Study of arterial and autonomic effects of cyclosporine in humans

Altered sympathetic activity and peripheral vascular function are suspected as a mechanism of the development of arterial hypertension in organ transplantation recipients treated with cyclosporine. We assessed whether cyclosporine might alter peripheral vascular properties or autonomic modulation of the sinus node and the vasculature during rest and standing. We examined 17 orthotopic heart transplantation recipients, 8 solid organ transplantation recipients, 17 patients with essential hypertension, and 42 normotensive control subjects. All except the normotensive control subjects were treated with a long-acting dihydropyridine calcium entry blocker; transplantation recipients also received cyclosporine-based immunosuppression. Radial artery compliance was reduced in patients with essential hypertension and in patients with heart and solid organ transplantation as compared with normotensive control subjects, with this reduction being more marked in heart transplantation recipients. At rest, R-R variance was lowest in heart transplantation recipients, denoting denervation. The spectral profile of both R-R and systolic blood pressure variability as well as the index of baroreflex gain was normal at rest in patients with solid organ transplantation. On standing, both transplantation groups demonstrated reduced responsiveness in markers of autonomic modulation. The decrease in arterial compliance in cyclosporine-induced hypertension seems to imply a degree of ventricular vascular uncoupling more apparent in heart transplantation recipients. These changes are associated with alterations in autonomic modulation that are evidenced by an orthostatic stimulus.

Assessment of arterial and cardiopulmonary baroreflex gains from simultaneous recordings of spontaneous cardiovascular and respiratory variability

OBJECTIVES

In usual models of cardiovascular regulation, arterial pressure drives RR interval through a simple baroreflex, and the influence of respiration is dismissed. We examined the applicability of a trivariate autoregressive model to obtain separate values of the gain of the arterial and non-arterial, i.e. cardiopulmonary, components of the lumped baroreflex, employing spontaneous RR interval, systolic arterial pressure and respiration variability.

DESIGN

We studied 30 normal subjects (age 37 +/- 1 years), both at rest and during standing, a condition known to enhance sympathetic activity while reducing venous return. Electrocardiogram was obtained by telemetry, arterial pressure by Finapres and respiration with a piezoelectric respiratory belt Data were acquired with a PC and processed with an ad hoc Windows program.

METHODS

We employed an additive and a linear multivariate approach to approximate overall gain of the arterial pressure-heart beat period baroreflex (alphalumped) and of its arterial (alphaart) and non-arterial, i.e. cardiopulmonary (alphacp), components, from continuous beat-by-beat series of RR interval, systolic arterial pressure variability and respiration, without using any non-physiological intervention.

RESULTS

The overall baroreflex gain at rest (alphalumped = 23.7 +/- 3.4 ms/mmHg) was subdivided into arterial (alphaart = 5.2 +/- 1.0 ms/mmHg) and cardiopulmonary (alphacp = 18.5 +/- 3.2ms/mmHg) components. During active orthostatism, alphaluumped was diminished to 10.0 +/- 2.2 ms/ mmHg. In addition, standing selectively reduced alphacp to 4.8 +/- 1.3 ms/mmHg, while alphaart was not significantly changed.

CONCLUSIONS

A trivariate autoregressive model, that considers explicitly the influence of respiration, can subdivide overall, lumped, arterial pressure-heart period baroreflex gain, into two separate components, alphaart and alphacp. Only the latter is reduced by active orthostatism.

Cardiac autonomic adjustments to normal human pregnancy: insight from spectral analysis of R-R interval and systolic arterial pressure variability

OBJECTIVE

To assess the adaptation in autonomic control mechanisms that accompanies the marked haemodynamic changes, such as increases in cardiac size and output, that occur in the course of normal human pregnancy.

DESIGN

We studied 14 healthy pregnant women (aged 30+/-1 years) before the 6th week (early stage) and within weeks 32-34 (late stage) of pregnancy, while they were at rest or in a state of active orthostatism (standing), which enhances sympathetic activity.

METHODS

We used echocardiography to assess cardiac volumes and mass, and spectral analysis of the R-R interval and systolic arterial pressure variability to obtain indices of autonomic regulation of the circulation. This non-invasive methodology, recently validated with direct recordings of muscle sympathetic nerve activity, furnishes quantitative markers of sympathetic modulation of the sino-atrial node (low frequency component, LF in normalized units, nu), vagal modulation (high frequency component, HF in normalized units, nu) and the overall arterial pressure-heart rate baroreflex gain (alpha index).

