Altered Sympathovagal Balance Research Articles

Influence of postexercise cooling techniques on heart rate variability in men

The reduction of core body temperature (T(C)) is vitally important in the treatment of hyperthermia; however, little is known regarding the impact of cooling treatments on the autonomic control of heart rate (HR). The aim of the present study was to examine the influence of three field-based hyperthermia treatments on the neural control of HR via heart rate variability (HRV). Following exercise-induced hyperthermia (T(C) approximately 40.0 degrees C) in a warm environment (34.2 +/- 0.5 degrees C), nine healthy, active men were treated during recovery, in a randomized order, with intravenous cold saline infusion (IV) or ice packs (ICE) or fan cooling with intermittent water spray (FAN) for 40 min. During each treatment, HR dynamics via power spectral (VLF, LF, HF), Poincare plot (SD1, SD2), approximate entropy (ApEn) and short- (alpha(1)) and long-term (alpha(2)) fractal scaling analyses were determined every 10 min. At recovery onset, HR and T(C) were similar between treatments and were significantly reduced over the 40 min recovery period. During recovery, HR and alpha(2) were significantly reduced from initial levels but were significantly greater for IV compared with ICE and FAN. In contrast, VLF, LF, HF, SD1, SD2 and ApEn increased during recovery, with all being significantly lower for IV compared with ICE and/or FAN. The present results demonstrated that IV, compared with ICE and FAN, resulted in significantly greater HR, reduced spectral and geometrical HRV, lower HR complexity and reduced long-term HR control, indicative of reduced vagal and/or increased sympathetic modulation. Specific treatments for exercise-induced hyperthermia may result in an altered sympathovagal balance that requires further examination.

Stress and Heart Rate Variability in Surgeons During a 24-Hour Shift

To determine the specific effects of working long hours in surgery and potential cardiac stress in the individual surgeon by measuring heart rate variability (HRV). This prospective study measured HRV before, during, and after a 24-hour shift in a standardized resting period of 10 minutes. Measurements were repeated over 10 shifts for each participant. Eight surgeons from a high-volume inner-city surgery department took part in the study. Time and frequency domain parameters of HRV as parameters of cardiac stress and correlations with perceived stress and fatigue on a visual analog scale. Perceived fatigue increased over 24 hours (P < .001), whereas stress levels decreased slightly (P = .06). Time domain parameters of HRV increased from before the shift to after the shift (standard deviation of normal to normal intervals, square root of the mean normal to normal interval, and percentage of adjacent pairs of normal to normal intervals differing by more than 50 milliseconds: all P < .01), denoting more cardiac relaxation. Both the low- and high-frequency components increased (P = .04 and P < .001, respectively), showing a heightened activity of the autonomic nervous system. Measurements of HRV during a 24-hour surgical shift did not show an increase in cardiac stress concerning time domain parameters despite intense workloads for a median of 20 hours. Frequency components increased in parallel, though, suggesting alterations in sympathovagal balance. Perceived stress levels correlated with HRV, whereas fatigue did not. Further studies on occupational stress and its cardiac effects in surgeons are needed.

Ethnic differences in heart rate: can these be explained by conventional cardiovascular risk factors?

