Reduction of long COVID symptoms after stellate ganglion block: A retrospective chart review study.

The SARS-CoV-2 pandemic has left millions of individuals with a host of post-viral symptoms that can be debilitating and persist indefinitely. To date there are no definitive tests or treatments for the collection of symptoms known as "Long COVID" or Post-acute sequelae of COVID-19 (PASC). Following our initial case report detailing improvement of Long COVID symptoms after sequential bilateral stellate ganglion blockade (SGB), we performed a retrospective chart analysis study on individuals treated with the same protocol over the course of six months (2021-2022) in our clinic. Patients self-reported symptoms on a 10-point scale as part of optional patient follow-up using an online survey. After one month or more following treatment, patients reported striking reductions in Fatigue, Worsening of Symptoms following Mental and Physical Activity, Memory Problems, Problems Concentrating, Sleep Problems, Anxiety, and Depression. Loss of Taste and Loss of Smell in some individuals did not respond to treatment, likely indicating structural damage following infection. This study suggests that neuromodulation may provide relief of Long COVID symptoms for at least a subset of individuals, and provides support for prospective studies of this potential treatment.

Post-adoption experiences of discrimination moderated by sleep quality are associated with depressive symptoms in previously institutionalized youth over and above deprivation-induced depression risk.

The association of post-adoption experiences of discrimination with depressive symptoms was examined in 93 previously institutionalized (PI) youth (84% transracially adopted). Additionally, we explored whether sleep quality statistically moderated this association. Notably, we examined these associations after covarying a measure of autonomic balance (high/low frequency ratio in heart rate variability) affected by early institutional deprivation and a known risk factor for depression. PI youth exhibited more depressive symptoms and experiences of discrimination than 95 comparison youth (non-adopted, NA) raised in their biological families in the United States. In the final regression model, there was a significant interaction between sleep quality and discrimination, such that at higher levels of sleep quality, the association between discrimination and depression symptoms was non-significant. Despite being cross-sectional, the results suggest that the risk of depression in PI youth involves post-adoption experiences that appear unrelated to the impacts of early deprivation on neurobiological processes associated with depression risk. It may be crucial to examine methods of improving sleep quality and socializing PI youth to cope with discrimination as protection against discrimination and microaggressions.

Voluntary wheel running as a promising strategy to promote autonomic resilience to social stress in females: Vagal tone lies at the heart of the matter.

Social stress is a major risk factor for comorbid conditions including cardiovascular disease and depression. While women exhibit 2-3× the risk for these stress-related disorders compared to men, the mechanisms underlying heightened stress susceptibility among females remain largely unknown. Due to a lack in understanding of the pathophysiology underlying stress-induced comorbidities among women, there has been a significant challenge in developing effective therapeutics. Recently, a causal role for inflammation has been established in the onset and progression of comorbid cardiovascular disease/depression, with women exhibiting increased sensitivity to stress-induced immune signaling. Importantly, reduced vagal tone is also implicated in stress susceptibility, through a reduction in the vagus nerve's well-recognized anti-inflammatory properties. Thus, examining therapeutic strategies that stabilize vagal tone during stress may shed light on novel targets for promoting stress resilience among women. Recently, accumulating evidence has demonstrated that physical activity exerts cardio- and neuro-protective effects by enhancing vagal tone. Based on this evidence, this mini review provides an overview of comorbid cardiovascular and behavioral dysfunction in females, the role of inflammation in these disorders, how stress may impart its negative effects on the vagus nerve, and how exercise may act as a preventative. Further, we highlight a critical gap in the literature with regard to the study of females in this field. This review also presents novel data that are the first to demonstrate a protective role for voluntary wheel running over vagal tone and biomarkers of cardiac dysfunction in the face of social stress exposure in female rats.

Exploring sleep heart rate variability: linear, nonlinear, and circadian rhythm perspectives.

