Reproducibility of heart rate variability from short-term recordings during five manoeuvres in normal subjects

COVID-19 is getting on our nerves: sympathetic neural activity and haemodynamics in young adults recovering from SARS-CoV-2

KEY POINTS

The impact of SARS-CoV-2 infection on autonomic and cardiovascular function in otherwise healthy individuals is unknown. For the first time it is shown that young adults recovering from SARS-CoV-2 have elevated resting sympathetic activity, but similar heart rate and blood pressure, compared with control subjects. Survivors of SARS-CoV-2 also exhibit similar sympathetic nerve activity and haemodynamics, but decreased pain perception, during a cold pressor test compared with healthy controls. Further, these individuals display higher sympathetic nerve activity throughout an orthostatic challenge, as well as an exaggerated heart rate response to orthostasis. If similar autonomic dysregulation, like that found here in young individuals, is present in older adults following SARS-CoV-2 infection, there may be substantial adverse implications for cardiovascular health.

ABSTRACT

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can elicit systemic adverse physiological effects. However, the impact of SARS-CoV-2 on autonomic and cardiovascular function in otherwise healthy individuals remains unclear. Young adults who tested positive for SARS-CoV-2 (COV+; n = 16, 8 F) visited the laboratory 35 ± 16 days following diagnosis. Muscle sympathetic nerve activity (MSNA), systolic (SBP) and diastolic (DBP) blood pressure, and heart rate (HR) were measured in participants at rest and during a 2 min cold pressor test (CPT) and 5 min each at 30° and 60° head-up tilt (HUT). Data were compared with age-matched healthy controls (CON; n = 14, 9 F). COV+ participants (18.2 ± 6.6 bursts min-1 ) had higher resting MSNA burst frequency compared with CON (12.7 ± 3.4 bursts min-1 ) (P = 0.020), as well as higher MSNA burst incidence and total activity. Resting HR, SBP and DBP were not different. During CPT, there were no differences in MSNA, HR, SBP or DBP between groups. COV+ participants reported less pain during the CPT compared with CON (5.7 ± 1.8 vs. 7.2 ± 1.9 a.u., P = 0.036). MSNA was higher in COV+ compared with CON during HUT. There was a group-by-position interaction in MSNA burst incidence, as well as HR, in response to HUT. These results indicate resting sympathetic activity, but not HR or BP, may be elevated following SARS-CoV-2 infection. Further, cardiovascular and perceptual responses to physiological stress may be altered, including both exaggerated (orthostasis) and suppressed (pain perception) responses, compared with healthy young adults.

COVID-19 is getting on our nerves: sympathetic neural activity and haemodynamics in young adults recovering from SARS-CoV-2

Key points

The impact of SARS‐CoV‐2 infection on autonomic and cardiovascular function in otherwise healthy individuals is unknown.

For the first time it is shown that young adults recovering from SARS‐CoV‐2 have elevated resting sympathetic activity, but similar heart rate and blood pressure, compared with control subjects.

Survivors of SARS‐CoV‐2 also exhibit similar sympathetic nerve activity and haemodynamics, but decreased pain perception, during a cold pressor test compared with healthy controls.

Further, these individuals display higher sympathetic nerve activity throughout an orthostatic challenge, as well as an exaggerated heart rate response to orthostasis.

If similar autonomic dysregulation, like that found here in young individuals, is present in older adults following SARS‐CoV‐2 infection, there may be substantial adverse implications for cardiovascular health.

Abstract

The novel severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) can elicit systemic adverse physiological effects. However, the impact of SARS‐CoV‐2 on autonomic and cardiovascular function in otherwise healthy individuals remains unclear. Young adults who tested positive for SARS‐CoV‐2 (COV+; n = 16, 8 F) visited the laboratory 35 ± 16 days following diagnosis. Muscle sympathetic nerve activity (MSNA), systolic (SBP) and diastolic (DBP) blood pressure, and heart rate (HR) were measured in participants at rest and during a 2 min cold pressor test (CPT) and 5 min each at 30° and 60° head‐up tilt (HUT). Data were compared with age‐matched healthy controls (CON; n = 14, 9 F). COV+ participants (18.2 ± 6.6 bursts min⁻¹) had higher resting MSNA burst frequency compared with CON (12.7 ± 3.4 bursts min⁻¹) (P = 0.020), as well as higher MSNA burst incidence and total activity. Resting HR, SBP and DBP were not different. During CPT, there were no differences in MSNA, HR, SBP or DBP between groups. COV+ participants reported less pain during the CPT compared with CON (5.7 ± 1.8 vs. 7.2 ± 1.9 a.u., P = 0.036). MSNA was higher in COV+ compared with CON during HUT. There was a group‐by‐position interaction in MSNA burst incidence, as well as HR, in response to HUT. These results indicate resting sympathetic activity, but not HR or BP, may be elevated following SARS‐CoV‐2 infection. Further, cardiovascular and perceptual responses to physiological stress may be altered, including both exaggerated (orthostasis) and suppressed (pain perception) responses, compared with healthy young adults.

