Reproducibility Of Heart Rate Variability Research Articles

Relation between Heart Rate Variability and Disease Course in Multiple Sclerosis.

Little is known about the interplay between the autonomic nervous system and disease activity in multiple sclerosis (MS). We examined the relationship between heart rate variability (HRV), a reliable measure of vagal nerve function, and disease characteristics in a prospective MS cohort. Standard deviation of each normal-to-normal inter-beat interval (SDNN) and root mean square of successive differences (RMSSD), global indices of HRV, were measured in 114 MS patients, which included four predefined subgroups, and 30 age and sex-matched healthy controls (HC). We assessed group differences at baseline, HRV reproducibility at month 3, and used logistic regression modeling to relate baseline HRV with relapse occurrence. No significant HRV differences were found between MS and HC and between MS subgroups. In MS patients, both HRV indices correlated with age (r = −0.278, p = 0.018 and r = −0.319, p < 0.001, respectively) and with month 3 assessments (r = 0.695 and r = 0.760, p < 0.001). Higher SDNN and RMSSD at baseline were associated with self-reported relapses at month 3 (OR = 1.053, 95% CI (1.013–1.095), p = 0.009 and OR = 1.065, 95% CI (1.016–1.117), p = 0.009), and SDNN at baseline with relapses at month 12 (OR = 1.034, 95% CI (1.009–1.059), p = 0.008; ROC, AUC = 0.733, p = 0.002). There were no baseline HRV differences between MS and HC or between subgroups. Post-hoc analysis showed an association with an increased relapse risk.

Reproducibility of Heart Rate Variability Revealed by Repeated Measurements during and after Hemodialysis

Background/Aims: Trajectory of heart rate variability (HRV) represents a noninvasive real-time measure of autonomous nervous system (ANS) and carries the capability of providing new insights into the hemodynamic compensation reserve during hemodialysis (HD). However, studies on HRV reproducibility during HD are scarce and did not refer to different reading periods. In this observational study, we aimed to establish the best suited and most reliable and reproducible HRV index in routine HD treatments including different reading rates. Methods: HRV was characterized by standardized mathematical variation expressions of R/R’ intervals: SD of all R/R’ intervals (ms), square root of the root mean square of the sum of all differences between adjacent R/R’ intervals (ms), percentage of consecutive R/R’ intervals that differ by >50 ms (%), low-frequency spectral analysis HRV (LF, expressing sympathetic activity), and high-frequency HRV (HF, expressing parasympathetic activity). To compare robustness of these HRV indices during HD procedures, we compared HRV indices means between different HD sessions and controlled for association with clinical parameters. Results: In 72 HD treatments of 34 patients, we detected the highest reproducibility (89%) of HRV measures when analyzing the low-frequency to high-frequency (LF/HF) ratio in long-term (3 h) readings. Long-term LF/HF was able to discriminate ­between patients with and without heart failure NYHA classes ≥3 (p = 0.009) and type 2 diabetes (p = 0.023). We were unable to study relationships between ANS and intradialytic complications because they did not appear in our cohort. Short-term readings of HRV indices did not show any significance of pattern change during HD. Conclusion: In summary, our data provide evidence for high robustness of long-term LF/HF in analyzing HRV in HD patients using future automated monitoring systems. For short-term analysis, mathematical real-time analysis must evolve.

Analysis of Reproducibility of Noninvasive Measures of Sympathetic Autonomic Control Based on Electrodermal Activity and Heart Rate Variability

