Short-term Heart Rate Variability Recordings Research Articles

Modifications of short-term heart rate variability in metabolic syndrome: a systematic review and meta-analysis

Abstract Introduction Metabolic syndrome (MS) is a clinical condition in which different non-communicable chronic diseases converge, such as hypertension, diabetes, dyslipidemia and obesity. MS has been related to dysregulation of the autonomic nervous system (ANS). Heart rate variability (HRV) has been widely used as a tool to assess the activity of autonomic function, which could be very useful for diagnosis or monitoring in patients with MS; however, to date, no quantitative analysis of ANS dysfunction in MS has been performed. For this reason, the objective of this systematic review and meta-analysis (MA) is to determine the impact that MS produces in short-term HRV, characterizing the cardiac autonomic dysfunction induced by this pathological condition and the most frequently reported explanatory variables. Methods We searched PubMed, Web of Science and Scopus electronic databases for original works with short-term HRV recordings (15 minutes or shorter) that compared people with MS (MS+) versus healthy people as a control group (MS-). The search was carried out between June 25th, 2022 and September 1st, 2022. Within these databases, the terms used were "metabolic syndrome" linked to "heart rate variability" (HRV), "cardiac autonomic control", "cardiac autonomic function", or "cardiac autonomic modulation". This systematic review and MA was performed according with PRISMA guidelines and registered at the International Prospective Register of Systematic Reviews. Results are reported as standard mean difference [95% CI]. Results Twenty-eight articles were included in the qualitative synthesis and nineteen of them met required criteria to be included in the MA. MS decreased SDNN (-0.40 [-0.5, -0.3], p<0.001), rMSSD (-7.59 [-9.98, -5.19], p<0.001), HF (-0.32 [-0.46, -0.18], p<0.001) and LF (-0.22 [-0.39, -0.06], p<0.01). The ratio LF/HF did not change (0.24 [-0.22, 0.69]). In subsequent subanalyses, we found a decreased in SDNN (-0.99 (-1.45, -0.52], p<0.001), rMSSD (-10.18 [-16.85, -3.52], p<0.01) and HF (-1.04 [-1.97, -0.1] p<0.05) in women. In men, only LF showed a significant decrease (-0.26 [-0.5, -0.2], p<0.05). We could not perform MA for the non-linear variables, but the qualitative analyses showed a decrease in SD1 and increase in SD2 of the Poincare-plot for the MS group. Conclusions MS produced changes in short-term HRV in the time-domain analyses, showing a decrease of SDNN and rMSSD. Regarding the frequency-domain analyses, MS induced a decrease in HF and LF, with the exception of the LF/HF relationship, which was not modified. When gender was taken into account, the MA was only possible in one of both genders (men or women) in rMSSD and LF/HF. Lastly, when data for both men and women were available, gender subanalyses showed a different behavior than the mixed analyses for SDNN, HF and LF, which might point towards a different impact of MS in men and women.

Short-Term Heart Rate Variability in Metabolic Syndrome: A Systematic Review and Meta-Analysis.

Our aim was to determine the differences in short-term heart rate variability (HRV) between patients with metabolic syndrome (MS) and healthy controls. We searched electronic databases for primary works with short-term HRV recordings (≤30 min) that made comparisons between individuals with MS versus healthy controls. This systematic review and meta-analysis (MA) was performed according to PRISMA guidelines and registered at PROSPERO (CRD42022358975). Twenty-eight articles were included in the qualitative synthesis and nineteen met the criteria for the MA. Patients with MS showed decreased SDNN (-0.36 [-0.44, -0.28], p < 0.001), rMSSD (-7.59 [-9.98, -5.19], p < 0.001), HF (-0.36 [-0.51, -0.20], p < 0.00001) and LF (-0.24 [-0.38, -0.1], p = 0.001). In subsequent subanalyses, we found a decrease in SDNN (-0.99 (-1.45, -0.52], p < 0.001), rMSSD (-10.18 [-16.85, -3.52], p < 0.01) and HF (-1.04 [-1.97, -0.1] p < 0.05) in women. In men, only LF showed a significant lower value (-0.26 [-0.5, -0.02], p < 0.05). We could not perform MA for non-linear variables. Patients with MS showed changes in time-domain analyses, with lower values in SDNN and rMSSD. Regarding frequency-domain analyses, MS patients showed a decrease in HF and LF When sex was used as a grouping variable, the MA was only possible in one of both sexes (men or women) in rMSSD and LF/HF. Lastly, when data for both men and women were available, subanalyses showed a different behavior compared to mixed analyses for SDNN, HF and LF, which might point towards a different impact of MS in men and women.