Background: Heart rate variability (HRV) is believed to possess the potential for disease detection. However, early identification of heart disease remains challenging, as HRV analysis in dogs primarily reflects the advanced stages of the disease. Hypothesis/objective: The aim of this study is to compare 24-h HRV with sleep HRV to assess the potential utility of sleep HRV analysis. Animals: Thirty healthy dogs with no echocardiographic abnormalities were included in the study, comprising 23 females and 7 males ranging in age from 2 months to 8 years (mean [standard deviation], 1.4 [1.6]). Methods: This study employed a cross-sectional study. 24-h HRV and sleep HRV were measured from 48-h Holter recordings. Both linear analysis, a traditional method of heart rate variability analysis, and nonlinear analysis, a novel approach, were conducted. Additionally, circadian rhythm parameters were assessed. Results: In frequency analysis of linear analysis, the parasympathetic index nHF was significantly higher during sleep compared to the mean 24-h period (mean sleep HRV [standard deviation] vs. mean 24 h [standard deviation], 95% confidence interval, p value, r-family: 0.24 [0.057] vs. 0.23 [0.045], 0.006-0.031, p = 0.005, r = 0.49). Regarding time domain analysis, the parasympathetic indices SDNN and RMSSD were also significantly higher during sleep (SDNN: 179.7 [66.9] vs. 156.6 [53.2], 14.5-31.7, p < 0.001, r = 0.71 RMSSD: 187.0 [74.0] vs. 165.4 [62.2], 13.2-30.0, p < 0.001, r = 0.70). In a geometric method of nonlinear analysis, the parasympathetic indices SD1 and SD2 showed significantly higher values during sleep (SD1: 132.4 [52.4] vs. 117.1 [44.0], 9.3-21.1, p < 0.001, r = 0.70 SD2: 215.0 [80.5] vs. 185.9 [62.0], 17.6-40.6, p < 0.001, r = 0.69). Furthermore, the circadian rhythm items of the parasympathetic indices SDNN, RMSSD, SD1, and SD2 exhibited positive peaks during sleep. Conclusion: The findings suggest that focusing on HRV during sleep can provide a more accurate representation of parasympathetic activity, as it captures the peak circadian rhythm items.

Unveiling gender differences in psychophysiological dynamics: support for a two-dimensional autonomic space approach.

Introduction: To date, studies focusing on the connection between psychological functioning and autonomic nervous system (ANS) activity usually adopted the one-dimensional model of autonomic balance, according to which activation of one branch of the ANS is accompanied by an inhibition of the other. However, the sympathetic and parasympathetic branches also activate independently; thus, co-activation and co-inhibition may occur, which is demonstrated by a two-dimensional model of ANS activity. Here, we apply such models to assess how markers of the autonomic space relate to several critical psychological constructs: emotional contagion (EC), general anxiety, and positive and negative affect (PA and NA). We also examined gender differences in those psychophysiological relations. Methods: In the present study, we analyzed data from 408 healthy students, who underwent a 5-min group baseline period as part of their participation in several experiments and completed self-reported questionnaires. Electrocardiogram (ECG), electrodermal activity (EDA), and respiration were recorded. Respiratory sinus arrhythmia (RSA), pre-ejection period (PEP), as well as cardiac autonomic balance (CAB) and regulation (CAR) and cross-system autonomic balance (CSAB) and regulation (CSAR), were calculated. Results: Notably, two-dimensional models were more suitable for predicting and describing most psychological constructs. Gender differences were found in psychological and physiological aspects as well as in psychophysiological relations. Women's EC scores were negatively correlated with sympathetic activity and positively linked to parasympathetic dominance. Men's PA and NA scores were positively associated with sympathetic activity. PA in men also had a positive link to an overall activation of the ANS, and a negative link to parasympathetic dominance. Discussion: The current results expand our understanding of the psychological aspects of the autonomic space model and psychophysiological associations. Gender differences and strengths and weaknesses of alternative physiological models are discussed.

Parameters of Heart Rate Variability in Male Wistar Rats under Conditions of Different Motor Activity.

We studied heart rate variability indexes in freely moving male Wistar rats at rest and under conditions of increased motor activity (treadmill exercise). Some regularities were revealed in the dynamics of HR, RRNN, Mo, indicator of the adequacy of regulation processes, VLF (msec2, %), HF, LF (%), LF/HF, and IC that characterize changes in the neurohumoral regulation and shifts in the level of cardiac rhythm control at the different stages of the experiment. It was found that changes in motor activity of male Wistar rats were accompanied by the transition of the functional state of the organism to a new level of regulation, which was confirmed by the dynamics of HR, RRNN, Mo, LF, VLF, LF/HF, and IC. These findings can be used as prognostic indicators for assessment of regulatory mechanisms in the body.

Autonomic Correlates of Letter Cancelation Task: What the Attention Load May Evoke?