Heart rate variability (HRV) and electrodermal activity (EDA) are useful tools for assessing the central and peripheral dynamics of the sympathetic nervous system and detecting the effects of numerous systemic diseases and life-challenging situations. However, the indices of HRV and EDA are highly influenced by mental stress, environmental conditions, body position, and other physiological conditions that introduce variability. In this paper, we assessed the five-day reproducibility of HRV and EDA measures of sympathetic control, for N = 20 subjects undergoing 70° head-up tilt test (HUT) and Stroop task tests. We made the assessment in highly controlled conditions without environmental causes of variability, to have a good baseline understanding of the consistency of the various indices of HRV and EDA. Therefore, we assessed intra-subject variation (using the coefficient of variation, CV) and consistency (using the intra-class correlation coefficient, ICC) of the test-to-baseline differences produced by both tests on the studied measures. The low-frequency component of HRV (HRVLF), and its normalized variant was computed as HRV measures of sympathetic control. For EDA, the skin conductance level, frequency of non-specific skin conductance responses, spectral index (EDASympn), and time-varying index (TVSymp) were computed. TVSymp (ICC = 0.85) and HRV indices exhibited higher consistency during the HUT (ICC ≥ 0.8), compared to other EDA measures, and HRVLF was the least variable measure (CV = 85.4%). EDA indices exhibited higher consistency (except for the EDASympn) during the Stroop task (ICC ≥ 0.79) when compared to HRV, and TVSymp was the least variable measure (CV = 97.2%). Remarkably, TVSymp proved to be a reproducible measurement (low variation and high consistency) in both scenarios. These results are the necessary groundwork for studying the use of EDA and HRV in real-world conditions, as reproducibility of the indices has remarkable importance in clinical practice.

Reproducibility for Heart Rate Variability Analysis during 6-Min Walk Test in Patients with Heart Failure and Agreement between Devices.

Heart rate variability (HRV) analysis is a useful method to assess abnormal functioning in the autonomic nervous system and to predict cardiac events in patients with heart failure (HF). HRV measurements with heart rate monitors have been validated with an electrocardiograph in healthy subjects but not in patients with HF. We explored the reproducibility of HRV in two consecutive six-minute walk tests (6MW), 60-minute apart, using a heart rate monitor (PolarS810i) and a portable electrocardiograph (called Holter) in 50 HF patients (mean age 59 years, NYHA II, left ventricular ejection fraction ~35%). The reproducibility for each device was analysed using a paired t-test or the Wilcoxon signed-rank test. Additionally, we assessed the agreement between the two devices based on the HRV indices at rest, during the 6MW and during recovery using concordance correlation coefficients (CCC), 95% confidence intervals and Bland-Altman plots. The test-retest for the HRV analyses was reproducible using Holter and PolarS810i at rest but not during recovery. In the second 6MW, patients showed significant increases in rMSSD and walking distance. The PolarS810i measurements had remarkably high concordance correlation [0.86<CCC<0.99] based on Holter at rest, during 6MW and recovery. At higher rates, a small effect in increasing differences between Holter and Polar in R-R intervals was observed. In conclusion, our study showed good reproducibility of HRV at rest in two consecutive 6MW using Holter and PolarS810i. Additionally, PolarS810i produced good agreements in short-term HRV indices based on Holter simultaneous recordings at rest, during the 6MW and recovery in HF patients.

Recording duration and short-term reproducibility of heart rate and QT interval variability in patients with myocardial infarction

Beat-to-beat variability of the QT interval (QTV) measured on surface ECG has emerged as a potential marker for ventricular repolarization instability and has been used along with heart rate variability (HRV) to predict arrhythmic risk. Since measurement modalities of QTV have not been standardized, the objective of this study was to investigate the effect of ECG recording duration on QTV as well as HRV. Using a database of 30 min ECG recorded from 500 patients with acute myocardial infraction during rest, we extracted RR and QT interval time series and estimated different HRV and QTV metrics over windows of varying length. Analysis of variance (ANOVA) and intra-class correlation analyses were computed to investigate the effect of recording length on consistency and short-term reproducibility of HRV and QTV variables. Good consistency (non-significant ANOVA results) and short-term reproducibility (intra-class correlation coefficients >0.8) were demonstrated for all but standard deviation based metrics when at least 200 beats were included in the estimation. In conclusion, QTV can be quantified from resting ECG with good short-term consistency and reproducibility that is comparable to that of HRV.

Heart Rate and Respiratory Rate Influence on Heart Rate Variability Repeatability: Effects of the Correction for the Prevailing Heart Rate.