The impact of SARS‐CoV‐2 infection on autonomic and cardiovascular function in otherwise healthy individuals is unknown.

For the first time it is shown that young adults recovering from SARS‐CoV‐2 have elevated resting sympathetic activity, but similar heart rate and blood pressure, compared with control subjects.

Survivors of SARS‐CoV‐2 also exhibit similar sympathetic nerve activity and haemodynamics, but decreased pain perception, during a cold pressor test compared with healthy controls.

Further, these individuals display higher sympathetic nerve activity throughout an orthostatic challenge, as well as an exaggerated heart rate response to orthostasis.

If similar autonomic dysregulation, like that found here in young individuals, is present in older adults following SARS‐CoV‐2 infection, there may be substantial adverse implications for cardiovascular health.

Reliability of short-term measurements of heart rate variability: Findings from a longitudinal study

Research on heart rate variability (HRV) received increasing attention. This study analysed the reliability of the most common HRV parameters for baseline measurements. 103 healthy students (83 women, M = 21.72 ± 3.31 years) participated in five short-term HRV sessions, each including supine, sitting, and standing positions, respectively, spanning a time interval of eleven months. Relative reliability was evaluated by intraclass correlation coefficients, and absolute reliability by standard errors of measurement, smallest real differences, and 95 % limits of random variation. No systematic mean differences between measurements emerged. Intraclass correlation coefficients were quite low (supine: .49-.64, sitting: .40-.57, standing: .35-.56). Absolute reliability indicators revealed pronounced variations between test and retest. Influences of posture and time between measurements on reliability were small and unsystematic. We conclude that such high levels of within-subjects variability in HRV measurements (a) hamper the detection of changes over time, and (b) should be considered carefully in future analyses.

Short-term Heart-rate Variability in Healthy Small and Medium-sized Dogs Over a Five-minute Measuring Period

Introduction

Five-minute heart-rate variability (HRV) measurement is a useful tool for assessing the autonomic nervous system (ANS) balance in humans, but there are no studies on healthy dogs. The aim of the study was, therefore, to provide the reference ranges in small and medium-sized breeds for short-term HRV time and frequency domain (TFD) analyses.

Material and Methods

A total of 79 healthy dogs were included in the study between 2015 and 2019. Grouping by age with the breakpoint at six years and subgrouping by reproductive status and sex was imposed. All the dogs were included after physical and cardiological examinations and blood analyses. The TFD of HRV were analysed from a five-minute-long digital ECG recording after removal of non-sinus complexes.

Results

There were no statistically significant differences in any TFD parameters between age, reproductive status or sex groups. A mild increase in all time domain parameters and the high-frequency (HF) band was observed in older dogs, and the low frequency (LF):HF ratio decreased in these dogs. In males, the time domain parameters and HF band increased slightly.

Conclusion

The normal ranges for HRV derived from short-term ECG recording in the usual clinical environment now have proposed reference ranges. Our findings suggest that accommodation time, age, sex, or reproductive status do not influence the results derived from these recordings, indicating that this method is reliable for assessing the ANS function in small and medium-sized dog breeds.

Cardiac Autonomic Responses during Exercise and Post-exercise Recovery Using Heart Rate Variability and Systolic Time Intervals-A Review

