Microcomputer-based monitoring of cardiovascular functions in simulated microgravity

Age dependency of cardiovascular autonomic responses to head-up tilt in healthy subjects

In elderly subjects, heart rate responses to postural change are attenuated, whereas their vascular responses are augmented. Altered strategy in maintaining blood pressure homeostasis during upright position may result from various cardiovascular changes, including age-related cardiovascular autonomic dysfunction. This exploratory study was conducted to evaluate impact of age on cardiovascular autonomic responses to head-up tilt (HUT) in healthy subjects covering a wide age range. The study population consisted of 63 healthy, normal-weight, nonsmoking subjects aged 23–77 yr. Five-minute electrocardiogram and finger blood pressure recordings were performed in the supine position and in the upright position 5 min after 70° HUT. Stroke volume was assessed from noninvasive blood pressure signals by the arterial pulse contour method. Heart rate variability (HRV) and systolic blood pressure variability (SBPV) were analyzed by using spectral analysis, and baroreflex sensitivity (BRS) was assessed by using sequence and cross-spectral methods. Cardiovascular autonomic activation during HUT consisted of decreases in HRV and BRS and an increase in SBPV. These changes became attenuated with aging. Age correlated significantly with amplitude of HUT-stimulated response of the high-frequency component ( r = -0.61, P < 0.001) and the ratio of low-frequency to high-frequency power of HRV ( r = -0.31, P < 0.05) and indexes of BRS (local BRS: r = -0.62, P < 0.001; cross-spectral baroreflex sensitivity in the low-frequency range: r = -0.38, P < 0.01). Blood pressure in the upright position was maintained well irrespective of age. However, the HUT-induced increase in heart rate was more pronounced in the younger subjects, whereas the increase in peripheral resistance was predominantly observed in the older subjects. Thus it is likely that whereas the dynamic capacity of cardiac autonomic regulation decreases, vascular responses related to vasoactive mechanisms and vascular sympathetic regulation become augmented with increasing age.

A deletion in the alpha2B-adrenergic receptor gene and autonomic nervous function in central obesity

OBJECTIVE

We investigated the impact of a three-amino acid deletion (12Glu9) polymorphism in the alpha(2B)-adrenergic receptor gene on autonomic nervous function. The short form (Glu(9)/Glu(9)) of the polymorphism has previously been associated with a reduced basal metabolic rate in obese subjects. Because autonomic nervous function participates in the regulation of energy metabolism, there could be a link between this polymorphism and autonomic nervous function.

RESEARCH METHODS AND PROCEDURES

Data of a 10-year follow-up study with 126 nondiabetic control subjects and 84 type 2 diabetic patients were used to determine the effects of the 12Glu9 polymorphism on autonomic nervous function. A deep breathing test and an orthostatic test were used to investigate parasympathetic and sympathetic autonomic nervous function. In addition, cardiovascular autonomic function was studied using power spectral analysis of heart rate variability.

RESULTS

No significant differences were found in the frequency of the 12Glu9 deletion polymorphism between nondiabetic and diabetic subjects. The nondiabetic men with the Glu(9)/Glu(9) genotype, especially those with abdominal obesity, had significantly lower total and low-frequency power values in the power spectral analysis when compared with other men. Furthermore, in a longitudinal analysis of 10 years, the decrease in parasympathetic function was greater in nondiabetic men with the Glu(9)/Glu(9) genotype than in the men with the Glu(9)/Glu(12) or Glu(12)/Glu(12) genotypes.

DISCUSSION

The results of the present study suggest that the 12Glu9 polymorphism of the alpha(2B)-adrenergic receptor gene modulates autonomic nervous function in Finnish nondiabetic men. In the nondiabetic men with the Glu(9)/Glu(9) genotype, the general autonomic tone is depressed, and vagal activity especially becomes impaired with time. Furthermore, this association is accentuated by central obesity.

