Vagal Modulation Of Heart Rate Research Articles

Heart rate variability in athletes with symptoms of non-functional overload

The article examines the effect on heart rate variability (HRV) indices in athletes depending on training status, different types of physical exertion, gender and age, presented in both cross-sectional and longitudinal studies. Also included is the predictability of HRV during overtraining, athletic condition, and athletic performance. Heart rate variability (HRV) has long been used as a diagnostic marker of overexertion and overtraining. A large body of evidence shows that in athletes of all ages, regular aerobic training usually results in significant improvements in total and instantaneous HRV. These changes, which are accompanied by a significant decrease in heart rate both at rest and during submaximal exercise, reflect an increase in autonomic efferent activity and a shift in favor of enhanced vagal modulation of heart rate. At present, the available data do not allow us to draw definitive conclusions about the usefulness of traditional HRV indices for evaluating the performance of physical exercises and monitoring the training load. The discrepancies in the results published so far are due to several factors, including insufficient study size and design, and different HRV methods. It also remains to be seen whether traditional HRV indices will be useful for diagnosing overexertion and overtraining.

The heart to make the right choice: Vagal (re)activity and recovery predict advantageous decision-making

From simple everyday choices to life-altering decisions, decision-making is a crucial cognitive process in our daily life. Psychophysiological theories of heart-brain interactions involvement in cognition predict that general self-regulation capacities underlie cognitive processes including decision-making. Yet, in the context of decision-making, the somatic maker hypothesis postulates that the adaptability of the current physiological state should be the best predictor of advantageous decision-making. The present study tests compare self-regulation in general (indexed by resting vagal activity) and in a specific decisional context (vagal reactivity and recovery) to explain advantageous decision-making. Young adults (n = 54) completed a decision-making task while wearing a heart rate monitor. Bayesian regressions show that vagal reactivity and recovery combined is the preferred statistical model to explain advantageous decision-making (BF10 = 163.85). Those findings 1) support the somatic marker hypothesis highlighting the key role of in situ self-regulation in decision-making processes and 2) show that the popular and often used index of general self-regulation, resting vagal activity, is not the best predictor of decision-making performance, and perhaps even for other cognitive functions. A next step could be interventional studies to test whether vagal modulation of heart rate underlies decision-making through interventions that influence vagal activity, which could provide relevant clinical leads.

Maybe angiotensin II is getting on our nerves, and the role of exercise.

Maybe angiotensin II is getting on our nerves, and the role of exercise.

The effect of deep breathing test on heart rate variability in obese and non-obese patients with myocardial infarction

Introduction and Aim:Obesity and metabolic syndrome increases the risk of cardiovascular diseases (CVD).The acute myocardial infarction may be associated with autonomic dysfunction and it may have a bearing on the prognosis. The objective of the study wasto examine the effect of deep breathing test on heart rate variability in obese and non-obese patients with myocardial infarction (MI).
 
 Materials and Methods:The patients with acute myocardial infarction were confirmed by universal definition and treatment was administered. At 12 weeks of follow up, the MI patients were screened and divided into two groups. 30 patients of MI with BMI 25 to 30 kg/m2 formed the obese group.30 patients of MI with BMI 18.5 to 24.9 kg/m2 formed the non-obese group. The baseline ECG was taken for 5 minutes by using Niviqure B3 machine for HRV analysis. Then, deep breathing test (DBT) was performed in a standardized manner.
 
 Results:The two groupswere well matched for the age (53.7±11.5 vs.55.2±9.2years).In the baseline there was a statistically significant decrease in the total power (TP) of the heart i.e., HF plus LF (2178±762ms2 vs2991±771ms2 with a ‘p’ value 0.001) in the obese group when compared to non-obese group. On DBT there was a significant decrease in heart rate (81bpm to 65bpm) in non-obese group. However, in obese group there was no significant decrease in heart rate (79bpm to 72bpm) on DBT.
 
