Autonomic nervous function in essential hypertension in the elderly. Evaluation by power spectral analysis of heart rate variability

Do walking and social support always relate to autonomic nervous system function in later life? Reexamining an age-based moderating model

Although walking and social support relate to healthy function of the autonomic nervous system (ANS) in later life, it is unclear whether age groups moderate the relationships of walking frequency and social support with ANS function. To address this area of limited research, we conducted a cross-sectional study with 300 older adults to examine these moderating relationships. Results of multiple regression analysis indicated that walking frequency and social support correlated positively with ANS function. The correlation between walking frequency and ANS function was moderated by age groups, but that between social support and ANS function was not. Therefore, increasing frequency of walking and levels of social support should be considered critical elements of healthy ANS function in later life. However, increasing frequency of walking may be ineffective for old-old adults. We recommend that healthcare practitioners guide old-old adults in seeking sources of social support to promote ANS function.

Real-Time Analysis of the Heart Rate Variability During Incremental Exercise for the Detection of the Ventilatory Threshold

Background

It has never been possible to immediately evaluate heart rate variability (HRV) during exercise. We aimed to visualize the real‐time changes in the power spectrum of HRV during exercise and to investigate its relationship to the ventilatory threshold (VT).

Methods and Results

Thirty healthy subjects (29.1±5.7 years of age) and 35 consecutive patients (59.0±13.2 years of age) with myocardial infarctions underwent cardiopulmonary exercise tests with an RAMP protocol ergometer. The HRV was continuously assessed with power spectral analyses using the maximum entropy method and projected on a screen without delay. During exercise, a significant decrease in the high frequency (HF) was followed by a drastic shift in the power spectrum of the HRV with a periodic augmentation in the low frequency/HF (L/H) and steady low HF. When the HRV threshold (HRVT) was defined as conversion from a predominant high frequency (HF) to a predominant low frequency/HF (L/H), the VO₂ at the HRVT (HRVT‐VO₂) was substantially correlated with the VO₂ at the lactate threshold and VT) in the healthy subjects (r=0.853 and 0.921, respectively). The mean difference between each threshold (0.65 mL/kg per minute for lactate threshold and HRVT, 0.53 mL/kg per minute for VT and HRVT) was nonsignificant (P>0.05). Furthermore, the HRVT‐VO₂ was also correlated with the VT‐VO₂ in these myocardial infarction patients (r=0.867), and the mean difference was −0.72 mL/kg per minute and was nonsignificant (P>0.05).

Conclusions

A HRV analysis with our method enabled real‐time visualization of the changes in the power spectrum during exercise. This can provide additional information for detecting the VT.

Complexity Change in Cardiovascular Disease

With the fast development of wearable medical device in recent years, it becomes critical to conduct research on continuously measured physiological signals. Entropy is a key metric for quantifying the irregularity and/or complexity contained in human physiological signals. In this review, we focus on exploring how entropy changes in various physiological signals in cardiovascular diseases. Our review concludes that the direction of entropy change relies on the physiological signals under investigation. For heart rate variability and pulse index, the entropy of a healthy person is higher than that of a patient with cardiovascular diseases. For diastolic period variability and diastolic heart sound, the direction of entropy change is reversed. Our conclusion should not only give valuable guidance for further research on the application of entropy in cardiovascular diseases but also provide a foundation for using entropy to analyze the irregularity and/or complexity of physiological signals measured by wearable medical device.

DIFFERENTIATING PHYSIOLOGICAL EFFECTS OF MIDTERM BREAK IN A PROLONGED ONLINE GAME PLAYING

With the development of widespread Internet access, online game playing has become a popular event. As a result, more attention is being paid to the potentially negative physical and psychological effects on prolonged computer worker or online game player. To date, related physical problems that have been identified include fatigue, physical pain, insomnia, epileptic seizures, and even sudden death. Therefore, midterm break may be necessary for an online game player. This study tries to differentiate the physiological effects of two groups, with and without a midterm break, during a prolonged online game playing. Our experimental results showed that sympathetic system is overwhelming the parasympathetic nervous system significantly in group B without break, while it remains unchanged in group A. Due to the fight or flight response of the sympathetic system, participants with midterm break wanted to play more after event. Participants without break did not feel stressed after a continuous two hours' online game playing. These interesting findings may need further investigation in the future.