South Asians worldwide have an elevated risk of coronary heart disease (CHD), only partly explicable by a higher prevalence of diabetes. Diabetes and dysglycaemia are associated with increased heart rates and abnormal cardiac sympathovagal balance, and are predictive of increased coronary mortality. This study investigated ethnic differences in heart rate, sympathovagal balance, and baroreflex sensitivity (BRS) to establish if they were explained by dysglycaemia/insulin resistance. 84 South Asian and 83 European men (age 45-85 yrs), half with established CHD and half without proven CHD, underwent metabolic profiling and assessment of mean RR interval, heart rate variablility (HRV) and BRS. Mean resting RR interval was greater in Europeans than South Asians (1014 (149) ms vs. 936 (158) ms respectively, means (SD); P = 0.005). This corresponded to resting heart rates of 59.1 bpm for Europeans and 64.1 bpm for South Asians. No ethnic differences were detected in HRV or BRS. Insulin resistance, assessed by the homeostasis model of assessment of insulin resistance (HOMA-IR), correlated with mean RR interval (beta coefficient = -0.189, P = 0.04) and BRS (beta coefficient = -0.246, P = 0.006) and similar correlations were seen with fasting serum glucose. However, ethnic differences in mean RR interval persisted after adjustment for age, systolic BP, beta blocker use, and HOMA-IR. South Asian men have higher heart rates compared with European men. This difference was not explained by measures of insulin resistance or other risk factors. This may be indicative of altered sympathovagal balance, and contribute to the greater coronary disease risk in people of South Asian ethnicity.

Age-associated alteration of sympatho-vagal balance in a female population assessed through the tone–entropy analysis

Through our recent studies on heart rate variability (Oida et al. J Appl Physiol 82:1794-1801, 1997; J Gerontol 54A:M219-M224, 1999a; Acta Physiol Scand 165:129-134, 1999b; Acta Physiol Scand 165:421-422, 1999c), we discover that autonomic functions could be assessed quantitatively in time domain by the tone-entropy (T-E) methodology, where the tone represents sympatho-vagal balance, and the entropy, autonomic regulatory activity. The purpose of this study was then to elucidate an age-associated alteration of sympatho-vagal balance in a female population through this T-E method. ECG R-R time intervals at rest were acquired on 10 min for 73 female subjects. Ageing influence was examined by comparisons between two groups: middle-aged group (40-50), (51.5 +/- 0.7 year, n = 28) and old-aged (60-70), (69.5 +/- 0.8 year, n = 45)]. Evaluated tone: [-0.058 +/- 0.011 (40-50), and 0.027 +/- 0.003 (60-70) (P < 0.01)], and entropy: [3.46 +/- 0.11 (40-50), and 3.06 +/- 0.08 bit (60-70) (P<0.01)]. The result showed that the tone was high and the entropy was low in the old-aged compared with the middle-aged group. When the result was plotted in two-dimensional T-E space, it revealed a curvi-linear relation between the tone and the entropy, consistent with our previous studies on pharmacological blockades, on heart recovery after dynamic exercise and on a male ageing. In conclusion, the result suggested that the sympatho-vagal balance altered or the vagal predominance was impaired with age significantly in this female population. Interestingly, comparing with corresponding male, the female had better autonomic functions.

Cardiovascular Responses in Unrestrained WKY Rats to Inhaled Ultrafine Carbon Particles

Based on epidemiologic observations, the issue of adverse health effects of inhaled ultrafine particles (UFP) is currently under intensive discussion. We therefore examined cardiovascular effects of UFP in a controlled animal exposure on young, healthy WKY rats. Short-term exposure (24 h) to carbon UFPs (38 nm, 180 μg m−3), generated by spark discharging, induced a mild but consistent increase in heart rate (18 bpm, 4.8%), which was associated with a significant decrease in heart-rate variability during particle inhalation. The timing and the transient character of these responses point to a particle induced alteration of cardiac autonomic balance, mediated by a pulmonary receptor activation. After 24 h of inhalation exposure, bronchoalveolar lavage revealed significant but low-grade pulmonary inflammation (clean air 1.9% vs. UFPs 6.9% polymorphonuclear cells) and on histopathology sporadic accumulation of particle-laden macrophages was found in the alveolar region. There was no evidence of an inflammation-mediated increase in blood coagulability, as UFP inhalation did not induce any significant changes in plasma fibrinogen or factor VIIa levels and there were no prothrombotic changes in the lung or the heart at both the protein and mRNA level. Histological analysis revealed no signs of cardiac inflammation or cardiomyopathy. This study therefore provides toxicological evidence for UFP-associated pulmonary and cardiac effects in healthy rats. Our findings suggest that the observed changes are mediated by an altered sympatho-vagal balance in response to UFP inhalation, but do not support the concept of an inflammation-mediated prothrombotic state by UFP.