Heart Rate Fractality Disruption as a Footprint of Subthreshold Depressive Symptoms in a Healthy Population.

ObjectivePsychopathology (and depression in particular) is a cardiovascular risk factor independent from any co-occurring pathology. This link is traced back to the mind-heart-body connection, whose underlying mechanisms are still not completely known. To study psychopathology in relation to the heart, it is necessary to observe the autonomic nervous system, which mediates among the parts of that connection. Its gold standard of evaluation is the study of heart rate variability (HRV). To investigate whether any association exists between the HRV parameters and sub-threshold depressive symptoms in a sample of healthy subjects.MethodIn this cross-sectional study, two short-term HRV recordings (5 min - supine and sitting) have been analyzed in 77 healthy subjects. Here we adopted a three-fold approach to evaluate HRV: a set of scores belonging to the time domain; to the frequency domain (high, low, and very low frequencies) and a set of ‘nonlinear’ parameters. The PHQ-9 (Patient Health Questionnaire-9) scale was used to detect depressive symptoms.ResultsDepressive symptoms were associated only with a parameter from the non-linear approach and specifically the long-term fluctuations of fractal dimensions (DFA-α2). This association remained significant even after controlling for age, gender, BMI (Body-Mass-Index), arterial hypertension, anti-hypertensive drugs, dyslipidemia, and smoking habits. Moreover, the DFA-α2 was not affected by the baroreflex (postural change), unlike other autonomic markers.ConclusionsFractal analysis of HRV (DFA-α2) allows then to predict depressive symptoms below the diagnostic threshold in healthy subjects regardless of their health status. DFA-α2 may be considered as an imprint of subclinical depression on the heart rhythm.

Short-term heart rate variability in resting conditions: methodological considerations.

Low values on heart rate variability (HRV) derived parameters at resting have been used to predict cardiovascular diseases (CVD) and mortality. In this regard, short-term HRV recordings (usually from 5 to 15 minutes) are increasing their popularity because data acquisition can be performed under more controlled conditions than long-term recordings (e.g., 24 hours). However, different methodological aspects before, during, and after the HRV assessment could affect the quantification and the clinical interpretations of the HRV-derived parameters, as well as hamper comparisons across different studies. In the present study, we summarize these methodological aspects that should be considered in both the research and the clinical settings. These are: (1) the validity and reproducibility of the device used to assess the HRV; (2) the influence of the software used to perform the artefact correction; (3) previous conditions before the testing day; (4) establishing the proper conditions during the HRV assessment (e.g., controlled respiratory frequency); (5) after assessing the HRV, considering the "best" data selection and statistical analysis approach; and (6) the role of the heart rate on the associations between the different CVD risk factors outcomes (e.g., cardiorespiratory fitness) and the HRV-derived parameters.

A Novel Smartphone App for the Measurement of Ultra–Short-Term and Short-Term Heart Rate Variability: Validity and Reliability Study