Autonomic dysfunction in normal tension glaucoma: the short-term heart rate variability analysis

INTRODUCTION

The purpose of this study was to investigate the dysfunction of autonomic control that may be a contributing factor in normal tension glaucoma (NTG) by showing the short-term heart rate variability in NTG patients.

MATERIALS AND METHODS

Newly diagnosed NTG patients and an age-matched normal control group were enrolled in this prospective study. Blood pressure was obtained and the electrocardiogram was monitored for 5 minutes after 30-minute rest in a supine position. Electrocardiographic signals were transferred to a heart rate analyzer. The time and frequency domain parameters of heart rate variability were analyzed between two groups.

RESULT

In all, 77 NTG patients and 30 healthy controls were included in the study. There were no significant differences between NTG and controls with respect to age, sex, and a hypertensive history, heart rate, systolic pressure, and diastolic pressure. NTG patients showed a significant reduction in the standard deviation of the mean of qualified normal-to-normal intervals in comparison with controls (27.64+/-10.90 vs. 36.22+/-10.21, P=0.041). Low-frequency values in NTG patients were statistically lower than in healthy controls (P=0.001) and the low-frequency/high-frequency ratio was significantly higher in the NTG group (P=0.000).

DISCUSSION

Our study results showed that the dysfunction of an autonomic control is associated with NTG patients.

The effect of pulse rate and blood pressure dipping status on the risk of stroke and cardiovascular disease in Japanese hypertensive patients

BACKGROUND

There have been few reports on the relationship between variation in the diurnal pulse rate (PR) in relation to a nondipper blood pressure (BP) pattern and cardiovascular events in elderly hypertensives.

METHODS

Ambulatory BP monitoring (ABPM) was conducted at baseline in 811 older Japanese hypertensives (clinical BP >140/90 mm Hg; age >50 years old) enrolled in the Jichi Medical School ABPM study, wave 1. They were followed up for an average of 41 months, and the incidence of subsequent cardiovascular event and death was evaluated. PR nondipping status was defined as (awake PR - sleep PR)/awake PR <0.1.

RESULTS

The mean age of patients was 72.3 +/- 9.8 years (311 men and 500 women). The nondipper patients had a higher risk of cardiovascular events (11.5% vs. 6.1%, P = 0.006) and stroke (9.9% vs. 5.7%, P = 0.039) than the dippers. Patients were classified into four subgroups: BP dipping plus PR dipping status (n = 471), BP dipping plus PR nondipping (n = 37), BP nondipping plus PR dipping (n = 250), and BP nondipping plus PR nondipping (n = 53). The combination of BP and PR nondipping constituted a higher risk of cardiovascular events and stroke than the other three combinations combined (cardiovascular events: 17.0% vs. 7.5%, P = 0.015; stroke: 17.0% vs. 6.6%, P = 0.005). On Cox proportional hazards modeling, BP nondipping with PR nondipping led to a significant synergistic increase in the risk of stroke (hazard ratio: 8.92; 95% confidence interval: 1.03-77.5, P = 0.048).

CONCLUSIONS

A blunted PR dip might predict a stroke in elderly hypertensives with a nondipping BP status.

The effects of a 6-month sodium restriction on cardiac autonomic function in patients with mild to moderate essential hypertension

BACKGROUND

The blood pressure-lowering mechanism of low-sodium diet is not fully understood.

