Differential effects of parasympathetic blockade and parasympathetic withdrawal on heart rate variability

Adynamic response to cold pain reflects dysautonomia in type 1 diabetes and polyneuropathy

Cardiac autonomic neuropathy (CAN), widely assessed by heart rate variability (HRV), is a common complication of long-term diabetes. We hypothesized that HRV dynamics during tonic cold pain in individuals with type 1 diabetes mellitus (T1DM) could potentially demask CAN. Forty-eight individuals with long-term T1DM and distal symmetrical polyneuropathy and 21 healthy controls were included. HRV measures were retrieved from 24-h electrocardiograms. Moreover, ultra-short-term HRV recordings were used to assess the dynamic response to the immersion of the hand into 2 °C cold water for 120 s. Compared to healthy, the T1DM group had expectedly lower 24-h HRV measures for most components (p < 0.01), indicating dysautonomia. In the T1DM group, exposure to cold pain caused diminished sympathetic (p < 0.001) and adynamic parasympathetic (p < 0.01) HRV responses. Furthermore, compared to healthy, cold pain exposure caused lower parasympathetic (RMSSD: 4% vs. 20%; p = 0.002) and sympathetic responses (LF: 11% vs. 73%; p = 0.044) in the T1MD group. QRISK3-scores are negatively correlated with HRV measures in 24-h and ultra-short-term recordings. In T1DM, an attenuated sympathovagal response was shown as convincingly adynamic parasympathetic responses and diminished sympathetic adaptability, causing chronometric heart rhythm and rigid neurocardiac regulation threatening homeostasis. The findings associate with an increased risk of cardiovascular disease, emphasizing clinical relevance.

The connection between heart rate variability (HRV), neurological health, and cognition: A literature review

The heart and brain have bi-directional influences on each other, including autonomic regulation and hemodynamic connections. Heart rate variability (HRV) measures variation in beat-to-beat intervals. New findings about disorganized sinus rhythm (erratic rhythm, quantified as heart rate fragmentation, HRF) are discussed and suggest overestimation of autonomic activities in HRV changes, especially during aging or cardiovascular events. When excluding HRF, HRV is regulated via the central autonomic network (CAN). HRV acts as a proxy of autonomic activity and is associated with executive functions, decision-making, and emotional regulation in our health and wellbeing. Abnormal changes of HRV (e.g., decreased vagal functioning) are observed in various neurological conditions including mild cognitive impairments, dementia, mild traumatic brain injury, migraine, COVID-19, stroke, epilepsy, and psychological conditions (e.g., anxiety, stress, and schizophrenia). Efforts are needed to improve the dynamic and intriguing heart-brain interactions.

Overnight heart rate variability responses to military combat engineer training

The study aimed to determine if overnight heart rate variability (HRV) is reflective of workload and stress during military training. Measures of cognitive load, perceived exertion, physical activity, nocturnal HRV, cognitive performance and sleep were recorded for a 15-day assessment period in 32 combat engineers. The assessment period consisted of 4 phases, PRE, FIELD, BASE and RECOVERY that exposed trainees to periods of sleep deprivation and restriction. The FIELD phase was characterised by an increase in mood disturbance, perceived exertion, physical activity, HRV and a reduction in sleep quantity (p < 0.05). Measures of HRV returned to PRE-values quicker than subjective wellbeing responses. The combination of sleep duration (β = -0.002, F = 13.42, p < 0.001) and physical activity (metabolic equivalents, β = -0.483, F = 5.95, p = 0.017), the main stressors of the exercise, provided a significant effect in the best predictive model of HRV. The different recovery rates of HRV and subjective wellbeing suggest a different physiological and psychological response.

Dynamics of cardiovascular and baroreflex readjustments during a light-to-moderate exercise transient in humans

Purpose

We hypothesised that, during a light-to-moderate exercise transient, compared to an equivalent rest-to-exercise transient, (1) a further baroreflex sensitivity (BRS) decrease would be slower, (2) no rapid heart rate (HR) response would occur, and (3) the rapid cardiac output (CO) response would have a smaller amplitude (A1). Hence, we analysed the dynamics of arterial baroreflexes and the HR and CO kinetics during rest-to-50 W (0–50 W) and 50-to-100 W (50–100 W) exercise transients.