Background: Since heart rate variability (HRV) is associated with average heart rate (HR) and respiratory rate (RespRate), alterations in these parameters may impose changes in HRV. Hence the repeatability of HRV measurements may be affected by differences in HR and RespRate. The study aimed to evaluate HRV repeatability and its association with changes in HR and RespRate.Methods: Forty healthy volunteers underwent two ECG examinations 7 days apart. Standard HRV indices were calculated from 5-min ECG recordings. The ECG-derived respiration signal was estimated to assess RespRate. To investigate HR impact on HRV, HRV parameters were corrected for prevailing HR.Results: Differences in HRV parameters between the measurements were associated with the changes in HR and RespRate. However, in multiple regression analysis only HR alteration proved to be independent determinant of the HRV differences—every change in HR by 1 bpm changed HRV values by 16.5% on average. After overall removal of HR impact on HRV, coefficients of variation of the HRV parameters significantly dropped on average by 26.8% (p < 0.001), i.e., by the same extent HRV reproducibility improved. Additionally, the HRV correction for HR decreased association between RespRate and HRV.Conclusions: In stable conditions, HR but not RespRate is the most powerful factor determining HRV reproducibility and even a minimal change of HR may considerably alter HRV. However, the removal of HR impact may significantly improve HRV repeatability. The association between HRV and RespRate seems to be, at least in part, HR dependent.

Reproducibility of Heart Rate Variability Indices in Children with Cystic Fibrosis.

Fundamental to the potential utilisation of heart rate variability (HRV) indices as a prognostic tool is the reproducibility of these measures. The purpose of the present study was therefore to investigate the reproducibility of 24-hour derived HRV indices in a clinical paediatric population. Eighteen children (10 boys; 12.4 ± 2.8 years) with mild to moderate Cystic Fibrosis (CF; FVC: 83 ± 12% predicted; FEV1: 80 ± 9% predicted) and eighteen age- and sex-matched controls (10 boys; 12.5 ± 2.7 years) wore a combined ECG and accelerometer for two consecutive days. Standard time and frequency domain indices of HRV were subsequently derived. Reproducibility was assessed by Bland-Altman plots, 95% limits of agreement and intra-class correlation coefficients (ICC). In both groups, there was no systematic difference between days, with the variables demonstrating a symmetrical, homoscedastic distribution around the zero line. The time domain parameters demonstrated a good to excellent reproducibility irrespective of the population considered (ICC: 0.56 to 0.86). In contrast, whilst the frequency domain parameters similarly showed excellent reproducibility in the healthy children (ICC: 0.70 to 0.96), the majority of the frequency domain parameters illustrated a poor to moderate reproducibility in those with CF (ICC: 0.22 to 0.43). The exceptions to this trend were the normalised LF and HF components which were associated with a good to excellent reproducibility. These findings thereby support the utilisation of time and relative frequency domain HRV indices as a prognostic tool in children with CF. Furthermore, the present results highlight the excellent reproducibility of HRV in healthy children, indicating that this may be a useful tool to assess intervention effectiveness in this population.

Good reproducibility of heart rate variability after orthostatic challenge in patients with a history of acute coronary syndrome

BackgroundSeveral parameters of heart rate variability (HRV) have been shown to predict the risk of sudden cardiac death (SCD) in cardiac patients. There is consensus that risk prediction is increased when measuring HRV during specific provocations such as orthostatic challenge. For the first time, we provide data on reproducibility of such a test in patients with a history of acute coronary syndrome. MethodsSixty male patients (65±8years) with a history of acute coronary syndrome on stable medication were included. HRV was measured in supine (5min) and standing (5min) position on 2 occasions separated by two weeks. For risk assessment relevant time-domain [standard deviation of all R-R intervals (SDNN) and root mean squared standard differences between adjacent R-R intervals (RMSSD)], frequency domain [low-frequency power (LF), high-frequency power (HF) and LF/HF power ratio] and short-term fractal scaling component (DF1) were computed. Absolute reproducibility was assessed with the standard errors of the mean (SEM) and 95% limits of random variation, and relative reproducibility by the intraclass correlation coefficient (ICC). ResultsWe found comparable SEMs and ICCs in supine position and after an orthostatic challenge test. All ICCs were good to excellent (ICCs between 0.636 and 0.869). ConclusionsReproducibility of HRV parameters during orthostatic challenge is good and comparable with supine position.