METHODS

We assessed the effects of salt restriction on cardiac parasympathetic function as measured by heart-rate variability (HRV) in mild to moderate hypertensive patients. Eighty patients were randomized to a 6-month low- (N = 40) or normal (N = 40) sodium diet and a 24-h electrocardiogram (ECG) was carried out in the beginning of the study and at 6 months. Five time-domain and six frequency-domain HRV variables were analyzed: mean RR interval, standard deviation of normal RR intervals, mean of the standard deviations of all RR intervals for 5-min segments of the entire recording, percentage of differences between adjacent normal RR intervals exceeding 50 ms, square root of the mean of squared differences between adjacent normal RR intervals, total (0.01-0.40 Hz), high frequency (HF, 0.15-0.40 Hz), low frequency (LF, 0.04-0.15 Hz), very LF (0.01-0.04 Hz) and LF/HF ratio.

RESULTS

Although blood pressure diminished significantly (systolic blood pressure (SBP) from 149.9 +/- 14.7 mm Hg to 130.3 +/- 11.8 mm Hg, P < 0.001 and diastolic blood pressure (DBP) from 98.0 +/- 6.4 mm Hg to 87.1 +/- 6.2 mm Hg, P <0.001) after 6 months in the salt reduction group, no significant differences in the change between the groups could be detected.

CONCLUSIONS

A moderate, prolonged dietary sodium restriction does not alter HRV. Therefore, mechanisms other than cardiac autonomic mechanisms are likely to predominate in the blood pressure-lowering effect of salt restriction.

Autonomic nervous system activity and decline as prognostic indicators of cardiovascular and cerebrovascular events: the 'PROOF' Study. Study design and population sample. Associations with sleep-related breathing disorders: the 'SYNAPSE' Study

BACKGROUND

Transversal studies have underlined the association between the decline in autonomic nervous system (ANS) activity and all-cause mortality. However, the predictive value of ANS has never been prospectively assessed in a general population-based cohort.

METHOD

The PROOF (PROgnostic indicator OF cardiovascular and cerebrovascular events) cohort study was designed to prospectively assess the predictive value of ANS activity level in the general population, with regard to cardiovascular and cerebrovascular events, and death. This predictive power will be compared with the usual and newly discovered risk factors for the purposes of developing a risk model.

RESULTS

A prospective cohort of elderly subjects aged 65 years upon study entry were recruited from the electoral list of the city of Saint-Etienne, France. Three initial 2-year examination programs were scheduled for 7 years (2001-2007), followed by late events monitoring. At each examination, ANS activity was assessed along with clinical and biological cardiovascular risk factors, brain MRI, neuropsychological evaluation, physical activity profile, and sleep-related breathing disorders. The main study outcomes are stroke, myocardial infarction and death from any cause. A cohort consisting of 1,011 subjects aged 65.6 (0.8) years was constituted.

CONCLUSION

Despite other selective characteristics, the associations between ANS activity and events will be applicable to other populations.

Evaluation of morning blood pressure elevation and autonomic nervous activity in hypertensive patients using wavelet transform of heart rate variability

To evaluate morning autonomic nervous activity and blood pressure profiles in hypertensive patients by analyzing heart rate variability and ambulatory blood pressure. Data from 82 patients with untreated essential hypertension were analyzed. We evaluated the 24-h profile of blood pressure and that of indices of autonomic nervous activity, i.e., the high frequency component (HF) and low frequency component/HF (LF/HF), which were obtained by wavelet transform of heart rate variability. Patients were classified by dipping status (nondippers, n=28; dippers, n=32; extreme-dippers, n=8; and risers, n=14) and morning blood pressure profile (large, n=9; small, n=60; and inverted, n=13). Nocturnal systolic blood pressure in extreme-dippers was significantly lower than that in the other groups; that in the risers was significantly higher (p<0.05). There were no significant group differences in daytime systolic blood pressure. Daytime and 24-h HF levels were significantly higher in the dipper vs. the riser group (p<0.05). Morning blood pressure elevation negatively correlated to preawake (p<0.01) and nocturnal blood pressure (p<0.05), but not to daytime and post-awake blood pressure. The preawake/postawake ratio of systolic blood pressure positively correlated to that of LF/HF (p<0.01) and negatively correlated to preawake HF levels (p<0.05). Multivariate regression analysis revealed that preawake HF levels (p=0.037) and preawake/postawake ratio of LF/HF (p=0.033) were independently correlated with morning blood pressure elevation ratio. Our results suggest that activation of HF before waking and LF/HF during waking might play an important role in the development of morning blood pressure elevation.