Cardiac parasympathetic activity may be non-invasively investigated using heart rate variability (HRV), although HRV is not widely accepted to reflect sympathetic activity. Instead, cardiac sympathetic activity may be investigated using systolic time intervals (STI), such as the pre-ejection period. Although these autonomic indices are typically measured during rest, the “reactivity hypothesis” suggests that investigating responses to a stressor (e.g., exercise) may be a valuable monitoring approach in clinical and high-performance settings. However, when interpreting these indices it is important to consider how the exercise dose itself (i.e., intensity, duration, and modality) may influence the response. Therefore, the purpose of this investigation was to review the literature regarding how the exercise dosage influences these autonomic indices during exercise and acute post-exercise recovery. There are substantial methodological variations throughout the literature regarding HRV responses to exercise, in terms of exercise protocols and HRV analysis techniques. Exercise intensity is the primary factor influencing HRV, with a greater intensity eliciting a lower HRV during exercise up to moderate-high intensity, with minimal change observed as intensity is increased further. Post-exercise, a greater preceding intensity is associated with a slower HRV recovery, although the dose-response remains unclear. A longer exercise duration has been reported to elicit a lower HRV only during low-moderate intensity and when accompanied by cardiovascular drift, while a small number of studies have reported conflicting results regarding whether a longer duration delays HRV recovery. “Modality” has been defined multiple ways, with limited evidence suggesting exercise of a greater muscle mass and/or energy expenditure may delay HRV recovery. STI responses during exercise and recovery have seldom been reported, although limited data suggests that intensity is a key determining factor. Concurrent monitoring of HRV and STI may be a valuable non-invasive approach to investigate autonomic stress reactivity; however, this integrative approach has not yet been applied with regards to exercise stressors.

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.

Telemetry-derived heart rate variability responses to a physical stressor

Analysis of heart rate variability (HRV) responses to an orthostatic challenge can be used to investigate autonomic control of heart rate, an index of cardiovascular function. HRV is typically assessed using the electrocardiogram (ECG), which can be impractical for use with large population-based studies.

PURPOSE

To assess the validity and reliability of telemetry-derived HRV responses to an orthostatic challenge.

METHODS

Twenty healthy adults (26 + 5 years, 45% male) were tested on three separate mornings. Following 20-min supine rest, R-R intervals were recorded using a telemetric device during three conditions: BASE, TILT and RECOVERY. ECG was simultaneously used on 1 day for validity comparison. Measures of HRV included the following: standard deviation of normal-to-normal intervals (SDNN), the root-mean-square of successive differences (RMSSD) and the low-frequency (LF) and high-frequency (HF) spectral power.

RESULTS

For all parameters, there was excellent agreement between devices for BASE (r = 0·96-0·99), TILT (r = 0·89-1·00) and RECOVERY (r = 0·96-1·00). For the telemetric device, between-day intraclass coefficient values for RMSDD, SDNN and HF were all above the 0·75 criterion for each condition, indicating excellent between-day reliability. For each condition, the reliability coefficient, expressed as a percentage of the mean (RC%), was marginally lower (greater reliability) for RMSDD (RC% 11-13) and SDNN (RC% 10-12) compared to HF (RC% 12-17). However, SDNN did not significantly respond to the orthostatic challenge.

CONCLUSION

Telemetric HRV, particularly RMSDD and HF, can be used to provide a sensitive, valid and reliable assessment of autonomic control of heart rate.

Normative references of heart rate variability and salivary alpha-amylase in a healthy young male population

Background

This study aimed to present normative reference values of heart rate variability and salivary alpha-amylase in a healthy young male population with a particular focus on their distribution and reproducibility.

Methods

The short-term heart rate variability of 417 young healthy Japanese men was studied. Furthermore, salivary alpha-amylase was measured in 430 men. The average age of the subjects were 21.9 years with standard deviation of 1.6 years. Interindividual variations in heart rate variability indices and salivary alpha-amylase levels were plotted as histograms. Data are presented as the mean, median, standard deviation, coefficient of variation, skewness, kurtosis, and fifth and 95th percentiles of each physiological index.

Results

Mean recorded values were heart period 945.85 ms, log-transformed high frequency component 9.84 ln-ms², log-transformed low frequency component 10.42 ln-ms², log-transformed low frequency to high frequency ratio 0.58 ln-ratio, standard deviation of beat-to-beat interval 27.17 ms and root mean square of successive difference 37.49 ms. The mean value of raw salivary alpha-amylase was 17.48 U/mL, square root salivary alpha-amylase 3.96 sqrt[U/mL] and log-transformed salivary alpha-amylase 2.65 ln[U/mL]. Log-transformed heart rate variability indices exhibited almost symmetrical distributions; however, time-domain indices of heart rate variability (standard deviation of beat-to-beat interval and root mean square of successive difference) exhibited right-skewed (positive skewness) distributions. A considerable right-skewed distribution was observed for raw salivary alpha-amylase. Logarithmic transformation improved the distribution of salivary alpha-amylase, although square root transformation was insufficient. The day-to-day reproducibility of these indices was assessed using intraclass correlation coefficients. Intraclass correlation coefficients of most heart rate variability and salivary indices were approximately 0.5 to 0.6. Intraclass correlation coefficients of raw salivary markers were approximately 0.6, which was similar to those of heart rate variability; however, log transformation of the salivary markers did not considerably improve their reproducibility. Correlations between sympathetic indicators of heart rate variability and salivary alpha-amylase were not observed.