Weight loss and weight maintenance, ambulatory blood pressure and cardiac autonomic tone in obese persons with the metabolic syndrome

BACKGROUND

Cardiac autonomic function may play a role in obesity-associated hypertension. Most studies on the effects of weight loss on blood pressure and autonomic function do not distinguish between acute or continuing weight loss and steady-state weight maintenance after weight loss.

OBJECTIVES

We sought to clarify the changes in ambulatory blood pressure, heart rate and heart rate variability as assessed by spectral analysis during rapid weight loss and extended weight maintenance.

PARTICIPANTS

Abdominally obese (body mass index 35.2 +/- 2.1 kg/m2, waist 114.3 +/- 9.0 cm) men and women (n = 41) with the metabolic syndrome.

METHODS AND RESULTS

The 34 men and women completing the 1-year weight maintenance period lost 14.6 +/- 3.5 kg during the 9-week very-low-calorie diet and maintained a 12.5 +/- 7.5 kg weight loss to the end of the trial. Ambulatory 24-h blood pressure decreased dramatically during the diet (-9.0 +/- 8.0/-4.6 +/- 4.9 mmHg), but had risen to near baseline levels by the end of weight maintenance (-2.2 +/- 8.2 /-1.2 +/- 6.1 mmHg). Night-time heart rate decreased (-5.5 +/- 9.6 beats/min, P = 0.012), and heart rate variability total and low-frequency power measured during 5 min of controlled breathing increased by 46-56% (P = 0.003-0.09) during rapid weight loss. These changes gradually attenuated during weight maintenance, and only the change in night-time heart rate was still of borderline significance after 1 year of weight maintenance (-3.6 +/- 8.6 beats/min, P = 0.063). Heart rate variability high-frequency power tended to increase during weight loss and weight maintenance.

CONCLUSION

Despite successful weight maintenance, the decrease in ambulatory blood pressure after rapid weight loss was largely transient. The increase in parasympathetic tone was more sustained, but also gradually attenuated during 1 year of weight maintenance.

Does postmenopausal hormone replacement therapy affect cardiac autonomic regulation in osteoporotic women?

OBJECTIVE

Postmenopausal hormone replacement therapy (HRT) has been associated with reduced risk of cardiovascular disease; however, the mechanisms remain obscure, and it is not known whether this applies to regimens containing both estrogen and progestin. One possibility is that estrogen would act via enhancement of cardiac autonomic regulation.

DESIGN

In this prospective, controlled study of 6-months duration, 22 osteoporotic, postmenopausal women in the intervention group were treated with combined estradiol hemihydrate corresponding to estradiol 2 mg and norethisterone acetate 1 mg with or without clodronate (HRT group). Nine women in the control group received clodronate only. Indices of heart rate variability (HRV) by power spectral analyses and baroreceptor sensitivity (BRS) by phenylephrine test were measured before and after 3 and 6 months of treatment.

RESULTS

The total power of HRV remained identical within the groups, although it was higher at 3 and 6-month measurements in the control group than the HRT group. This was mainly due to lower very low frequency and high frequency power in the HRT group. However, no changes in the low frequency/high frequency-ratio of HRV, an index of sympathovagal balance, were observed between and within the groups. Further, during the intervention, no significant changes in BRS (baseline and 6 months: 5.0 +/- 2.1 and 5.1 +/- 2.5 ms/mmHg) within the HRT group was observed.

CONCLUSIONS

The impact of estrogen and progesterone on cardiac autonomic regulation seems to be quite modest. Therefore, cardiac morbidity and mortality are probably not mediated by their effects on cardiac autonomic regulation. However, the effects of estrogen alone or more selective estrogen receptor modulators need yet to be clarified in future studies.

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.