OBJECTIVE: Attention can be assessed through Letter cancelation tasks (LCT) that employ visuospatial selection and appropriate motor responses. We examined the performance in the LCT with increasing attention load, and determined the related autonomic changes. METHODS: Autonomic parameters were estimated in healthy males at baseline and during three different cognitive load conditions using the LCT. RESULTS: Results revealed a statistically significant difference (n = 30) in the percent accuracy (χ2(2) = 15.2, p < .001) and percent omission (χ2(2) = 13.3, p = 0.001) with the increasing challenge in the LCT. The vagally-mediated measures of heart rate variability were significantly decreased with the commencement of the task revealing a parasympathetic withdrawal. The respiratory sinus arrythmia was decreased, and the photoplethysmography amplitude was significantly reduced (χ2(3) = 14.2, p = 0.003) as the attention demand increased. CONCLUSION: The performance declined with the increasing attention load. LCT evokes autonomic perturbations though overall autonomic variability does not change remarkably.

Effects of Therapeutic Calf Massage on Cardiac Autonomic Function in Healthy Volunteers-a Pilot Study.

Background: Calf massage is a therapeutic intervention that improves circulation and relieves us from pain & tightness. The calf massage also improves autonomic performance by modulating the vagal tone of the cardiovascular system. Therefore, the current study was intended to determine therapeutic calf massage on cardio autonomic activity in healthy subjects. Objective: To assess the immediate effect of a single 20-min session of calf massage on cardiac autonomic modulation through heart rate variability (HRV) measurement. Materials & Methods: In this study, 26 apparent healthy female participants aged between 18 and 25 years participated. Massage over the calf muscles on both legs for 20 min was performed, and resting cardiovascular parameters and HRV parameters were measured at baseline, immediately after the massage, and during the recovery periods (10 and 30 min after the massage). Data were analyzed using one-way ANOVA followed with post hoc analysis. Results: Immediately after the massage intervention, heart rate (HR), systolic (SBP), and diastolic (DBP) blood pressure were decreased (p < .01), and the reduction was persisted at 10 min and 30 min of the recovery period (p < .01). In HRV parameters, the root mean square of successive differences (RMSSD) and high-frequency normalized unit (HF n.u.) increased, and low frequency (LF n.u.) decreased after the massage, and at the 10 and 30 min of the recovery period. Conclusion: The present study reports suggest a significant reduction in heart rate and blood pressure after the massage therapy. A drop in sympathetic tone and raise in parasympathetic tone can also attribute to the therapeutic effect.

The role of youths' cardiac autonomic balance and parental responses to youth emotion in vulnerability to borderline personality disorder development.

Developmental models of borderline personality disorder (BPD) emphasize the effects of youths' biological vulnerabilities and their experiences of parental responses to emotion, as well as the interaction between these two elements. The current study evaluated the independent and interactive effects of two indices of autonomic nervous system response and parental responses to youth negative emotions on severity and exacerbation of youths' BPD features during the transition to adolescence. The sample consisted of 162 psychiatric youth (10-14 years; 47.2% female) and their parents. At baseline, youth and their parents completed a lab-based conflict discussion during which parasympathetic and sympathetic nervous system response were measured and indices of sympathetic-parasympathetic balance and coactivation/coinhibition were calculated. Youth also reported on supportive and non-supportive parental responses. At baseline and after 9 months, youth self-reported on their BPD features. Results demonstrated that shifting toward sympathetic dominance independently predicted exacerbation of BPD across 9 months. Additionally, fewer experiences of supportive parental responses and more non-supportive parental responses were associated with greater severity of BPD features in youth. This study highlights the role of autonomic response to parent-child conflict as well as the significance of parental responses to youth emotion for the development of BPD during this developmental window.

Effects of Temporary Respiration Exercise with Individual Harmonic Frequency on Blood Pressure and Autonomic Balance.

This study investigated the effects of modulated respiration on blood pressure and autonomic balance to develop a healthcare application system for stabilizing autonomic balance. Thirty-two participants were asked to perform self-regulated tasks with 18 different respiration sequences, and their electrocardiograms (ECG) and blood pressure were measured. Changes in cardiovascular system functions and blood pressure were compared between free-breathing and various respiration conditions. Systolic and diastolic blood pressures stabilized after individual harmonic breathing. Autonomic balance, characterized by heart rate variability, was also stabilized with brief respiration training according to harmonic frequency. Five machine-learning algorithms were used to classify the two opposing factors between the free and modulated breathing conditions. The random forest models outperformed the other classifiers in the training data of systolic blood pressure and heart rate variability. The mean areas under the curves (AUCs) were 0.82 for systolic blood pressure and 0.98 for heart rate variability. Our findings lend support that blood pressure and autonomic balance were improved by temporary harmonic frequency respiration. This study provides a self-regulated respiration system that can control and help stabilize blood pressure and autonomic balance, which would help reduce mental stress and enhance human task performance in various fields.

