The Effects of Transcranial Direct Current Stimulation on Heart Rate Variability and Cardiac Autonomic Function: A Systematic Review

Maternal Pregnancy Diet Quality Is Directly Associated with Autonomic Nervous System Function in 6-Month-Old Offspring

Objective To investigate the characteristics of heart rate variability (HRV) of ambulatory electrocardiogram in patients with acute stroke, and evaluate the predictive value of HRV in stroke prognosis. Methods Eighty-three patients acute stroke (study group) and 83 cases of healthy subjects (control group) from October 2016 to October 2017 in Dalian Municipal Central Hospital Affiliated of Dalian Medical University were selected. The 24 h ambulatory electrocardiogram was performed to determine HRV in 2 groups, including standard deviation of NN intervals (SDNN), standard deviation of the 5 min mean cycle lengths (SDANN), root-mean-square successive difference (RMSSD) and percentage value of NN50 count (PNN50). Results The SDNN, SDANN, RMSSD and PNN50 in study group were significantly lower than those in control group: (80.83 ± 10.52) ms vs. (148.11 ± 22.59) ms, (79.98 ± 8.89) ms vs. (129.35 ± 5.34) ms, (19.28 ± 4.25) ms vs. (39.57 ± 2.38) ms and (5.91 ± 2.12)% vs. (19.35 ± 12.15)%, and there were statistical differences (P 0.05). The SDNN, SDANN, RMSSD and PNN50 in right stroke (43 cases) were significantly lower than those in left stroke (40 cases):(75.18 ± 2.32) ms vs. (88.12 ± 3.58) ms, (73.36 ± 2.18) ms vs. (85.69 ± 7.29) ms, (17.57 ± 1.67) ms vs. (20.58 ± 4.23) ms and (4.39 ± 1.57)% vs. (8.61 ± 1.12)%, and there were statistical differences (P<0.05). Patients were followed up for 1 year, 24 died and 59 survived. The SDNN, SDANN, RMSSD and PNN50 in dead patients were significantly lower than those in survived patients: (92.35 ± 4.58) ms vs. (154.37 ± 4.65) ms, (76.23 ± 4.03) ms vs. (143.95 ± 4.34) ms, (7.43 ± 2.12) ms vs. (31.65 ± 1.52) ms and (2.35 ± 0.46)% vs. (11.65 ± 0.48)%, and there were statistical differences (P<0.05). Conclusions The autonomic nervous function of patients with acute stroke is seriously unbalanced, with increased sympathetic excitability and decreased vagus excitability. The decrease of HRV can easily induce cardiac events and seriously affect the prognosis. Key words: Stroke; Prognosis; Heart rate viability; Autonomic nervous function

Heart rate variability (HRV) is a non-invasive measure of autonomic function. The relationship between unselected long-term traumatic injury (TI) and HRV has not been investigated. This systematic review examines the impact of non-acute TI (>7 days post-injury) on standard HRV indices in adults. Four electronic databases (CINAHL, Medline, Scopus, and Web of Science) were searched. The quality of studies, risk of bias (RoB), and quality of evidence (QoE) were assessed using Axis, RoBANS and GRADE, respectively. Using the random-effects model, mean difference (MD) for root mean square of successive differences (RMSSD) and standard deviation of NN-intervals (SDNN), and standardized mean difference (SMD) for Low-frequency (LF): High-Frequency (HF) were pooled in RevMan guided by the heterogeneity score (I2). 2152 records were screened followed by full-text retrieval of 72 studies. 31 studies were assessed on the inclusion and exclusion criteria. Only four studies met the inclusion criteria. Three studies demonstrated a high RoB (mean RoBANS score 14.5±3.31) with a low QoE. TI was associated with a significantly higher resting heart rate. Meta-analysis of three cross-sectional studies demonstrated a statistically significant reduction in RMSSD (MD -8.45ms, 95%CI-12.78, -4.12, p<0.0001) and SDNN (MD -9.93ms, 95%CI-14.82, -5.03, p<0.0001) (low QoE) in participants with TI relative to the uninjured control. The pooled analysis of four studies showed a higher LF: HF ratio among injured versus uninjured (SMD 0.20, 95%CI 0.01–0.39, p<0.04) (very low QoE). Albeit low QoE, non-acute TI is associated with attenuated HRV indicating autonomic imbalance. The findings might explain greater cardiovascular risk following TI.Trial registration PROSPERO registration number: CRD: CRD42021298530.