Effect of losartan plus hydrochlorothiazide on nitric oxide status in 'nondipper' hypertensive patients

The objective of this study was to investigate the effects of losartan (100 mg) plus hydrochlorothiazide (HCTZ; 25 mg) on nitric oxide (NO) production and blood pressure (BP) in "nondipper" severe hypertensive patients. Twelve hypertensive "nondipper patients" (6 of each gender) with sitting systolic/diastolic BP of 188.0 +/- 5.2/116.2 +/- 1.2 mm Hg were studied by 24-hour ambulatory blood pressure monitoring (ABPM) after daily administration of 100 mg losartan plus 25 mg HCTZ for a period of 12 weeks. Office and mean 24-hour, as well as mean awake- and sleep-time systolic/diastolic BP, serum NO levels, and urinary excretion of NO were measured after the placebo period (3 weeks) and after 12 weeks of therapy. At the end of the 12-week treatment period, the mean 24-hour systolic/diastolic BP decreased significantly from 158.6 +/- 4.7/102.2 +/- 2.6 mm Hg (placebo period) to 140.3 +/- 4.8/90.9 +/- 3.3 mm Hg (P = 0.001/< or = 0.002). The mean BP (systolic/diastolic) during the waking period was reduced from 159.3 +/- 4.4/103.0 +/- 2.5 mm Hg to 135.0 +/- 4.4/88.2 +/- 3.1 (P < or = 0.007/P < or = 0.002), whereas the mean BP (systolic/diastolic) during the sleeping hours changed from 154.9 +/- 5.3/98.9 +/- 3.1 to 140.9 +/- 4.6 (P = 0.035)/91.7 +/- 3.2 mm Hg (P = 0.035/P = 0.051). Serum NO levels increased from 40.89 +/- 5.69 microM/L (placebo period) to 67.35 +/- 6.96 microM/L (posttreatment; P < or = 0.007), whereas the 24-hour urinary NO excretion did not change significantly (69.71 +/- 3.68 microM/L [placebo period] vs 79.64 +/- 4.25 microM/L [posttreatment]; P < or = 0.16). Urinary clearance of NO also did not change. Serum NO levels increased significantly without a significant change in urinary NO excretion. BP was significantly reduced but without modifying the nondipper pattern in these patients.

“Diabetes of the elderly” and type 2 diabetes in younger patients: Possible role of the biological clock

The increased prevalence of type 2 diabetes in the aged has been recognized for a long time. Within the last decades, a growing number of younger subjects and even children are prone to develop type 2 diabetes. In both groups, aged and young, the biological clock, located in the suprachiasmatic nucleus of the hypothalamus (SCN) is malfunctioning as evidenced by disturbed sleep cycles and altered circadian rhythms. While elderly patients have an impaired function of the SCN due to the degeneration of neurons, we propose that in younger subjects the clock loses its "feeling" for internal and external rhythms caused by the modern lifestyle. Sleeping late and less coupled with constant metabolic excess alter both internal and external environmental stimuli to the brain. In response to these alterations, the rhythm of the biological clock is disrupted which may lead to the metabolic syndrome and type 2 diabetes.

Hyperhomocysteinemia is a significant risk factor for silent cerebral infarction in patients with chronic renal failure undergoing hemodialysis