 Conclusion: Accordingly, we concludethat in obese patients with MI there is a reduction in respiratory vagal modulation of heart rate during DBT.

Reduced vagal modulations of heart rate during overwintering in Antarctica

Long-duration Antarctic expeditions are characterized by isolation, confinement, and extreme environments. Here we describe the time course of cardiac autonomic modulation assessed by heart rate variability (HRV) during 14-month expeditions at the German Neumayer III station in Antarctica. Heart rate recordings were acquired in supine position in the morning at rest once before the expedition (baseline) and monthly during the expedition from February to October. The total set comprised twenty-five healthy crewmembers (n = 15 men, 38 ± 6 yrs, n = 10 women, 32 ± 6 yrs, mean ± SD). High frequency (HF) power and the ratio of low to high frequency power (LF/HF) were used as indices of vagal modulation and sympathovagal balance. HF power adjusted for baseline differences decreased significantly during the expedition, indicating a gradual reduction in vagal tone. LF/HF powers ratio progressively shifted toward a sympathetic predominance reaching statistical significance in the final trimester (August to October) relative to the first trimester (February to April). This effect was particularly pronounced in women. The depression of cardio-vagal tone and the shift toward a sympathetic predominance observed throughout the overwintering suggest a long-term cardiac autonomic modulation in response to isolation and confinement during Antartic overwintering.

Heart rate variability in different intensities of static and dynamic exercises graded using similar heart rate

The intensity and the type of the cardiovascular responses differ depending on the exercise type and intensity and the muscle groups involved. However, the responses in static and dynamic exercises are hardly comparable since the protocol used for grading the intensity of these exercises are different. Thus, we compared the cardiovascular autonomic responses in dynamic and static exercises of same muscle groups at increasing intensities graded using similar heart rate. 32 subjects performed dynamic and static exercises of lower limbs at 50% (HR50max) and 60% (HR60max) of their maximum achievable heart rates. Continuous ECG was recorded for 2 min during the exercise. Target heart rate specific single beat R–R intervals were extracted from the recorded ECG, and heart rate variability was determined. A factorial two way analysis of variance was conducted on the influence of two independent variables (load and exercise type) on the heart rate variability during different manoeuvres with baseline values taken as covariates. Exercise load had a main effect on HFnu and RMSSD. HFnu increased (p = 0.001) while RMSSD decreased (p = 0.025) with an increase in the exercise load. Exercise type also had a main effect on RMSSD with RMSSD being higher in dynamic exercise (p = 0.028). With increased load, LFnu decreased in dynamic exercise but was maintained in static exercise. Time domain parameter RMSSD decreases with an increase in the exercise load indicating a decrease in vagal modulation of heart rate with an increase in exercise load. RMSSD is more in dynamic exercise compared with static exercise indicating higher vagal modulation in dynamic exercise. However, increase in HFnu with exercise load may be due to the influence of increased ventilation on heart rate modulation.

The Effects of Controlled Tempo Manipulations on Cardiovascular Autonomic Function

Music has been associated with alterations in autonomic function. Tempo, the speed of music, is one of many musical parameters that may drive autonomic modulation. However, direct measures of sympathetic nervous system activity and control groups and/or control stimuli do not feature in prior work. This article therefore reports an investigation into the autonomic effects of increases and decreases in tempo. Fifty-eight healthy participants (age range: 22–80 years) were randomly allocated to either an experimental ( n = 29, tune) or control (rhythm of the same tune) group. All participants underwent five conditions: baseline, stable tempo (tune/rhythm repeatedly played at 120 bpm), tempo increase (tune/rhythm played at 60 bpm, 90 bpm, 120 bpm, 150 bpm, 180 bpm), tempo decrease (tune/rhythm played at 180 bpm, 150 bpm, 120 bpm, 90 bpm, 60 bpm) and recovery. Heart rate, blood pressure, respiration, and muscle sympathetic nerve activity were continuously recorded. The 60 bpm in the tempo decrease stimulus was associated with increases in measures of parasympathetic activity. The 180 bpm in the tempo increase stimulus was also associated with shifts towards parasympathetic predominance. Responses to the stimuli were predicted by baseline %LF. It is concluded that the individual tempi impacted upon autonomic function, despite the entire stimulus having little effect. The 60 bpm in an increasingly slower stimulus was associated with greater vagal modulations of heart rate than faster tempi. For the first time, this study shows that response direction and magnitude to tempo manipulations were predicted by resting values, suggesting that music responders may be autonomically distinct from non-responders.