RESULTS

Late pregnancy was characterized by an increase in cardiac size and volumes and by a reduction of R-R interval, R-R interval variance and the alpha index, together with an increase in the LF/HF ratio (from 1.4+/-0.4 to 5.6+/-1.9). Changes in markers of autonomic modulation of the sino-atrial node normally induced by the standing position were blunted.

CONCLUSIONS

The late stage of normal human pregnancy appears to be characterized by alterations in the autonomic control of the circulation and by attenuated responsiveness to active standing, possibly as a consequence of the accompanying increase in cardiac size.

Chronic fatigue syndrome: a hypothesis focusing on the autonomic nervous system

Chronic fatigue syndrome is a debilitating illness of unknown aetiology, with estimated levels of prevalence of up to about 8. 7/100 000 in the U.S.A. Like pain fatigue it is a personal, emotionally rich experience, which may originate from peripheral or central sites (or both). The nature of the symptoms is complex and reflects the interaction of the patient with the environment and cultural milieu. Accordingly the common use of the same terminology for different types of fatigue may be misleading. Autonomic activation is a key component of both real and simulated physical exercise. Alterations in autonomic nervous system activity are a key component of several physiopathological conditions. In chronic fatigue syndrome disturbances in autonomic activity, and in other homoeostatic mechanisms, such as the hormonal and immune systems, have been reported recently. In this review we followed the hypothesis that in chronic fatigue syndrome the paradoxical condition of disturbing somatic symptoms in the absence of organic evidence of disease might be addressed by focusing on attending functional correlates. In particular we addressed possible alterations in cardiovascular autonomic control, as can be assessed by spectral analysis of R-R interval and systolic arterial pressure variability. With this approach, in subjects complaining of unexplained fatigue, we obtained data suggesting a condition of prevailing sympathetic modulation of the sino-atrial node at rest, and reduced responsiveness to excitatory stimuli. Far from considering the issue resolved, we propose that in the context of the multiple physiological and psychological interactions involved in the perception and self-reporting of symptoms, attendant changes in physiological equivalents might furnish a convenient assessment independent from subjective components. Indices of sympathetic modulation could, accordingly, provide quantifiable signs of the interaction between subject's efforts and environmental demands, independently of self descriptions, which could provide convenient measurable outcomes, both for diagnosis and treatment titration in chronic fatigue syndrome.

Autonomic effects of nicotine patch administration in habitual cigarette smokers: a double-blind, placebo-controlled study using spectral analysis of RR interval and systolic arterial pressure variabilities

Nicotine patch administration is often used to sustain tobacco abstinence in smoking-cessation programs. There is some concern regarding safety issues, as a consequence of the sympathomimetic action of nicotine. We used spectral analysis of RR interval and (noninvasive) systolic arterial pressure (SAP) beat-by-beat variabilities in a crossover double-blind design to assess the autonomic effects of cigarette smoking, of transdermal nicotine, and of placebo. The study group consisted of 27 heavy smokers (age 43 +/- 2 years). The RR interval and its variability were significantly reduced in the smoking group, as compared with nicotine or placebo groups. The LF component of RR interval variability (in normalized units, nu), and the LF/HF ratio showed greatest values during smoking, as compared with placebo. Values of LF(RR) and LF/HF during nicotine patch treatment were slightly, but not significantly, greater than observed with placebo. No differences were observed in SAP and its variability components. The index alpha (a frequency domain measure of baroreflex gain) was minimal in the smoking period. Habitual cigarette smoking is associated with signs of sympathetic predominance in the autonomic control of the sinoatrial (SA) node. Nicotine patches produce only minor disturbances of autonomic regulation. This corroborates their safe use in smoking-cessation strategies.

Individual recognition by heart rate variability of two different autonomic profiles related to posture

BACKGROUND

Power spectrum analysis of heart rate variability (HRV) can estimate the state of sympathovagal balance modulating sinus node activity. In view of the large distribution of spectral variables, a recognition of well-defined physiological conditions has never been attempted on an individual basis.