In patients with chronic renal failure undergoing hemodialysis (HD), the presence of silent cerebral infarction (SCI) is associated with high mortality. Plasma total homocysteine (tHcy), which increases with renal dysfunction, has been flagged as a novel predictor for cerebrovascular events. We tested the hypothesis that the presence of SCI correlates with tHcy in HD patients. Based on brain magnetic resonance imaging findings, 44 patients undergoing HD were divided into a with-SCI group (61+/-9 years [mean+/-SD]; n=24) and a without-SCI group (60+/-8 years, n=20), in whom 24-hour ambulatory blood pressure monitoring was performed. The number of patients with diabetes or hypertension was not different between the 2 groups. We made the following observations: (1) the percentage of smokers was higher in the with-SCI group than in the without-SCI group (P<.05); (2) plasma levels of high-density lipoprotein cholesterol were lower and tHcy was higher in the with-SCI group than in the without-SCI group (P<.05 and P<.0001, respectively); (3) and systolic ambulatory blood pressure and mean heart rate during nighttime were higher in the with-SCI group than in the without-SCI group (P<.05). Multivariate logistic analysis identified hyperhomocysteinemia as an independent and significant risk factor for SCI (odds ratio, 1.22; 95% CI, 1.10-1.36; P<.01). Our findings indicate that plasma tHcy may be a novel useful predictor for SCI in patients with chronic renal failure undergoing HD.

Attenuation of heart rate recovery after exercise in hypertensive patients with blunting of the nighttime blood pressure fall

OBJECTIVES

To evaluate whether hypertensive patients with attenuation of nighttime blood pressure (BP) fall exhibit a delay of the recovery of heart rate (HR) after exercise as an index of a general decrease in the vagal tone.

METHODS

Mild-moderate hypertensive patients (n = 219, age 55 +/- 3, 77% men) underwent a maximal exercise test (Bruce > 85% heart rate limited) in whom we calculated the recovery of HR as the percent decrease of HR from peak to 1 min after stopping exercise (%HR fall-1 min), a 24-h ambulatory BP monitoring, calculating the percent decrease of nighttime vs. daytime BP (% night SBP fall). Left ventricular mass index (LVMI) was measured by echo and aortic stiffness by pulse wave velocity (PWV). Sixty percent were on antihypertensive drugs (not on beta-blockers nor on non-dihydropiridine calcium blockers); 12 subjects were type 2 diabetics.

RESULTS

The "% night SBP fall" ranged from - 6.3% to 38.9% and the "%HR fall-1 min" ranged from 3.3% to 43.7%. There was a significant positive correlation between these two variables (r = 0.594, p < 0.001). Population was divided into five groups according to quintiles of values for the "% night SBP fall". For similar daytime BP and age, the lowest quintile for % night SBP fall (- 6.3% to 7.2%) showed the lower "%HR fall-1 min" (3.1 +/- 0.5%), and the higher LVMI (92 +/- 3 g/m(2)) and PWV (12.1 +/- 0.4 m/s) values comparing to the other quintiles (p < 0.02).

CONCLUSIONS

In hypertensives, blunting of the nocturnal fall of BP is associated with a delayed recovery in heart rate after graded maximal exercise and with greater aortic stiffness and ventricular mass. This may indicate that in non-dipper subjects a relative general decrease of parasympathetic reactivation after exercise is linked to the failure of nighttime fall of BP, both of which might contribute to target-organs deterioration.

Effects of valsartan and perindopril combination therapy on left ventricular hypertrophy and aortic arterial stiffness in patients with essential hypertension

OBJECTIVE

To compare the effects of combined therapy of an angiotensin II receptor blocker (ARB; valsartan) and an angiotensin converting enzyme inhibitor (ACEI; perindopril) on blood pressure (BP), metabolic profiles, plasma brain natriuretic peptide (BNP) levels, echocardiographic findings, and aortic pulse wave velocity (PWV) with those of respective monotherapy in never-treated patients with essential hypertension.

METHODS

This was a prospective randomized trial, in which there were 31 patients with essential hypertension and left ventricular hypertrophy (LVH) who visited the outpatient clinic of Oita Red Cross Hospital (14 women and 17 men; mean+/-SD age, 59+/-5 years). Each patient was randomly assigned to receive valsartan (160 mg/day, V group, n=10), perindopril (8 mg/day, P group, n=11), or a combination of valsartan (80 mg/day) and perindopril (4 mg/day, V+P group, n=10) for 40 weeks. Ambulatory BP monitoring (ABPM), echocardiographic findings, metabolic findings, plasma BNP levels, and brachial-ankle PWV (baPWV) were evaluated before and after the 40-week therapy.