Heart rate variability in sarcoidosis: a frequency domain analysis

BACKGROUND: Little is known about autonomic dysfunction in patients with sarcoidosis. Heart rate variability (HRV) studies provide information regarding sympathetic and vagal tone and are both noninvasive and relatively simple to perform. The objective of this study was to compare HRV in sarcoidosis patients and in healthy controls. METHODS: We prospectively analyzed data from 12 sarcoidosis patients and 12 healthy volunteers. Electrocardiographic (ECG) data were recorded from all study participants, and HRV analysis was performed in the frequency domain. The sarcoidosis patients underwent echocardiography as well. RESULTS: Mean values for HRV in the high-frequency (HF) domain were significantly reduced in sarcoidosis patients (182+/-102 ms(2) vs. 758+/-457 in controls, p=0.001). We also observed a trend (p=0.055) towards an increased ratio of low-frequency (LF) to high-frequency power in sarcoidosis patients. CONCLUSIONS: Our findings indicate the possibility of altered sympathovagal balance in sarcoidosis. Since 5 of these 12 sarcoidosis patients had mild echocardiographic abnormalities, possibly related to sarcoidosis, we were unable to conclude whether the HRV findings were attributable solely to an autonomic dysfunction in sarcoidosis or whether they were related to a structural myocardial involvement of the disease.

Autonomic nervous system and microvascular alterations in normotensives with a family history of hypertension

Autonomic nervous system and microvascular alterations at pre‐hypertensive stage of hypertension have still not been fully elucidated. We aimed at addressing central and local influences on microvascular reactivity at pre‐hypertensive stage of hypertension. To that end, we studied microvascular reactivity in 59 normotensives with a family history of hypertension and 46 controls. We measured laser‐Doppler flow on the finger nailfold skin in the resting condition, after an 8‐min occlusion of digital arteries and during local nitroglycerin application. Finger pressure, pulse and ECG were monitored by a Finapres device. Heart rate power spectral analysis was performed using Fast Fourier transformation. Baroreflex sensitivity was estimated by the sequence method. Normotensives with a family history of hypertension showed higher systolic pressure, decreased high‐frequency power of the heart rate variability spectrum and reduced baroreflex sensitivity in the resting condition as well as decreased fundamental frequency of laser‐Doppler flow oscillations during nitroglycerin application. We conclude that normotensives with a family history of hypertension exhibit altered sympathovagal balance with decreased parasympathetic activity at the cardiac level as well as increased myogenic microvascular reactivity.

Sympathovagal balance, nighttime blood pressure, and QT intervals in normotensive obese women.

We describe associations among the heart-rate-corrected QT (QTc) interval, QTc dispersion (QTc-d), circadian BP variation, and autonomic function in obese normotensive women and the effect of sustained weight loss. In 71 obese (BMI = 37.14 +/- 2.6 kg/m(2)) women, 25 to 44 years of age, circadian BP variations (24-hour ambulatory BP monitoring), autonomic function (power spectral analysis of RR interval oscillations), and cardiac repolarization times (QTc-d and QTc interval) were recorded at baseline and after 1 year of a multidisciplinary program of weight reduction. Compared with nonobese age-matched women (n = 28, BMI = 23 +/- 2.0 kg/m(2)), obese women had higher values of QTc-d (p < 0.05) and QTc (p < 0.05), an altered sympathovagal balance (ratio of low-frequency/high-frequency power, p < 0.01), and a blunted nocturnal drop in BP (p < 0.01). In obese women, QTc-d and the QTc interval correlated with diastolic nighttime BP (p < 0.01) and sympathovagal balance (p < 0.01). Waist-to-hip ratio, free fatty acids, and plasma insulin levels correlated with QT intervals and reduced nocturnal drops in both systolic and diastolic BP and sympathovagal balance (p < 0.01). After 1 year, obese women lost at least 10% of their original weight, which was associated with decrements of QTc-d (p < 0.02), the QTc interval (p < 0.05), nighttime BP (p < 0.01), and sympathovagal balance (p < 0.02). Sustained weight loss is a safe method to ameliorate diastolic nighttime BP drop and sympathetic overactivity, which may reduce the cardiovascular risk in obese women.

