A comparison of factor analytic methods of obtaining cardiovascular autonomic components for the assessment of mental workload

The diagnosticity of heart rate for mental workload assessment can be improved with an autonomic space model of sympathetic and parasympathetic nervous system influences on the heart. Methods of deriving autonomic components to estimate the underlying sympathetic and parasympathetic activity needed to identify autonomic modes of control for heart period were examined. Alternative factor extraction and rotation methods were compared using data from a laboratory study that measured the electrocardiogram and impedance cardiogram simultaneously. Principal components analysis with varimax rotation was found to validly estimate the sympathetic and parasympathetic activity when computed on multiple psychophysiological measures obtained from raw EKG data. Use of the method was illustrated with single and dual mental arithmetic and second-order compensatory manual tracking tasks. Different autonomic modes of control were found for divided attention that were not evident in heart period. Uncoupled sympathetic activation was indicated for divided attention when the mental arithmetic tasks were added to the tracking single tasks, but uncoupled parasympathetic inhibition was indicated for divided attention when the tracking tasks were added to the mental arithmetic single tasks.     

Direct in situ reverse transcriptase polymerase chain reaction for detection of measles virus

Behavioral contexts can evoke a variety of autonomic modes of response, characterized by reciprocal, coactive, or independent changes in the autonomic divisions. The present study investigated the modes of autonomic response to visual illusion and mental arithmetic tasks, by the use of noninvasive measures of sympathetic (pre-ejection period; PEP) and parasympathetic (respiratory sinus arrhythmia; RSA) cardiac control. As previously demonstrated, mental arithmetic was associated with a reciprocal pattern of sympathetic activation and vagal withdrawal. The illusion task, however, yielded a distinct mode of vagal activation in the absence of sympathetic change. Responses within tasks were reliable. In contrast to the general intertask consistency reported for stress tasks that yield similar autonomic modes of response, however, neither PEP nor RSA responses were correlated across the illusion and arithmetic tasks. This may be attributable to the dissimilar modes of autonomic control evoked by these tasks. The distinct modes of autonomic response to arithmetic and illusions emphasize the importance of a bivariate model of autonomic control, and may offer important experimental tools for psychophysiological studies of autonomic control.     

Effects of simulated microgravity on closed-loop cardiovascular regulation and orthostatic intolerance: analysis by means of system identification

Microgravity-induced orthostatic intolerance (OI) continues to be a primary concern for the human space program. To test the hypothesis that exposure to simulated microgravity significantly alters autonomic nervous control and, thus, contributes to increased incidence of OI, we employed the cardiovascular system identification (CSI) technique to evaluate quantitatively parasympathetic and sympathetic regulation of heart rate (HR). The CSI method analyzes second-to-second fluctuations in noninvasively measured HR, arterial blood pressure, and instantaneous lung volume. The coupling mechanisms between these signals are characterized by using a closed-loop model. Parameters reflecting parasympathetic and sympathetic responsiveness with regard to HR regulation can be extracted from the identified coupling mechanisms. We analyzed data collected from 29 human subjects before and after 16 days of head-down-tilt bed rest (simulated microgravity). Statistical analyses showed that parasympathetic and sympathetic responsiveness was impaired by bed rest. A lower sympathetic responsiveness and a higher parasympathetic responsiveness measured before bed rest identified individuals at greater risk of OI before and after bed rest. We propose an algorithm to predict OI after bed rest from measures obtained before bed rest.     