Epilepsy is associated with near-fatal and fatal arrhythmias, and sudden unexpected death in epilepsy (SUDEP) is partly related to cardiac events. Dysfunction of the autonomous nervous system causes arrhythmias and, although previous studies have investigated the effects of epilepsy on the autonomic control of the heart, the results are still mixed regarding whether imbalance of sympathetic, vagal, or both systems is present in epilepsy, and also the importance of anticonvulsant treatment on the autonomic system. Therefore, we aimed to investigate epilepsy and its treatment impact on heart rate variability (HRV), assessed by sympathetic and parasympathetic activity expressed as low-frequency (LF) and high-frequency (HF) power spectrum, respectively. We performed a systematic review from the first date available to July 2011 in Medline and other databases; key search terms were "epilepsy"; "anticonvulsants"; "heart rate variability"; "vagal"; and "autonomous nervous system." Original studies that reported data and/or statistics of at least one HRV value were included, with data being extracted by two independent authors. We used a random-effects model with Hedges's g as the measurement of effect size to perform two main meta-analyses comparing LF and HF HRV values in (1) epilepsy patients versus controls; (2) patients receiving versus not receiving treatment; and (3) well-controlled versus refractory patients. Secondary analyses assessed other time- and frequency-domain measurements (nonlinear methods were not analyzed due to lack of sufficient data sets). Quality assessment of each study was verified and also meta-analytic techniques to identify and control bias. Meta-regression for age and gender was performed. Initially, 366 references were identified. According to our eligibility criteria, 30 references (39 studies) were included in our analysis. Regarding HF, epilepsy patients presented lower values (g -0.69) than controls, with the 95% confidence interval (CI) ranging from -1.05 to -0.33. No significant differences were observed for LF (g -0.18; 95% CI -0.71 to 0.35). Patients receiving treatment presented HF values to those not receiving treatment (g -0.05; 95% CI -0.37 to 0.27), with a trend for having higher LF values (g 0.1; 95% CI -0.13 to 0.33), which was more pronounced in those receiving antiepileptic drugs (vs. vagus nerve stimulation). No differences were observed for well-controlled versus refractory patients, possibly due to the low number of studies. Regression for age and gender did not influence the results. Finally, secondary time-domain analyses also showed lower HRV and lower vagal activity in patients with epilepsy, as shown by the standard deviation of normal-to-normal interval (SDNN) and the root mean square of successive differences (RMSSD) indexes, respectively. We confirmed and extended the hypothesis of sympathovagal imbalance in epilepsy, as showed by lower HF, SDNN, and RMSSD values when compared to controls. In addition, there was a trend for higher LF values in patients receiving pharmacotherapy. As lower vagal (HF) and higher sympathetic (LF) tone are predictors of morbidity and mortality in cardiovascular samples, our findings highlight the importance of investigating autonomic function in patients with epilepsy in clinical practice. Assessing HRV might also be useful when planning therapeutic interventions, as some antiepileptic drugs can show hazardous effects in cardiac excitability, potentially leading to cardiac arrhythmia.