METHODS AND RESULTS

We considered 10 spectral variables extracted from short segments (200 to 500 cardiac cycles) of 350 ECG tracings recorded in normal subjects in both supine and upright positions (700 patterns). The tracings were first ordered consecutively and subsequently assigned alternatively to a training or to a test set (each consisting of 175 cases, providing 350 patterns considered to be independent). A forecasting linear method estimated a normalized activation index (ranging from -1 for supine to +1 for upright) that concentrated the information derived from spectral variables and that identified, in the test set, individual by individual, approximately 84% of corresponding body postures.

CONCLUSIONS

The combined use of spectral methodology and forecasting analysis has revealed an information content embedded, per se, in a short series of RR intervals capable of recognizing, individual by individual, two different autonomic profiles related to posture.

Maintained autonomic responses to moderate exercise in hypertensive patients treated with lacidipine

OBJECTIVE

Excessive adrenergic responses have been reported in hypertensive patients treated with short-acting dihydropiridine calcium channel antagonists that might worsen cardiovascular risk. In this study we addressed whether lacidipine, a long-acting dihydropiridine, increases the sympathetic excitation produced by moderate dynamic exercise.

DESIGN

Because of the wide changes in autonomic drive during everyday life, the possible influence of antihypertensive regimens should be assessed not only at rest but also during spontaneous, behaviourally induced alterations of sympathovagal balance. This study was designed to test whether treatment with lacidipine might alter the autonomic response to supine moderate dynamic exercise.

METHODS

We studied 16 moderate hypertensive patients (arterial pressure 151/102 mmHg) at rest and during 30% of nominal maximum recumbent bicycle exercise. The low frequency spectral component of RR interval and of systolic variability (Finapres) furnished markers of sympathetic modulation of the sinoatrial node and of the vasculature, respectively. Studies were performed during placebo and active treatment (lacidipine 4 mg per day).

RESULTS

Lacidipine treatment significantly reduces arterial pressure values at rest and during moderate dynamic exercise, without affecting RR interval and systolic arterial pressure variabilities, both at rest and during moderate exercise.

CONCLUSIONS

In conclusion, spectral analysis of RR interval and systolic arterial pressure variabilities indicate that antihypertensive treatment with lacidipine is not associated to an excessive sympathetic drive during moderate exercise.

Non-invasive assessment of the changes in static and oscillatory components of peripheral pressure/flow relationships produced by moderate exercise in humans

OBJECTIVE

The generalized sympathetic activation induced by exercise is accompanied by an increase in heart rate, blood pressure and vascular resistance in non-exercising vascular beds. The aim of the present study was to test the feasibility of assessing, non-invasively, the static and oscillatory pressure/flow relationships of peripheral arteries and their continuous changes during dynamic exercise.

DESIGN

We studied 44 healthy humans at rest, during moderate exercise (recumbent bicycle exercise) and recovery using a totally non-invasive approach.

METHODS

Arterial pressure was measured using a plethysmographic device, and ipsilateral brachial artery flow and palmar skin microcirculation flow were assessed with continuous wave Doppler and laser Doppler, respectively. Continuous, long data segments (> 90 s) were acquired with a personal computer and used to determine the changes of pressure/flow relationships of peripheral arteries during dynamic exercise. A new simplified method utilizing a transfer function analysis extracted automatically unequivocal indexes of static and oscillatory properties of vascular system.

RESULTS

Moderate exercise induced significant increases of the static (Zo) and oscillatory (Zc) components of peripheral pressure/flow relationships in both brachial artery and skin microcirculation beds. Both indexes returned to control values during early recovery.

CONCLUSIONS

This simple, non-invasive approach was capable of assessing the changes of static and oscillatory vascular properties induced by dynamic exercise. This method could be applied for a better understanding of the vascular modifications that occur in other physiological or pathophysiological conditions also characterized by increases in sympathetic drive.

A controlled study of the effects of mental relaxation on autonomic excitatory responses in healthy subjects

OBJECTIVE

Circumstantial evidence indicates that, in the presence of a suitable substratum, sudden, behaviorally induced increases in sympathetic drive to the cardiovascular system might play an important physiopathological role in various conditions, ranging from arterial hypertension to sudden coronary death. Accordingly, it might be useful to study the effects of behavioral interventions, such as mental relaxation, that might be capable of blunting excitatory autonomic responses. It would also be preferable to study healthy subjects in whom autonomic control is not modified by the presence of disease, and to use noninvasive approaches to minimize the possible emotional impact produced by invasive recordings.