DNA single strand breakage, DNA adducts, and sister chromatid exchange in lymphocytes and phenanthrene and pyrene metabolites in urine of coke oven workers

During heart transplantation (HTX) all neural connections are severed. In humans, signs of autonomic reinnervation have been found. In this study non-invasive tests were used to compare signs of sympathetic and parasympathetic reinnervation. Non-invasive autonomic function tests and heart rate variability parameters (HRV; 24 h electrocardiographic registration) were used to investigate signs of reinnervation. 16 HTX patients (14 males) were compared with age-and sex-matched controls. Parasympathetic heart rate changes in HTX compared to controls were attenuated during the diving test, deep breathing, the Valsalva maneuver and standing up but not during carotid sinus massage. Sympathetic heart rate increases were lower during the cold pressor test and mental stress. The blood pressure responses were comparable to the control group, but not during active standing and tilting. This finding suggests an obligatory 'blood pressure' role for the innervated heart in these two tests. All HRV parameters were lower in HTX. One or more normal parasympathetic responses were found in 13 out of 16 patients versus 4 out of 16 with normal sympathetic responses (p < 0.05). Heart rate variations were less in case of a higher donor age, and higher in case of a longer time after HTX. Parasympathetic signs of reinnervation are more common than sympathetic signs of reinnervation. A higher donor age reduces signs of reinnervation. If the sympatho-vagal balance is a prognostic factor in HTX patients as it is in other cardiac diseases these findings are clinically relevant.     

The capsule biosynthetic locus of Pasteurella multocida A:1

OBJECTIVES: The purpose of this study was to investigate the progression of autonomic dysfunction in patients with Duchenne-type progressive muscular dystrophy (DMD) over time by using heart rate variability. BACKGROUND: Although previous studies suggest the presence of autonomic dysfunction in patients with DMD, the precise cause is not known. On the other hand, it is well known that analysis of heart rate variability provides a useful, noninvasive means of quantifying autonomic activity. High frequency power is determined predominantly by the parasympathetic nervous system, whereas low frequency power is determined by both the parasympathetic and sympathetic nervous systems. METHODS AND RESULTS: Frequency and time domain analyses of heart rate variability during ambulatory electrocardiographic monitoring were performed in 17 patients with DMD over a 9-year period. At the time of entry, the mean patient age was 11 years and the mean Swinyard-Deaver stage was 4. In the first year, high frequency power was significantly lower and the ratio of low frequency to high frequency was significantly higher in patients with DMD than in the normal control subjects. These differences become significantly greater as the disease progressed. At the time of entry, low and high frequency powers increased at night in both groups. However, over time, high and low frequency powers at night tended to decrease. All of the time domain parameters were significantly lower in the patients with DMD at all time points compared with the normal control subjects. CONCLUSIONS: We concluded that DMD patients have either a decrease in parasympathetic activity, an increase in sympathetic activity, or both as their disease progresses.     

Effects of selective breeding for infant rat ultrasonic vocalization on cardiac responses to isolation.

Heart rates (HR) and autonomic control of heart period (HP) during maternal separation and isolation were measured at postnatal days (P) 10 and 18 in rat pups selectively bred for high, low, and random rates of infant ultrasonic vocalization. P10 pups displayed no significant line differences in HRs, strong tonic basal sympathetic control of HP and little sympathetic reactivity to isolation, and no evidence of tonic baseline or phasic parasympathetic responses to isolation. At P18, during isolation and recovery, Low HRs were significantly higher compared with Random and High pups. High HRs were significantly higher compared with the Random line in the last third of isolation and through recovery. The higher HRs of Low pups during stress were due to greater parasympathetic withdrawal, but greater sympathetic activation could not be ruled out. Higher HRs in High pups were due to increased sympathetic activation. Thus, increases in HR responses in the selected lines are due to different underlying autonomic processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of autonomic tone on QT interval duration