Methods

10 subjects performed three 0–50 W and three 50–100 W on a cycle ergometer. We recorded arterial blood pressure profiles (photo-plethysmography) and R-to-R interval (RRi, electrocardiography). The former were analysed to obtain beat-by-beat mean arterial pressure (MAP) and stroke volume (SV). CO was calculated as SV times HR. BRS was measured by modified sequence method.

Results

During 0–50 W, MAP transiently fell (− 9.0 ± 5.7 mmHg, p < 0.01) and BRS passed from 15.0 ± 3.7 at rest to 7.3 ± 2.4 ms mmHg⁻¹ at 50 W (p < 0.01) promptly (first BRS sequence: 8.1 ± 4.6 ms mmHg⁻¹, p < 0.01 vs. rest). During 50–100 W, MAP did not fall and BRS passed from 7.2 ± 2.6 at 50 W to 3.3 ± 1.3 ms mmHg⁻¹ at 100 W (p < 0.01) slowly (first BRS sequence: 5.3 ± 3.1 ms mmHg⁻¹, p = 0.07 vs. 50 W). A1 for HR was 9.2 ± 6.0 and 6.0 ± 4.5 min⁻¹ in 0–50 W and 50–100 W, respectively (p = 0.19). The corresponding A1 for CO were 2.80 ± 1.54 and 0.91 ± 0.55 l∙min⁻¹ (p < 0.01).

Conclusion

During 50–100 W, with respect to 0–50 W, BRS decreased more slowly, in absence of a prompt pressure decrease. BRS decrease and rapid HR response in 50–100 W were unexpected and ascribed to possible persistence of some vagal tone at 50 W.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-022-05011-4.

Monitoring Responses to Basic Military Training with Heart Rate Variability

INTRODUCTION

Heart rate variability (HRV) has shown sensitivity to the acute stressors experienced by defence personnel. This study examines the suitability of overnight HRV as a repeated measure of allostatic load in defence personnel.

METHODS

Daily measures of sleep, cognitive load and perceived exertion were reported for the 12-week duration of basic military training (BMT) in 48 recruits. Measures of physical activity, subjective wellbeing and HRV were measured weekly. The natural log of the root mean square of successive differences of inter-beat intervals (Ln RMSSD) and the Ln RMSSD to inter-beat interval ratio (Ln RMSSD:RRi ratio) during predicted slow wave sleep were used for HRV. Physical performance was assessed via the 20-m shuttle run and maximal push-up test in week two and eight of BMT with predicted V̇O2 peak values calculated.

RESULTS

Predicted V̇O2 peak increased from 42.6 ± 4.5 to 48.0 ± 2.7 mL·kg·min (p < 0.001). Ln RMSSD was elevated in week seven and ten and the Ln RMSSD:RRi ratio was elevated in week ten above all other weeks (p < 0.05). An increase in perceived exertion (F = 9.10, p = 0.003) and subjective fatigue (F = 6.97, p = 0.009), as well as a reduction in V̇O2 peak (F = 7.95, p = 0.009), individually predicted an increase in Ln RMSSD. The best predictive model of Ln RMSSD included perceived exertion (F = 8.16, p = 0.005), subjective fatigue (F = 8.49, p = 0.004), the number of awakenings during sleep (F = 7.79, p = 0.006) and the change in V̇O2 peak (F = 19.110, p < 0.001).

CONCLUSIONS

HRV was predicted by subjective recruit responses to BMT workloads rather than objective measures of physical activity. Improvements in cardiorespiratory fitness depicted recruits who experienced enough stress to facilitate physiological adaptation which was reflected by a reduction in HRV during BMT. Monitoring HRV and HRV in relation to inter-beat interval length may provide a better tool for determining allostatic load than HRV alone.

Slow deep breathing modulates cardiac vagal activity but does not affect peripheral glucose metabolism in healthy men