METHODS

We examined healthy subjects who were either subjected to relaxation training (N = 13) or sham relaxation (N = 12). An additional group, treated with beta-adrenergic blockade (N = 12), was also examined. Spectral and cross-spectral analysis of RR interval and systolic arterial pressure (SAP) variabilities provided quantitative markers of sympathovagal balance modulating the sinoatrial (SA) node, of sympathetic vasomotor modulation, and of the gain of the arterial pressure/heart period baroreflex (index alpha). Subjects were studied at rest, during standing, and during mental arithmetic.

RESULTS

Data indicate that both beta-adrenergic blockade and relaxation training significantly blunted the excitatory autonomic responses to standing and to mental arithmetic. Indices of sympathetic modulation also seemed reduced by beta blockade at rest. No changes were observed with sham training.

CONCLUSIONS

Frequency domain analysis of cardiovascular variabilities, using a totally noninvasive approach, indicates that relaxation training significantly blunts the excitatory autonomic changes produced by standardized behavioral laboratory stimuli.

Cyclosporine-induced hypertension: evidence for maintained baroreflex circulatory control

BACKGROUND

The clinical use of cyclosporine as an immunosuppressive agent enhanced long-term survival in transplant recipients at the expense of a high incidence of induced hypertension. Altered neurovegetative (autonomic) cardiovascular control is suspected as a mechanism of this form of hypertension.

METHODS

Spectral analysis of systolic arterial pressure and R-R interval variability (electrocardiographic recordings) were performed, and the index alpha of baroreflex gain was computed in four groups of subjects matched for age: 13 orthotopic heart transplant recipients; 13 solid organ transplant recipients; 13 patients with essential hypertension; and 18 control subjects with normal blood pressure. All but the control subjects were treated with similar dihydropyridine calcium entry blockers. Heart and solid organ transplant recipients also received cyclosporine.

RESULTS

R-R variance was lowest in the heart transplant recipients. The spectral profile of R-R interval was suggestive of sympathetic predominance in the patients with hypertension, but not in the solid organ transplant recipients or the control subjects. Systolic blood pressure variability and low frequency component (a marker of sympathetic vasomotor modulation) were similar in the four groups. The index alpha was 1.8 +/- 2.2 in heart transplant recipients, 11.7 +/- 6.6 in solid organ transplant recipients, 7.3 +/- 3.6 in patients with hypertension, and 13.5 +/- 6.4 msec/mm Hg in control subjects (p = 0.0001).

CONCLUSIONS

These data indicate that (1) cyclosporine-induced hypertension in heart transplant recipients is associated with a loss of baroreflex function as a result of cardiac denervation-related uncoupling; (2) compared with patients with hypertension, organ transplant recipients with hypertension demonstrated a maintained baroreflex function as indicated by a lack of reduction of the index alpha; (3) baroreflex heart rate control in dihydropyridine-treated cyclosporine-induced hypertension is well maintained.

Evidence of increased sympathetic vasomotor drive with shorter acting dihydropyridine calcium channel antagonists in human hypertension: a study using spectral analysis of RR interval and systolic arterial pressure variability

We studied the effects of common antihypertensive regimens on autonomic cardiovascular control. We considered calcium channel antagonists (nicardipine twice a day and isradipine once a day, respectively) and also examined, as reference treatments, once-a-day atenolol and cilazapril. A noninvasive evaluation of autonomic cardiovascular profile was obtained with spectral analysis of RR interval and systolic arterial pressure variability. We studied moderate essential hypertensives before and after 2 weeks of treatment, both at rest and during active standing and mental arithmetic. All treatments reduced arterial pressure equally well; however, marked differences in spectral profiles were observed. The low-frequency spectral component of RR interval variability [in normalized units, marker of sympathetic modulation of the sinoatrial (SA) node] tended to be greater at rest and during stimuli (p < 0.001) in subjects treated with dihydropyridines. No differences at rest, but striking increases of the low-frequency component of systolic arterial pressure variability were observed in nicardipine-treated patients during both standardized excitatory stimuli, suggesting a marked increase in sympathetic vasomotor drive. As to reference treatments, patients treated with atenolol displayed the lowest values, and patients treated with cilazapril (for 4 weeks) provided intermediate values. In conclusion, shorter acting dihydropyridine calcium channel antagonists may induce an exaggerated increase in sympathetic vasomotor drive during standardized laboratory stressors.

