Aging alteration of cardiac vagosympathetic balance assessed through the tone-entropy analysis

Effects of Resistance Training Intensity on Heart Rate Variability at Rest and in Response to Orthostasis in Middle-Aged and Older Adults

OBJECTIVE

Aging and deficits related to decreased physical activity can lead to higher risks of autonomic nervous system (ANS) dysfunction. The aim of this study was to evaluate the effects of 24 weeks of resistance training (RT) at various intensities on hemodynamics as well as heart rate variability (HRV) at rest and in response to orthostatic tests in middle-aged and older adults.

METHODS

Forty adults were randomized into three groups: high-intensity (HEX) (80% 1-RM) (11 female, 4 male; 60 ± 4 years); low-moderate-intensity (LEX) (50% 1-RM) (nine female, four male; 61 ± 5 years); and a control group (CON) (eight female, four male; 60 ± 4 years). The RT program consisted of nine exercises, with two sets performed of each exercise two times per week for 24 weeks. Data collected included 1-RM, heart rate, and blood pressure and HRV at rest and in response to orthostasis.

RESULTS

Both the HEX (42-94%) and LEX (31.3-51.7%) groups showed increases in 1-RM (p < 0.01). The HEX group showed decreases in resting heart rate (-4.0%), diastolic blood pressure (-3.2 mmHg (-4.2%)), and low frequency/high frequency (LF/HF) (Ln ratio) (p < 0.05). Post-study, the HEX group had higher HF (Ln ms²) than the CON, adjusted for pre-study value and age (p < 0.05). Post-study, the supine-standing ratio (SSR) of LFn (normalized unit) in the HEX group was greater than that in the LEX and CON groups, while the SSR of LF/HF in the HEX group was greater than the CON (p < 0.05). In conclusion, high-intensity RT can improve resting heart rate and HRV by enhancing cardiac vagal control. High-intensity RT might also improve the orthostatic response in terms of HRV. High intensity RT might assist ANS modification and could perhaps decrease the risks of cardiovascular disease and orthostatic intolerance.

Burden of premature atrial beats in middle-aged endurance athletes with and without lone atrial fibrillation versus sedentary controls

BACKGROUND

The burden of premature atrial beats (PABs) at 24-h electrocardiographic (ECG) monitoring correlates with the risk of atrial fibrillation. It is unknown whether prolonged and intense exercise increases the burden of PABs, thus contributing to the higher prevalence of atrial fibrillation observed in middle-aged athletes.

METHODS

We compared the burden of PABs at 24-h ECG monitoring off therapy in 134 healthy middle-aged (30-60-year-old) competitive athletes who had practised 9 (7-11) h of endurance sports for 8 (4-15) consecutive years, 134 age- and gender-matched healthy sedentary individuals, and 66 middle-aged patients (20 athletes and 46 non-athletes) with 'lone' paroxysmal atrial fibrillation.

RESULTS

More than 50 PABs/24 h or ≥1 run of ≥3 PABs were recorded in 23/134 (17%) healthy athletes and in 29/134 (22%) sedentary controls (p = 0.61). Healthy athletes with frequent or repetitive PABs were older (median 50 years vs. 43 years, p < 0.01) and had practised sport for a longer time (median 10 years vs. 6 years, p = 0.03). At multivariable analysis only age (odds ratio 1.11, 95% confidence interval 1.04-1.20, p < 0.01) remained an independent predictor of a higher burden of PABs. Also among patients with 'lone' paroxysmal atrial fibrillation, there was no difference in the prevalence of >50 PABs/24 h or ≥1 run of ≥3 PABs between athletes (40%) and controls (48%, p = 0.74).

CONCLUSIONS

Middle-aged endurance athletes, with or without paroxysmal atrial fibrillation, did not show a higher burden of PABs at 24-h ECG monitoring than sedentary controls. Age, but not intensity and duration of sports activity, predicted a higher burden of PABs among healthy athletes.