Deceleration and acceleration capacities of heart rate in patients with drug-resistant epilepsy.

Epilepsy and seizures can have dramatic effects on cardiac function. The aim of the present study was to investigate deceleration capacity, acceleration capacity and their 24-h fluctuations of heart rate variability in patients with drug-resistant epilepsy. Deceleration capacity, acceleration capacity of heart rate and their 24-h dynamics derived from the phase rectified signal averaging method as well as traditional measures were analyzed in 39 patients with drug-resistant epilepsy and 33 healthy control subjects using 24-h electrocardiogram recordings. The discriminatory power of heart rate variability measures were validated by assessment of the area under the receiver operating characteristic curve. Net reclassification improvement and integrated discrimination improvement models were also estimated. Both deceleration capacity and absolute values of acceleration capacity were significantly lower in patients with drug-resistant epilepsy. The abnormal suppression of absolute deceleration capacity and acceleration capacity values were observed throughout the 24-h recording time (peaked at about 3 to 5 A.M.). Deceleration capacity had the greatest discriminatory power to differentiate the patients from the healthy controls. Moreover, in both net reclassification improvement and integrated discrimination improvement models, the combination of acceleration capacity or deceleration capacity with traditional heart rate variability measures has greater discriminatory power than any of the single heart rate variability features. Drug-resistant epilepsy was associated with a significant inhibition of vagal modulation of heart rate, which was more pronounced during the night than during the day. These findings indicate that phase rectified signal averaging method may serve as a complementary approach for characterizing and understanding the neuro-pathophysiology in epilepsy, and may provide a new clue to sudden unexpected death in epilepsy.

Reduced NPY Y1 receptor hippocampal expression and signs of decreased vagal modulation of heart rate in mice

Central neuropeptide Y (NPY) signaling participates in the regulation of cardiac autonomic outflow, particularly via activation of NPY-Y1 receptors (Y1Rs). However, the specific brain areas and neural pathways involved have not been completely identified yet. Here, we evaluate the role of hippocampal Y1Rs in the modulation of the autonomic control of cardiac function using a conditional knockout mouse model. Radiotelemetric transmitters were implanted in 4-month-old male mice exhibiting reduced forebrain expression (rfb) of the Y1R (Npy1rrfb, n=10) and their corresponding controls (Npy1r2lox, n=8). ECG signals were recorded (i) during resting conditions, (ii) under selective pharmacological manipulation of cardiac vagal activity, and (iii) during acute and chronic psychosocial stress challenges, and analyzed via time- and frequency-domain analysis of heart rate variability. Npy1rrfb mice showed a lower Npy1r mRNA density in the dentate gyrus and in the CA1 region of the hippocampus. Under resting undisturbed conditions, Npy1rrfb mice exhibited (i) a higher heart rate, (ii) a reduced overall heart rate variability, and (iii) lower values of the indices of vagal modulation compared to Npy1r2lox counterparts. Following pharmacological vagal inhibition, heart rate was higher in control but not in Npy1rrfb mice compared to their respective baseline values, suggesting that tonic vagal influences on heart rate were reduced in Npy1rrfb mice. The magnitude of the heart rate response to acute stressors was smaller in Npy1rrfb mice compared to Npy1r2lox counterparts, likely due to a concurrent lower vagal withdrawal. These findings suggest that reduced Y1R expression leads to a decrease in resting vagal modulation and heart rate variability, which, in turn, may determine a reduced cardiac autonomic responsiveness to acute stress challenges.