Interaction between Heart Rate and Heart Rate Variability

Heart rate variability (HRV) is significantly associated with average heart rate (HR), therefore, HRV actually provides information on two quantities, that is, on HR and its variability. It is difficult to conclude which of these two plays a principal role in the HRV clinical value, or in other words, what is the HR contribution to the clinical significance of HRV. Moreover, the association between HRV and HR is both a physiological phenomenon and a mathematical one. The physiological HRV dependence on HR is determined by the autonomic nervous system activity, but the mathematical one is caused by the nonlinear relationship between RR interval and HR. By employing modification methods of the HRV and HR relationship, it is possible to investigate the HR contribution to the HRV clinical value. Recent studies have shown that the removal of the HR impact on HRV makes HRV more predictive for noncardiac death, however, the enhancement of this impact causes HRV to be a better predictor of cardiovascular mortality. Thus, HR seems to constitute a cardiovascular factor of the HRV predictive ability. HR also influences the reproducibility of HRV, therefore, HR changes should be considered when one compares HRV measurements in a given patient. This review summarizes methodological aspects of investigations of the HRV and HR interaction as well as latest observations concerning its clinical utility. The issues discussed in this article should also refer to any other heart rate dynamics analysis which indices are significantly associated with HR.

Heart rate variability reproducibility during exercise

The use of heart rate variability (HRV) parameters during exercise is not supported by appropriate reliability studies. In 80 healthy adults, ECG was recorded during three 6 min bouts of exercise, separated by 6 min of unloaded cycling. Two bouts were at a moderate intensity while the final bout was at a heavy exercise intensity. This protocol was repeated under the same conditions on three occasions, with a controlled start time (pre-determined at the first visit). Standard time and frequency domain indices of HRV were derived. Reliability was assessed by Bland–Altman plots, 95% limits of agreement and intraclass correlation coefficients (ICC). The sample size required to detect a mean difference ≥30% of the between-subject standard deviation was also estimated. There was no systematic change between days. All HRV parameters demonstrated a high degree of reproducibility during baseline (ICC range: 0.58–0.75), moderate (ICC: 0.58–0.85) and heavy intensity exercise (ICC range: 0.40–0.76). The reproducibility was slightly diminished during heavy intensity exercise relative to both unloaded baseline cycling and moderate exercise. This study indicates that HRV parameters can be reliably determined during exercise, and it underlines the importance of standardizing exercise intensity with regard to fitness levels if HRV is to be reliably determined.

Reproducibility of Heart Rate Variability during Rest, Paced Breathing and Light-to-Moderate Intense Exercise in Patients One Month after Stroke

Aim: To examine test-retest reliability of time and frequency domain heart rate variability (HRV) in patients 1 month after stroke during rest, paced breathing and light-to-moderate physical activity. Methods: Fifteen patients up to 1 month after stroke underwent two measurements of HRV, with the measurements 4 days apart. Measurements took place under three conditions while sitting: (1) at rest with self-select breathing frequency, (2) paced breathing and (3) cycling while sitting. Reliability was assessed statistically by calculating intraclass correlation coefficients (ICC), standard error of measurement and coefficient of variance (CV). Results: The relative reliability was found to be good-to-excellent for SDNN (ICC: 0.86–0.91), RMSSD (ICC: 0.81–0.87) and HF (ICC: 0.91–0.94) in all three conditions and poor for LF at rest and paced breathing (ICC: 0.43–0.47). The absolute reliability for all measures was found to be poor (CV >15%). Conclusions: HRV can be reliably assessed at rest, paced breathing and light-to-moderate physical activity for identifying differences between patients, while individual changes in autonomic functioning exhibited large random variations between test-retest measurements.