Objectives. This paper aims at exploring the effects of GUASHA on heart rate variability between healthy volunteers under normal condition and weightlifters after training sessions. Methods. Ten healthy male volunteers under normal condition and 15 male weightlifters after weightlifting training sessions were recruited into two groups. Electrocardiography was recorded before and immediately after 20-minute GUASHA. HRV was calculated in both the time domain and the frequency domain. Results. Stress index was reduced, while standard deviation of N-N intervals (SDNN), proportion derived by dividing the number of interval differences of successive N-N intervals greater than 50 ms, and root mean square of successive differences (RMSSD) were enhanced after GUASHA therapy in the two groups. The changes in SDNN and RMSSD were higher in the healthy men group than in the weightlifters group. In addition, low frequency was decreased whereas high frequency was significantly increased in healthy men after the GUASHA session. Conclusions. GUASHA therapy facilitates the parasympathetic nervous activity and modulates the balance between parasympathetic and sympathetic activities in both healthy men under normal condition and weightlifters after training sessions as indicated. Although the changes of the HRV parameters were similar in both groups, the responsiveness was more pronounced in healthy men than in male weightlifters.

Individuals with an intellectual disability (ID) are at increased risk for cardiovascular disease (CVD), which may be attributed to autonomic dysfunction. Sex differences in autonomic function are apparent in the general population but have not been investigated in persons with ID, and may help to further explain the high prevalence of CVD. Heart rate variability (HRV) is a non‐invasive measure for autonomic modulation and using a sympatho‐excitatory stimulus such as isometric handgrip (HG) exercise, may reveal altered autonomic function not observed at rest. PURPOSE To assess sex differences in cardiac autonomic function in individuals with and without ID using an isometric handgrip (HG) exercise test. METHODS HRV was assessed in 18 individuals with ID (Male: 9; 28±6yrs, 33±11.1kg/m 2 ) and 23 without ID (Male: 13; 30±9.0yrs, 26±3.8kg/m 2 ) in response to isometric HG exercise at 30% of maximal voluntary contraction. Heart rate was continuously recorded via ECG and the last 2 minutes of quiet rest and HG exercise were analyzed. HRV was analyzed in both the time (root mean square of successive differences (RMSSD) and percentage of RR intervals differing by &lt;50ms (PNN50)) and frequency domains (low and high frequency (LF, HF), and LF/HF ratio). A change score was calculated from HG exercise ‐ baseline. RESULTS There were no differences between controls and ID. However, males in both groups demonstrated a blunted response to HG exercise in RMSSD, pNN50, and LF (p&lt;0.05) compared to females. CONCLUSION Males in both groups appear to have a suppressed vagal withdrawal to HG when compared to the females. Future research should investigate autonomic regulation in sex‐specific groups with and without ID in a larger sample size. Control ID ANOVA Male Female Male Female Group Sex Group*Sex Time‐Domain RMSSD (ms 2 ) −8±9 −21±24 −0±14 −12±12 0.05 0.00 0.35 pNN50 (%) −6±8 −13± 17 −4± 13 −9± 12 0.26 0.02 0.25 Frequency‐Domain LF (ms 2 ) −337± 1098 −1401± 1638 125± 1038 −245±361 0.56 0.00 0.29 HF (ms 2 ) −211±254 −350±428 −118±510 −221±277 0.27 0.10 0.27 LF/HF Ratio 6± 1 6± 1 6±0 6± 1 0.64 0.65 0.39 Data presented as mean change ± standard deviation. Control= M (n=13), F (n=9); ID= M (n=9), F (n=9) Log‐transformed for the case of non‐normal data This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

BackgroundDiabetes affects approximately 250 million people in the world.Cardiovascular autonomic neuropathy is a common complication of diabetesthat leads to severe postural hypotension, exercise intolerance, andincreased incidence of silent myocardial infarction.ObjectiveTo determine the variability of heart rate (HR) and systolic blood pressure(SBP) in recently diagnosed diabetic patients.MethodsThe study included 30 patients with a diagnosis of type 2 diabetes of lessthan 2 years and 30 healthy controls. We used a Finapres® device to measureduring five minutes beat-to-beat HR and blood pressure in three experimentalconditions: supine position, standing position, and rhythmic breathing at0.1 Hz. The results were analyzed in the time and frequency domains.ResultsIn the HR analysis, statistically significant differences were found in thetime domain, specifically on short-term values such as standard deviation ofNN intervals (SDNN), root mean square of successive differences (RMSSD), andnumber of pairs of successive NNs that differ by more than 50 ms (pNN50). Inthe BP analysis, there were no significant differences, but there was asympathetic dominance in all three conditions. The baroreflex sensitivity(BRS) decreased in patients with early diabetes compared with healthysubjects during the standing maneuver.ConclusionsThere is a decrease in HR variability in patients with early type 2 diabetes.No changes were observed in the BP analysis in the supine position, butthere were changes in BRS with the standing maneuver, probably due tosympathetic hyperactivity.