After-exercise heart rate variability is attenuated in postmenopausal women and unaffected by estrogen therapy.

Delayed heart rate (HR) recovery in the immediate postexercise period has been linked to adverse cardiovascular prognosis. The after effects of an acute bout of exercise on HR modulation in postmenopausal women (PMW) and the influence of estrogen therapy are unknown. In 13 sedentary PMW (54 ± 2 y, mean ± SEM), we assessed HR variability (HRV)--an index of HR modulation--and the influence of estrogen therapy on HRV. HRV in the frequency domain was quantified during supine rest and again 60 minutes after treadmill exercise for 45 minutes, at 60% VO2peak. PMW were studied before and after 4 weeks of oral estradiol. To obtain reference values for the after effects of exercise on HRV in healthy young women, 14 premenopausal women (PreM) completed the identical exercise protocol. Compared with PreM, PMW demonstrated lower high frequency (vagal modulation) and total HRV (P < 0.05) at rest. In PreM, all HRV values were similar before and after exercise. In contrast, in PMW after exercise, despite having identical HR to PreM, high frequency and total HRV were all lower (all P ≤ 0.01) compared with pre-exercise HRV values. Estrogen therapy had no effect on pre or postexercise values for HRV. When compared with PreM, PMW have identical HR, but lower vagal HR modulation at rest and delayed HRV recovery after exercise. Estrogen does not restore baseline HRV or accelerate HRV recovery postexercise, suggesting aging rather than estrogen deficiency per se may lower HRV in PMW.

Autonomic Findings in Takotsubo Cardiomyopathy

Takotsubo cardiomyopathy (TC) often occurs after emotional or physical stress. Norepinephrine levels are unusually high in the acute phase, suggesting a hyperadrenergic mechanism. Comparatively little is known about parasympathetic function in patients with TC. We sought to characterize autonomic function at rest and in response to physical and emotional stimuli in 10 women with a confirmed history of TC and 10 age-matched healthy women. Sympathetic and parasympathetic activity was assessed at rest and during baroreflex stimulation (Valsalva maneuver and tilt testing), cognitive stimulation (Stroop test), and emotional stimulation (event recall, patients). Ambulatory blood pressure monitoring and measurement of brachial artery flow-mediated vasodilation were also performed. TC women (tested an average of 37 months after the event) had excessive pressor responses to cognitive stress (Stroop test: p <0.001 vs baseline and p = 0.03 vs controls) and emotional arousal (recall of TC event: p = 0.03 vs baseline). Pressor responses to hemodynamic stimuli were also amplified (Valsalva overshoot: p <0.05) and prolonged (duration: p <0.01) in the TC women compared with controls. Plasma catecholamine levels did not differ between TC women and controls. Indexes of parasympathetic (vagal) modulation of heart rate induced by respiration and cardiovagal baroreflex gain were significantly decreased in the TC women versus controls. In conclusion, even long after the initial episode, women with previous episode of TC have excessive sympathetic responsiveness and reduced parasympathetic modulation of heart rate. Impaired baroreflex control may therefore play a role in TC.

Augmented vagal heart rate modulation in active hypoestrogenic pre-menopausal women with functional hypothalamic amenorrhoea.