Influence of different breathing patterns on heart rate variability indices and reproducibility during experimental endotoxaemia in human subjects

HRV (heart rate variability) analysis is a widely employed method to assess cardiac autonomic nervous system activity. Accurate HRV measurement is critical to its value as a diagnostic and prognostic tool. Different breathing patterns may affect HRV, but results obtained under static conditions are conflicting. HRV indices decrease considerably during systemic inflammation evoked by experimental endotoxaemia, enabling the determination of the effects of different breathing patterns on HRV in a dynamic setting. We investigated the impact of different breathing patterns on short-term HRV measurements during experimental endotoxaemia. Furthermore, we assessed whether paced breathing improved HRV reproducibility. Twelve healthy male volunteers received an intravenous bolus (2ng/kg of body weight) of endotoxin [LPS (lipopolysaccharide), derived from Escherichia coli O:113] on two occasions with an interval of 2weeks. Five-minute HRV recordings were performed just prior to LPS administration and hourly thereafter until 8h post-LPS. Three breathing protocols were employed every hour: (i) spontaneous breathing, (ii) metronome-guided breathing at the subject's normal respiratory rate ('paced') and (iii) metronome-guided breathing at 150% of the subject's normal respiratory rate ('mild hyperventilation'). LPS administration resulted in a sharp decrease in all of the HRV indices measured, which was similar during both LPS administrations. Neither paced breathing nor mild hyperventilation influenced HRV indices compared with spontaneous breathing. Paced breathing did not improve reproducibility as it did not exert a significant effect on intra-subject coefficients of variation and intra-class correlation coefficients (calculated between both visits). In conclusion, over a wide range of HRV magnitudes during experimental endotoxaemia, neither paced breathing nor mild hyperventilation affected HRV indices. Moreover, paced breathing did not result in a significant improvement in reproducibility. Therefore employing a paced breathing protocol is not required to obtain valid HRV data during endotoxaemia.

Reproducibility of heart rate variability and baroreflex sensitivity measurements in children

Despite their extensive use, the reproducibility of cardiac autonomic measurements in children is not well-known. We investigated the reproducibility of short-term continuous measurements of heart rate (HR), heart rate variability (HRV, time and frequency domain), and spontaneous baroreflex sensitivity (BRS, frequency domain) in the supine and standing position in 57 children (11.2±0.7 years, 52.6% boys). Reproducibility between two sessions within a two-week interval was evaluated by intraclass correlation coefficients (ICCs), standard error of measurement, coefficients of variation (CVs), limits of agreement, and Bland–Altman plots. HR and HRV were moderately-to-highly (ICC=.63–.79; CV=5.7%–9.7%) and BRS moderately (ICC=.49–.63; CV=11.4%–14.0%) reproducible. While the BRS measurements were slightly less reproducible than the HR and HRV measurements, all can be reliably applied in research, thus implicating sufficient capacity to detect real differences between children. Still, clinical studies focusing on individual changes in cardiac autonomic functioning need to address the considerable random variations that may occur between test–retest measurements.

S6.4 Examination of the short-term reproducibility of heart rate variability in humans

S6.4 Examination of the short-term reproducibility of heart rate variability in humans

Does Paced Breathing Improve the Reproducibility of Heart Rate Variability Measurements?

The effects of paced breathing (PB) on the reproducibility of heart rate variability (HRV) measurements were examined in 55 male subjects (age range: 20-54 years). Spectral components of HRV were measured under a combination of two respiratory conditions (spontaneous and 4s PB) and two postures (standing and supine). The procedures were repeated 3 weeks after the first measurement. Log-transformed low-frequency (lnLF) and high-frequency (lnHF) components of HRV were calculated from a 205s electrocardiography (ECG) recording. The coefficients of interindividual variations of lnHF and lnLF (ca. 13-16%) and the intraindividual variations of the frequency components (5-6%) were not significantly affected by PB. The coefficients of intraindividual variation of heart rate, ln HF and ln LF did not correlate with age in either posture. Effect sizes of PB on the intraindividual variation ranged from -0.04 to 0.13. Although intraclass correlation coefficients (ICCs) were slightly improved by PB in some cases, the differences were negligible. The above results suggest that PB provides a limited improvement in the reproducibility of HRV measurements, and metronome-guided respiration is not necessarily required for HRV measurement if subjects are reminded to avoid irregular respiration.