Multi-lag tone-entropy in neonatal stress

Heart rate variability (HRV) has been analysed using linear and nonlinear methods. In the framework of a controlled neonatal stress model, we applied tone-entropy (T-E) analysis at multiple lags to understand the influence of external stressors on healthy term neonates. Forty term neonates were included in the study. HRV was analysed using multi-lag T-E at two resting and two stress phases (heel stimulation and a heel stick blood drawing phase). Higher mean entropy values and lower mean tone values when stressed showed a reduction in randomness with increased sympathetic and reduced parasympathetic activity. A ROC analysis was used to estimate the diagnostic performances of tone and entropy and combining both features. Comparing the resting and simulation phase separately, the performance of tone outperformed entropy, but combining the two in a quadratic linear regression model, neonates in resting as compared to stress phases could be distinguished with high accuracy. This raises the possibility that when applied across short time segments, multi-lag T-E becomes an additional tool for more objective assessment of neonatal stress.

Predicting depressed patients with suicidal ideation from ECG recordings

Globally suicidal behavior is the third most common cause of death among patients with major depressive disorder (MDD). This study presents multi-lag tone-entropy (T-E) analysis of heart rate variability (HRV) as a screening tool for identifying MDD patients with suicidal ideation. Sixty-one ECG recordings (10 min) were acquired and analyzed from control subjects (29 CONT), 16 MDD subjects with (MDDSI+) and 16 without suicidal ideation (MDDSI-). After ECG preprocessing, tone and entropy values were calculated for multiple lags (m: 1-10). The MDDSI+ group was found to have a higher mean tone value compared to that of the MDDSI- group for lags 1-8, whereas the mean entropy value was lower in MDDSI+ than that in CONT group at all lags (1-10). Leave-one-out cross-validation tests, using a classification and regression tree (CART), obtained 94.83 % accuracy in predicting MDDSI+ subjects by using a combination of tone and entropy values at all lags and including demographic factors (age, BMI and waist circumference) compared to results with time and frequency domain HRV analysis. The results of this pilot study demonstrate the usefulness of multi-lag T-E analysis in identifying MDD patients with suicidal ideation and highlight the change in autonomic nervous system modulation of the heart rate associated with depression and suicidal ideation.

Dynamic response of cardiac autonomic nervous system activity to habitual exercise during gradual variation of breathing frequency

The purpose of this study is to measure cardiac autonomic nervous system activity during breathing control with gradual alteration of the frequency between habitual exercise and sedentary young male subjects. In this study, to evaluate CANS activity, Tone-Entropy analysis, which is based on statistical property of acceleration between consecutive R-R intervals, was used. Sixteen healthy young male subjects (21.6+/-1.4yrs) were participated in these experiments and their R-R interval sequences were recorded. The controlled breathing trials let the subjects synchronize their breathing frequency ranging 3 to 30 breathing per minute. After that, breathing frequency was gradually and reversely decreased from 30 to 3 breathing per minute. Before and after the breathing controlled trials, 5 minute voluntary breathing trials were performed. Our results showed that total CANS activities of HE group were activated more than those of SE group in the entire sections and also that, as compared with HE group, maximum of average HR in SE group was appeared at 30 breathing per minute and it is recognized that the statistically significant difference between HE and SE group was shown. In conclusion, our results suggest that efficiency of cardiac function on habitual exercise in breathing control may be quantitatively and graphically evaluated with HR and Tone-Entropy analysis without any physical stimulation.

Association of cardiovascular risk using non-linear heart rate variability measures with the framingham risk score in a rural population