The autonomic tone has been shown to influence the duration of the QT interval, however the independent contribution of sympathetic and parasympathetic tone is not fully elucidated. The influence of autonomic tone on QT duration was studied in 10 young healthy volunteers by evaluating the changes in QT and RR duration induced by i.v. isoproterenol infusion and by standing before and after i.v. administration of propranolol or atropine. Furthermore, the relationship between RR interval and QT duration was evaluated during nocturnal sinus arrhythmia and submaximal exercise test. Low doses of isoproterenol reduced RR (p < 0.01) but not QT interval duration, while higher doses influenced both RR (p < 0.0001) and QT (p < 0.001) duration. Propranolol did not influence standing-induced shortening of RR and QT intervals; on the contrary, atropine administration abolished standing-induced QT interval shortening, without influencing RR changes. QT duration resulted significantly related to preceding RR interval at peak exercise (r = 0.87, p < 0.001) and during nocturnal sinus arrhythmia (r = 0.73, p < 0.0005), however, the regression lines showing the correlation between QT and preceding RR interval were different. Both sympathetic and parasympathetic tone appear to contribute to heart rate-independent changes in QT duration. In the basal state parasympathetic more than sympathetic tone influences the relation QT-heart rate. Major increases of sympathetic nervous system activity may change the relation QT-heart rate. Thus, in case of abrupt autonomic changes, any proposed formula for heart rate correction of QT may result inappropriate, also in the normal range of heart rate.     

Spectral analysis of heart rate variability in patients with irritable bowel syndrome

BACKGROUND: Autonomic dysfunction, both adrenergic and cholinergic, has been associated with the irritable bowel syndrome (IBS). The accuracy of the methods in use, however, has been limited by the need for active co-operation by the patients, with consequent difficulties in standardization. The aim of this study was to investigate the function of the autonomic nervous system in patients with IBS by using spectral analysis of the heart rate variability, an accurate method depending very little on patient cooperation. METHODS: Eighteen patients with IBS were compared with 36 sex- and age-matched controls. Spectral analysis of heart rate variability was performed to quantify sympathetic and parasympathetic nerve activity. RESULTS: The patients with IBS had significantly higher sympathetic activity than controls (P = 0.005). There was no significant (P = 0.308) increase in parasympathetic activity. There were no significant differences in heart rate or blood pressure between the patients and controls. CONCLUSION: Spectral analysis of heart rate variability has been used to assess the function of the autonomic nervous system in patients with IBS. IBS patients have significantly increased symphathetic activity, whereas parasympathetic activity does not differ from that of controls.     

N(N)-nicotinic blockade as an acute human model of autonomic failure

Pure autonomic failure has been conceptualized as deficient sympathetic and parasympathetic innervation. Several recent observations in chronic autonomic failure, however, cannot be explained simply by loss of autonomic innervation, at least according to our current understanding. To simulate acute autonomic failure, we blocked N(N)-nicotinic receptors with intravenous trimethaphan (6+/-0.4 mg/min) in 7 healthy subjects (4 men, 3 women, aged 32+/-3 years, 68+/-4 kg, 171+/-5 cm). N(N)-Nicotinic receptor blockade resulted in near-complete interruption of sympathetic and parasympathetic efferents as indicated by a battery of autonomic function tests. With trimethaphan, small postural changes from the horizontal were associated with significant blood pressure changes without compensatory changes in heart rate. Gastrointestinal motility, pupillary function, saliva production, and tearing were profoundly suppressed with trimethaphan. Plasma norepinephrine level decreased from 1.1+/-0.12 nmol/L (180+/-20 pg/mL) at baseline to 0.23+/-0.05 nmol/L (39+/-8 pg/mL) with trimethaphan (P<.001). There was a more than 16-fold increase in plasma vasopressin (P<.01) and no change in plasma renin activity. We conclude that blockade of N(N)-cholinergic receptors is useful to simulate the hemodynamic alterations of acute autonomic failure in humans. The loss of function with acute N(N)-cholinergic blockade is more complete than in most cases of chronic autonomic failure. This difference may be exploited to elucidate the contributions of acute denervation and chronic adaptation to the pathophysiology of autonomic failure. N(N)-Cholinergic blockade may also be applied to study human cardiovascular physiology and pharmacology in the absence of confounding baroreflexes.     