Heart Rate Variability Biofeedback in Cancer Patients: A Scoping Review.

Heart Rate Variability (HRV) Biofeedback (BFB) has been shown to improve autonomic balance and wellbeing in chronic diseases. As cardiac variability represents an index of cognitive and emotional regulation, HRV-BFB has been shown to lead to improvements in physiological and psychological adaptability and quality of life. However, knowledge of HRV-BFB in cancer patients is lacking, and available results are diversified according to methods and outcomes. The present paper undertakes a scoping review, exploring the use of HRV-BFB to modulate autonomic balance, cancer symptom management, and quality of life in cancer. This scoping review analyzes empirical evidence considering study designs, BFB methods, and psychophysiological outcomes. Research that focused on HRV-BFB effects in cancer patients was selected (79%). In addition, a systematic review and meta-analysis (31%) focusing on HRV, or BFB in chronic conditions, including cancer, were considered. The studies examined BFB treatment for thyroid, lung, brain or colon cancer, hematologic cancer, and survivors or terminal cancer patients. Retrieved studies reported physiological and psychological indices as primary outcomes: they included HRV values, sleep, pain, fatigue, depression, anxiety, and quality of life. Although the heterogeneity of publications makes it difficult to generalize the effectiveness of HRV-BFB, the training has been proven to improve cancer symptoms and well-being.

Effects of Chronic Mild Stress on Cardiac Autonomic Activity, Cardiac Structure and Renin-Angiotensin-Aldosterone System in Male Rats.

Stress is associated with cardiovascular disease. One accepted mechanism is autonomic imbalance. In this study, we investigated the effects of chronic mild stress (CMS) on cardiac autonomic control, cardiac structure and renin-angiotensin-aldosterone system (RAAS) activity in adult male Sprague Dawley rats. The CMS model provides a more realistic simulation of daily stress. The animals were divided into control and CMS, and were exposed to 4-week mild stressors. The electrocardiogram recording, sucrose intake and parameters related to stress, cardiac alterations and RAAS were determined. The results showed that CMS had lower body weight and higher sucrose intake. The heart rate variability (HRV) revealed that CMS increased autonomic activity without affecting its balance. The increased RAAS activity with upregulated angiotensin type 1 receptor mRNA expression was shown in CMS. The increased sympathetic activity or RAAS was correlated with stress. Moreover, the altered cardiac structure (i.e., heart weight and cardiomyocyte cross-sectional area) were correlated with stress-, sympathetic- and RAAS-related parameters. These indicated that CMS-induced cardiac hypertrophy was the result of both sympathetic and RAAS activation. Therefore, it could be concluded that 4-week CMS in male rats induced negative emotion as shown by increased sucrose intake, and increased cardiac autonomic and RAAS activities, which may be responsible for mild cardiac hypertrophy. The cardiac hypertrophy herein was possibly in an adaptive, not pathological, stage, and the cardiac autonomic function was preserved as the autonomic activities were in balance.

Sex differences in autonomic responses to stress: implications for cardiometabolic physiology.

Chronic stress is a significant risk factor for negative health outcomes. Furthermore, imbalance of autonomic nervous system control leads to dysregulation of physiological responses to stress and contributes to the pathogenesis of cardiometabolic and psychiatric disorders. However, research on autonomic stress responses has historically focused on males, despite evidence that females are disproportionality affected by stress-related disorders. Accordingly, this mini-review focuses on the influence of biological sex on autonomic responses to stress in humans and rodent models. The reviewed literature points to sex differences in the consequences of chronic stress, including cardiovascular and metabolic disease. We also explore basic rodent studies of sex-specific autonomic responses to stress with a focus on sex hormones and hypothalamic-pituitary-adrenal axis regulation of cardiovascular and metabolic physiology. Ultimately, emerging evidence of sex differences in autonomic-endocrine integration highlights the importance of sex-specific studies to understand and treat cardiometabolic dysfunction.

The autonomic balance of heart rhythm complexity after renal artery denervation: insight from entropy of entropy and average entropy analysis.