Cardiovascular risk can be calculated using the Framingham cardiovascular disease (CVD) risk score and provides a risk stratification from mild to very high CVD risk percentage over 10 years. This equation represents a complex interaction between age, gender, cholesterol status, blood pressure, diabetes status, and smoking. Heart rate variability (HRV) is a measure of how the autonomic nervous system (ANS) modulates the heart rate. HRV measures are sensitive to age, gender, disease status such as diabetes and hypertension and processes leading to atherosclerosis. We investigated whether HRV measures are a suitable, simple, noninvasive alternative to differentiate between the four main Framingham associated CVD risk categories. In this study we applied the tone-entropy (T-E) algorithm and complex correlation measure (CCM) for analysis of HRV obtained from 20 min. ECG recordings and correlated the HRV score with the stratification results using the Framingham risk equation. Both entropy and CCM had significant analysis of variance (ANOVA) results [F (172, 3) = 9.51; <0.0001]. Bonferroni post hoc analysis indicated a significant difference between mild, high and very high cardiac risk groups applying tone-entropy (p < 0.01). CCM detected a difference in temporal dynamics of the RR intervals between the mild and very high CVD risk groups (p < 0.01). Our results indicate a good agreement between the T-E and CCM algorithm and the Framingham CVD risk score, suggesting that this algorithm may be of use for initial screening of cardiovascular risk as it is noninvasive, economical and easy to use in clinical practice.

Resistance exercise improves autonomic regulation at rest and haemodynamic response to exercise in non-alcoholic fatty liver disease

Autonomic dysfunction has been reported in patients with NAFLD (non-alcoholic fatty liver disease) and is associated with clinical presentations. To date, there are no therapies to improve autonomic regulation in people with NAFLD. The present study defines the impact of a short-term exercise programme on cardiac autonomic and haemodynamic regulation in patients with NAFLD. A total of 17 patients with clinically defined NAFLD [age, 55±12 years; BMI (body mass index), 33±5 kg/m²; liver fat, 17±9%] were randomized to 8 weeks of resistance exercise or a control group to continue standard care. Resting and submaximal exercise (50% of peak oxygen consumption) autonomic and cardiac haemodynamic measures were assessed before and after the intervention. Resistance exercise resulted in a 14% reduction in HR (heart rate) and 7% lower SBP (systolic blood pressure) during submaximal exercise (16 beats/min, P=0.03 and 16 mmHg, P=0.22). Sympathovagal balance, expressed as LF/HF (low-frequency/high-frequency) ratio of the mean HR beat-to-beat (R-R) interval, was reduced by 37% (P=0.26). Similarly sympathovagal balance of DBP (diastolic blood pressure) and SBP variability decreased by 29% (P=0.33) and 19% (P=0.55), respectively in the exercise group only. BRS (baroreflex sensitivity) increased by 31% (P=0.08) following exercise. The mean R-R interval increased by 23% (159 ms, P=0.09). Parasympathetic regulation was decreased by 17% (P=0.05) and overall sympathovagal balance in BP regulation (LF/HF ratio) increased by 26% (P=0.02) following resistance exercise. Resting haemodynamic measures remained similar between groups. Resistance exercise therapy seems to improve autonomic and submaximal exercise haemodynamic regulation in NAFLD. Further studies are required to define its role in clinical management of the condition.

Risk stratification of cardiac autonomic neuropathy based on multi-lag Tone-Entropy

Cardiac autonomic neuropathy (CAN) is an irreversible condition affecting the autonomic nervous system, which leads to abnormal functioning of the visceral organs and affects critical body functions such as blood pressure, heart rate and kidney filtration. This study presents multi-lag Tone-Entropy (T-E) analysis of heart rate variability (HRV) at multiple lags as a screening tool for CAN. A total of 41 ECG recordings were acquired from diabetic subjects with definite CAN (CAN+) and without CAN (CAN-) and analyzed. Tone and entropy values of each patient were calculated for different beat sequence lengths (len: 50-900) and lags (m: 1-8). The CAN- group was found to have a lower mean tone value compared to that of CAN+ group for all m and len, whereas the mean entropy value was higher in CAN- than that in CAN+ group. Leave-one-out (LOO) cross-validation tests using a quadratic discriminant (QD) classifier were applied to investigate the performance of multi-lag T-E features. We obtained 100 % accuracy for tone and entropy with len = 250 and m = {2, 3} settings, which is better than the performance of T-E technique based on lag m = 1. The results demonstrate the usefulness of multi-lag T-E analysis over single lag analysis in CAN diagnosis for risk stratification and highlight the change in autonomic nervous system modulation of the heart rate associated with cardiac autonomic neuropathy.