BackgroundSmartphone apps for heart rate variability (HRV) measurement have been extensively developed in the last decade. However, ultra–short-term HRV recordings taken by wearable devices have not been examined.ObjectiveThe aims of this study were the following: (1) to compare the validity and reliability of ultra–short-term and short-term HRV time-domain and frequency-domain variables in a novel smartphone app, Pulse Express Pro (PEP), and (2) to determine the agreement of HRV assessments between an electrocardiogram (ECG) and PEP.MethodsIn total, 60 healthy adults were recruited to participate in this study (mean age 22.3 years [SD 3.0 years], mean height 168.4 cm [SD 8.0 cm], mean body weight 64.2 kg [SD 11.5 kg]). A 5-minute resting HRV measurement was recorded via ECG and PEP in a sitting position. Standard deviation of normal R-R interval (SDNN), root mean square of successive R-R interval (RMSSD), proportion of NN50 divided by the total number of RR intervals (pNN50), normalized very-low–frequency power (nVLF), normalized low-frequency power (nLF), and normalized high-frequency power (nHF) were analyzed within 9 time segments of HRV recordings: 0-1 minute, 1-2 minutes, 2-3 minutes, 3-4 minutes, 4-5 minutes, 0-2 minutes, 0-3 minutes, 0-4 minutes, and 0-5 minutes (standard). Standardized differences (ES), intraclass correlation coefficients (ICC), and the Spearman product-moment correlation were used to compare the validity and reliability of each time segment to the standard measurement (0-5 minutes). Limits of agreement were assessed by using Bland-Altman plot analysis.ResultsCompared to standard measures in both ECG and PEP, pNN50, SDNN, and RMSSD variables showed trivial ES (<0.2) and very large to nearly perfect ICC and Spearman correlation coefficient values in all time segments (>0.8). The nVLF, nLF, and nHF demonstrated a variation of ES (from trivial to small effects, 0.01-0.40), ICC (from moderate to nearly perfect, 0.39-0.96), and Spearman correlation coefficient values (from moderate to nearly perfect, 0.40-0.96). Furthermore, the Bland-Altman plots showed relatively narrow values of mean difference between the ECG and PEP after consecutive 1-minute recordings for SDNN, RMSSD, and pNN50. Acceptable limits of agreement were found after consecutive 3-minute recordings for nLF and nHF.ConclusionsUsing the PEP app to facilitate a 1-minute ultra–short-term recording is suggested for time-domain HRV indices (SDNN, RMSSD, and pNN50) to interpret autonomic functions during stabilization. When using frequency-domain HRV indices (nLF and nHF) via the PEP app, a recording of at least 3 minutes is needed for accurate measurement.

Inter- and intra-researcher reproducibility of heart rate variability parameters in three human cohorts

Heart rate variability (HRV) is a valid and non-invasive indicator of cardiac autonomic nervous system functioning. Short-term HRV recordings (e.g., 10 min long) produce data that usually is manually processed. Researcher subjective decision-making on data processing could produce inter- or intra-researcher differences whose magnitude has not been previously quantified in three independent human cohorts. This study examines the inter- and intra-researcher reproducibility of HRV parameters (i.e., the influence of R–R interval selection by different researchers and by the same researcher in different moments on the quantification of HRV parameters, respectively) derived from short-term recordings in a cohort of children with overweight/obesity, young adults and middle-age adults. Participants were recruited from 3 different studies: 107 children (10.03 ± 1.13 years, 58% male), 132 young adults (22.22 ± 2.20 years, 33% males) and 73 middle-aged adults (53.62 ± 5.18 years, 48% males). HRV was measured using a Polar RS800CX heart rate monitor. The intraclass correlation coefficient (ICC) ranged from 0.703 to 0.989 and from 0.950 to 0.998 for inter-and intra-researcher reproducibility, respectively. Limits of agreement for HRV parameters were higher for the inter-researcher processing compared with the intra-researcher processing. On average, the intra-researcher differences were 31%, 62%, and 80% smaller than the inter-researchers differences based on Coefficient of Variation in children, young and middle-aged adults, respectively. Our study provides the quantification of the inter-researcher and intra-researcher differences in three independent human cohorts, which could elicit some clinical relevant differences for HRV parameters. Based on our findings, we recommend the HRV data signal processing to be performed always by the same trained researcher and we postulate a development of algorithms for an automatic ECG selection.

Profiles of Heart Rate Variability and Bar Velocity after Resistance Exercise.