Sympathovagal balance is major determinant of short-term blood pressure variability in healthy subjects

Short-term blood pressure variability (BPV) has been suggested to provide important information about cardiovascular regulation. However, the background of BPV, its determinants, and physiological correlates have remained obscure. The aim of this study was to characterize physiological correlates of BPV and to investigate associations between BPV and neural and hormonal regulatory systems at rest in healthy subjects. We studied 117 healthy, normal-weight, nonsmoking male and female subjects aged 23-77 yr. Spectral analysis of BPV and heart rate variability (HRV) was performed from 5-min blood pressure (Finapres) and electrocardiogram recordings during controlled breathing. Baroreflex sensitivity (BRS) was measured using the phenylephrine method. In addition, plasma concentrations of norepinephrine, epinephrine, and arginine vasopressin and plasma renin activity were measured. We found that the ratio between the low- and high-frequency components of HRV, an index of cardiac sympathovagal balance, correlated positively with total power and very low- and low-frequency components of systolic and diastolic BPV and inversely with high-frequency components of systolic and diastolic BPV. BRS, predominantly a measure of cardiac vagal regulation, correlated inversely with BPV. Furthermore, age, gender, body mass index, and systolic blood pressure contributed to BPV. Vasoactive hormones were not significant correlates of BPV. We conclude that sympathovagal balance of cardiovascular regulation is the major determinant of BPV. Other factors associated with BPV are age, gender, body mass index, blood pressure, and BRS.

Climacteric vasomotor symptoms do not imply autonomic dysfunction

OBJECTIVE

To study whether oestrogen replacement therapy has an effect on autonomic haemodynamic control in postmenopausal women.

DESIGN

A placebo-controlled, prospective, randomised, double-blind cross-over trial.

POPULATION

Fourteen healthy postmenopausal women who had had a hysterectomy, of whom 12 were double-blind.

METHODS

At the end of each treatment period we conducted autonomic nervous system tests: the Valsalva manoeuvre, the deep breathing test, study at rest and the active orthostatic test. Baroreflex sensitivity was evaluated non-invasively from the Valsalva manoeuvre. Heart rate variability was assessed in time and frequency domains during supine rest and standing. Serum oestradiol was also measured and the previous two weeks' symptoms were assessed.

RESULTS

Autonomic nervous function was mostly normal for age and unchanged by oestrogen. Vasomotor symptoms were not associated with autonomic dysfunction. Baroreflex sensitivity was 13.3 ms/mmHg (SD 7.4 ms/mmHg) with placebo and 10.5 ms/mmHg (SD 5.4 ms/mmHg) with oestrogen (P = 0.052). This was mostly due to a fall in three of the highest indices. In the orthostatic test the 30 s blood pressure overshoot in two women exceeded the normal 90% confidence interval upper limit, making the mean response strong, especially in the symptomatic group (n = 7). Oestrogen attenuated this overshoot.

CONCLUSIONS

Oestrogen did not have a consistent effect on the autonomic nervous system. Oestrogen attenuated a highly sensitive baroreflex and a strong 30 s blood pressure rise in the orthostatic test. This minor effect of oestrogen could be due to the fact that, in general, women with menopausal symptoms do not have impaired autonomic haemodynamic control. The effect of oestrogen in women with autonomic nervous system dysfunction remains to be studied.

Endurance training, overtraining and baroreflex sensitivity in female athletes

We examined heavy training-induced changes in baroreflex sensitivity, plasma volume and resting heart rate and blood pressure variability in female endurance athletes. Nine athletes (experimental training group, ETG) increased intense training (70-90% VO2max) volume by 130% and low-intensity training (< 70% Vo2max) volume by 100% during 6-9 weeks, whereas the corresponding increases in six control athletes (CG) were 5% and 10% respectively. Maximal oxygen uptake (VO2max) in the ETG and CG did not change, but in five ETG athletes VO2max decreased from 53.0 +/- 2.2 (mean +/- SEM) (CI 46.8-59.2) ml kg-1 min-1 to 50.2 +/- 2.3 (43.8-56.6) ml kg-1 min-1 (P < 0.01), indicating overtraining. Baroreflex sensitivity (BRS) measured using the phenylephrine technique and blood pressure variability (BPV) did not change, but the low-frequency power of the R-R interval variability increased in the ETG (P < 0.05). The relative change in plasma volume was 7% in the ETG and 3% in the CG. The changes in BRS did not correlate with the changes in plasma volume, heart rate variability and BPV. We conclude that heavy endurance training and overtraining did not change baroreflex sensitivity or BPV but significantly increased the low-frequency power of the R-R interval variability during supine rest in female athletes as a marker of increased cardiac sympathetic modulation.