ObjectiveThis study compared children with Attention-Deficit/Hyperactivity Disorder (ADHD) and typically developing (TD) controls on heart rate variability (HRV) and motor proficiency, and examined their combined role in predicting ADHD symptom severity.MethodsTwenty-nine children with ADHD and 33 TD children, matched for age and sex, underwent assessment. ADHD symptoms were assessed using the Strengths and Weaknesses of ADHD Symptoms and Normal Behavior (SWAN) scale, motor skills were evaluated using the Movement Assessment Battery for Children-2 (MABC-2), and resting-state HRV was recorded via a 5-minute electrocardiogram.ResultsThe ADHD group demonstrated significantly poorer performance across all MABC-2 domains (fine motor, coordination, balance, total score; all P < 0.05). They also exhibited altered autonomic nervous system function, evidenced by significantly lower log-transformed Root Mean Square of Successive Differences and Standard Deviation of Normal-to-Normal Intervals, and a higher log-transformed LF/HF ratio (all P < 0.05). Correlation analyses revealed significant associations between motor coordination and HRV indices (logSDNN, logRMSSD). Hierarchical regression analysis identified logSDNN as a significant independent predictor of ADHD symptom severity, even after controlling for age, sex, and motor abilities.ConclusionChildren with ADHD show concurrent deficits in motor skills and autonomic regulation. HRV, particularly SDNN, serves as a robust physiological marker for symptom severity, suggesting that integrated assessment of motor and autonomic function provides a more comprehensive understanding of ADHD.

Power spectral analysis of fetal heart rate variability has been proposed to provide a non-invasive estimate of autonomic balance. However, there are few systematic data before birth. We therefore examined developmental changes in the frequency power spectrum at very low (0-0.04 Hz), low (0.04-0.15 Hz) and high frequencies (0.15-0.4 Hz), as well as the ratio of low- to high-frequency power (LF/HF), in chronically catheterized, healthy fetal sheep at 0.6 (n = 8), 0.7 (n = 7) and 0.8 gestational age (ga; n = 11). In a second study, 0.8 ga fetuses received either atropine (4.8 mg bolus, then 4.8 mg h(-1) for 30 min, n = 6) or 6-hydroxydopamine (20 mg ml(-1) at 2.5 ml h(-1) for 3 h; n = 9). Data were analysed by sleep state, defined by low-voltage-high-frequency (LV) or high-voltage-low-frequency (HV) EEG. Total spectral power increased with gestational age (P < 0.05), while LF/HF decreased from 0.6 to 0.7 ga. At 0.8 ga, heart rate and LF/HF were significantly higher during HV than LV sleep (P < 0.05). Consistent with this, although total spectral power was not significantly greater during HV sleep, there was a significant interaction between sleep state and frequency band (P = 0.02). Both atropine (P = 0.05) and 6-hydroxydopamine (P < 0.05) were associated with an overall reduction in spectral power but no significant effect on the LF/HF ratio. This study does not support substantial, consistent differences between the frequencies of sympathetic and parasympathetic activity in late-gestation fetal sheep.