The aim of this investigation was to observe the association in the time course in recovery between multiple heart rate variability (HRV) metrics and neuromuscular performance, as assessed by mean bar velocity (BVM) in the back squat, over a 72-h period after an exhaustive back squat protocol. Eight resistance-trained males completed five laboratory visits within a 7-d period. The first visit involved short-term HRV recordings followed by a familiarization of BVM procedures and a one-repetition maximum test of the back squat. Forty-eight hours later, participants returned to the laboratory for prestimulus measurements, immediately followed by a back squat protocol (8 sets of 10 repetitions at 70% of one-repetition maximum with a 2-min rest). The HRV and the BVM measurements were replicated at 0.5, 24, 48, and 72 h after squat protocol. A multivariate profile analysis and repeated-measures correlation between recovery scores [(new/prestimulus) × 100] for each HRV metric and BVM was computed. All log-transformed (ln) HRV metrics, except low frequency (lnLF) (P = 0.051), had a significant interaction with BVM over time (P < 0.05), indicating that recovery scores in BVM and HRV were not parallel. In addition, recovery scores in all HRV metrics significantly differed from BVM (P < 0.05) in at least one time point across the 72-h period. Furthermore, repeated-measures correlation analysis indicated a lack of intraindividual association (P > 0.05) between the change in BVM and all HRV measurements over time. The time course in recovery in HRV measurements after an exhaustive bout of lower-body resistance exercise was not associated with neuromuscular performance recovery.

Short-term assessment of autonomic nervous system as a potential tool to quantify pain experience.

Various pain conditions may result in altered autonomic nervous system regulation. We evaluated whether autonomic regulation, analyzed with short-term heart rate variability (HRV), differs between low back pain (LBP) patients and healthy controls. Additionally, we tested if short-term HRV recordings are feasible and informative in planning home monitoring of LBP patients. The study population consisted of 16 volunteers (8 LBP patients and 8 healthy subjects) (age 42±10 years, body mass index 26±4 kg/m2, 7 men and 9 women). Usually 3- to 5-minute R-R interval recordings have been used as short-term recordings of HRV, but recent evidence supports even shorter R-R interval recording procedure for short-term HRV assessment. We collected R-R interval data for 1 minute in sitting, standing and bending down tasks. Mean heart rate (HR) and vagally mediated beat-to-beat variability (SD1 and rMSSD) were analyzed. The results showed that autonomic nervous system function assessed with the short-term measurement HRV method differentiates LBP patients from healthy controls in sitting and standing. Vagally mediated SD1 and rMSSD were significantly lower and the HR was higher among the patients compared to the controls. A novel finding was also the feasibility of 1-minute measurement of HRV, which may open entirely new opportunities to assess accurately concomitant changes in autonomic nervous system function and self-reported individual pain experience. This could lead to a more personalized pain treatment and more efficient health care resource allocation as the new measurement methods is more suitable for home monitoring than the previously used ones.

An adaptive technique for multiscale approximate entropy (MAEbin) threshold (r) selection: application to heart rate variability (HRV) and systolic blood pressure variability (SBPV) under postural stress.

Multiscale approximate entropy (MAE) is used to quantify the complexity of a time series as a function of time scale τ. Approximate entropy (ApEn) tolerance threshold selection 'r' is based on either: (1) arbitrary selection in the recommended range (0.1-0.25) times standard deviation of time series (2) or finding maximum ApEn (ApEnmax) i.e., the point where self-matches start to prevail over other matches and choosing the corresponding 'r' (rmax) as threshold (3) or computing rchon by empirically finding the relation between rmax, SD1/SD2 ratio and N using curve fitting, where, SD1 and SD2 are short-term and long-term variability of a time series respectively. None of these methods is gold standard for selection of 'r'. In our previous study [1], an adaptive procedure for selection of 'r' is proposed for approximate entropy (ApEn). In this paper, this is extended to multiple time scales using MAEbin and multiscale cross-MAEbin (XMAEbin). We applied this to simulations i.e. 50 realizations (n=50) of random number series, fractional Brownian motion (fBm) and MIX (P) [1] series of data length of N=300 and short term recordings of HRV and SBPV performed under postural stress from supine to standing. MAEbin and XMAEbin analysis was performed on laboratory recorded data of 50 healthy young subjects experiencing postural stress from supine to upright. The study showed that (i) ApEnbin of HRV is more than SBPV in supine position but is lower than SBPV in upright position (ii) ApEnbin of HRV decreases from supine i.e. 1.7324±0.112 (mean±SD) to upright 1.4916±0.108 due to vagal inhibition (iii) ApEnbin of SBPV increases from supine i.e. 1.5535±0.098 to upright i.e. 1.6241±0.101 due sympathetic activation (iv) individual and cross complexities of RRi and systolic blood pressure (SBP) series depend on time scale under consideration (v) XMAEbin calculated using ApEnmax is correlated with cross-MAE calculated using ApEn (0.1-0.26) in steps of 0.02 at each time scale in supine and upright position and is concluded that ApEn0.26 has highest correlation at most scales (vi) choice of 'r' is critical in interpreting interactions between RRi and SBP and in ascertaining true complexity of the individual RRi and SBP series.