The effect of a very low-calorie diet-induced weight loss on the severity of obstructive sleep apnoea and autonomic nervous function in obese patients with obstructive sleep apnoea syndrome

The aim of this study was to examine the effect of a very low-calorie diet (VLCD)-induced weight loss on the severity of obstructive sleep apnoea (OSA), blood pressure and cardiac autonomic regulation in obese patients with obstructive sleep apnoea syndrome (OSAS). A total of 15 overweight patients (14 men and one woman, body weight 114 +/- 20 kg, age 52 +/- 9 years, range 39-67 years) with OSAS were studied prospectively. They were advised to follow a 2.51-3.35 MJ (600-800 kcal) diet daily for a 3-month period. In the beginning of the study, the patients underwent nocturnal sleep studies, autonomic function tests and 24-h electrocardiograph (ECG) recording. In addition, 15 age-matched, normal-weight subjects were studied. They underwent the Valsalva test, the deep-breathing test and assessment of heart rate variability at rest. The sleep studies and autonomic function tests were repeated after the weight loss period. There was a significant reduction in weight (114 +/- 20 kg to 105 +/- 21 kg, P < 0.001), the weight loss being 9.2 +/- 4.0 kg (range 2.3-19.5 kg). This was associated with a significant improvement in the oxygen desaturation index (ODI4) during sleep (31 +/- 20-19 +/- 18, P < 0.001). Before the weight loss the OSAS patients had significantly higher blood pressure (150 +/- 18 vs. 134 +/- 20, P < 0.05, for systolic blood pressure, 98 +/- 10 vs. 85 +/- 13, P < 0.05, for diastolic blood pressure) and heart rate (67 +/- 10 beats min-1 vs. 60 +/- 13, P < 0.05) at rest than the control group. They had also lower baroreflex sensitivity (4.7 +/- 2.8 ms mmHg-1 vs. 10.8 +/- 7.1 ms mmHg-1, P < 0.01). During the weight reduction, the blood pressure declined significantly, and the baroreflex sensitivity increased by 49%. In conclusion, our experience shows that weight loss with VLCD is an effective treatment for OSAS. Weight loss improved significantly sleep apnoea and had favourable effects on blood pressure and baroreflex sensitivity that may have prognostic implications.

Altered cardiovascular autonomic regulation after salmeterol treatment in asthmatic children

The effects of therapeutic 4 weeks' inhaled salmeterol treatment on the cardiovascular and respiratory autonomic nervous regulation was studied in 11 asthmatic children using inhaled corticosteroid medication. The study followed a randomized, double-blind, placebo-controlled cross-over design. The salmeterol dose was 50 micrograms twice daily. The 4-week salmeterol treatment increased baseline heart rate, low-frequency/high-frequency (LF/HF) variability ratio of R-R intervals, LF variability of systolic arterial pressure (SAP) and maximum tidal volume during the deep breathing test, as well as morning and evening peak expiratory flow (PEF) values. The 4-week salmeterol treatment decreased baseline HF variability of R-R intervals. As a response to the acute 600 micrograms of salbutamol, the changes in heart rate, HF variability of R-R intervals and diastolic blood pressure were significantly smaller after 4 weeks' salmeterol treatment. In conclusion, 4 weeks' therapeutic salmeterol treatment decreases basal cardiovagal reactivity, increases sympathetic dominance in the cardiovascular autonomic balance and improves pulmonary function. A tolerance develops in the cardiovascular response but not in the bronchodilatory response.