Compared with eumenorrhoeic women, exercise-trained women with functional hypothalamic amenorrhoea (ExFHA) exhibit low heart rates (HRs) and absent reflex renin-angiotensin-system activation and augmentation of their muscle sympathetic nerve response to orthostatic stress. To test the hypothesis that their autonomic HR modulation is altered concurrently, three age-matched (pooled mean, 24 ± 1 years; mean ± S.E.M.) groups of women were studied: active with either FHA (ExFHA; n=11) or eumenorrhoeic cycles (ExOv; n=17) and sedentary with eumenorrhoeic cycles (SedOv; n=17). Blood pressure (BP), HR and HR variability (HRV) in the frequency domain were determined during both supine rest and graded lower body negative pressure (LBNP; -10, -20 and -40 mmHg). Very low (VLF), low (LF) and high (HF) frequency power spectra (ms(2)) were determined and, owing to skewness, log10-transformed. LF/HF ratio and total power (VLF + LF + HF) were calculated. At baseline, HR and systolic BP (SBP) were lower (P<0.05) and HF and total power were higher (P<0.05) in ExFHA than in eumenorrhoeic women. In all groups, LBNP decreased (P<0.05) SBP, HF and total power and increased (P<0.05) HR and LF/HF ratio. However, HF and total power remained higher (P<0.05) and HR, SBP and LF/HF ratio remained lower (P<0.05) in ExFHA than in eumenorrhoeic women, in whom measures did not differ (P>0.05). At each stage, HR correlated inversely (P<0.05) with HF. In conclusion, ExFHA women demonstrate augmented vagal yet unchanged sympathetic HR modulation, both at rest and during orthostatic stress. Although the role of oestrogen deficiency is unclear, these findings are in contrast with studies reporting decreased HRV in hypoestrogenic post-menopausal women.

Divergent relationship between arterial baroreflex sensitivity and mental stress‐induced blood pressure reactivity in women and men of Oman Family Study

The arterial baroreflex is important for buffering blood pressure (BP) responses to stress. Whether the sensitivity of the arterial baroreflex (BRS) is associated with hemodynamic responses to mental stress is sex dependent is unclear. We tested the relationships between BRS, BP and heart rate (HR) responses to a modified Word Conflict Test (WCT) in a cohort of semi‐rural, healthy Omani Arab women (n=69; 25±7 years; BMI: 23±5 kg/m2 [mean±SD]; BP: 104±10/65±8mmHg) and men (n=55; 24±7 years; BMI: 23±5 kg/m2; BP: 120±18/76±15mmHg). Resting BRS was similar in women and men (16±10 vs. 16±8 ms/mmHg). In women, the WCT increased (All P&lt;0.01) systolic (Δ10±17mmHg), diastolic (Δ6±13mmHg), mean arterial pressure (Δ8±15mmHg), and HR (Δ8±15bpm). In men, the WCT increased (All P&lt;0.01) systolic (Δ10±18mmHg), diastolic (Δ7±16mmHg), mean arterial pressure (Δ9±17mmHg), and HR (Δ13±15bpm). Resting BRS was +ve associated with changes in systolic (r=0.40, P=0.001), diastolic (r=0.34, P=0.003), mean arterial pressure (r=0.33, P=0.005) and HR (r=0.27, P=0.03) in women but ‐ve correlated with systolic BP (r=‐0.30, P=0.03) and HR (r=‐0.24, P=0.08) in men. These findings demonstrate a sex‐based difference in the role of the arterial baroreflex in buffering BP where mental stress in women showed higher vagal modulations of HR that may play a larger role in determining BP. As exaggerated stress reactivity is predictive of future hypertension, high BRS in women and low BRS in men may be important factors to identify individuals at risk.

Elevated Cardiac Vagal Tone in Hypoestrogenic Active Premenopausal Women with Functional Hypothalamic Amenorrhea