Parasympathetic nervous system innervates peripheral organs including pancreas, hepatic portal system, and gastrointestinal tract. It thereby contributes to the regulation of whole-body glucose metabolism especially in the postprandial state when it promotes secretion of insulin and enhances its action in major target organs. We now aimed to evaluate the effect of parasympathetic modulation on human glucose metabolism. We used slow deep breathing maneuvers to activate the parasympathetic nervous system and tested for effects on metabolism during an oral glucose tolerance test in a randomized, controlled, cross-over trial in 15 healthy young men. We used projections towards the heart as a readout for parasympathetic activity. When analyzing heart rate variability, there was a significant increase of RMSSD (root mean square of successive differences) when participants performed slow deep breathing compared to the control condition, indicating a modulation of parasympathetic activity. However, no statistically significant effects on peripheral glucose metabolism or energy expenditure after the glucose tolerance test were detected. Of note, we detected a significant association between mean heart rate and serum insulin and C-peptide concentrations. While we did not find major effects of slow deep breathing on glucose metabolism, our correlational results suggest a link between the autonomic nervous system and insulin secretion after oral glucose intake. Future studies need to unravel involved mechanisms and develop potential novel treatment approaches for impaired insulin secretion in diabetes.

Development and validation of an integrated portable heart rate variability (HRV) analysis system - STREME

In this paper, we introduce an integrated, portable, affordable and simple to use heart rate variability (HRV) analysis tool STREME. The system consists of an ECG acquisition device and software for HRV analysis. We assessed the reliability and validity of using STREME against the reference standards RMS VarioWin and Kubios HRV for the short term HRV analysis. The validation study was carried out with the participation of 46 healthy subjects that included 15 men and 31 women with an average age of 27.67 ± 7.75yrs. The results showed that there is a significantly strong correlation (r > 0.95, p < 0.001) between STREME and reference systems in HRV indices. The Bland-Altman analysis of all features computed from STREME and reference system represent a close agreement for all the parameters. Hence STREME HRV analysis tool can be recommended to researchers and other professionals for the evaluation of autonomic function using short term HRV.

TESTING THE VAGAL WITHDRAWAL HYPOTHESIS DURING LIGHT EXERCISE UNDER AUTONOMIC BLOCKADE: A HEART RATE VARIABILITY STUDY

INTRODUCTION

We performed the first analysis of heart rate variability (HRV) at rest and exercise under full autonomic blockade on the same subjects, to test the conjecture that vagal tone withdrawal occurs at exercise onset. We hypothesized that, between rest and exercise: i) no differences in total power (PTOT) under parasympathetic blockade; ii) a PTOT fall under β1-sympathetic blockade; iii) no differences in Ptot under blockade of both ANS branches.

METHODS

7 males (24±3 years) performed 5-min cycling (80W) supine, preceded by 5-min rest during control and with administration of atropine, metoprolol and atropine+metoprolol (double blockade). Heart rate and arterial blood pressure were continuously recorded. HRV and blood pressure variability were determined by power spectral analysis, and baroreflex sensitivity (BRS) by the sequence method.

RESULTS

At rest, PTOT and the powers of low (LF) and high (HF) frequency components of HRV were dramatically decreased in atropine and double blockade compared to control and metoprolol, with no effects on LF/HF ratio and on the normalised LF (LFnu) and HF (HFnu). At exercise, patterns were the same as at rest. Comparing exercise to rest, PTOT varied as hypothesized. For SAP and DAP, resting P_TOT was the same in all conditions. At exercise, in all conditions, P_TOT was lower than in control. BRS decreased under atropine and double blockade at rest, under control and metoprolol during exercise.

CONCLUSIONS

The results support the hypothesis that vagal suppression determined disappearance of HRV during exercise.

Beta-Adrenergic Blockade Therapy for Autonomic Dysfunction is Less Effective for Elderly Patients with Heart Failure and Reduced Left Ventricular Ejection Fraction

OBJECTIVE

Heart rate variability (HRV) has been reported to be an independent predictor of all-cause and sudden cardiac death in patients with heart failure. In the aging heart, however, both autonomic and cardiac functions appear to be altered. We assessed the relationship between aging and responsiveness of HRV and ventricular remodeling to beta-adrenergic blockade therapy in patients with heart failure and reduced ejection fraction (HFREF).

METHODS

Twenty-eight clinically stable patients with chronic heart failure, sinus rhythm, and left ventricular ejection fraction <50% as confirmed by echocardiography were included. At baseline and after carvedilol treatment, 24-hour ambulatory Holter monitor recording was used to analyze HRV indices by the maximum entropy method. Changes in these parameters were compared among three age groups.

