip angles between the three tasks indicates that similar information about knee and hip kinematics was gained from each of these tasks, while pelvis and trunk angles were less well predicted.     

Molecular and Functional Differences between Heart mKv1.7 Channel Isoforms

Ion channels are membrane-spanning proteins that allow ions to permeate at high rates. The kinetic characteristics of the channels present in a cell determine the cell signaling profile and therefore cell function in many different physiological processes. We found that Kv1.7 channels from mouse heart muscle have two putative translation initiation start sites that generate two channel isoforms with different functional characteristics, mKv1.7L (489 aa) and a shorter mKv1.7S (457 aa). The electrophysiological analysis of mKv1.7L and mKv1.7S channels revealed that the two channel isoforms have different inactivation kinetics. The channel resulting from the longer protein (L) inactivates faster than the shorter channels (S). Our data supports the hypothesis that mKv1.7L channels inactivate predominantly due to an N-type related mechanism, which is impaired in the mKv1.7S form. Furthermore, only the longer version mKv1.7L is regulated by the cell redox state, whereas the shorter form mKv1.7S is not. Thus, expression starting at each translation initiation site results in significant functional divergence. Our data suggest that the redox modulation of mKv1.7L may occur through a site in the cytoplasmic N-terminal domain that seems to encompass a metal coordination motif resembling those found in many redox-sensitive proteins. The mRNA expression profile and redox modulation of mKv1.7 kinetics identify these channels as molecular entities of potential importance in cellular redox-stress states such as hypoxia.     

Link between Peripheral Artery Disease and Heart Rate Variability in Hemodialysis Patients

Peripheral artery disease (PAD) and low heart rate variability (HRV) are highly prevalent in hemodialysis patients, and both are associated with increased cardiovascular morbidity and mortality. This study aims to examine the suggested relationship between PAD and HRV, and the relationship of parameters before and after hemodialysis. This study enrolled 161 maintenance hemodialysis patients. PAD was defined as ABI < 0.9 in either leg. HRV was performed to assess changes before and after hemodialysis. The change in HRV (△HRV) was defined as post-hemodialysis HRV minus pre-hemodialysis HRV. Patients’ clinical parameters were collected from the dialysis records. All HRV parameters except high frequency (HF) % were lower in patients with PAD than patients without PAD, though not achieving significant level. In patients without PAD, HF (P = 0.013), low frequency (LF) % (P = 0.028) and LF/HF (P = 0.034) were significantly elevated after hemodialysis, whereas no significant HRV parameters change was noted in patients with PAD. Serum intact parathyroid hormone was independently associated with △HF (β = -0.970, P = 0.032) and △LF% (β = -12.609, P = 0.049). Uric acid level (β = -0.154, P = 0.027) was negatively associated with △LF/HF in patients without PAD. Our results demonstrated that some of the HRV parameters were significantly increased after hemodialysis in patients without PAD, but not in patients with PAD, reflecting a state of impaired sympatho-vagal equilibrium. Severity of secondary hyperparathyroidism and hyperuricemia contributed to lesser HRV parameters increase after hemodialysis in patients without PAD.     

Heart Rate and Heart Rate Variability in Dairy Cows with Different Temperament and Behavioural Reactivity to Humans