Effects of aging and of chronic obstructive pulmonary disease on RR interval variability

Clinical and experimental investigations suggest that spectral analysis of RR interval variability might be employed to assess changes in autonomic regulation of the SA node occurring in various chronic, cardiac or respiratory conditions. We studied three groups of subjects: young healthy, older healthy, and old patients with chronic obstructive pulmonary disease (COPD), considering RR interval and breathing, i.e. tidal volume, variability in the frequency domain (AR algorithms), in order to obtain markers of the sympathetic and vagal modulation of the SA node [by way, respectively, of the low (LF) and high frequency (HF) spectral components]. The gain of the relationship between tidal volume and heart period variation (index beta) was also examined. COPD patients demonstrated a reduced resting RR variance with maintained spectral power distribution; upon tilting they did not manifest the usual increase of LF (and attendant decrease of HF) component. Additionally, we observed that the index beta at rest was significantly reduced in older as opposed to younger subjects. This index was also reduced by tilt, in both groups. In patients the index beta was reduced as compared to the group of similar age and younger subjects, and did not diminish further with tilt. This study indicates that in patients with COPD, sympathetic excitatory modulation of the SA node is depressed. Furthermore, the index beta, which provides an assessment of the gain of respiratory modulation of RR interval variability is significantly reduced in patients, as compared to healthy subjects of similar age. These abnormalities of autonomic control, may represent a functional correlation of the hyperinflated state present in this clinical condition which can be assessed non-invasively with spectral analysis of RR interval and respiration.

A controlled study of the autonomic changes produced by habitual cigarette smoking in healthy subjects

OBJECTIVES

An increased sympathetic drive, in view of its proarrhythmic, proatherosclerotic, and prothrombotic actions, could contribute to the elevated cardiovascular risk of habitual smokers. However, the underlying mechanisms are still debated. In this study we address the hypothesis that spectral analysis of RR interval and systolic arterial pressure short-term variabilities may be used to assess the complex autonomic changes produced by habitual cigarette smoking.

METHODS

A cross-sectional design compared heavy (> 20 cigarettes/day) habitual smokers (n = 20; 40 +/- 3 years), with similar age controls. Spectral analysis of RR interval variability provided markers of the sympatho-vagal balance modulating the SA node, by way of the normalised low frequency (LF approximately equal to 0.10 Hz) and high frequency (HF approximately equal to 0.25 Hz) components. The LF component of systolic arterial pressure (SAP) variability assessed the sympathetic vasomotor modulation. The frequency domain index (alpha) measured the baroreflex gain of the SA node. Subjects were studied at rest, and during the sympathetic excitation produced by active standing.

RESULTS

In smokers LFRR was, at rest, greater than in controls (70.6 +/- 3.8 vs 46.0 +/- 2.5 normalised units, nu); concurrently HFRR was reduced (22.1 +/- 3.2 vs 42.0 +/- 2.8 nu). Baroreflex gain and RR variance were also smaller in smokers. LFSAP was, instead, similar in the smokers and control groups. The standing induced increase in LFRR was blunted (P < 0.001) in smokers.

CONCLUSIONS

Spectral analysis of RR interval and systolic arterial pressure variability indicates that habitual cigarette smoking induces selective alterations in neural control of the SA node. An increase at rest in markers of sympathetic modulation is accompanied by signs of reduced vagal drive and depressed baroreflex gain; while sympathetic vasomotor modulation appears similar in controls and smokers. Data are consistent with the hypothesis that autonomic alterations may contribute to the increased cardiovascular risk present in smokers.

Analysis of initial autonomic adjustments to moderate exercise in humans

OBJECTIVE

To determine whether signs of cardiac sympathetic activation (together with vagal withdrawal) can be observed in the autonomic balance modulating the sino-atrial node as early as the initial levels of a graded light dynamic exercise.

PATIENTS AND METHODS

We studied 15 healthy ambulant subjects (mean +/- SD age 32 +/- 9 years; systolic/diastolic blood pressure 120 +/- 19/77 +/- 7 mmHg; heart rate 65 +/- 9 beats/min), who underwent a control recording of 10 min, followed by a three-step progressive (10, 20 and 30% of nominal maximum for age and sex) supine bicycle exercise. Spectral and cross-spectral analysis of RR and systolic arterial pressure variabilities were used to obtain non-invasive markers of the autonomic adjustments to exercise.