Evaluating cardiovascular risk using the tone-entropy algorithm

Currently the Framingham equation is the most often used cardiovascular risk calculator in health care. The equation requires data for age, gender, cholesterol status, blood pressure, diabetes status and smoking. A large proportion of the morbidity and mortality associated with cardiovascular disease is due to arrhythmic events that are multifactorial including dysregulation by the autonomic nervous system. In this study we applied the tone-entropy algorithm for analysis of heart rate variability obtained from 20 minute ECG recordings and compared the outcome with the Framingham risk stratification. Our results indicate a good agreement between the T-E algorithm and the Framingham risk equation suggesting that this algorithm may be of use for initial screening of cardiovascular risk as it is noninvasive, economical and easy to use in clinical practice.

Multi-scale Tone Entropy in differentiating physiologic and synthetic RR time series

Heart rhythm is extrinsically modulated by the autonomic nervous system and recently, the Tone-Entropy (TE) measurement was reported as a measure of autonomic balance and activity in time domain HRV analysis. Current algorithm for T-E measurement describes only beat-to-beat or influence of a heart beat on a train of succeeding beats on a single scale. Therefore, conventional T-E analysis has often not been able to discern various physiological conditions using heart rate variability (HRV) signal. In this study, we will present a mathematical framework to define multi-scale T-E analysis, apply this in differentiating physiological and synthetic RR time series. Finally, we compare the performance of proposed parameters with conventional T-E measurements.

Association of cardiac autonomic neuropathy with alteration of sympatho-vagal balance through heart rate variability analysis

Early sub-clinical assessment of severity of cardiac autonomic neuropathy (CAN) and intervention are of prime importance for risk stratification and early treatment in preventing sudden death due to silent myocardial infarction. The Ewing battery is currently the diagnostic tool of choice but is unable to detect sub-clinical disease and requires patient cooperation. Time and frequency domain analysis have several shortcomings including sensitivity to recording length, respiratory activity and non-stationarities in the ECG signal. An important step forward is to have a non-invasive method of detecting CAN that is robust against these shortcomings and has a higher sensitivity for the presence of both sub-clinical and overt clinical disease. This study presents a novel parameter, tone-entropy (T-E) that analyses heart rate variability (HRV) of 20 min lead II ECG recordings. Tone (T) represents sympatho-vagal balance and entropy (E) the autonomic regularity activity. Thirteen normal subjects without (CAN-) and 21 with CAN (CAN+) participated in this study. Among 21 CAN+ subjects, 13 are early CAN+ (eCAN+), eight are definite CAN+ (dCAN+) according to autonomic nervous system function tests as described by Ewing. The results showed that tone was higher and the entropy was lower in the dCAN+ group (T=-0.033 to -0.010 and E=1.73-2.24) compared with the eCAN+ (T=-0.0927 to -0.0311 and E=2.0-2.65) and normal (T=-0.128 to -0.0635 and E=2.64-3.15) group. The research verified that T-E is a suitable method to determine the presence of CAN that correctly identifies experimentally induced changes in cardiac function akin to parasympathetic and sympathetic dysfunction and differentiates between stages in CAN disease progression identified using the Ewing battery.

Relation of vigorous exercise to risk of atrial fibrillation

Limited data suggest that athletes may have a higher risk of developing atrial fibrillation (AF); however, there has been no large prospective assessment of the relation between vigorous exercise and AF. Logistic regression analyses stratified by time were used to assess the association between frequency of vigorous exercise and risk of developing AF in 16,921 apparently healthy men in the Physicians' Health Study. During 12 years of follow-up, 1,661 men reported developing AF. With increasing frequency of vigorous exercise (0, 1, 1 to 2, 3 to 4, 5 to 7 days/week), multivariate relative risks for the full cohort were 1.0 (referent), 0.90, 1.09, 1.04, and 1.20 (p = 0.04). This risk was not significantly increased when exercise habits were updated or in models excluding variables that may be in the biological pathway through which exercise influences AF risk. In subgroup analyses, this increased risk was observed only in men <50 years of age (1.0, 0.94, 1.20, 1.05, 1.74, p <0.01) and joggers (1.0, 0.91, 1.03, 1.30, 1.53, p <0.01), where risks remained increased in all analyses. In conclusion, frequency of vigorous exercise was associated with an increased risk of developing AF in young men and joggers. This risk decreased as the population aged and was offset by known beneficial effects of vigorous exercise on other AF risk factors.