Protein and calorie effects on progression of induced chronic renal failure in cats

This study was designed to determine if there is a difference in autonomic regulation induced by posture change between postmenopausal and young women. To evaluate autonomic nervous system function, spectral analysis of heart rate variability (HRV) was done in postmenopausal women (n = 13, 46-59 years of age), age-matched men (n = 8, 45-55 years of age), and young women (n = 10, 20-37 years of age) for 3-min periods of controlled frequency breathing (15 breaths/min) in supine followed by sitting positions. In the supine position, the R-R interval variation in older persons decreased significantly compared with that during the follicular phase in young women. Furthermore, the high-frequency (HF) components of HRV, which reflect only parasympathetic activity, were lower in older subjects than in young women. Following a change of position from supine to sitting, the HF component did not change significantly in the postmenopausal women or the men, but the low/high frequency (LF/HF) component ratio, which reflects the balance of autonomic nerve activities, increased significantly in the men. These results suggest that cardiac parasympathetic tone may be reduced in older persons in comparison with young women. Furthermore, arterial baroreflex control of parasympathetic nerve activity caused by posture changes is impaired in the postmenopausal women and aged-matched men. The baroreflex control of the sympathetic component is maintained in the men but not in the postmenopausal women. These differences might result in part from changes in the level of female hormones.     

Prevalence of central autonomic neuropathy in elderly dialysis patients

BACKGROUND: Autonomic neuropathy is frequently present in dialysis patients. In addition, deterioration of autonomic function occurs with ageing. This study examines the true prevalence of autonomic neuropathy in elderly dialysis patients and questions whether the combination of age and uraemia further increases the chance of dysautonomia being present. METHODS: We compared the results of five different tests (30:15 ratio; Valsalva ratio; heart rate response to deep breathing and the blood pressure responses to sustained hand grip and standing) of parasympathetic and combined parasympathetic and sympathetic dysfunction in older haemodialysis patients (mean age 70.2 years), younger haemodialysis patients (mean age 48.1 years) and two groups of subjects with normal renal function (mean age 73.0 years and 42.5 years respectively). RESULTS: Parasympathetic dysfunction was most prevalent in older patients on dialysis (65.9% (95% confidence intervals 51.4-80.4%), compared with 33.3% (95% confidence intervals 19.0-47.5% in younger dialysis patients), and 11.8 and 0% in the old and young control groups respectively). Combined parasympathetic and sympathetic dysfunction was seen in 41.5% (95% confidence intervals 26.5-56.5%) and 11.9% (95% confidence intervals 2.1-56.5%) of the old and young dialysis patients respectively but not in any of the control subjects. No interaction was seen between age and subject type. CONCLUSIONS: We conclude that although older dialysis patients have severe impairment of cardiovascular autonomic innervation, the prevalence of dysfunction is not higher than would be expected in an ageing population with uraemia.     

Autonomic control of cardiovascular performance and whole body O2 delivery and utilization in swine during treadmill exercise

OBJECTIVE: The present study determined the role of the autonomic nervous system (ANS) in the regulation of systemic and pulmonary circulation and of O2 delivery and utilization in swine at rest and during graded treadmill exercise. METHODS: Instrumented swine (n = 12) were subjected to treadmill exercise (1-5 km/h) under control conditions and in the presence of single and combined beta-adrenergic, alpha-adrenergic and muscarinic (M) receptor blockade. RESULTS: Exercise produced a four-fold increase in body O2 consumption, due to a doubling of both cardiac output and the arterio-mixed-venous O2 content difference. The latter resulted from an increase in O2 extraction, from 45 +/- 1% at rest to 74 +/- 1% at 5 km/h, as the O2 carrying capacity [haemoglobin concentration (Hb)] increased by only approximately 10%. The increase in cardiac output resulted from a doubling of the heart rate and a small (< 10%) increase in stroke volume. The mean aortic pressure (MAP) was unchanged, implying a 50% decrease in systemic vascular resistance (P < or = 0.05). In contrast, exercise had no significant effect on pulmonary vascular resistance. The sympathetic division of the ANS controlled O2 delivery via beta-adrenoceptors (heart rate and contractility) and Hb concentration via alpha-adrenoceptor-mediated splenic contraction. In addition, the sympathetic division modulated systemic vascular tone via alpha- and beta-adrenoceptors, but also exerted a vasodilator influence on the pulmonary circulation via beta-adrenoceptors. The parasympathetic division controlled O2 delivery in part directly (heart rate) and in part indirectly via inhibition of beta-adrenoceptor activity (heart rate and contractility), even during heavy exercise. In addition, the parasympathetic division exerted a direct vasodilator influence on the pulmonary, but not on the systemic, circulation. CONCLUSIONS: Thus, in swine, in a manner similar to that in humans, both the sympathetic and parasympathetic division of the ANS contribute to cardiovascular homeostasis during exercise up to levels of high intensity.     