BACKGROUND: The current method to evaluate the autonomic balance after renal denervation (RDN) relies on heart rate variability (HRV). However, parameters of HRV were not always predictive of response to RDN. Therefore, the complexity and disorder of heart rhythm, measured by entropy of entropy (EoE) and average entropy (AE), have been used to analyze autonomic dysfunction. This study evaluated the dynamic changes in autonomic status after RDN via EoE and AE analysis. METHODS: Five patients were prospectively enrolled in the Global SYMPLICITY Registry from 2020 to 2021. 24-h Holter and ambulatory blood pressure monitoring (ABPM) was performed at baseline and 3 months after RDN procedures. The autonomic status was analyzed using the entropy-based AE and EoE analysis and the conventional HRV-based low frequency (LF), high frequency (HF), and LF/HF. RESULTS: After RDN, the ABPM of all patients showed a significant reduction in blood pressure (BP) and heart rate. Only AE and HF values of all patients had consistent changes after RDN (p < 0.05). The spearman rank-order correlation coefficient of AE vs. HF was 0.86, but AE had a lower coefficient of variation than HF. CONCLUSIONS: Monitoring the AE and EoE analysis could be an alternative to interpreting autonomic status. In addition, a relative change of autonomic tone, especially an increasing parasympathetic activity, could restore autonomic balance after RDN.

Mechanisms underlying the blood pressure lowering effects of dapagliflozin, exenatide, and their combination in people with type 2 diabetes: a secondary analysis of a randomized trial.

BACKGROUND: Sodium-glucose cotransporter-2 inhibitors (SGLT2i) and glucagon-like peptide-1 receptor agonists (GLP-1RA) lower blood pressure (BP). When SGLT2i and GLP-1RA are combined, synergistic effects on BP have been observed. The mechanisms underlying these BP reductions are incompletely understood. The aim of this study was to assess the mechanisms underlying the BP reduction with the SGLT2i dapagliflozin, GLP-1RA exenatide, and dapagliflozin-exenatide compared with placebo in people with obesity and type 2 diabetes. METHODS: Sixty-six people with type 2 diabetes were randomized to 16 weeks of dapagliflozin 10 mg/day, exenatide 10 µg twice daily, dapagliflozin-exenatide, or placebo treatment. The effect of treatments on estimates of: (1) plasma volume (calculated by Strauss formula, bioimpedance spectroscopy, hematocrit, (2) autonomic nervous system activity (heart rate variability), (3) arterial stiffness (pulse wave applanometry), (4) systemic hemodynamic parameters including peripheral vascular resistance, cardiac output and stroke volume (all derived from non-invasively systemic hemodynamic monitoring), and (5) natriuresis (24-hour urine collection) were assessed after 10 days and 16 weeks of treatment. RESULTS: After 10 days, dapagliflozin reduced systolic BP (SBP) by - 4.7 mmHg, and reduced plasma volume. After 16 weeks, dapagliflozin reduced SBP by - 4.4 mmHg, and reduced sympathetic nervous system (SNS) activity. Exenatide had no effect on SBP, but reduced parasympathetic nervous system activity after 10 days and 16 weeks. After 10 days, dapagliflozin-exenatide reduced SBP by - 4.2 mmHg, and reduced plasma volume. After 16 weeks, dapagliflozin-exenatide reduced SBP by - 6.8 mmHg, and the reduction in plasma volume was still observed, but SNS activity was unaffected. CONCLUSIONS: The dapagliflozin-induced plasma volume contraction may contribute to the initial SBP reduction, while a reduction in SNS activity may contribute to the persistent SBP reduction. Dapagliflozin-exenatide resulted in the largest decrease in SBP. The effect on plasma volume was comparable to dapagliflozin monotherapy, and SNS activity was not reduced, therefore other mechanisms are likely to contribute to the blood pressure lowering effect of this combination, which need further investigation. Trial registration Clinicaltrials.gov, NCT03361098.

Cardiac autonomic functioning across stress and reward: Links with depression in emerging adults.