Evaluation of diabetic neuropathy using the tone-entropy analysis, a noninvasive method to estimate the autonomic nervous function

It is clinically important to diagnose diabetic neuropathy at the early stage. In this study, the toneentropy analysis of electrocardiogram was applied to diabetic patients to evaluate its usability in the screening of diabetic neuropathy. Consecutive 102 diabetic patients were invited to the study. Electrocardiogram was obtained and analyzed for the tone and the entropy using an original software developed previously. Nerve conduction velocity (NCV) was examined on the median, the posterior tibial and the sural nerves. Patients were divided into quartile subpopulations according to the NCVs in the analysis. Both the tone and the entropy significantly correlated with NCVs, while coefficient of variation in R-R intervals did not show a significant correlation. The correlation was most significant between the entropy and the NCV on the sural nerve. When a multivariate analysis (ordinary regression) was applied to examine independent effects of the factors influencing the NCV on the sural nerve, the entropy was the most potent independent factor (beta = 1.14 +/- 0.32, P = 0.0004) along with sex (beta = 0.43 +/- 0.19, P = 0.02) and BMI (beta = 0.11 +/- 0.05, P = 0.04). The tone-entropy analysis on electrocardiogram may be a promising non-invasive screening method for diabetic neuropathy.

Autonomic activity during desflurane anesthesia in patients with brain tumors

OBJECTIVE

Although intracranial tumors may affect autonomic function, there are few reports of autonomic changes during anesthesia. The purpose of this study was to evaluate autonomic effects of anesthesia in patients with brain tumors compared to neurosurgical controls.

METHODS

Two groups were evaluated: group 1 = 10 neurosurgical patients undergoing spinal cord surgery, group 2 = 10 patients with intracranial tumors. After placement of electrocardiogram and Response Entropy electroencephalogram (EEG) electrodes, 10 min baseline measures were made. Heart periods were transformed into a percentage index and heart rate entropy determined as a measure of variance of autonomic activity. Tone was evaluated as the balance between accelerator and inhibitory activity. Tone-entropy was measured during propofol anesthetic induction and the first 60 min of desflurane anesthesia before the start of surgery.

RESULTS

Blood pressure and heart rate were similar between the groups. Starting at awake levels, vagal heart tone was observed. Anesthesia decreased vagal dominance to near zero in both groups. Heart rate entropy and EEG activity decreased during anesthesia with no significant difference between the groups. Desflurane concentrations required to maintain anesthesia were significantly lower in patients in brain tumors.

CONCLUSION

Tone-entropy analysis of heart rate indicates anesthetic related depression of autonomic activity with no difference between groups. Normal titration of desflurane concentrations to maintain adequate blood pressure produced desflurane requirements that were lower in patients with brain tumors, while autonomic and EEG activity were similar.

A comparative scale of autonomic function with age through the tone-entropy analysis on heart period variation