Background: Serum bilirubin levels beyond the physiological limits, may lead to alterations in autonomic regulation in a newborn infant. Heart rate variability (HRV), is a noninvasive and quantitative marker of the activity of the autonomic nervous system (ANS). To date, few studies have demonstrated the undesirable effects of severe unconjugated hyperbilirubinemia (UHB) on autonomic functions, and only one study has used HRV as a marker of the autonomic activity. However, the relationship between altered cardiac autonomic functions and UHB by using the HRV derived from 24-hour Holter electrocardiography (ECG) recording has not been investigated previously.Objective: We aimed to assess whether a relationship exists between severe UHB and cardiac autonomic dysfunction by evaluating HRV via 24-hour Holter ECG recording.Methods: This single-center, prospective, case-control study was conducted on 50 full-term newborn infants with severe UHB requiring phototherapy and 50 healthy infants as controls. HRV assessment was performed by using 24-hour Holter ECG recording.Results: There was no significant difference in terms of mean average heart rate, mean maximum heart rate and mean RR duration between the groups. However, mean minimum heart rate was significantly lower in the study group. When 24-hour time and frequency domain parameters were compared, time and frequency domain parameters rMSDD as well as high frequency (HF), which represent parasymphathetic activity, were significantly higher in the study group. Furthermore, low frequency to high frequency (LF/HF) ratio, that serves as an indicator of sympathovagal balance, was significantly lower in the study group.Conclusion: Severe UHB may cause cardiac autonomic dysfunction in favor of parasympathetic predominance in jaundiced neonates.

Neurocardiac autonomic impairment with reduced heart rate variability (HRV) has been linked to SARS-CoV-2 infection and may persist in patients with post-COVID-19 syndrome. We synthesised meta-analytic data on HRV in post-COVID-19 syndrome. Our systematic review and meta-analysis were guided by PRISMA standards. We used MEDLINE, Embase and Web of Science to identify non-randomised studies of HRV in patients with post-COVID-19 syndrome, conducted more than 3 months after infection and compared with healthy controls. The search covered the period from 01/2020 to 09/2023. We pooled data on the following HRV parameters: standard deviation of normal-to-normal intervals (SDNN), root mean square of successive differences (rMSSD) and low-frequency to high-frequency ratio (LF/HF ratio). We applied a random effects model to account for heterogeneity. Risk of bias was assessed. From 856 initially identified records, we included 11 studies with a total of 1162 participants (593 post-COVID-19 patients and 565 healthy controls). We observed a trend toward lower HRV in post-COVID patients compared to controls, with small to medium effects for SDNN (SMD: 0.26, 95% CI: -0.03 to 0.56, p = 0.09), rMSSD (SMD: 0.11, 95% CI: -0.15 to 0.36, p = 0.41) and LF/HF ratio (SMD: -0.271, 95% CI: -0.61 to 0.07, p = 0.12). Moderate to high statistical heterogeneity of the effects was observed (I2 = 83% for SDNN and 78% for rMSSD) and nine of 11 studies had a high risk of bias. This meta-analysis suggests a possible association between post-COVID condition and alterations in neurocardiac autonomic function.

This study investigates how physiological signals respond to real-world traffic complexity, aiming to support the development of intelligent systems for driver state recognition. A total of eight participants were monitored using synchronized Electroencephalography (EEG) and Electrocardiography (ECG) recordings while driving along an urban route segmented into low, medium, and high traffic conditions. Time-domain Heart Rate Variability (HRV) metrics Root Mean Square of Successive Differences (RMSSD), and standard deviation of NN intervals (SDNN) and EEG spectral power (theta, alpha, beta bands) were extracted and analyzed per traffic segment. The results show significant and consistent physiological changes across traffic conditions. RMSSD and SDNN values decreased by 22.8% and 18.4%, respectively, under high traffic load, indicating increased sympathetic activation. Simultaneously, frontal theta power increased by 31.6%, suggesting elevated cognitive demand. These effects were observed in 4 out of 8 participants and exhibited region-specific patterns, particularly in frontal and temporal lobes. From a computational intelligence perspective, this work contributes (i) a well-structured, manually labeled dataset combining EEG and ECG in real traffic, (ii) evidence of feature separability across traffic conditions, and (iii) a methodological basis for developing data-driven models for stress and workload detection. The extracted features and synchronized multimodal structure are suitable for training classification models, enabling future implementation of personalized and context-aware cognitive state monitoring in intelligent transportation systems.