The dose-response effects of terbutaline on the variability, approximate entropy and fractal dimension of heart rate and blood pressure

AIMS

To study the dose-response effects of intravenous terbutaline on the cardiovascular and respiratory autonomic nervous regulation.

METHODS

The study followed a randomized, placebo-controlled crossover design in six healthy adult volunteers. The terbutaline dose ranged from 10 to 30 microg min(-1) We continuously measured electrocardiogram, finger systolic arterial pressure (SAP) and flow-volume spirometry in supine and upright positions at baseline and during 3 h drug infusion. The periodic variability components of R-R intervals (time between successive heart beats) and SAP in relation to respiration were assessed using spectral analysis techniques. The regularity of the time series was assessed by approximate entropy (ApEn) and the convolutedness by fractal dimension (FD).

RESULTS

Terbutaline dose-dependently decreased total variability of R-R intervals, low frequency (LF) variability of R-R intervals (10 s waves), high frequency (HF) variability of R-R intervals (respiratory variability), total variability of SAP, HF variability of SAP, baroreflex sensitivity, plasma potassium concentration, approximate entropy of R-R interval and of SAP as well as fractal dimension of R-R interval. Terbutaline dose-dependently increased heart rate, LF/HF ratios of R-R intervals and of SAP, LF variability of SAP, minute ventilation and plasma terbutaline concentration.

CONCLUSIONS

Terbutaline infusion decreases parasympathetic cardiovascular reactivity, baroreflex sensitivity, dimensionality of heart rate and plasma potassium concentration; it increases sympathetic dominance in cardiovascular autonomic balance, minute ventilation, and the regularity of heart rate and blood pressure time series.

Age and gender dependency of baroreflex sensitivity in healthy subjects

We evaluated the correlates of baroreflex sensitivity (BRS) in healthy subjects. The study consisted of 117 healthy, normal-weight, nonsmoking male and female subjects aged 23-77 yr. Baroreflex control of heart rate was measured by using the phenylephrine bolus-injection technique. Frequency- and time-domain analysis of heart rate variability and an exercise test were performed. Plasma norepinephrine, epinephrine, insulin, and arginine vasopressin concentrations and plasma renin activity were measured. In the univariate analysis, BRS correlated with age (r = -0.65, P < 0.001), diastolic blood pressure (r = -0.47, P < 0.001), exercise capacity (r = 0.60, P < 0.001), and the high-frequency component of heart rate variability (r = 0.64, P < 0.001). There was also a significant correlation between BRS and plasma norepinephrine concentration (r = -0.22, P < 0.05) and plasma renin activity (r = 0.32, P < 0.001). According to the multivariate analysis, age and gender were the most important physiological correlates of BRS. They accounted for 52% of interindividual BRS variation. In addition, diastolic blood pressure and high-frequency component of heart rate variability were significant independent correlates of BRS. BRS was significantly higher in men than in women (15.0 +/- 1.2 vs. 10.2 +/- 1.1 ms/mmHg, respectively; P < 0.01). Twenty-four percent of women > 40 yr old and 18% of men > 60 yr old had markedly depressed BRS (< 3 ms/mmHg). We conclude that physiological factors, particularly age and gender, have significant impact on BRS in healthy subjects. In addition, we demonstrate that BRS values that have been proposed to be useful in identifying postinfarction patients at high risk of sudden death are frequently found in healthy subjects.

Valsalva manoeuvre can be used to study baroreflex sensitivity in pregnancy

OBJECTIVE

The aim of this study was to assess whether baroreflex sensitivity can be measured in a non-invasive manner with the Valsalva manoeuvre in pregnancy.

STUDY DESIGN

Baroreflex sensitivity was measured from the reflex response to phenylephrine injection and phase four of the Valsalva manoeuvre in nine pregnant women at 27 (range 24-33) gestational weeks.