RESULTS

The low-frequency component of RR interval variability (which, in normalized units, is a marker of sympathetic modulation of the sino-atrial (SA) node) was progressively increased during all three stages of bicycle exercise. No significant changes were observed in the low-frequency component of systolic arterial pressure variability (i.e. a marker of sympathetic drive to the vasculature) in the early stages of exercise, while a significant increase was observed at 30% of maximum. The index alpha (which provides a measure of the gain of the arterial pressure-heart period baroreflex) was progressively reduced during all three stages of exercise.

CONCLUSIONS

While the sympathovagal balance modulating the SA node is immediately shifted towards sympathetic predominance (and vagal withdrawal), markers of peripheral vascular sympathetic activation appear increased only when 30% of maximum exercise is attained.

Adaptational changes in the neural control of cardiorespiratory function in a confined environment: the CNEC#3 experiment

The goal of the study was to characterize the changes in neurovegetative control of the circulation, attending the presumed physiological and psychological stress originated by the isolation and confinement typical of the living condition of space stations, as simulated in a ground based unit, using time and frequency domain analysis. As a secondary goal we sought to verify the implementation of real time data acquisition, for off line spectral analysis of R-R interval, systolic arterial pressure (by Finapres) and respiration (by PVF2 piezoelectric sensors). We addressed the cardiorespiratory and neurovegetative responses to standardized, simple stressors (active standing, dynamic and static handgrip) on the EXEMSI 92 crew, before, during and after the isolation period. On average the appropriate excitatory responses (to stand, dynamic and static handgrip) were elicited also in isolation and confinement. Active standing and small masses muscular exercises are easy to be performed in a confined and isolated environment and provide a valuable tool for investigating the adaptational changes in neural control mechanisms. The possibility there exists of using this time and frequency domain approach to monitor the level of performance and well being of the space crew in (quasi) real time.

Sympathetic overactivity in subjects complaining of unexplained fatigue

1. Theoretical and practical considerations suggest that in subjects complaining of fatigue, in the absence of evident organ dysfunction, an alteration in the autonomic nervous system might be present as a functional correlate. 2. Autoregressive spectral analysis of R-R interval variability from a surface ECG, was used in healthy control subjects (n = 24, age 45 +/- 4 years) and in subjects complaining of unexplained fatigue (n = 53, age 46 +/- 9 years) to obtain quantitative indices of the state of the sympathovagal balance, both at rest and during a mental stimulus (mental arithmetic), capable of enhancing sympathetic drive. Sympathetic and vagal modulations were inferred from the normalized powers of the low frequency and high frequency spectral components respectively. 3. We observed in patients, at rest, a prevailing low frequency component of R-R variability (patients low frequency = 73 +/- 11, control subjects 51 +/- 10 normalized units, P < 0.05). The responsiveness to mental arithmetic was reduced in patients as compared with controls. Systolic blood pressure variability did not differ. This suggested a selective imbalance in autonomic control of the sinoatrial node, characterized by sympathetic predominance as well as by vagal withdrawal, at rest. 4. The possibility of discriminating patients from control subjects on the basis of simple non-invasive functional markers might provide a better understanding of the mechanisms, clinical evolution and outcome of conditions such as the chronic fatigue syndrome, which lack ordinary evidence of disease, but comprise, as physiopathological correlate, a quantitative alteration of autonomic control.

Sympathetic restraint of baroreflex control of heart period in normotensive and hypertensive subjects

1. We assessed the effects of changing levels of sympathetic drive on the gain of baroreflex control of the sino-atrial node, in normotensive and hypertensive subjects. 2. Autoregressive spectral and cross-spectral analysis of R-R interval and systolic arterial pressure (non-invasive Finapres method) variabilities providing an estimate of baroreflex gain through the frequency domain index alpha were performed on data from 63 normotensive and 78 mild hypertensive subjects. Subjects were studied at rest and during active orthostatism, which induces sympathetic predominance. Seven control subjects and 14 hypertensive subjects were also studied after chronic atenolol treatment, to attenuate beta-adrenoceptor-mediated responses. 3. In both normotensive and hypertensive subjects, the index alpha was reduced by active standing and increased by chronic beta-adrenoceptor blockade. Furthermore, at rest, the index alpha was correlated with R-R variance and appeared significantly reduced with age. The age-related negative correlation of the index alpha was no longer evident during the standing-induced increase in sympathetic drive, in both normotensive and hypertensive subjects. 4. The index alpha, a non-invasive frequency domain estimate of the overall gain of baroreflex control of the sino-atrial node, which appears to be reduced in essential hypertension, is negatively modulated by physiological increases in sympathetic drive, and augmented by pharmacological blockade of beta-adrenoceptors. 5. In essential hypertension the enhanced sympathetic drive present already at rest, and the simultaneous reduction of the gain of baroreflex mechanisms, are the expression of a complex alteration in neural cardiovascular control.