Autonomic dysfunction associates with prolongation of QT intervals and blunted night BP in obese women with visceral obesity.

Prolonged QT intervals and a reduced fall of nocturnal blood pressure (BP) both predict an increased risk of cardiovascular events in obese subjects. We evaluated circadian BP variations (24-h ambulatory BP monitoring), autonomic function (power spectral analysis of RR interval oscillations) and cardiac repolarization times (QTc-dispersion and QTc interval) in 70 obese women, aged 25-44 yr, grouped by WHR into group A (WHR > 0.85, no.=38) and group B (WHR < or = 0.85, no.=32). Compared with non-obese age-matched women (no.=25, BMI=23+/-1.8) and obese women of group B, obese women of group A had higher values of QTc-d (p<0.05) and QTc (p<0.05), an altered sympathovagal balance (ratio of low-frequency/high-frequency power, p<0.01), and a blunted nocturnal drop in BP (p<0.01). In group A, QTc-d and the QTc interval correlated with diastolic night BP (p<0.01) and sympathovagal balance (p<0.01). WHR and plasma insulin levels correlated with QT intervals, reduced nocturnal fall in diastolic BP and sympathovagal balance (p<0.01). Prolongation of cardiac repolarization times and the reduction of nocturnal fall in BP coexist in obese women with visceral obesity, and might contribute to their raised cardiovascular risk. Autonomic dysfunction may be the common mechanism for this association.

Increased QTc dispersion is related to blunted circadian blood pressure variation in normoalbuminuric type 1 diabetic patients.

A reduced nocturnal fall in blood pressure (BP) and increased QT dispersion both predict an increased risk of cardiovascular events in diabetic as well as nondiabetic subjects. The relationship between these two parameters remains unclear. The role of diabetic autonomic neuropathy in both QT dispersion and circadian BP variation has been proposed, but data have been conflicting. The aim of the present study was to describe associations between QT dispersion and circadian BP variation as well as autonomic function in type 1 diabetic patients. In 106 normoalbuminuric (urinary albumin excretion <20 microg/min) normotensive patients, we performed 24-h ambulatory BP (Spacelabs 90207) and short-term (three times in 5 min) power spectral analysis of RR interval oscillations, as well as cardiovascular reflex tests (deep breathing test, postural heart rate, and BP response). No patient had received (or had earlier received) antihypertensive or other medical treatment apart from insulin. In a resting 12-lead electrocardiogram, the QT interval was measured by the tangent method in all leads with well-defined T-waves. The measurement was made by one observer blinded to other data. The QT interval was corrected for heart rate using Bazett's formula. The QTc dispersion was defined as the difference between the maximum and the minimum QTc interval in any of the 12 leads. When comparing patients with QTc dispersion below and above the median (43 ms), the latter had significantly higher night BP (114/67 vs. 109/62 mmHg, P < 0.003/P < 0.001), whereas day BP was comparable (129/81 vs. 127/79 mmHg). Diurnal BP variation was blunted in the group with QTc dispersion >43 ms with significantly higher night/day ratio, both for systolic (88.8 vs. 86.2%, P < 0.01) and diastolic (83.1 vs. 79.5%, P < 0.01) BP. The association between QTc dispersion and diastolic night BP persisted after controlling for potential confounders such as sex, age, duration of diabetes, urinary albumin excretion, and HbA1c. Power spectral analysis suggested an altered sympathovagal balance in patients with QTc dispersion above the median (ratio of low-frequency/high-frequency power: 1.0 vs. 0.85, P < 0.01). In normoalbuminuric type 1 diabetic patients, increased QTc dispersion is associated with reduced nocturnal fall in BP and an altered sympathovagal balance. This coexistence may be operative in the ability of these parameters to predict cardiovascular events.