RESULTS

Both the phenylephrine test and the Valsalva manoeuvre yielded similar estimates of baroreflex sensitivity (9.3 (4.1) ms/mmHg vs. 8.0 (5.2) ms/mmHg, Pearson's correlation coefficient r = 0.81, P < 0.008, linear regression BRSValsalva (ms/mmHg) = 1.03 x BRSPhenylephrine + 1.59). Comparable changes in heart rate and blood pressure were obtained with the phenylephrine test and the Valsalva manoeuvre.

CONCLUSION

The physiological challenge caused by the Valsalva manoeuvre can be used to measure baroreflex sensitivity in pregnancy. A possibility to study baroreflex function non-invasively, without pharmacological intervention, benefits future research of blood pressure regulation in pregnancy.

Heart rate and blood pressure variabilities are increased in pregnancy-induced hypertension

OBJECTIVE

Our purpose was to study whether cardiovascular changes in pregnancy-induced hypertension are associated with the increase in sympathetic control of hemodynamics and change in sympathovagal balance.

STUDY DESIGN

Fourteen women with pregnancy-induced hypertension and 16 women with uncomplicated pregnancies of similar duration were studied. Electrocardiographic signals and arterial blood pressure (Finapres monitor, Ohmeda) were continuously measured noninvasively throughout the study. Heart rate and blood pressure were measured while the subject was breathing (1) with her normal tidal volume at a frequency of 15 breaths per minute and (2) as deeply as possible at a frequency of six breaths per minute. Heart rate and systolic blood pressure variability were calculated with use of the autoregressive model of spectral analysis.

RESULTS

Heart rate and systolic blood pressure variabilities were significantly increased in women with pregnancy-induced hypertension compared with normotensive pregnant women. This increase was greatest in the high frequency component of heart rate variability (p = 0.02) while the women were breathing with a normal tidal volume. Further, the medium frequency (p = 0.03) and high-frequency variabilities (p = 0.03) of systolic blood pressure were significantly increased in women with preeclampsia compared with normotensive pregnant subjects.

CONCLUSIONS

Neural control of the heart rate and blood pressure are disturbed in pregnancy-induced hypertension, as shown by increased heart rate and blood pressure variability. Both the sympathetic and parasympathetic control of the heart rate and blood pressure appear to be increased. The maladaptation of the cardiovascular system in women with pregnancy-induced hypertension is manifested as a lack of the physiologic decline in cardiovascular oscillations.

Paclitaxel changes sympathetic control of blood pressure

Paclitaxel has become part of standard therapy in the treatment of ovarian and breast cancer. Concern has been raised about the effects of paclitaxel on cardiovascular function. Therefore, this study of the effects of paclitaxel on autonomic cardiovascular control was initiated. Eighteen women treated for ovarian or breast cancer were examined with autonomic cardiovascular function tests, once before the treatment and once after the second course of paclitaxel. Heart rate and blood pressure variability and changes in heart rate and blood pressure responses to the tests were measured. Baroreflex sensitivity was calculated from the Valsalva manoeuvre non-invasively. Paclitaxel did not change heart rate variability at rest compared with the pretreatment level. However, medium frequency variability of blood pressure was smaller after treatment with paclitaxel. Paclitaxel treatment did not impair the heart rate and blood pressure responses to the autonomic function tests. The results do imply that paclitaxel alters sympathetic control of blood pressure. Nevertheless, paclitaxel does not appear to precipitate autonomic cardiac neuropathy.