RESULTS

The baseline and post-therapeutic BP levels were similar among the three groups. At baseline ABPM, non-dipping was observed in 80, 82, and 80% in the V, P, and V+P groups, respectively. Each 40-week therapy regimen comparably reduced ABP. The plasma BNP levels (P<0.0001 for each), left ventricular mass index (LVMI) (P<0.01 for each), and PWV values (P<0.0001 for each) were also reduced. However, when compared with either V or P group, the percentage reduction in LVMI (P<0.05 and P<0.005, respectively), BNP (P<0.05 for each), and baPWV values (P<0.005 and P<0.001, respectively) was greater in the V+P group.

CONCLUSIONS

Our findings suggest that, when compared with each monotherapy, perindopril and valsartan combination therapy exerts greater beneficial effects regarding the regression of LVH, reduction in BNP, and improvement of PWV in a selected group of essential hypertensive patients with LVH and high prevalence of non-dipping patterns.

On the genesis of myocardial ischemia

About three quarters of myocardial ischemic events are triggered by the autonomic nervous system. The pathognomonic constellation is a combination of an almost complete withdrawal of tonic vagal activity with increased sympathetic activity. The reduction of tonic vagal activity, which is characteristic for ischemic heart disease, and the acute withdrawal of vagal drive preceding the onset of ischemia are not dependent on coronary artery disease. In this paper, the pathophysiological steps that lead from sympathetic-parasympathetic imbalance to myocardial ischemia shall be discussed. A considerable increase of aerobic glycolysis within the myocardium as a result of the autonomic imbalance is of special importance in this process.

Role of Insulin Resistance in Nondipper Essential Hypertensive Patients

In hypertensive patients, diminished nocturnal blood pressure (BP) fall is associated with poor prognosis for cardiovascular events. However, the relation of insulin resistance with the etiology of nondipper essential hypertension remains unclear. The aim of the present study was to assess the role of insulin resistance in diminished nocturnal BP fall, left ventricular hypertrophy (LVH), and increased plasma atrial (ANP) and brain natriuretic peptides (BNP) in essential hypertensive patients. One hundred and three patients with essential hypertension were divided into dippers (n = 57; age: 57 +/- 5 years, mean +/- SD) or age-matched nondippers (n = 46; 57 +/- 4 years), based on ambulatory BP (ABP) monitoring. Although the systolic and diastolic ABP values were similar during the day, those at night were higher in nondippers than in dippers ( p < 0.0001 for each). Echocardiographic findings revealed that the left ventricular mass index (LVMI) was higher in nondippers (p < 0.0001). Plasma ANP and BNP were also higher in nondippers (p < 0.0001 for each). Fasting plasma concentrations of glucose and insulin (p < 0.0001 for each) and the homeostasis model assessment (HOMA) index (p < 0.0001) were also higher in nondippers. Multivariate analysis revealed that systolic ABP at night was a significant factor for LVMI, ANP and BNP. In addition, the HOMA index was a significant factor for LVMI and BNP. These observations suggest that diminished nocturnal BP fall is closely related to the development of LVH with concomitant increase in BNP in essential hypertensive patients, and that insulin resistance may play a key role in these processes.

Reproducibility of blood pressure variation in older ambulatory and bedridden subjects

OBJECTIVES

We investigated the influence of ambulation on the reproducibility of circadian blood pressure variation in older nursing home residents.

DESIGN

Ambulatory blood pressure monitoring was performed twice in 37 older nursing home residents.

SETTING

Nursing home in Japan.

PARTICIPANTS

Subjects included 18 ambulatory nursing home residents who had no limitation on physical activity and 19 bedridden residents who did not participate in physical activity.

MEASUREMENTS

Twenty-four-hour, daytime, and nighttime blood pressure levels and their variability.