Tremendous numbers of heart rate variability studies have aimed to elucidate age-associated alterations of autonomic function in the past decades. However, the studies, far from clarifying ageing mechanisms, fell into confusion by a lack of common scales. The purpose of this study is to show a possibility to establish a comparative scale of autonomic function through a method, tone-entropy (T-E) analysis on heart period variation, whose validity has been already examined on typical physiological cases (Oida et al. in J Appl Physiol 82:1794-1801, 1997; Oida et al. in J Gerontol 54A:M219-M224, 1999a; Oida et al. in Acta Physiol Scand 165:129-134, 1999b; Oida et al. in Acta Physiol Scand 165:421-422, 1999c; Amano et al. in Eur J Appl Physiol 94:602-610, 2005). In this study, 276 subjects from teens to seventies were examined at rest by T-E analysis together with conventional time and frequency domain analyses. The tone (negativity represents vagal predominance) became significantly high [-0.174 +/- 0.026 (teens) to -0.024 +/- 0.004 (seventies), P < 0.05 for one-way ANOVA], and the entropy (total autonomic activity), significantly low [4.40 +/- 0.12 (teens) to 2.90 +/- 0.09 bit (seventies), P < 0.05] with advancing age. The result, plotted in 2-D T-E space, showed that the ageing traced a curvi-linear relation from right-bottom to left-top, and was consistent with previously studied typical physiological cases. The conventional analyses showed almost the same autonomic reduction as T-E did, but failed in detecting delicate alteration of autonomic balance. The results, showing that autonomic activity reduced in both pathways impairing vagal predominance significantly with ageing, suggested a possibility to assess autonomic function in 2-D T-E space in a comparative way.

Reliability of heart rate variability in healthy older women at rest and during orthostatic testing

BACKGROUND AND AIMS

In the older population, the reliability of heart rate variability (HRV) has only been evaluated in a few studies, in the supine position, and covering a broad sample of age and patients of both sexes. To document the relevance of using HRV analysis in healthy older women, the aim of this study was to evaluate the reliability of HRV indexes during three classical tests.

METHODS

33 healthy women (66.9+/-0.7 years old) performed two test sessions. Each session consisted of an ECG recorded in the supine position, first with free breathing (Test 1), then with controlled breathing (Test 2), and in the upright position (Test 3). Time and frequency HRV indexes were obtained by processing the ECG signals. Reliability was assessed between sessions using Student's paired t-test, intraclass correlation coefficient (ICC) and coefficient of variation (CV).

RESULTS

There were no differences between the sessions. ICC showed good reliability for all HRV indexes. CV was low for absolute HRV indexes, except in Test 3 for parasympathetic indexes with modest CV. The CV of HRV ratio indexes were modest to high in all three tests.

CONCLUSIONS

Time and absolute frequency HRV indexes are reliable when testing healthy older women. Our results support the use of such indexes in gerontology research, to assess the effects of clinical or pharmacological interventions on the autonomic nervous system.

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.

Exercise prescription based upon cardiac vagal activity for middle-aged obese women

OBJECTIVE

The purposes of this study were to examine a new method to determine exercise intensity for obese people based on the cardiac vagal activity and to determine the effect of this approach on myocardial stress.

SUBJECTS

Forty-three middle aged obese female volunteers (age 43.7+/-6.5 y; height 1.56+/-0.05 m; body mass 66.5+/-9.3 kg; body mass index 27.3+/-2.8 kg m(2); percentage body fat 40.7+/-5.9%).

MEASUREMENT

In the first experiment, 43 subjects performed a ramp exercise test on a bicycle ergometer with measurement of ECG and gas exchange parameters. In the second experiment, 11 subjects performed 45 min of constant walking exercise on a treadmill at a level corresponding to exercise intensity determined by vagal activity obtained from a ramp bicycle test. Blood pressure, endothelin 1 (ET-1), catecholamine, atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP) were measured before and after exercise.

RESULTS

The heart rate variability power decreased with increasing work rate, and changed little after reaching individual-specific work rate. We presumed that vagal activity disappeared at this point and that the heart rate at this exercise intensity was determined as the vagal activity threshold (T(VA)). The results showed a significant positive correlation (r=0.742, P<0.0001) between T(VA) and ventilatory threshold (VT) heart rates, although the mean heart rate of T(VA) (114.3+/-8.5 beats/min) was significantly lower (P<0.001) than that at VT (119.0+/-11.7), suggesting the cardiac vagal withdrawal occurred prior to the onset of lactate acidosis (lactic acid accumulation). Furthermore, exercise intervention experiment at T(VA) indicated that ET-1, catecholamine and BNP levels were not significantly different before and after exercise. However, ANP levels increased significantly after exercise (pre-exercise 18.6+/-5.38 vs post-exercise 44.0+/-24.87 pg/ml, P<0.001), which in turn brought about a significant post-exercise reduction in the blood pressure (SBP 117.6+/-13.7 vs 110.5+/-7.4 mmHg, P<0.05; DBP 78.6+/-6.7 vs 73.5+/-6.6 mmHg, P<0.01).