Body mass index is related to autonomic nervous system activity as measured by heart rate variability--a replication using short term measurements.

The present analysis is a replication of previous findings presenting first evidence of an association between body mass index (BMI) and autonomic nervous system (ANS) activity as measured by heart rate variability (HRV), in healthy non-obese adults. A total of fifty-nine apparently healthy male (M) and female (F) individuals (M/F = 15/44) were included in the trial. HRV data for analysis was derived from 5 minutes of baseline recordings, while the subject was sitting on a comfortable chair. Subjects' body measures (weight and height) were taken and BMI was obtained according to common calculation (kg/m²). BMI was inversely related to pNN50 and RMSSD components of HRV. Statistically significant differences between stratified groups (BMI<20, BMI 20-25, BMI >25) only occurred for analysis of pNN50 components. The pNN50 components and RMSSD are strongly associated with cardiac vagal influence, and thus represents parasympathetic activity. The present data supports previous findings, that sympatho-vagal balance is related to BMI in non-obese, healthy individuals, providing evidence for a prominent role of the vagus nerve in the modulation of the energy expenditure of the human organism. Furthermore, this relation can be observed in short term recordings of HRV of 5 minutes in length.

Heart rate variability in physically active individuals: reliability and gender characteristics.

To evaluate the reliability of short-term recordings (five minutes) of heart rate variability (HRV) and the association between HRV and gender. HRV time- and frequency-domain parameters were calculated in 44 physically active students (21 males and 23 females) over four consecutive days. A Suunto t6 heart rate monitor was used to obtain inter-beat intervals (IBIs) that were then transferred to Kubios HRV analysis software. The relative reliability [intra-class correlation (ICC)] and absolute reliability, [typical error of measurement (TEM) and typical error of measurement as a percentage (TEM%)] of the HRV parameters were then calculated for day 2 versus day 3 and day 3 versus day 4, with day 1 being a familiarisation day. The following HRV parameters were calculated: (1) time domain: resting heart rate (RHR), R-R intervals (IBI), standard deviation of normal-to-normal intervals (SDNN), root mean square differences of the standard deviation (RMSSD), percentage of beats that changed more than 50 ms from the previous beat (pNN50); and (2) frequency domain: low-frequency normalised units (LFnu), high-frequency normalised units (HFnu), low-frequency to high-frequency ratio in normalised units (LF/HFnu). An analysis of variance (ANOVA) with Tukey post-hoc testing was performed to compare HRV parameters in males and females. Significance was set at p ≤ 0.05. The ICCs for both relationship 1 and 2 indicated primarily good to excellent (> 0.8) relative reliability. The lowest value was found in the LF/HFnu ratio (ICC = 0.36) for males. Absolute reliability was low with TEM% greater than 10% for all HRV parameters, except IBIs. Females demonstrated better relative (higher ICCs) and absolute reliability (lower TEM and TEM% ) compared to males for the frequency domain. The relative and absolute reliability for the time domains were similar except for SDNN where the absolute reliability was higher in males. ANOVA illustrated significant gender differences for the LF/HFnu ratio (41% higher in males, p = 0.003), HFnu (12% higher in females, p = 0.02) and IBI (21% higher in females, p < 0.0001). Short-term recordings of HRV over three consecutive days demonstrated a high relative reliability. However, a low absolute reliability indicated large day-to-day random variation in HRV, which would make the detection of intervention effects using HRV difficult in individual participants. Females were shown to have a higher parasympathetic modulation of HRV, which may indicate an underlying cardioprotective mechanism in females compared to males.