RESULTS

HR decreased in all groups after carvedilol treatment, but was still highest in the youngest group despite the same treatment doses. Time and frequency domain variables improved. The response of time domain variables (the standard deviation of all normal sinus to normal sinus [NN] intervals and the standard deviation of the averages of NN intervals in all 5-minute or 30-minute segments) to carvedilol therapy significantly decreased with increasing age. Ventricular reverse remodeling induced by carvedilol therapy significantly decreased with increasing age. Increases in time domain variables and a low-frequency domain moderately correlated with left ventricular reverse remodeling.

CONCLUSION

Beta-adrenergic blockade therapy improved HRV variables and ventricular remodeling in HFREF patients; however, the response tended to be milder in the elderly. HRV improvement was associated with ventricular reverse remodeling.

Is 5-minute heart rate variability a useful measure for monitoring the autonomic nervous system of workers?

Heart rate variability (HRV) is a noninvasive physiological marker used to assess autonomic nervous function and can be recorded over the short or long term. Long-term recording is a good method for assessing mortality and patient prognosis, while short-term measurement is widely used due to practical advantages and reproducibility. However, little is known about whether a short-term assessment reflects the variation in the overall heart rate of workers. This study evaluated the relationship between the 24-hour and 5-minute HRV, which was selected from a 24-hour recording. The study population was 153 male workers at the National Rail Company in Korea, who had their heart rates assessed for 24 hours. In the time and frequency domains, the correlations of the HRV between 24 hours and 5 minutes were calculated for the entire time and limited times (09:00-17:00). We found modest correlations in the time (R = 0.614-0.668) and frequency (R = 0.508-0.817) domains, but the best correlation was for the high-frequency spectra (HF; R = 0.817). Our findings suggest that the short-term HRV remains stable and may be applicable for screening the variation in the heart rate of workers, although not all of the correlations were sufficiently strong.

Assessment of autonomic function in cardiovascular disease: physiological basis and prognostic implications

Certain abnormalities of autonomic function in the setting of structural cardiovascular disease have been associated with an adverse prognosis. Various markers of autonomic activity have received increased attention as methods for identifying patients at risk for sudden death. Both the sympathetic and the parasympathetic limbs can be characterized by tonic levels of activity, which are modulated by, and respond reflexively to, physiological changes. Heart rate provides an index of the net effects of autonomic tone on the sinus node, and carries prognostic significance. Heart rate variability, though related to heart rate, assesses modulation of autonomic control of heart rate and carries additional prognostic information, which in some cases is more powerful than heart rate alone. Heart rate recovery after exercise represents the changes in autonomic tone that occur immediately after cessation of exercise. This index has also been shown to have prognostic significance. Autonomic evaluation during exercise and recovery may be important prognostically, because these are high-risk periods for sudden death, and the autonomic changes that occur with exercise could modulate this high risk. These markers provide related, but not redundant information about different aspects of autonomic effects on the sinus node.

Changes in Heart Rate Variability Are Correlated to Hemodynamic Improvement With Chronic CARVEDILOL Therapy in Heart Failure

BACKGROUND

Reduced heart rate variability (HRV) has been shown to predict mortality in heart failure (CHF). The relationship between improved cardiac function and improvement in HRV has not been previously studied.

METHODS AND RESULTS

This was substudy of a randomized, placebo-controlled, double-blinded trial of carvedilol of four months duration. Analysis of HRV was performed on 24-hour Holter monitors obtained at baseline and completion of study. All subjects had symptomatic CHF and an left ventricular ejection fraction (LVEF) <0.35. Study medication was titrated over 1 month to 50 mg/day (< or =75 kg) or 100 mg/day (<75 kg). A total of 17 subjects were randomized to carvedilol and 12 to placebo. Treatment with carvedilol was associated with significant increases in total frequency power, very low frequency power, high frequency power, SDNN, the root-mean square of difference of successive RRs, and pNN50. Change in time and frequency domain measures of HRV had a positive correlation with change in LVEF and negative correlation with change in coronary sinus norepinephrine levels.

CONCLUSION

Carvedilol therapy in patients with CHF significantly increased HRV. Change in HRV correlates to improved hemodynamics. This suggests that carvedilol therapy partially normalizes autonomic modulation of heart rate in patients with CHF.