&lt;p&gt;&lt;strong&gt;Introduction:&lt;/strong&gt; Heart rate variability (HRV) is a measure of cardiac autonomic regulation that examines the variation in beat-to-beat fluctuations in heart rate. While many exposure-based studies have examined the effects of single or similar groups of contaminants on HRV parameters, none have examined the association between complex environmental mixtures, including organic and elemental contaminants, and HRV.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Methods:&lt;/strong&gt; Using data collected from the Multi-Community Environment-and-Health Study in Eeyou Istchee (Quebec, Canada), we assessed HRV in two time domain measures: root mean square of successive differences (RMSSD) and standard deviation of the N-N (RR) intervals (SDNN); and in three frequency domains: high frequency (HF), low-frequency (LF), and very-low frequency (VLF) in 443 participants. We first examined mixture effects of nineteen organic and metal contaminants in blood using principal component analysis (PCA) and a multivariable general linear regression on HRV responses, adjusting for age, sex, body mass index, smoking status, and kidney disease covariates. We subsequently assessed HRV outcome response variables using Bayesian kernel machine regression (BKMR) to further examine individual contaminant contribution and overall mixture effects.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Results:&lt;/strong&gt; In the PCA, a significant positive association was observed between RMSSD and principal component (PC) axis 2, which was highly positively-loaded for nickel and moderately negatively-loaded for mercury. A negative association between SDNN and PC-1, which was highly positively-loaded for all PCBs (polychlorinated biphenyls) and organochlorines and moderately positively-loaded for mercury, was observed. Additionally, a significant and positive association was observed between PC-2 and SDNN and a significant and negative association between PC-3 (negatively loaded for cadmium) and LF. Associations with contaminants were not observed for HF or VLF. BKMR results suggest that trans-nonachlor and cis-nonachlor are primarily responsible for reductions in HRV; however, their contributions to HRV deficits was non-significant when examined as a complete mixture.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Conclusions:&lt;/strong&gt; While PCA results suggested that organochlorines, mercury, nickel, and cadmium may all play a role in altering various HRV, subsequent BKMR analysis illustrated the individual components driving these effects may be trans- and cis-nonachlor and nickel and likely not mercury or cadmium. However, other contaminants appear to temper this effect when the entire mixture of chemicals is assessed as a whole. This study expands our knowledge of the effects of environmental contaminant mixtures on HRV, which is especially important in exposed populations such as those in the Eeyou Istchee territory, whilst utilizing novel statistical methods such as PCA and BKMR to examine co-exposures concurrently.&lt;/p&gt;

Concussion may negatively influence cardiovascular function and the autonomic nervous system, defined by alteration in heart rate variability (HRV). Differences in HRV most commonly emerge during a physical challenge, such as the final steps of the return-to-sport progression. To assess the effect of concussion history on aspects of cardio-autonomic function during recovery from a bout of submaximal exercise in adolescent male hockey athletes. Case-control study. Research laboratory. Thirty-three male athletes participating in Midget-AAA hockey were divided into those with (n = 15; age = 16 ± 1 years, height = 1.78 ± 0.06 m, mass = 73.9 ± 7.4 kg, 10.5 ± 1.6 years of sport experience, 25.2 ± 18.3 months since last injury) or without (n = 18; age = 16 ± 1 years, height = 1.78 ± 0.05 m, mass = 74.8 ± 7.6 kg, 10.6 ± 1.9 years of sport experience) a concussion history. Those with a concussion history were binned on total count: 1 concussion or 2 or more concussions. All athletes underwent 5 minutes of resting HRV assessment, followed by 20 minutes of aerobic exercise at 60% to 70% of their maximal target heart rate and a 9-minute, postexercise HRV assessment. Heart rate variability measures of mean NN interval, root mean square of successive differences, and standard deviation of NN interval (SDNN). Group demographic characteristics were not different. When the control and concussed groups were compared, group and time main effects for heart rate recovery, root mean square of successive differences, and SDNN (P values < .01), and an interaction effect for SDNN (P < .05) were demonstrated. Recovery trends for each group indicated that a history of 2 or more concussions may negatively affect cardio-autonomic recovery postexercise. Our findings suggest that those with more than 1 previous concussion may be associated with a greater risk for long-term dysautonomia. Future use of HRV may provide clinicians with objective guidelines for concussion-management and safe return-to-participation protocols.