Cardiac autonomic functions derived from short-term heart rate variability recordings associated with heart rate recovery after treadmill exercise test in young individuals

Analysis of short-term heart rate variability (HRV) may provide useful information about autonomic nervous control of heart rate recovery. We studied 495 individuals (273 men), age range 19-85 years, submitted to treadmill exercise tests and short-term HRV evaluations over time (standard deviation of the normal-to-normal interval [SDNN], the square root of the mean squared differences of successive normal-to-normal intervals [RMSSD], the number of interval differences of successive normal-to-normal intervals greater than 50 ms [NN50 count], the proportion derived by dividing NN50 count by the total number of normal-to-normal intervals [pNN50]) and frequency (low-frequency power [LF], high-frequency power [HF], total power) domains. Among 495 patients, 106 patients (68 men) were elderly (age ≥ 65 years). Male gender and hypertension were significantly higher in elderly patients. The young patients had higher HRR after exercise. HRR at 4 min (54 ± 13 vs 60 ± 12 beats/min; P = 0.003) was the most significant predictor for positive exercise test result. In the young group, both time domain measures (SDNN: correlation coefficient 0.34, P < 0.001; RMSSD: correlation coefficient 0.37, P < 0.001) and frequency domain measures (LF: correlation coefficient 0.21, P < 0.001; HF: correlation coefficient 0.13, P = 0.01; total power: correlation coefficient 0.22, P < 0.001) were significantly associated with HRR at 4 min. HRR at 4 min was significantly associated with short-term HRV of time and frequency domains in young individuals, but not elderly ones, receiving treadmill exercise test.

Metabolic Syndrome and Short-Term and Long-Term Heart Rate Variability in Elderly Free of Clinical Cardiovascular Disease: The PROOF Study

Autonomic nervous system (ANS) activity decrease has been associated with a higher risk of sudden cardiovascular and cerebrovascular disease. Thus, we explored the relationship between ANS control of the cardiovascular system and metabolic syndrome. We analyzed the relationship with both short-term and long-term heart rate variability (HRV) and metabolic syndrome in the cross-sectional PROgnostic indicator OF cardiovascular and cerebrovascular events (PROOF) cohort study of 1,011 elderly subjects recruited amongst the inhabitants of the city of Saint Etienne, France, aged 65.6 ± 0.8 years at the inclusion date. Physical examination included measurements of height, weight, systolic and diastolic blood pressure, waist circumference, and biological parameters. HRV variables were measured over 5-min, nighttime, and 24-h periods using Holter monitoring. After adjustment for current type 2 diabetes, depression, and smoking, we found that metabolic syndrome status, high-density lipoprotein cholesterol (HDL-C), and waist circumference were significantly (p < 0.05) associated with total power, very-low frequency, low-frequency/high-frequency (LF/HF) ratio, and normalized LF. HDL-C and metabolic syndrome status were significantly associated with decreased long-term HRV variables. Both nighttime and 24-h HRV showed closer associations with metabolic syndrome than did short-term HRV (5-min). Metabolic syndrome severity was associated with a decrease in both the long-term and short-term HRV variables. ANS control alteration of the cardiovascular system was more pronounced when evaluated by long-term than short-term HRV recordings, particularly in women.