Influence of parasympathetic dysfunction and hyperinsulinemia on the hemodynamic response to an isometric exercise in non-insulin-dependent diabetic patients

The handgrip test has long been used as a test for investigating cardiac autonomic neuropathy in diabetic patients. However, the factors involved in the hemodynamic response to the handgrip test have not been thoroughly studied. The aim of this study was to investigate blood pressure (BP) and heart rate (HR) responses to an isometric test in non-insulin-dependent diabetics (NIDDs) and to correlate the results with vagal function evaluated by three standardized tests and with plasma insulin levels. Fifty-five NIDDs, 35 of whom had one to three abnormal parasympathetic tests (PS+), were compared with 10 healthy control subjects. Fasting and postprandial plasma insulin levels were significantly higher in the PS+ than in the PS- patients. Resting HR correlated significantly with log fasting and postprandial insulin. In PS+ NIDDs, resting HR was significantly higher than in PS- patients. Age-matched comparisons also showed that resting systolic BP was significantly higher in PS+ patients than in controls. In PS- patients, the mean acceleration of HR was significantly higher than in the control group from the second to the fifth minute, and the BP response was also higher than in controls. These data suggest that (1) sympathetic response to an isometric exercise is increased in PS- NIDDs; (2) cardiac parasympathetic dysfunction is associated with a more severe insulin resistance; and (3) the subsequent higher plasma insulin level may contribute to the increase in resting HR and BP through sympathetic activation while limiting the hemodynamic response to an isometric exercise through its vasodilative effect.     

Impairment of autonomically mediated heart rate control in patients with cardiac dysfunction

Patients with cardiac disorders have defective parasympathetic control of heart rate. To evaluate the possibility of similar changes in sympathetic control of heart rate, we compared reflex chronotropic responses to 80 degree upright tilt and nitroglycerin-induced hypotension in 31 cardiac patients and 7 normal individuals before and after partial parasympathetic blockade with atropine. Tilting revealed an attenuation of the normal heart rate increase in patients; the magnitude of this defect was greatest in patients with more severe symptoms (class III) and evidence of left ventricular dysfunction (the heart rate increase averaged 25 plus or minus 3 beats/min in normal subjects, 12 plus or minus 2 beats/min in class I-II patients, and 7 plus or minus 1 beats/min in class III patients). Class III symptoms due to mechanical causes (mitral stenosis), however, were not associated with this defect. A marked reduction in heart rate rise with hypotension was seen only in those class III patients without mitral stenosis (0.4 plus or minus 0.1 beats min-minus 1 mm Hg-minus 1 vs. 3.0 plus or minus 0.5 beats min-minus 1 mm Hg-minus 1 in normal subjects). This abnormality also persisted after atropine administration, thus confirming a defect in the sympathetic as well as the parasympathetic component of baroreceptor-mediated reflex heart rate control in patients with cardiac dysfunction. Infusions of isoproterenol produced equivalent rises in heart rate in patients and normal individuals, excluding a reduction in beta-receptor responsiveness as a cause of impaired sympathetic influence. Norepinephrine depletion, however, is a well-recognized concomitant of cardiac failure. It is possible that the reduction in sympathetically mediated heart rate responses results in part from depletion of the sympathetic neurotransmitter.     