Conclusion

Because the sample population examined in this study involved limited age and gender variations, the present results were independent of these factors and were indicative of pure interindividual variation.

The reproducibility of heart rate recovery after treadmill exercise test

BACKGROUND

Although predictive value of heart rate recovery (HRR) has been tested in large populations, the reproducibility of HRR in treadmill exercise test has not been assessed prospectively. This prospective study examined whether HRR index has test-retest stability in the short term.

METHODS

A total of 52 healthy volunteers without cardiovascular risk factors (mean age, 30 ± 10 years, 30 females) underwent standardized graded treadmill exercise test, and the test was repeated on the 7th and the 30th days. The subjects' maximal heart rates and the decrease of heart rate from the peak exercise level to the level of 1, 2, 3, 4, and 5 minutes after the termination of the exercise were examined on each test, and heart rates for each minute from the first, second, and third tests were compared for each individual.

RESULTS

The maximal heart rates on the 1st, 7th, and the 30th days were 179 ± 11, 177 ± 10, 178 ± 10 beats/min, respectively [P = 0.07, intraclass correlation coefficient (ICC) = 0.92], and the 1st minute HRR indices after peak exercise were 33 ± 10, 33 ± 10, 33 ± 11, respectively (P = 0.66, ICC = 0.88). There was no statistical difference in the 2nd, 3rd, 4th, and 5th minute heart rates of the recovery phase among the 1st, 7th, and 30th day treadmill exercise tests, either.

CONCLUSION

Maximal heart rates and the decline of heart rate to the 5th minute on recovery phase after treadmill exercise test have short-term reproducibility.

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 (2 ng/kg of body weight) of endotoxin [LPS (lipopolysaccharide), derived from Escherichia coli O:113] on two occasions with an interval of 2 weeks. Five-minute HRV recordings were performed just prior to LPS administration and hourly thereafter until 8 h 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.

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.

Test-Retest Reliability of Heart Rate Variability and Respiration Rate at Rest and during Light Physical Activity in Normal Subjects

BACKGROUND

A variable that remains stable over repeated measurements (in stable conditions) is ideal for tracking modifications of the clinical state. The aim of the present study is to examine test-retest reliability of time-domain heart rate variability and respiration rate measurements using a portable device on normal subjects during rest and light physical activity.

METHODS

Twenty-six normal subjects [18 females and 8 males aged 28 +/- 6 years and 34 +/- 12 years (mean +/- SD), respectively] underwent two measurements for time-domain heart rate variability (SDNN and RMSSD) and respiration rate, with 7 days in between. Measurements took place under three conditions: lying down in a laboratory, cycling in a laboratory and sleeping in an ambulatory surrounding. Reliability was assessed statistically by calculating intra-class correlation coefficients (ICC).

RESULTS

Reliability was found to be good to excellent for both time-domain heart rate variability (SDNN: ICC values between 0.74 and 0.85, RMSSD: ICC values between 0.75 and 0.98) and for respiration rate (ICC values between 0.77 and 0.96).

CONCLUSIONS

Both time-domain heart rate variability and respiration rate can be reliably assessed. However, we advise reliability research in a clinical setting before using the device for tracking modifications in a clinical state.

Reliability and accuracy of heart rate variability metrics versus ECG segment duration

Despite the exponential growth in heart rate variability (HRV) research, the reproducibility and reliability of HRV metrics continues to be debated. We estimated the reliability of 11 metrics calculated from 5 min records. We also compared the accuracy of the HRV metrics calculated from ECG records spanning 10 s to 10 min as compared with the metrics calculated from 5 min records. The mean heart rate was more reproducible and could be more accurately estimated from very short segments (<1 min) than any of the other HRV metrics. HRV metrics that effectively highpass filter the R-R interval series were more reliable than the other metrics and could be more accurately estimated from very short segments. This indicates that most of the HRV is caused by drift and nonstationary effects. Metrics that are sensitive to low frequency components of HRV have poor repeatability and cannot be estimated accurately from short segments (<10 min).