Cardiac Vagal Modulation with Combined Endurance and Strength Training: Use of pNN Time Domain Statistics

Cardiac vagal modulation can be quantified from heart rate variability (HRV) using time and frequency domain measures, including pNN50 and high frequency (HF) power. The use of pNN thresholds lower than the traditional 50 ms may provide more information about cardiac vagal modulation, and be useful in detecting changes in parasympathetic activity induced by endurance training. Due to the specific effects of endurance and strength training, information is limited about the effects of combining these two training modes on cardiac autonomic function. PURPOSE: To examine the effects of combined endurance and strength training on cardiac vagal modulation in short (< 15 min) recordings of RR intervals. METHODS: 93 healthy men (mean age = 55 yr, SD = 7 yr) completed a 21 week progressive training period consisting one of the following: two endurance (E, n=23), two strength (S, n=25), two endurance and two strength (ES, n=29) training sessions per week, or no systematic training (control group, n=16). RR intervals were recorded during 10 min supine rest, and probability distributions for pNN10, 20, 30, 40, and 50 were calculated. HF domain power was computed using Fourier spectral methods. RESULTS: At baseline, for low pNN50 (< 5 %) or low HF power (< 250 ms2), pNN10 ranged widely from approximately 15 to 70 %. These results indicate that pNN10 describes different characteristics of short-term RR interval dynamics than traditional pNN50 or HF power among healthy middle-aged men. After training, significant changes (p < 0.05 between groups) were only observed in the ES group in pNN10 [from 59 (18) % to 63 (20) %, p = 0.023] and pNN20 [from 34 (20) % to 39 (23) %, p = 0.043]. Other training groups did not show significant changes after the 21 week training period. No significant changes were seen in HF power. CONCLUSION: pNN time domain statistics with thresholds lower than the conventional 50 ms may be sensitive in detecting training-induced changes in short term recordings of HRV. Based on the increases in pNN10 and pNN20, combining endurance and strength training may be especially beneficial for enhancing cardiac autonomic function in middle-aged men, even though endurance or strength training alone did not lead to significant changes in these measures in very short-term recordings. Supported by Ministry of Education, Finland.

Cardiac Autonomic Functions Derived From Short-Term Heart Rate Variability Recordings Associated With Nondiagnostic Results of Treadmill Exercise Testing

Analysis of short-term (5-minute) heart rate variability (HRV) may provide useful information about autonomic nervous control of the cardiovascular system. The aim of the present study was to evaluate the association between the results of treadmill exercise testing (TET) and short-term (5-minute) HRV. Patients undertaking TET were anteriorly evaluated with short-term (5-minute) HRV over time (SDNN, RMSSD, NN50 count, pNN50) and frequency (LF, HF, total power) domains. Among 414 patients, 32 individuals (7.7%; 14 men) had nondiagnostic results. The nondiagnostic group had older age, higher body mass index, more hypertension, lower SDNN, lower LF, and higher HF than the negative group. After adjustment for potential confounders, SDNN (OR 0.94, 95% CI 0.91-0.97; P = 0.01), RMSSD (OR 0.96, 95% CI 0.93-0.99; P = 0.02), NN50 count (OR 0.98, 95% CI 0.97-1.00; P = 0.04) and LF (OR 0.96, 95% CI 0.96-0.99; P = 0.03) were negatively related to nondiagnostic results, and HF showed a positive effect (OR 1.04, 95% CI 1.01-1.05; P = 0.02). No HRV indices were significantly associated with positive results. Our study suggested that cardiac autonomic indices derived from short-term HRV recordings might predict nondiagnostic results of TET.

Sympatho-vagale Balance und kardiale Reaktionen bei standardisierten psychomentalen Belastungen / Sympatho-vagal balance and cardiac response to mental challenge

Based on functional relations between the central autonomic network and cortical areas involved in motivational, attentional, affective, and executive function, autonomic regulation can mediate cognitive performance as well as cardiovascular and psychosomatic diseases. Our objective was to test the predictive value of resting heart rate variability (HRV), a measure of sympatho-vagal balance, with regard to the type and intensity of cardiovascular responses to mental challenge. A total of 248 healthy subjects (85 females, aged 47.3+/-7.6 years; 163 males, aged 47.5+/-6.7 years) were included in the study. All participants underwent standardized psychometric testing (e.g., Stroop's color-word-conflict test). First, we found significant increases of heart rate and sympatho-vagal balance (low frequency/high frequency) and significant decreases of absolute LF- and HF-power in response to mental tasks. Second, there were significant differences in cardiovascular response to mental challenge when clustering our population on the basis of sympatho-vagal balance at rest. We conclude that short-term recordings of HRV can provide health-related information of cardio-vascular response to mental challenge. However, there is no association between sympatho-vagal balance at rest and classical cardiovascular risk factors.