Orthostatic Hypotension in the Elderly: Contributions of Impaired LV Filling and Altered Sympathovagal Balance

Orthostatic hypotension, which occurs in 5%-18% of the elderly, may contribute to age-related disability. While autonomic dysfunction and alterations of cardiac structure and function likely to impair postural maintenance of blood pressure are common in the elderly, these have not been jointly studied in large cohorts. The authors evaluated the association of orthostatic hypotension with echocardiographic measures of cardiac structure and function, and with autonomic function determined by analysis of heart rate variability, in a large population of community-dwelling elderly. A total of 5201 men and women, aged 65-100 years and living in four geographically separate communities, were recruited from Medicare eligibility lists. In this prospective, observational cohort study, measurements included clinical questionnaires, standing and supine blood pressures, mini-glucose tolerance testing, echocardiography, and 24-hour Holter recording for assessment of heart rate variability. Orthostatic hypotension, defined as a decrease in standing systolic blood pressure of 20 mm Hg or more, was positively associated in bivariate analyses with left ventricular wall thickness, peak velocity of late diastolic filling, vagal tone on heart rate variability analysis, supine systolic pressure, supine diastolic pressure, age, and diabetes, and inversely associated with body weight. After statistical adjustment for the presence of myocardial infarction, stroke, and use of antihypertensive medication, the associations were maintained, and a previous trend toward an association with decreased left ventricular cavity size became statistically significant. The data suggest that in elderly, community-based individuals, orthostatic hypotension is associated with increased blood pressure and decreased weight; it possibly acts mechanistically via altered sympathovagal balance, increased left ventricular wall thickness, decreased left ventricular preload, and alterations of left ventricular diastolic filling. (c) 2000 by CVRR, Inc.

Effects of clonidine on power spectral analysis of heart rate variability in mild essential hypertension

Patients with essential hypertension often show alterations of the autonomic nervous system. We evaluated the sympathetic and parasympathetic drive to the heart in 12 mildly hypertensive patients and 9 healthy subjects by power spectral analysis of heart rate variability. All subjects underwent measurements of RR interval, low (LF) and high frequency (HF) components of heart rate variability, LF/HF ratio and blood pressure in the resting and sitting positions, both before and after oral clonidine (300 microg), a central sympatholytic agent. In the supine position before clonidine, hypertensive patients had higher blood pressure and lower HF values than healthy subjects. Clonidine induced increases in RR interval and HF in both groups, while LF and LF/HF ratio decreased in healthy subjects, but not in hypertensive patients. On assuming the sitting position, both groups showed reductions in RR and HF and increments in LF and LF/HF. In healthy subjects, the response to the postural challenge was unaffected by clonidine. In contrast, hypertensive patients showed no changes in LF and LF/HF ratio, and a significantly lower decrease in HF. These differences were probably due to the existence of two subsets of patients, one exhibiting similar responses to clonidine as healthy subjects, and the other showing no appreciable response to the drug. These results suggest that hypertensive patients have an altered sympatho-vagal balance to the heart, which can be unmasked by clonidine. This phenomenon should be taken into account to achieve a better control of the overall cardiovascular risk of hypertensive patients.