Compared with eumenorrheic women, exercise-trained women with functional hypothalamic amenorrhea (ExFHA) have low heart rate (HR), absent reflex activation of their renin-angiotensin-system, and augmentation of the normal increase in muscle sympathetic nerve burst incidence during orthostatic stress, suggesting concurrently altered autonomic heart rate modulation. To test this hypothesis, three age-matched (pooled mean, 24±1 years; mean±SEM) groups of women were studied: ExFHA (n=11), exercise-trained and eumenorrheic (ExOv; n=17), and sedentary and eumenorrheic (SedOv; n=17). Blood pressure (BP), HR, and HR variability (HRV) in the frequency domain were measured at supine rest and during simulated orthostatic stress induced by graded lower body negative pressure (LBNP; -10, -20, and -40mmHg). Very low (VLF), low (LF) and high (HF) frequency power spectra (ms2) were determined, and due to skewness, were log10 transformed. LF/HF ratio and Total power (VLF+LF+HF) were calculated. At baseline, HR and systolic BP were lower (p<0.05), and HF and Total power higher (p<0.05) in ExFHA than eumenorrheic women. In all groups, LBNP decreased (p<0.05) systolic BP, HF and Total power, and increased (p<0.05) HR, and LF/HF ratio. However, in ExFHA, HF and Total power remained higher (p<0.05), and HR, systolic BP and LF/HF ratio lower (p<0.05) than in eumenorrheic women, in whom measures did not differ (p>0.05). In conclusion, ExFHA women demonstrate augmented vagal HR modulation, whereas sympathetic HR modulation is unchanged, both at rest and during orthostatic stress. Less central angiotensin II may play a role.

Similarities and Differences Between Renal Sympathetic Denervation and Carotid Baroreceptor Stimulation

The two novel approaches recently introduced for the treatment of resistant hypertension, i.e. carotid baroreceptor stimulation and renal denervation, share a number of similarities but are also characterized by important differences. The similarities include the evidence that both interventions have as common pathophysiological background the state of sympathetic overdrive characterizing essential hypertension. In addition both procedures 1) are invasive, 2) exert in the short-term period clearcut blood pressure lowering effects and 3) still face a number of open questions, particularly related to the long-term blood pressure lowering effects, impact on end-organ damage and on cardiovascular events. The differences include the fact that two procedures act on distinct targets that trigger sympathetic activation and consequently blood pressure increase. In addition, only in the case of carotid baroreceptor stimulation the blood pressure effects can be easily assessed immediately following the implantation. Finally, the economic costs, metabolic effects and impact on vagal modulation of heart rate are different between the two interventions. This paper will provide a comparison of the background, effects and outcome of renal denervation and carotid baroreceptor stimulation, stressing whenever possible the clinical implications of the main features of the two interventions.

An Internet-Based Counseling Intervention With Email Reminders that Promotes Self-Care in Adults With Chronic Heart Failure: Randomized Controlled Trial Protocol

BackgroundChronic heart failure (CHF) is a public health priority. Its age-standardized prevalence has increased over the past decade. A major challenge for the management of CHF is to promote long-term adherence to self-care behaviors without overtaxing available health care resources. Counseling by multidisciplinary health care teams helps to improve adherence to self-care behaviors and to reduce the rate of death and hospitalization. In the absence of intervention, adherence to self-care is below recommended standards.ObjectiveThis trial aims to establish and evaluate a Canadian e-platform that will provide a core, standardized protocol of behavioral counseling and education to facilitate long-term adherence to self-care among patients with CHF.MethodsCanadian e-Platform to Promote Behavioral Self-Management in Chronic Heart Failure (CHF-CePPORT) is a multi-site, double blind, randomized controlled trial with a 2 parallel-group (e-Counseling + Usual Care vs e-Info Control + Usual Care) by 3 assessments (baseline, 4-, and 12-month) design. We will identify subjects with New York Heart Association Class II or III systolic heart failure from collaborating CHF clinics and then recruit them (n=278) by phone. Subjects will be randomized in blocks within each site (Toronto, Montreal, and Vancouver). The primary outcome will be improved quality of life, defined as an increased number of subjects with an improvement of ≥5 points on the summary score of the Kansas City Cardiomyopathy Questionnaire. We will also assess the following secondary outcomes: (1) diet habits, depression, anxiety, smoking history, stress level, and readiness for change using self-report questionnaires, (2) physical activity level, current smoking status, and vagal-heart rate modulation by physiological tests, and (3) exercise capacity, prognostic indicators of cardiovascular functioning, and medication adherence through medical chart review. The primary outcome will be analyzed using generalized estimation equations with repeated measures on an intention-to-treat basis. Secondary outcomes will be analyzed using repeated-measures linear mixed models with a random effects intercept. All significant main effects or interactions in the statistical models will be followed up with post hoc contrasts using a Bonferroni correction with a 2-sided statistical significance criterion of P<.05.ResultsThis 3.5-year, proof-of-principle trial will establish the e-infrastructure for a pan-Canadian e-platform for CHF that is comprised of a standardized, evidence-based protocol of e-Counseling.ConclusionsCHF-CePPORT is designed to improve long-term adherence to self-care behaviors and quality of life among patients with CHF. It will demonstrate a distinct Canadian initiative to build capacity for preventive eHealth services for patients with CHF.Trial RegistrationClinicalTrials.gov NCT01864369; http://clinicaltrials.gov/ct2/show/NCT01864369 (Archived by WebCite at http://www.webcitation.org/6Iiv6so7E).