Autonomic Function in Children and Adolescents with Neurocardiogenic Syncope

This study aimed to clarify whether children with neurocardiogenic syncope (NCS) differ from healthy control subjects in baseline heart rate variability (HRV) and in their response to orthostatic stress induced by active standing and tilt table. This study analyzed the difference between 55 children with a history of NCS or presyncopal symptoms (PS) and healthy control subjects. Measurements included short-term HRV during resting position, tilt table testing, and active standing. Time and frequency domain HRV parameters were computed. Both the NCS and PS children differed significantly from healthy control subjects during resting position. During tilt table testing, nearly all NCS and PS subjects differed significantly from the control group in calculated HRV parameters. Moreover, for the low-frequency power and total power, the confidence intervals did not overlap. The findings suggest that chronic autonomic differences exist between healthy children and patients with NCS and PS. These changes could be detected even by short-term HRV recordings. The tilt table maneuver provoked the most prominent differences between the groups. Low-frequency power and total power during tilt table testing helps to detect children with NCS.

Maturation of the autonomic nervous system: differences in heart rate variability in premature vs. term infants

Aims Heart rate variability (HRV) reveals information on the functional state of the autonomic nervous system (ANS). This study was initiated to assess the physiological- and maturational development of the ANS by comparing HRV data of healthy prematures with term infants. Methods Short-term recordings of HRV in 39 premature healthy infants (29-35 weeks' gestation) were performed and compared with normative data of term infants. Frequency domain HRV parameters are computed in three frequency bands. Results Gestational age of newborn infants is correlated with HRV. Prematures showed significant lower HRV parameters than term infants. The most significant differences were discerned for HRV parameters reflecting parasympathetic activity, whereas the pulse of the baro-receptor reflex was similar for prematures and term infants at 0.07 Hz (0.1 Hz adults). A respiratory peak in the HF-band according to respiratory sinus arrhythmia (RSA), as is common in adults, was not detected for prematures as it is not detected in term infants. Conclusions Maturation of the ANS is accompanied by increasing HRV with a pronounced increase of parasympathetic activity. These changes are measurable by short-term recordings. The physiological pulses concerning baroreceptor reflex activity and respiratory modulation were similar in prematures and term infants.

The angiotensin-converting enzyme gene I/D polymorphism and heart rate variability following acute myocardial infarction.

Heart rate variability (HRV) is a measure of cardiac autonomic control and is therefore subject to regulation by the renin-angiotensin system. The primary objective of this study was to determine the effect of an insertion/deletion polymorphism within the angiotensin-converting enzyme (ACE) gene on HRV in the early stages after a myocardial infarction at a time when cardiac autonomic control is deranged. The secondary objective was to determine whether this polymorphism affected the HRV response to inhibition of ACE. 149 Caucasian subjects were studied 25 +/- 16 h following MI using time and frequency domain measures of HRV derived from two 5-minute ECG recordings. Recordings were repeated at 182 +/- 65 h following MI, when subjects had been stabilised on ramipril 2.5 mg bd. The study included 46 subjects with the DD genotype, 69 with the ID genotype, and 34 with the II genotype. No effect of the I/D polymorphism on short-term recordings of HRV was found. There was no difference in HRV response to the introduction of ramipril according to the genotypes. The I/D polymorphism within the ACE gene does not influence HRV after MI or the HRV response to ACE inhibitor therapy with ramipril. These findings may reflect the relative lack of importance of the I/D polymorphism and ACE activity in determining plasma and tissue angiotensin II concentration after a major stimulus to the renin-angiotensin system as occurs after myocardial infarction.