Non-invasive evaluation of sympathovagal balance in athletes by time and frequency domain analyses of heart rate and blood pressure variability

We examined how the time and frequency domain measures of heart rate and blood pressure variability at supine rest reflect the sympathovagal balance of 23 female and male endurance athletes. Pharmacological blocking by atropine and propranolol was used as a standard for defining autonomic control of the heart. The Rosenblueth and Simeone model for neural control of heart rate was used to calculate the sympathovagal balance index (Abal). Atropinization significantly decreased all time and frequency domain measures of heart rate and blood pressure variability. beta-Blockade significantly decreased further the low- (< 0.07 Hz) and medium-frequency power (0.07-0.15 Hz) variability of R-R intervals (RRI) and SD of RRI. Abal was 0.629 +/- 0.019, indicating that parasympathetic activity predominated in the athletes. Basal heart rate (r = 0.519, P < 0.01), SD of RRI (r = -0.533, P < 0.01), root-mean-square of successive RRIs (RRI RMSSD) (r = -0.579, P < 0.05), RRI total (r = -0.557, P < 0.01) and RRI high-frequency (HF) power (r = -0.582, P < 0.01) correlated significantly with Abal and parasympathetic activity index. We concluded that the best non-invasive method of evaluating the sympathovagal balance of athletes at supine rest is to measure SD of RRI, RRI RMSSD, HF and total power of RRI variability. All heart rate variability measures were mainly parasympathetically modulated. The nature of blood pressure variability measures remained unclear and they could not be used to evaluate the sympathovagal balance among athletes.

Cardiovascular autonomic regulation in asthmatic children evidenced by spectral analysis of heart rate and blood pressure variability

The objective of the study was to investigate the features of cardiovascular and respiratory autonomic nervous regulation in asthmatic and control children. Cardiorespiratory reactivity was studied by continuous and non-invasive recording of the electrocardiogram, finger systolic arterial pressure (SAP) and flow-volume spirometry in supine and upright positions and during a deep breathing test in 19 children with bronchial asthma and 10 healthy control children (age 8-11 years). The periodic variability components of R-R intervals (the time between successive heart beats) and SAP in relation to respiration were assessed using spectral analysis techniques. Nine asthmatic children without beta2-agonist medication had a lower respiratory rate and larger high frequency (HF) variability of SAP than the controls, and 10 asthmatic children with beta2-agonist medication had greater low-frequency (LF) variability of SAP and LF/HF ratio of R-R intervals, but their respiratory rate did not differ from the controls. No intergroup differences were found in the postural change of variables. Stable bronchial asthma appears to increase respiratory-induced alterations in systolic blood pressure in children. Beta2-agonist medication, on the other hand, increases sympathetic cardiovascular activity in children with asthma.

Cardiovascular autonomic control is disturbed in nocturnal teethgrinders

To examine the hypothesis of disturbed autonomic function, non-invasive cardiovascular reflex tests were performed on 11 sleep bruxists in the waking state. The tests included the Valsalva manoeuvre, a deep-breathing test, and an orthostatic test (standing up). The R-R intervals were monitored continuously, and blood pressure was measured non-invasively and continuously using the Finapres method. In total, 64% of bruxists showed abnormalities in at least two variables reflecting the cardiovascular autonomic function. Abnormalities were found in blood pressure regulation during the Valsalva strain, and in the immediate biphasic heart rate response during standing up, but not in the vagally mediated deep-breathing difference. These findings suggest that bruxism is accompanied by abnormalities in autonomic function, particularly in sympathetic vasoconstrictor function.

Baroreflex sensitivity and neurohormonal activation in patients with acute myocardial infarction

OBJECTIVE

To examine the relationship between baroreflex sensitivity and neurohormonal activation in patients with an acute myocardial infarction.

METHODS

Baroreflex sensitivity, plasma noradrenaline, atrial natriuretic factor, endothelin-1, and plasma renin activity were measured in 37 male patients about 10 days after their first myocardial infarction, and in 15 healthy controls. Baroreflex sensitivity was assessed from the regression line relating the change in RR interval to the change in systolic blood pressure following an intravenous bolus injection of phenylephrine. The measurements were repeated after a follow up of three months.