Association of hypertension status and cardiovascular risks with sympathovagal imbalance in first degree relatives of type 2 diabetics.

As reports show cardiovascular (CV) risks in first-degree relatives (FDR) of type2 diabetics, and autonomic imbalance predisposing to CV risks, in the present study we have assessed the contribution of sympathovagal imbalance (SVI) to CV risks in these subjects. Body mass index (BMI), waist-to-hip ratio (WHR), basal heart rate (BHR), blood pressure (BP), rate pressure product (RPP), and spectral indices of heart rate variability (HRV) were reordered and analyzed in FDR of type2 diabetics (study group, n=293) and in subjects with no family history of diabetes (control group, n=405). The ratio of low-frequency (LF) to high-frequency (HF) power of HRV (LF-HF), a sensitive marker of SVI, was significantly increased (P<0.001) in the study group compared with the control group. The SVI in the study group was due to concomitant sympathetic activation (increased LF) and vagal inhibition (decreased HF). In the study group, the LF-HF ratio was significantly correlated with BMI, WHR, BHR, BP and RPP. Multiple regression analysis showed an independent contribution of LF-HF to hypertension status (P=0.000), and bivariate logistic regression showed significant prediction (odds ratio 2.16, confidence interval 1.130-5.115) of LF-HF to increased RPP, the marker of CV risk, in the study group. Sympathovagal imbalance in the form of increased sympathetic and decreased parasympathetic activity is present in FDR of type2 diabetics. Increased resting heart rate, elevated hypertension status, decreased HRV and increased RPP in these subjects make them vulnerable to CV risks. SVI in these subjects contributes to CV risks independent of the degree of adiposity.

Estrogen Can Modulate Menopausal Women’s Heart Rate Variability

The aim of our study was to compare the responses of heart rate variability (HRV) with two different types of hormonal substitution therapy (HT) in post-menopausal women (cross-sectional study) and to reveal an effect of HT shortly after beginning of its administration (follow-up study). To elucidate the influence of menopause and effects of different protocols of a HT on autonomic control of heart rate, we evaluated the heart rate variability (HRV) in 5 groups: premenopausal women (n=140), postmenopausal women without HT (n=360), women on HT with conjugated estrogen only (n=168), women on continuous combined estrogen-progesterone HT (n=117), and men (n=140). Frequency-domain of short-term stationary R-R intervals was performed to evaluate the total variance, low frequency power (LF; 0.04-0.15 Hz), high frequency power (HF; 0.15-0.40 Hz), portion of low frequency power (LF%) and ratio of LF to HF (LF/HF). Significantly lower portion of the LF was found in premenopausal women [46.9 (+/-2.7) nu] when compared to untreated postmenopausal women [54.3 (+/-2.9) nu] and men [55.2 (+/-3.0) nu]. Treatment by estrogen only was proved to decrease the LF% [40.1 (+/-2.1) nu] while no effect on HRV was observed in women treated with combination of estrogen and progesterone [57.2 (+/-3.1) nu]. Also the HF was lower in postmenopausal women [4.16 (+/-0.16) ms(2)] than in premenopausal women [4.79 (+/-0.22) ms(2)] and women treated with estrogen only [4.98 (+/-0.25) ms(2)] while in women treated with combined hormonal therapy the average value [3.99 (+/-0.21) ms(2)] did not significantly differ from that of untreated postmenopausal women. The follow-up study also proved increase of high frequency power already after two months of estrogen substitution therapy [4.86 (+/-0.14) ms(2) vs. 4.19 (+/-0.15) ms(2)]. These results suggest that higher vagal modulation of heart rate that seems typical for younger women becomes after menopause similar to that of men. We also proved a positive shift of HRV parameters toward more beneficial values as for a cardiovascular risk in postmenopausal women treated with estrogens but not in those treated by combined estrogen - progesterone substitution therapy.