From the 1990s, extensive research was started on the physiological aspects of individual traits in animals. Previous research has established two extreme (proactive and reactive) coping styles in several animal species, but the means of reactivity with the autonomic nervous system (ANS) activity has not yet been investigated in cattle. The aim of this study was the characterization of cardiac autonomic activity under different conditions in cows with different individual characteristics. For this purpose, we investigated heart rate and ANS-related heart rate variability (HRV) parameters of dairy cows (N = 282) on smaller- and larger-scale farms grouped by (1) temperament and (2) behavioural reactivity to humans (BRH). Animals with high BRH scores were defined as impulsive, while animals with low BRH scores were defined as reserved. Cardiac parameters were calculated for undisturbed lying (baseline) and for milking bouts, the latter with the presence of an unfamiliar person (stressful situation). Sympathetic tone was higher, while vagal activity was lower in temperamental cows than in calm animals during rest both on smaller- and larger-scale farms. During milking, HRV parameters were indicative of a higher sympathetic and a lower vagal activity of temperamental cows as compared to calm ones in farms of both sizes. Basal heart rate did not differ between BRH groups either on smaller- or larger-scale farms. Differences between basal ANS activity of impulsive and reserved cows reflected a higher resting vagal and lower sympathetic activity of reserved animals compared to impulsive ones both on smaller- and larger-scale farms. There was no difference either in heart rate or in HRV parameters between groups during milking neither in smaller- nor in larger-scale farms. These two groupings allowed to draw possible parallels between personality and cardiac autonomic activity during both rest and milking in dairy cows. Heart rate and HRV seem to be useful for characterisation of physiological differences related to temperament and BRH.     

Modelling Heart Rate Kinetics

The objective of the present study was to formulate a simple and at the same time effective mathematical model of heart rate kinetics in response to movement (exercise). Based on an existing model, a system of two coupled differential equations which give the rate of change of heart rate and the rate of change of exercise intensity is used. The modifications introduced to the existing model are justified and discussed in detail, while models of blood lactate accumulation in respect to time and exercise intensity are also presented. The main modification is that the proposed model has now only one parameter which reflects the overall cardiovascular condition of the individual. The time elapsed after the beginning of the exercise, the intensity of the exercise, as well as blood lactate are also taken into account. Application of the model provides information regarding the individual’s cardiovascular condition and is able to detect possible changes in it, across the data recording periods. To demonstrate examples of successful numerical fit of the model, constant intensity experimental heart rate data sets of two individuals have been selected and numerical optimization was implemented. In addition, numerical simulations provided predictions for various exercise intensities and various cardiovascular condition levels. The proposed model can serve as a powerful tool for a complete means of heart rate analysis, not only in exercise physiology (for efficiently designing training sessions for healthy subjects) but also in the areas of cardiovascular health and rehabilitation (including application in population groups for which direct heart rate recordings at intense exercises are not possible or not allowed, such as elderly or pregnant women).     

Heart Rate Variability and Blood Pressure during Dynamic and Static Exercise at Similar Heart Rate Levels

Aim was to elucidate autonomic responses to dynamic and static (isometric) exercise of the lower limbs eliciting the same moderate heart rate (HR) response. Method: 23 males performed two kinds of voluntary exercise in a supine position at similar heart rates: static exercise (SE) of the lower limbs (static leg press) and dynamic exercise (DE) of the lower limbs (cycling). Subjective effort, systolic (SBP) and diastolic blood pressure (DBP), mean arterial pressure (MAP), rate pressure product (RPP) and the time between consecutive heart beats (RR-intervals) were measured. Time-domain (SDNN, RMSSD), frequency-domain (power in the low and high frequency band (LFP, HFP)) and geometric measures (SD1, SD2) as well as non-linear measures of regularity (approximate entropy (ApEn), sample entropy (SampEn) and correlation dimension D2) were calculated. Results: Although HR was similar during both exercise conditions (88±10 bpm), subjective effort, SBP, DBP, MAP and RPP were significantly enhanced during SE. HRV indicators representing overall variability (SDNN, SD 2) and vagal modulated variability (RMSSD, HFP, SD 1) were increased. LFP, thought to be modulated by both autonomic branches, tended to be higher during SE. ApEn and SampEn were decreased whereas D₂ was enhanced during SE. It can be concluded that autonomic control processes during SE and DE were qualitatively different despite similar heart rate levels. The differences were reflected by blood pressure and HRV indices. HRV-measures indicated a stronger vagal cardiac activity during SE, while blood pressure response indicated a stronger sympathetic efferent activity to the vessels. The elevated vagal cardiac activity during SE might be a response mechanism, compensating a possible co-activation of sympathetic cardiac efferents, as HR and LF/HF was similar and LFP tended to be higher. However, this conclusion must be drawn cautiously as there is no HRV-marker reflecting “pure” sympathetic cardiac activity.     