The autonomic nervous system (ANS) has received much attention as a potential low-cost, peripheral indicator of depression. Despite theoretical support, however, results have been mixed as to whether indices of the ANS reliably index depression. In response, the present study sought to clarify the relation between ANS activity and depression by examining cardiac autonomic balance (CAB) and cardiac autonomic regulation (CAR), two composite indices of the parasympathetic and sympathetic nervous system, within both a stressful and rewarding context. We hypothesized that CABStress, representing the difference between the parasympathetic and sympathetic branches in response to stress, and CARReward, representing the summation of the two branches in response to reward, will be most indicative of depressogenic risk. We examined the parasympathetic (i.e., respiratory sinus arrhythmia) and sympathetic (i.e., pre-ejection period) responses of 97 emerging adults (Mage = 18.93) for a stress (i.e., negative mood induction) and reward (i.e., probabilistic learning) task, as well as their depressive symptoms at baseline, 3-week, and 6-week follow-up. Analyses found partial support for our hypotheses, revealing greater CARReward (i.e., coactivation of both branches) was related to lower depressive symptoms. Further, exploratory analyses examining gender differences found lower CABStress (i.e., sympathetically-oriented response) was predictive of an increasing trajectory of depression, but only among males. Overall, the current study highlights the importance of simultaneously examining both branches of the ANS across various environmental contexts. Research and clinical implications of the current findings are discussed.

A Close Examination of the Use of Systolic Time Intervals in the Calculation of Impedance Derived Cardiac Autonomic Balance and Regulation.

Traditionally, impedance derived measures of cardiac autonomic balance (CAB) and regulation (CAR) are calculated using indices of heart rate variability (HRV) that primarily reflect parasympathetic nervous system activity (e.g., high-frequency HRV | HF-HRV) and pre-ejection period (PEP; a systolic time interval and measure of sympathetic activity). However, HF-HRV and PEP are considered measures of chronotropic and inotropic cardiac influence, respectively. Left ventricular ejection time (LVET) is a systolic time interval that reflects sympathetic chronotropic influence, and therefore may be a more appropriate measure for calculating CAB and CAR compared to PEP. Thus, the current study evaluates both PEP and LVET in the calculation of CAB and CAR. Data from 158 healthy participants (mean age = 19.09 years old, SD = 1.84 years) were available for analyses. CAB and CAR values were calculated using both HF-HRV and the root mean square of successive differences, in addition to both PEP and LVET, in accordance with previously established guidelines. Analyses showed that correlations were significantly weaker between CAB and CAR calculated using LVET for both HF (z = 5.12, p < 0.001) and RMSSD (z = 5.26, p < 0.001) than with PEP. These data suggest that LVET, compared to PEP, provides better "autonomic space" as evidenced by a lack of correlation between CAB and CAR computed using LVET. We stress that future research consider calculating CAB and CAR using chronotropic measures for both parasympathetic and sympathetic activity, as doing so may yield more accurate and independent measures of cardiac autonomic activity compared to a mixture of inotropic (i.e., PEP) and chronotropic (i.e., HF-HRV) measures.

Only time will tell: Acute stress response patterns with time series analysis.

Acute stress is often conceptualized as a response pattern that activates the fight-or-flight response via the sympathetic nervous system (SNS). However, other stress response patterns can manifest as well, such as parasympathetic nervous system (PNS) shutdown, and SNS-PNS coactive hypervigilance. Each response pattern engages many dimensions, including physiological, emotional, and behavioral. As stress unfolds over time, these patterns can change to adjust to the changing nature of the stressor. This proof of concept study introduces novel time series methodology to track the multidimensional patterns of acute stress. The defense cascade provides a model with which to understand and predict response patterns over the time course of an acute stressor. The time series methodology introduced in this study holds promise for identifying mechanisms of change in therapy and clinical settings.

Heart Rate Variability Monitoring during Interferential Current Application in the Lower Back Area: A Cross-Sectional Study.

Vasovagal reactions may occur occasionally during electrical stimulation using interferential current (IFC). The purpose of this study was to examine variations in autonomic activity during the application of IFC in asymptomatic participants by analysis of their heart rate variability (HRV). Seventy-three male volunteers were randomly assigned to a placebo group (n = 36; HRV was documented for 10 min, both at rest and during a placebo intervention) and an intervention group (n = 37; HRV was documented for 10 min in two conditions labelled as (1) rest and (2) application of IFC technique on the lumbar segment). The diameters of the Poincaré plot (SD1, SD2), stress score (SS), and the ratio between sympathetic and parasympathetic activity (S/PS) were measured. After interventions, differences amongst the placebo group and the IFC group were found in SD2 (p < 0.001), SS (p = 0.01) and S/PS ratio (p = 0.003). The IFC technique was associated with increased parasympathetic modulation, which could induce a vasovagal reaction. Monitorization of adverse reactions should be implemented during the application of IFC technique. HRV indicators might have a part in prevention of vasovagal reactions. Further studies in patients with lumbar pain are needed to explore possible differences in HRV responses due to the presence of chronic pain.