Lipid metabolism and renal protection by chronic cicletanine treatment in Dahl salt-sensitive rats with salt-induced hypertension

The role cardiac autonomic neuropathy (CAN) plays in diabetes is not well known. The aim of this study was to identify the factors involved in CAN in diabetic patients. One hundred patients, 44 insulin-dependent (IDDM) and 56 non-insulin-dependent (NIDDM), were investigated, using five standard tests. Three of these tests were for parasympathetic control (cardiac response to the lying-to-standing, deep breathing, and Valsalva tests), and the other two measured sympathetic control (testing for orthostatic hypotension and evaluating heart and blood pressure response to the handgrip test). Results were compared to those found in a series of 40 healthy volunteers. An age-adjusted comparison with the controls, showed that 34 patients had one abnormal parasympathetic test, 23 had two, and 6 patients had three. Cardiac parasympathetic neuropathy was thus present in 63% of the patients. The handgrip test was completed by 84 diabetic patients. There was evidence of orthostatic hypotension and/or an abnormal cardiac response to the handgrip in 15 of these patients, who all had a parasympathetic abnormality as well. There was no significant association between the type of diabetes and the presence of CAN. The duration of diabetes was significantly longer in patients with CAN (9.3 +/- 0.9 years) (p < 0.01) than in those with all three parasympathetic tests normal (5.8 +/- 0.9 years) (p < 0.01). The HbA1c level was also higher in patients with CAN than in those with three normal parasympathetic tests (9.95 +/- 0.35% versus 8.17 +/- 0.42%, p < 0.005). There was a significant association between the presence of retinopathy, observed by angiofluorography, and the presence of peripheral neuropathy confirmed by the electrophysiological investigation and the presence of CAN (p < 0.001). However, more than half the patients without retinopathy or nephropathy had CAN, and 11 of the 31 patients with a normal electrophysiological investigation also had CAN. Eighteen patients (6 IDDM) without retinopathy and nephropathy, who had been diabetic for less than 2 years, also had CAN. This study shows that CAN occurs early and is frequently found in a population of unselected diabetic patients. Metabolic factors may play an important role in its occurrence. CAN is significantly associated with the presence of retinopathy, which suggests that an impairment of autonomic peripheral blood flow control might be a contributing factor in the formation of microvascular lesions.     

Alteration of cardiovascular vagosympathetic control evaluated by spectral analysis of variations of heart rate and blood pressure in obesity

Several studies suggest alterations of parasympathetic and sympathetic control in obesity. We have already shown that more than 40% of non diabetic obese subjects have alterations of parasympathetic control of heart rate (HR) variations. The present study aimed to investigate parasympathetic and sympathetic cardiovascular control by using spectral analysis. Sixty-two non diabetic obese subjects were compared to 38 sex-matched healthy controls. Spectral analysis was performed by Anapres system and identified two particular peaks: the one of high frequency (0.20-0.25 Hz) for heart rate variations during controlled breathing which depends on parasympathetic activity, the other of low frequency (around 0.10 Hz) for systolic BP variations in the standing position which mainly depend on sympathetic activity. In control subjects the amplitude of the high frequency peak (r = -0.556, p < 0.0001) but not the amplitude of the low frequency peak correlated negatively with age. In the obese subjects both the high and low frequency peaks correlated negatively with age (r = -0.249; p = 0.05 and r = -0.289, p = 0.036 respectively) and did not correlate with body mass index. The high frequency peak was significantly lower than in controls (4.80 +/- 3.37 (SD) vs 8.38 +/- 4.14; p < 0.0001). In the 25 obese subjects over 40 years the low frequency peak was also significantly lower than in controls (10.00 +/- 3.10 vs 11.95 +/- 4.25; p < 0.05). This study suggests that 1) age must be taken into account when interpreting the cardiovascular parameters under vagosympathetic control; 2) in non diabetic obese subjects vagal activity is decreased and in those over 40 years sympathetic activity is also decreased.     