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.     

Nonstationary Heart Rate Variability in Respiratory Tests

A new method was proposed for processing a nonstationary heart rate by using frequency-modulated signals rather than amplitude-modulated signals equally spaced over several points of time as in the conventional method. A frequency-modulated signal is a set of identical Gaussian peaks that coincide with the true time points of heart beats. A continuous wavelet transform was used to quantitatively describe the heart rhythm signal. A test with controlled breathing was performed as an example and included three consecutive stages: rest, rhythmic breathing at a specified frequency, and exhalation. Tachograms recorded during the breath test was found to be a nonstationary signal with the alternation of peaks of different spectral ranges. A system of quantitative parameters was developed to describe the dynamics of changes in the spectral properties of the tachogram in transitional areas. A static clustering by the effect of the respiratory test and a dynamic clustering in order to identify the time points when the autonomic nervous system is stressed were performed for all subjects. The article discusses the prospects of using the method as a means to analyze the transient effects in various functional tests and as biofeedback that would help to change the heart rhythm.     

Long-Term Heart Rate Fluctuations in Postoperative and Brain-Dead Patients

Long-term heart rate fluctuations in postoperative and brain-dead patients were investigated. Heart rates were monitored continuously, and the data were stored, edited, and interpolated to allow for data lost during calibration and disconnection of the sensors for various treatments. Heart rate power spectra were calculated using the fast Fourier transform method. The power spectra of the patients who recovered showed that the heart rate fluctuated and produced a 1/f relationship, termed 1/f fluctuations, whereas those of patients who died in the intensive care unit (ICU) consisted of white-noise-like signals. The power spectra in brain-dead patients showed a 1/f relationship under steady-state conditions, while the power density and variation of the frequency distribution were lower than those in a normal subject. Therefore, 1/f fluctuations appear to be universal and occur independent of the central nervous system. (Chronobiology International, 15(6), 633-646, 1998)     

MicroRNA在靶向治疗缺血性心脏病中的研究进展

MicroRNA（MiRNA,miR）通过调节信使RNA（mRNA）的表达,广泛参与心血管系统细胞的增殖、迁移、分化、凋亡等病理生理过程,在心血管系统疾病的发生发展过程中起着重要的调控作用。越来越多的研究表明,针对缺血性心血管疾病的发病机制,通过特异性调节miRNA的活性,抑制相关蛋白的表达,对各种缺血性心脏病具有显著的治疗作用。但目前开发miRNA靶向治疗药物尚缺乏大规模的临床试验研究,其有效性和安全性需进一步证实。本文旨在综述MicroRNA在靶向治疗缺血性心脏病中的研究进展,以期为开发MiRNA靶向治疗药物治疗缺血性心脏病提供更多的理论依据。     

Congestive Heart Failure Effects on Atrial Fibroblast Phenotype: Differences between Freshly-Isolated and Cultured Cells

Introduction

Fibroblasts are important in the atrial fibrillation (AF) substrate resulting from congestive heart failure (CHF). We previously noted changes in in vivo indices of fibroblast function in a CHF dog model, but could not detect changes in isolated cells. This study assessed CHF-induced changes in the phenotype of fibroblasts freshly isolated from control versus CHF dogs, and examined effects of cell culture on these differences.