CONCLUSION

Our data suggest that it is possible to determine the exercise intensity (T(VA)) on the basis of cardiac vagal response. These results also suggest that exercise at T(VA) level is a safe exercise intensity in the light of cardiac stress, and that T(VA) may be recommended for obese people who might possess lower cardiac sympatho-vagal activity.

Cardiac autonomic nervous activities and cardiorespiratory fitness in older men

BACKGROUND

Aging associated changes in sympatho-vagal activities have been widely studied. However, little is known about the association between cardiorespiratory fitness level and cardiac autonomic nervous activities in conjunction with baroreflex sensitivity in healthy older men.

METHODS

We performed an incremental submaximal exercise test in 24 healthy, older men aged 60-70 years. They were divided into physically fit (PF, oxygen uptake at anaerobic threshold [ATO(2)] = 25.2 +/- 0.85 ml.kg(-1).min(-1)) and physically unfit (PU, ATO(2) = 19.6 +/- 0.42 ml.kg(-1).min(-1)) groups, based upon the results of an incremental exercise stress test. The cardiac autonomic nervous system (ANS) activities were assessed by means of power spectral analysis of heart rate variability. Baroreflex sensitivity (BRS) testing was performed using simultaneous beat-by-beat blood pressure and heart rate measurement during a transition from supine horizontal position to 60 degrees head-up-tilting (HUT).

RESULTS

At rest conditions, the high-frequency component ( p =.03) and total power ( p =.04) of heart rate variability spectrum were significantly higher in the PF group. The BRS assessed during passive HUT was also significantly higher (7.5 +/- 0.5 vs 3.0 +/- 0.4 ms.mm Hg(-1), p =.001) in the PF compared with the PU group. In addition, a significant correlation coefficient (r =.73, p =.001) was found between ATO(2) and BRS among the subjects.

CONCLUSIONS

The maintenance of high cardiorespiratory function, i.e., higher ATO(2) through a life-long active lifestyle including endurance exercise, may play an important role in reserving cardiac ANS and BRS in older men.

Exercise training and autonomic nervous system activity in obese individuals

PURPOSE

This study was designed to investigate the effects of 12 wk of exercise training on autonomic nervous system (ANS) in 18 obese middle-aged men (N = 9) and women (N = 9) (age: 41.6 +/- 1.2 yr; BMI: 27.3 +/- 0.4 kg x m(-2); %fat: 29.6 +/- 1.3%, mean +/- SE).

METHODS

Each subject participated in an aerobic exercise training at anaerobic threshold (AT), consisting of 30 min/session, 3 times/wk, for 12 consecutive weeks. The ANS activities were assessed by means of power spectral analysis of heart rate variability (HRV) at resting condition before, at 5 wk, and after the exercise program.

RESULTS

The exercise training resulted in a significant decrease in body mass, BMI, and % fat (P < 0.01) but not in lean body mass (P > 0.05) together with a significant increase in the AT VO2 (P < 0.01). Our power spectral data indicated that there were significant increases in the low-frequency component associated with the sympathovagal activity (0.03--0.15 Hz, 348.5 +/- 66.8 vs 694.7 +/- 91.5 ms(2), P < 0.01), the high-frequency vagal component (0.15--0.4 Hz, 146.3 +/- 30.4 vs 347.7 +/- 96.5 ms(2), P < 0.05), and the overall autonomic activity as evaluated by total power (0.03--0.4 Hz, 494.8 +/- 88.5 vs 1042.4 +/- 180.9 ms(2), P < 0.01) of HRV after the training.

CONCLUSIONS

Twelve weeks of exercise training has significantly improved both the sympathetic and parasympathetic nervous activities of the obese individuals with markedly reduced ANS activity, suggesting a possible reversal effect of human ANS functions. These favorable changes may also have an influence on the thermoregulatory control over the obesity.