Effect of remifentanil with and without atropine on heart rate variability and RR interval in children

Remifentanil can cause bradycardia either by parasympathetic activation or by other negative chronotropic effects. The high frequency (HF) component of heart rate variability (HRV) is a marker of parasympathetic activity. This study aimed to evaluate the effect of remifentanil on RR interval and on HRV in children. Forty children ASA I or II were studied after approval by the human studies committee and informed parental consent was obtained. After stabilisation at sevoflurane 1 MAC, they were randomly divided into two groups: one received a 20 microg.kg(-1) atropine injection (AT + REMI) and the other ringer lactate solution (REMI). Three minutes later, a 1 microg.kg(-1) bolus of remifentanil was administered over 1 min, followed by a continual infusion at 0.25 microg.kg(-1).min(-1) for 10 min increased to 0.5 microg.kg(-1).min(-1) for a further 10 min. A time varying, autoregressive analysis of RR sequences was used to estimate classical spectral parameters: low (0.04-0.15 Hz; LF) and high (0.15-0.45 Hz; HF) frequency, whereas the root mean square of successive differences of RR intervals (rmssd) was derived directly from the temporal sequence. Statistical analyses were conducted by means of the multiple correspondence analysis and with non parametrical tests. Remifentanil induced an RR interval lengthening, i.e. bradycardia, in both groups compared to pretreatment values and was associated with an increase of HF and rmssd only for the REMI group. The parasympathetic inhibition by atropine did not totally prevent remifentanil's negative chronotropic effect. A direct negative chronotropic effect of remifentanil is proposed.

Effect of endurance exercise on autonomic control of heart rate

Long-term endurance training significantly influences how the autonomic nervous system controls heart function. Endurance training increases parasympathetic activity and decreases sympathetic activity in the human heart at rest. These two training-induced autonomic effects, coupled with a possible reduction in intrinsic heart rate, decrease resting heart rate. Long-term endurance training also decreases submaximal exercise heart rate by reducing sympathetic activity to the heart. Physiological ageing is associated with a reduction in parasympathetic control of the heart; this decline in parasympathetic activity can be reduced by regular endurance exercise. Some research has indicated that females have increased parasympathetic and decreased sympathetic control of heart rate. These gender-specific autonomic differences probably contribute to a decreased cardiovascular risk and increased longevity observed in females.

Heart rate variability in critical illness and critical care

Although the rhythm of a healthy heart is clinically described as regular, the rate is variable. Studies of diverse populations have led to several generalizations about heart rate variability (HRV): (1) HRV is physiologic and normally declines with age, (2) acute changes in HRV are associated with several disease processes that require critical care, (3) measures of HRV can be used to describe the status of critically ill patients, and (4) measures of HRV can be used to predict events subsequent to at least one type of critical illness, myocardial infarction. This brief review considers the mechanisms underlying HRV, the measures that are used to describe HRV, and recent information regarding the use of HRV measures as predictive tools in critical care. The reviewers' opinion is that real-time analysis of HRV in critical illness may provide caregivers with additional information about patient status, effects of intervention, and prognosis.

Diminished circadian variation in heart rate variability before surgery in patients developing postoperative atrial fibrillation

OBJECTIVE

To evaluate the role of the autonomic nervous system for the development of atrial fibrillation (AF) after coronary artery bypass surgery.

DESIGN

Eighty patients without a previous history of AF were included. The sympathetic and parasympathetic activity were evaluated by the analysis of heart rate variability (HRV) in the frequency domain from 24-h Holter recordings and by measuring neuropeptides (neuropeptide Y, chromogranin A, chromogranin B, and pancreatic polypeptide (PP)) and catecholamines, obtained pre- and postoperatively.

RESULTS

Preoperatively, patients (36.3%) developing AF postoperatively showed a statistically significant less circadian variation in the HRV variables, the high-frequency (HF) component (p = 0.013) and the low-frequency (LF)/HF ratio (p = 0.007), than patients remaining in sinus rhythm. The HF component and PP. both reflecting parasympathetic activity, and all other variables in the frequency domain, decreased significantly after surgery in both patient groups (p < 0.0001). Although catecholamines increased significantly postoperatively in both patient groups, neither catecholamines nor neuropeptides expressing sympathetic activity, differed between the two groups. PP was, however, significantly higher in patients with postoperative AF than in those with sinus rhythm postoperatively on day 1.

CONCLUSION

The diminished circadian variation in HRV before surgery and the indirect signs of a higher parasympathetic activity in patients developing postoperative AF compared with patients remaining in sinus rhythm, may indicate a propensity for AF.