Effects of daily hemodialysis on heart rate variability: results from the Frequent Hemodialysis Network (FHN) Daily Trial.

End-stage renal disease is associated with reduced heart rate variability (HRV), components of which generally are associated with advanced age, diabetes mellitus and left ventricular hypertrophy. We hypothesized that daily in-center hemodialysis (HD) would increase HRV. The Frequent Hemodialysis Network (FHN) Daily Trial randomized 245 patients to receive 12 months of six versus three times per week in-center HD. Two hundred and seven patients had baseline Holter recordings. HRV measures were calculated from 24-h Holter electrocardiograms at both baseline and 12 months in 131 patients and included low-frequency power (LF, a measure of sympathetic modulation), high-frequency power (HF, a measure of parasympathetic modulation) and standard deviation (SD) of the R-R interval (SDNN, a measure of beat-to-beat variation). Baseline to Month 12 change in LF was augmented by 50% [95% confidence interval (95% CI) 6.1-112%, P =0.022] and LF + HF was augmented by 40% (95% CI 3.3-88.4%, P = 0.03) in patients assigned to daily hemodialysis (DHD) compared with conventional HD. Changes in HF and SDNN were similar between the randomized groups. The effects of DHD on LF were attenuated by advanced age and diabetes mellitus (predefined subgroups). Changes in HF (r = -0.20, P = 0.02) and SDNN (r = -0.18, P = 0.04) were inversely associated with changes in left ventricular mass (LVM). DHD increased the LF component of HRV. Reduction of LVM by DHD was associated with increased vagal modulation of heart rate (HF) and with increased beat-to-beat heart rate variation (SDNN), suggesting an important functional correlate to the structural effects of DHD on the heart in uremia.

SYMPATHOVAGAL IMBALANCE IN TAKOTSUBO CARDIOMYOPATHY

Takotsubo cardiomyopathy is an acute reversible cardiac dysfunction syndrome associated with high circulating catecholamine levels. Our objective was to investigate whether abnormal cardiovascular control might play a role in the pathophysiology.We studied autonomic cardiovascular reflexes in 10 women who had takotsubo (33±7 months after being hospitalized) and 10 age/BMI matched healthy women.In the women with takotsubo, indices of vagal modulation of heart rate induced by respiration were uniformly reduced (expiratory:inspiratory ratio: p&lt;0.01, pnn50%: p&lt;0.02, rMSSD: p&lt;0.03). Cognitive (stroop test: p&lt;0.03) and emotional arousal (event recall: p&lt;0.05) produced exaggerated pressor responses, without detectable ECG changes. Pressor responses to hemodynamic stimuli were also amplified (Valsalva SBP overshoot: p&lt;0.05). Takotsubo women had increased BP variability in the short‐term (St. Dev. SBP: p&lt;0.01). Ambulatory recordings captured an exaggerated morning surge in SBP after awakening from sleep (p&lt;0.05). Cardiovagal baroreflex gain was significantly lower in the takotsubo women (sequence analysis: p&lt;0.01, regression method: p&lt;0.001, transfer function gain: p&lt;0.001).Women with takotsubo have heightened sympathetic responsiveness, labile BP and reduced vagal modulation of the heart. This shift in sympathovagal balance could play a role in the pathophysiology.