RESULTS

There was a significant inverse correlation between baroreflex sensitivity and plasma noradrenaline measured before hospital discharge (r = -0.43, P < 0.01). Patients with increased plasma noradrenaline (> or = 2SD above the mean of the age matched control group) had significantly lower baroreflex sensitivity than patients with normal plasma noradrenaline (8.7 (SD 4.6) v 12.1 (6.1) ms/mm Hg, P < 0.05). The change in baroreflex sensitivity during the follow up showed a significant inverse correlation with the change of plasma noradrenaline (r = -0.450, P < 0.01). Furthermore, when patients with increased plasma noradrenaline before hospital discharge were analysed separately, baroreflex sensitivity at three months in patients in whom plasma noradrenaline had decreased to normal values was significantly higher than in patients in whom plasma noradrenaline had remained increased (14.6 (5.7) v 8.1 (8.1) ms/mm Hg, P < 0.05). On the other hand, baroreflex sensitivity was not related to the levels of plasma atrial natriuretic factor, plasma endothelin-1, or plasma renin activity. Neither was any relationship found between change in baroreflex sensitivity and change in plasma atrial natriuretic factor, endothelin-1, or plasma renin activity during the follow up.

CONCLUSIONS

The impairment baroreflex sensitivity after myocardial infarction was associated with increased concentration of plasma noradrenaline, that is, sympathetic activation, but not with plasma atrial natriuretic factor, endothelin-1, or plasma renin activity. Baroreflex sensitivity provides information about cardiac vagal control as well as about the balance of cardiac sympathetic-parasympathetic regulation.

Day-to-day variability of cardiac autonomic regulation parameters in normal subjects

We examined the reproducibility of day-to-day variability in cardiovascular autonomic nervous function parameters (classical clinical tests and domain analysis of heart rate variability) in four healthy men during a period of 1 working week. The results did not show any significant difference in any of the parameters over the five repeated measurements. The maximum-minimum difference as percentage of the mean was under 15% for expiration to inspiration (E/I) ratio, Valsalva ratio, tachycardia ratio, 30/15 ratio, acceleration index and brake index; about 45% for baroreflex sensitivity for systolic and diastolic blood pressure and for root mean square difference (RMSSD) of successive R-R intervals; about 65-85% for low and high frequency bands, total power and medium to high frequency ratio; and about 125% for medium frequency band. The intraclass correlation coefficient (ICC) values showed that the agreement for classical autonomic parameters (except for brake index) was good. ICC for RMSSD, baroreflex sensitivity for systolic blood pressure and the spectral estimates of heart rate variation were less good. Coefficient of variation (CV) was 4% for E/I ratio, 2% for 30/15 ratio, 6% for Valsalva, 3% for tachycardia ratio, 4% for acceleration index and 5% for brake index. CV for baroreflex sensitivity and for RMSSD was about 20%. It is concluded that the variation in baroreflex sensitivity is clearly larger than in the classical autonomic nervous function parameters. One-minute fixed pace breathing period seems to be too short to allow reproducible measurement of RMSSD and the spectral parameters of heart rate variation. Learning effect could be excluded.

Circadian variation of cardiac autonomic regulation during 24-h bed rest

We examined the effect of circadian variation on cardiac autonomic regulation in 11 young and middle-aged, healthy men during 24-h bed rest. Cardiac parasympathetic regulation expressed significant circadian variation: sensitivity of baroreceptor reflex, standard deviation of R-R intervals and the power of high frequency component of R-R interval variability (HFP) increased during the evening (2000-2100 h), were highest during the night (0200-0300 h), and gradually decreased again towards afternoon (1400-1500 h). Cardiac sympathetic regulation, the power of medium frequency component of R-R interval variability (MFP), did not show any significant circadian variation. The autonomic response to orthostatic stress changed after the 24-h bed rest; the sympathetic dominance in response to assuming upright position was before bed rest principally attributable to increased sympathetic activity (MFP increase), whereas after bed rest this was due to withdrawal of parasympathetic activity (HFP decrease). We conclude that the effect of circadian variation must be taken into account, while assessing cardiac autonomic regulation in patients with acute cardiovascular disorders.