Impaired cardiovascular autonomic response to passive tilting in cirrhosis with ascites

The autonomic regulation of cardiovascular function was evaluated in 15 cirrhotic patients with ascites and in 13 healthy subjects by the autoregressive power spectral analysis (PSA) of the intervals between adjacent R waves of the electrocardiogram (RR) interval and arterial pressure variability. Total power, low frequency (LF; index of the sympathetic activity of the heart and circulation), and high frequency (HF; index of vagal tone to the heart) components of the RR interval, systolic, and diastolic arterial pressure were evaluated in the supine position and during passive tilting, together with plasma norepinephrine levels. In the supine position, no significant differences in the PSA data were observed between the control subjects and cirrhotic patients, who had higher plasma norepinephrine levels. In healthy subjects, tilting was associated with an increase in the LF of the RR interval and arterial pressure and a decrease in the HF of the RR interval. In contrast, patients with cirrhosis showed a decrease of both LF and HF. Consequently, the LF/HF ratio significantly increased in healthy subjects, whereas it was unchanged in cirrhotic patients. The LF component of the diastolic pressure also decreased during tilting in cirrhotic patients. Plasma norepinephrine increased after tilting in both groups. These results indicate that the autonomic response to passive tilting is impaired in cirrhotic patients with ascites at both the cardiac and vascular levels, as a result of an altered sympatho-vagal balance, with reduced sympathetic predominance. These alterations occurred despite an appropriate response to the tilting of plasma norepinephrine, pointing to a receptorial or postreceptorial site of the autonomic impairment.

Anti-arrhythmic effect of converting enzyme inhibitor, enalapril in congestive heart failure: possible contribution of altered sympathovagal autonomic balance on the heart

Anti-arrhythmic effect of converting enzyme inhibitor, enalapril in congestive heart failure: possible contribution of altered sympathovagal autonomic balance on the heart

Effect of autonomic nervous system dysfunction on the circadian pattern of myocardial ischemia in diabetes mellitus

The aim of this study was to determine the prevalence and characteristics of ambulatory myocardial ischemia in patients with diabetes mellitus and to delineate the relation between the presence and severity of autonomic nervous system dysfunction and the incidence and time of onset of myocardial ischemia. Conflicting data exist with regard to the circadian pattern of myocardial infarction and other cardiovascular events, such as ambulatory ischemia, in diabetes. We performed ambulatory electrocardiographic monitoring in 60 patients with diabetes and coronary artery disease. Autonomic nervous system testing was performed in a subgroup of 25 patients with myocardial ischemia after discontinuation of all antianginal medications. Thirty-eight of 60 patients had evidence of ambulatory ischemia; 91% of all ischemic episodes were asymptomatic. The 25 patients with ambulatory ischemia who underwent autonomic nervous system testing had a peak incidence of ischemia between 6 AM and noon (46 of 133 ischemic episodes, p < 0.007), compared with the other three 6-h periods. Fifteen of the 25 patients had no or mild autonomic nervous system dysfunction and demonstrated a similar peak incidence of ischemia between 6 AM and noon (p = 0.0009). However, the 10 patients with moderate to severe autonomic nervous system dysfunction did not experience a morning peak of ischemia, and the number of ischemic episodes was distributed evenly throughout the day (p = 0.4). Silent ischemia is highly prevalent among patients with diabetes and coronary artery disease. Time of onset of ischemia in diabetic patients follows a circadian distribution, with a peak incidence in the morning hours. However, patients with significant autonomic nervous system dysfunction did not demonstrate such a peak, suggesting that alterations in sympathovagal balance may have an effect on the circadian pattern of cardiovascular events.

Sodium lactate increases sympathovagal ratios in normal control subjects: Spectral analysis of heart rate, blood pressure, and respiration

We used spectral analysis of heart rate (HR), blood pressure (BP), and respiration to examine the effects of lactate on cholinergic and adrenergic influences on HR and BP variability, a technique found to be very useful in cardiovascular research. We specifically used high frequency (0.2-0.5 Hz) and midfrequency (0.07-0.15 Hz) powers to study cholinergic and adrenergic activity in nine normal control subjects before and after lactate and placebo infusions. Our results demonstrate a marked decrease in cholinergic activity and a significant increase in sympathovagal ratios of HR modulation after lactate infusions. This altered sympathovagal balance may contribute to the panicogenic effects of lactate in panic disorder patients.