Clinical and laboratory indices that enhance the diagnosis of postural tachycardia syndrome

OBJECTIVE: To identify clinical and laboratory indices that improve the diagnosis of the postural tachycardia syndrome (POTS). DESIGN: We assessed associations of orthostatic intolerance by using multivariate regression analysis. MATERIAL AND METHODS: We evaluated autonomic symptoms and autonomic function in 30 patients with POTS, 30 patients with mild orthostatic intolerance, and 19 age- and gender-matched control subjects. Indices of parasympathetic and sympathetic functions were analyzed on the basis of (1) autonomic function tests (head-up tilt), (2) oscillations at respiratory and nonrespiratory frequencies (0.01 to 0.09 Hz) in R-R interval and blood pressure (Wigner distribution), and (3) deterministic component (rescaled range analysis). RESULTS: The four clinical and laboratory indices that independently supported the diagnosis of POTS are as follows: (1) orthostatic heart rate during the first minute of head-up tilt, (2) autonomic deficit (adrenergic autonomic score), (3) loss of spectral powers in R-R interval during head-up tilt at the fifth minute, and (4) severity of orthostatic dizziness, fatigue, palpitations, and shortness of breath. CONCLUSION: Enhancing the sensitivity and specificity of the diagnosis of POTS should be possible by using these four indices. A hyperadrenergic state and distal neuropathy, affecting adrenergic sympathetic cardiovagal fibers, seem to be involved in the pathophysiology of POTS. Certain features suggest brain-stem dysregulation.     

Autonomic nervous activity at episodes of myocardial ischemia in patients with coronary artery disease by heart rate power spectral analysis

Heart rate power spectral analysis in 44 patients with coronary artery disease was obtained from 24-hour dynamic electrocardiogram. 195 episodes of transient myocardial ischemia that was defined as horizontal or down sloping depression of the ST segment of > or = 0.1 mV and lasted for > or = 2 minutes were studied. The area of low frequency components (LF, 0.02-0.10 Hz) representing predominontly sympathetic tone with some contribution from the parasympathetic tone and that of high frequency components (HF, 0.15-0.40 Hz) representing mainly parasympathetic tone and the value of LF/HF on 4 minute heart rate power spectral graph at the deepest depression of ST segment were compared with that before the episode of myocardial ischemia. The area of HF of fast rate myocardial ischemia occurring in night reduces significantly (P < 0.001), the value of LF/HF increases markedly (P < 0.05) and the area of LF increases slightly. The results suggest that there is a change of autonomic nervous activity during the episode of fast rate myocardial ischemia in night, parasympathetic nervous tone decreases markedly, there may be secondary increase of sympathetic nervous activity.     

T-wave amplitude: relationships to phasic RSA and heart period changes

T-Wave Amplitude (TWA) has been suggested as an indicator of sympathetic influence on myocardial performance, but critics have argued that TWA is confounded by parasympathetic influence or that it is a non-specific feature of tachycardia. To help clarify the issue, we examined TWA as a function of parasympathetic activity, using cardiac vagal control as measured by high frequency components of heart period variability (respiratory sinus arrhythmia) and of interbeat intervals (IBI), across several stressful tasks. Sixteen male subjects were exposed to Valsalva, Serial Subtraction and Cold-Pressor tasks. After controlling for between-person variance, it was found that RSA did not contribute to TWA and that IBI contributed dependably to TWA only during the Valsalva maneuver, when heart rate was driven very high. In light of these results, we recommend that TWA continue to be considered a candidate indicator of sympathetic influence on myocardial performance, although caution should be used if heart rate is dramatically elevated.