Parasympathetic reactivation is the underlying mechanism for the rapid fall in heart rate (HR) post-exercise. A delayed decrease in the HR during the first minute after graded exercise is a powerful predictor of overall mortality and is linked to unfavorable clinical outcomes. Chronic kidney disease (CKD) is characterized by an altered autonomic function with heightened sympathetic and weakened parasympathetic activity. Given that exercise training has been shown to improve autonomic function and parasympathetic reactivation after exercise, the purpose of the present study was to test two hypotheses: 1) patients with CKD experience delayed HR recovery (HRR) compared to controls at the cessation of exercise due to attenuated cardiac vagal reactivation; 2) 12 weeks of aerobic exercise training would improve cardiac vagal reactivation in patients with CKD. Twenty-seven patients with CKD stages III and IV [eGFR between 15-59 mL/min/1.73m2] and eighteen age-matched controls were enrolled. All participants underwent cardiopulmonary exercise testing (CPET) in accordance with the modified Balke protocol. Participants were instrumented with a 12-lead ECG for HR assessment, and ventilation and pulmonary gas exchange were recorded breath-by-breath throughout the exercise tests using a metabolic analyzer. Post-exercise cardiac vagal reactivation was indexed via HRR [absolute HR decay (HRR60s)] and HR variability (HRV) metrics [root mean square of successive differences (RMSSD)] during 60 seconds of recovery following the test. To assess HRR kinetics over the entire recovery period, individual data were modeled with a monoexponential fit and the time constant (τ, time to reach ~63.2% of the total HRR, in seconds) was calculated. Comparisons between patients with CKD and controls were made based on the percentage of predicted HRmax obtained during the CPET using the following equation: HRmax= 208−0.7xage. Patients with CKD were then randomly assigned to exercise (n=17) or non-aerobic stretching (n=11) interventions consisting of three sessions per week for 12 weeks. Training sessions began at 20 minutes and increased by five minutes weekly to a maximum of 45 minutes. Intensity started at 50% of heart rate reserve and rose 5% each week to a target of 75%. CPET was repeated at the end of the 12 weeks. The percentage of predicted HRmax obtained at CPET was similar between patients and controls (CKD: 87±9 vs. CON: 86±5 %HRmax; P =0.448). The HRR60s was blunted in patients with CKD compared to controls (∆HRR60s; CKD: -11±4 vs. CON: -17±5 bpm; P =0.001), and τ was significantly longer in patients with CKD (τ; CKD: 144±31 vs. CON: 116±21 s; P = 0.002). Additionally, RMSSD increased at the cessation of exercise in both groups, but to a lesser extent in CKD patients compared to controls (ΔRMSSD; CKD: 0.5±4 vs. CON: 1.3±3 ms; P = 0.032). There was no significant difference in the maximum HR obtained during the CPET before and after 12 weeks of exercise training (pre: 142±10 vs. post: 136±20 bpm, P =0.178) or stretching (pre: 148±20 vs. post: 142±20 bpm, P =0.107). Twelve weeks of exercise training did not improve HRR60s (ΔHRR60s; pre: -11±4 vs. post: -11±8 bpm, P =0.692) nor vagal activity as measured by HRV. These findings support the hypothesis that patients with CKD exhibit impaired vagal reactivation, which may contribute to the increased cardiovascular risk associated with CKD. However, contrary to our hypothesis, 12 weeks of cycling exercise training may not be sufficient to enhance cardiac vagal reactivation. Future studies should explore different exercise modalities and manipulate training variables such as intensity, volume, and frequency to assess their potential impact on cardiac vagal reactivation in patients with CKD. This project was funded by the National Institutes of Health (NIH R01HL135183; NIH R61AT10457; NIH R33AT010457-03). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.