Reproducibility and validity of heart rate variability and respiration rate measurements in participants with prolonged fatigue complaints

(1) To evaluate reproducibility of heart rate variability (HRV) and respiration rate (RR) measurements during reclining and cycling in participants with prolonged fatigue and (2) to assess concurrent validity between HRV and RR measurements and fatigue. Twenty-seven subjects reporting prolonged fatigue complaints resulting in functional impairments participated in the study. Fatigue complaints and functional impairments were assessed. Two to 4 days later, they underwent two repeated measurements of time-domain HRV (SDNN and RMSSD) and RR with 3-4 days between. Intra-class correlation coefficients (ICCs) and standard error of measurement (SEM) were calculated to define reproducibility and Pearson correlations were calculated to define concurrent validity. ICC means for SDNN and RMSSD during reclining and cycling ranged from 0.86 to 0.93. For RR the ICC means were 0.65 and 0.85 for reclining and cycling, respectively. The SEM values (ms) for SDNN and RMSSD ranged from 1.08 to 7.71 while the SEM values for RR were 1.82 and 1.99 for reclining and cycling, respectively. The Pearson correlations were non-significant and ranged from -0.05 to 0.15. There was good reproducibility of HRV and RR in participants with prolonged fatigue complaints. Concurrent validity between HRV and RR measurements and fatigue was low.

Moderate-term reproducibility of heart rate variability during rest and light to moderate exercise in children

Previous studies have demonstrated the high reproducibility of heart rate variability (HRV) measures in adults while little information exists concerning HRV reproducibility in children. Subsequently, the aim of the current study was to examine the moderate-term reproducibility of heart rate and frequency domain measures of HRV during rest and light to moderate exercise in children. Ten healthy children (6 males, 4 females) aged between 7 and 12 years of age volunteered for this study with HRV recordings obtained during supine rest and three treadmill walking exercise work rates (< or =60% maximum heart rate), initially and then 8 weeks later. Differences (P < 0.05) between variables were examined using paired t-tests or Wilcoxon signed rank tests while reliability and reproducibility were examined by intraclass correlation coefficients (ICC), coefficients of variation (CV), and mean bias ratio and ratio limits of agreement (LOA). Heart rate and all measures of HRV at rest and exercise were unchanged after 8 weeks. Significant ICC were documented primarily during rest (0.72-0.85) while weaker relationships (-0.02-0.87) were evident during exercise. A large range of CV was identified during rest (6-33%) and exercise (3-128%) while the ratio LOA were variable and substantial (1.04-2.73). Despite similar HRV over an 8-week period, variable ICC and sizable CV and ratio LOA indicate moderate to poor reproducibility of HRV in children, particularly during light to moderate exercise. Studies examining HRV in children should include age- or maturation stage-matched control participants to address the age-related change in HRV and inadequate HRV reliability.

Reproducibility of heart rate variability and blood pressure variability in individuals with spinal cord injury