Methods/Results

Left-atrial fibroblasts were isolated from control and CHF dogs (ventricular tachypacing 240 bpm×2 weeks). Freshly-isolated fibroblasts were compared to fibroblasts in primary culture. Extracellular-matrix (ECM) gene-expression was assessed by qPCR, protein by Western blot, fibroblast morphology with immunocytochemistry, and K⁺-current with patch-clamp. Freshly-isolated CHF fibroblasts had increased expression-levels of collagen-1 (10-fold), collagen-3 (5-fold), and fibronectin-1 (3-fold) vs. control, along with increased cell diameter (13.4±0.4 µm vs control 8.4±0.3 µm) and cell spreading (shape factor 0.81±0.02 vs. control 0.87±0.02), consistent with an activated phenotype. Freshly-isolated control fibroblasts displayed robust tetraethylammonium (TEA)-sensitive K⁺-currents that were strongly downregulated in CHF. The TEA-sensitive K⁺-current differences between control and CHF fibroblasts were attenuated after 2-day culture and eliminated after 7 days. Similarly, cell-culture eliminated the ECM protein-expression and shape differences between control and CHF fibroblasts.

Conclusions

Freshly-isolated CHF and control atrial fibroblasts display distinct ECM-gene and morphological differences consistent with in vivo pathology. Culture for as little as 48 hours activates fibroblasts and obscures the effects of CHF. These results demonstrate potentially-important atrial-fibroblast phenotype changes in CHF and emphasize the need for caution in relating properties of cultured fibroblasts to in vivo systems.     

Spectral and Coherent Analysis of the Relationship between Pulse Wave Forms in the Carotid Artery and Heart Rate

The purpose of this study was the assessment of the parameters of pulse waves in the carotid artery and their relationships with baroreflex-controlled heart rate variability. The early systolic peak (ESP) is closely connected with the filling of the carotid artery, whereas the late systolic peak (LSP) shows the amplitude of the wave reflected from the periphery and affects arterial pressure oscillations activating baroreceptors and changing the heart rate (HR). A cardiac rhythmogram and pulse pressure waves in the carotid artery were continuously recorded for 5 min. ESP and LSP amplitudes (in ml/l) were evaluated in each wave. Patients with coronary artery disease and healthy subjects were examined. Spectrum analysis and assessment of the coherent function between RR intervals, the ESP, and the LSP in the middle frequency band were performed. In healthy subjects, the amplitude of the ESP was higher than that of the LSP, whereas, in patients, the LSP amplitude surpassed that of the ESP. The LSP/ESP ratio was significantly higher in patients, indicating that artery dilation depended more on the reflected wave than on the primary wave. The study revealed that age had the most pronounced effect on the LSP/ESP ratio. Healthy subjects showed the highest age-dependent coherence between the RR interval and the ESP amplitude, whereas in patients this coherence was significantly lower. Measurement of the ESP and LSP amplitudes and their ratio allowed evaluation of vasomotor artery tone. Age and disease produced the maximum effects on the artery tone and decreased the correlation between the changes in the artery tone and the HR in the baroreflex range of frequency regulation.     

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.     

Analysis of Heart Rate Variability in Space Medicine

Space medicine was one of the first fields of science and practice to use the analysis of the heart rate variability (HRV) for obtaining new scientific information and solving the tasks of exercising medical control over humans working under extreme conditions. The theoretical basis of HRV analysis and different approaches to the assessment of the data obtained are presented in the work. The technique for HRV analysis with regard to the specifics of space studies is described. The results of investigations at different stages of the space flight, including the use of Holter monitoring, are presented. Special attention is given to the results of the investigations in a long-term 14-month space flight. The adaptation to long-term weightlessness was shown to be of a multistep character with the gradual involvement of additional regulatory mechanisms.     

Analysis of Heart Rate Variability in Masked Hypertension

To investigate heart rate variability (HRV) in patients with masked hypertension (MH), participants were classified based on clinic and 24-h ambulatory blood-pressure monitoring: essential hypertension (EH, n = 40; MH, n = 36) and normotension (NT, n = 48). The HRV parameters were observed using a 24-h Holter monitor. Compared with NT controls, the parameters of HRV (SDNN, SDANN, SDNN Index, RMSSD, HF) and parameters in EH and MH patients had significantly decreased. No statistically significant difference in the HRV parameters was found between the EH and MH groups. The changes in HRV parameters show cardiac autonomic nerve dysfunction in patients with MH.