RESULTS

The 24-hour and daytime variability of systolic blood pressure (SBP) was significantly greater in ambulatory than in bedridden subjects, whereas nighttime variability was similar. Significant correlations in SBP averaged for the whole day, daytime, and nighttime were observed between the two examinations in ambulatory (r =.80-.83) and bedridden (r =.83-.91) subjects, but the variabilities of SBP for the whole day and during the daytime of the first measurement were correlated with those of the second measurement in bedridden (r =.67 and r =.47, respectively) but not in ambulatory (r =.39 and r =.28, respectively) subjects. Significant correlations were found between the nocturnal SBP changes at two occasions in both ambulatory (r =.50) and bedridden (r =.51) subjects, but the dipper versus nondipper profiles, defined as reduction in SBP of greater than 10% versus not, showed low reproducibility in ambulatory subjects; five ambulatory (28%) and one bedridden (5%) subjects showed divergent profiles between the two examinations.

CONCLUSIONS

The reproducibility of blood pressure variation in nursing home residents is influenced by ambulation.

Heart rate variability and its determinants in patients with severe or mild essential hypertension

How cardiac autonomic nervous control is related to the severity of essential hypertension in patients receiving long-term antihypertensive therapy is not well known. The aim of this study was to examine heart rate variability (HRV), a non-invasive measure of cardiac autonomic function, in patients with long-term and medically treated mild and severe essential hypertension and healthy control subjects, and to assess the clinical determinants of HRV in these patients. Thirty-four patients with severe essential hypertension (SEHT) and 29 with mild essential hypertension (MEHT) as well as healthy age- and sex-matched control subjects were studied. HRV was assessed from 10 min ECG-recordings during paced (0.2 Hz) breathing at rest and expressed as time and frequency domain measures. In the SEHT group time (SDNN, RMSSD) and frequency domain measures (total power, low-frequency (LF) power and high-frequency (HF) power of HRV in absolute units, and LF and HF power of HRV in normalized units) of HRV were significantly lower when compared with those of the control group. The MEHT and control groups did not differ from each other with respect to time or frequency domain measures of HRV. Comparison between the hypertensive groups showed that SDNN, total power, LF power and HF power were lower in the SEHT group compared with the MEHT group (P<0.05 for all). Among hypertensive patients RR-interval, age, gender, systolic finger blood pressure and diastolic office blood pressure as well as 24-h blood pressure were significant determinants of HRV. In conclusion, we found that the severity of chronic essential hypertension seems to be related to the severity of impairment of cardiac autonomic control.

How to assess sympathetic activity in humans

Sympathetic factors play a central role not only in cardiovascular homeostatic control but also in the pathogenesis and/or in the progression of several cardiovascular diseases, such as essential hypertension, myocardial infarction, cardiac arrhythmias and congestive heart failure. This explains why assessment of adrenergic neural function in humans has been, and certainly still remains, one of the major fields in cardiovascular research. The present paper will review in detail the haemodynamic, pharmacological, biochemical, neurophysiological, neurochemical and neural imaging techniques by which sympathetic activity is assessed in humans, highlighting the main advantages and limitations of each of them. Although plasma noradrenaline measurement represents a useful guide to assess sympathetic neural function, direct recording of sympathetic nerve traffic via microneurography and noradrenaline radiotracer methods have in recent years largely supplanted the plasma noradrenaline approach. This is because they allow (1) discrimination between the central or peripheral nature of increased plasma noradrenaline levels, and (2) precise estimation of the behaviour of regional sympathetic neural function both under physiological and pathological conditions. In contrast, the approach based on spectral analysis of heart rate and blood pressure signals has been shown to have important limitations which prevent the method from faithfully reflecting sympathetic cardiovascular drive. Neural imaging techniques, which require expensive technical support, allow direct visualization of sympathetic enervation of human organs, thus providing information on the 'in vivo' metabolism of noradrenaline in different cardiovascular districts. Although technical improvements have allowed a more precise assessment of human adrenergic function, no technique so far available can be viewed as a 'gold standard' with which the others might be compared. Limitations and disadvantages of the various techniques may be reduced if these methods are seen as being complementary and employed in combination, allowing more reliable information to be achieved on the sympathetic abnormalities characterizing cardiovascular diseases, and thus hopefully providing a stronger rationale for newer therapeutic approaches involving pharmacological modification of the sympathetic nervous system and adrenoreceptors.