Individuals with spinal cord injury (SCI) are prone to orthostatic intolerance and an increased risk of cardiovascular disease. The use of heart rate variability (HRV) and blood pressure variability (BPV) as indices of cardiovascular regulation would be valuable in this population; however, their reproducibility has yet to be tested in those with SCI. The purpose of this study was to examine the day-to-day reproducibility of resting HRV and BPV in individuals with SCI. Ten individuals (age 35.9 +/- 13.2 yrs) with chronic (5.4 +/- 7.7 years post injury) SCI (C4-T12; ASIA A-C) participated. On two occasions within a two-week period, 10-minute supine electrocardiogram and Finapres blood pressure recordings were obtained during spontaneous breathing. Computer software calculated frequency domain measures of HRV and BPV (Low frequency (LF) power, High frequency (HF) power, and LF:HF ratio). Intraclass correlations coefficients (R) were used as an index of day-to-day reproducibility, and analyses were conducted on all participants and only those with tetraplegia. For HRV, measures of heart rate, LF, and LF:HF were found to be highly reproducible (R = 0.82-0.88); however, the reproducibility of HF was found to be poor (all participants: R = 0.53, tetraplegia: R = 0.66). Measures of blood pressure as well as systolic BPV also showed high reproducibility (R = 0.72-0.93). Measures of diastolic BPV were less reproducible but still acceptable (R = 0.71-0.89) with the exception of LF:HF(DBP) (R = 0.51). In conclusion, despite the autonomic dysfunction associated with SCI, measures of HRV and BPV may still be used as reproducible indices of autonomic cardiovascular regulation in this population.

Reproducibility of heart rate variability, blood pressure variability and baroreceptor sensitivity during rest and head-up tilt

Previous studies have indicated moderate-to-poor reproducibility of heart rate variability (HRV) but the reproducibility of blood pressure variability (BPV) and spectral measures of baroreceptor sensitivity (BRS) are not well established. We measured normal-to-normal heart beat (RR) interval and finger blood pressure (Finapres) in 14 healthy individuals on three different days. The protocol was 1 h of supine rest and 1 h of 60-degree head-up tilt. Time-series of consecutive 300-s segments as well as 1024-s segments of RR intervals and systolic, diastolic and mean blood pressures were extracted for the assessment of day-to-day and short-term reproducibility. Power spectrum analysis (Fourier) and transfer function analysis was performed. Reproducibility was assessed using the coefficient of variation (CV). The reproducibility of the mean RR interval, mean systolic, diastolic and mean blood pressure was good (CV<10 %). However, there was only moderate-to-poor reproducibility of the spectral parameters of HRV (CV range 18-36%) and BPV (16-44%) and moderate reproducibility of BRS (14-20%). Spectral estimates of BRS had only moderate reproducibility although it was better than the spectral estimates of HRV and BPV.

ONE-WEEK STABILITY OF HEART RATE VARIABILITY AT REST AND FOLLOWING A SET OF ISOMETRIC CONTRACTIONS

PURPOSE To examine the 1-week stability of heart rate variability (HRV) at rest and during recovery from a set of isometric contractions. METHODS Ten participants (age = 24.8±3 yrs) were tested on 2 visits to the laboratory separated by 1 week. On each visit, 2.5-minute EKGs were collected following 10 minutes of quiet rest in the seated position. EKG tracings were collected during spontaneous breathing (SB), paced breathing (PB; 12 breaths/min), and during PB following a set of 20 isometric contractions of knee extension exercise with the non-dominant leg (REC). Participants contracted at 70% of their maximal voluntary contraction with their knee positioned at 90 degrees. HRV was reported as the standard deviation of normal RR intervals (SDNN), and spectral power in the total (TP; 0.00–0.4 Hz), low- (LF; 0.04–0.15 Hz), and high- (HF; 0.15–0.40 Hz) frequency power ranges was derived via an FFT. LF and HF were further reported as normalized units (NU) to examine cardiac autonomic balance. The reproducibility of HRV under each condition was reported as the intraclass correlation coefficient (ICC), the coefficient of variation, and as the standard error of measurement. Additionally, repeated measures ANOVA was used to examine HRV during the various conditions. RESULTS During both testing days, the mean RR interval was lower and SDNN was greater during REC compared to SB and PB (p < 0.05). Additionally, HFNU was greater during REC and lower during SB compared to PB (p < 0.05), whereas LFNU behaved reciprocally on both testing days. ICCs ranged from 0.56 to 0.81 for all HRV indices measured during SB, PB, and REC. CONCLUSION These data indicate adequate reproducibility of HRV indices under conditions of SB, PB and REC. Furthermore, these data confirm previous studies indicating elevated HF during PB, and a marked vagal reactivation immediately following a set of isometric contractions.