[The effects of chronic cilazapril treatment on sympathetic vasomotor tonus: a spectral analysis study of pressure variability]

Animal experiments suggest that an important component of the antihypertensive effects of ACE inhibitors might derive from an inhibition of the sympathetic vasomotor tone. We addressed this problem on 22 mildly hypertensive subjects (48 +/- 2 years; arterial pressure 151 +/- 3/95 +/- 1 mmHg), in whom sympathetic vasomotor tone was non invasively inferred by the power of the low frequency component (0.1 Hz) of the spontaneous oscillations of systolic arterial pressure (LFSAP), during placebo and after 4 weeks of treatment with a new ACE inhibitor, cilazapril, 5 mg per os oid. LFSAP was computed at rest and during physical (active orthostatism) and mental (computerized attentional test and mental arithmetic) stimuli capable of enhancing sympathetic drive. Cilazapril treatment reduced resting arterial pressure to 128 +/- 3/80 +/- 2 mmHg, without affecting heart rate (78 +/- 2 and 74 +/- 2 b/min, respectively). The increases in LFSAP produced by standing were significantly greater during placebo than during active treatment (delta LFSAP = 10 +/- 3 and 5 +/- 2 mmHg2, respectively). These data suggest that an important reduction of sympathetic vasomotor tone accompanies the antihypertensive effects of chronic ACE-inhibitor treatment.

[A noninvasive assessment of the gain in baroceptor control of the heart rate in man]

In this study we addressed the problem of the noninvasive evaluation of the overall gain of baroreceptor control of heart period. We studied a population of healthy controls (n = 49, age 30 +/- 2 years, systolic arterial pressure [by Finapres] 114 +/- 1 mmHg) and a group of mild hypertensive subjects (n = 14, age 51 +/- 2 years, systolic arterial pressure 151 +/- 5 mmHg). Subjects were studied at rest both in absence and in presence of chronic beta-adrenergic receptor blockade (atenolol: controls 50 mg po oid x 4 days; hypertensives 100 mg po oid x 2 weeks). Spectral analysis of RR interval and of systolic arterial pressure variabilities provided noninvasive markers of autonomic control of the SA node and of the vasculature. The index alpha, obtained from bivariate cross spectral and spectral analysis provided a quantitative assessment of the closed loop gain of baroreceptor control of the heart period. The index alpha resulted more elevated in the normotensive than in the hypertensive group. Additionally it appeared significantly increased at the end of the treatment with the beta-adrenergic blocking drug atenolol. Furthermore, alpha appeared significantly and negatively correlated with age, systolic arterial pressure and, although weakly, with low frequency; it was positively correlated with the average RR interval. In conclusion, this study suggested an important link between the average level of sympathetic activity and baroreceptor control of heart rate in normotensive and mild hypertensive subjects. The clinical importance of this sympathetic modulation of the gain of the heart period/arterial pressure relationship can now be assessed with this noninvasive approach.

Effects of chronic cilazapril treatment on cardiovascular control: a spectral analytical approach

In 11 subjects with mild hypertension (sitting arterial pressure of 146 +/- 5/97 +/- 2 mm Hg), the effects of chronic angiotensin-converting enzyme (ACE) inhibition (cilazapril, 5 mg p.o. once daily for 4 weeks) were studied at rest and during active standing by means of spectral analysis. Sympathetic vascular control was inferred from the power of the low-frequency (LF) component of the systolic arterial pressure (SAP) variability, assessed noninvasively with a plethysmographic technique. Simultaneously, quantitative indices of neural control of the sinoatrial (SA) node were obtained with the power of the LF and of the high-frequency (respiration linked) component of R-R variability. Before treatment, active standing produced a clear increase in the LF components of R-R and SAP variabilities. At the end of the 4 weeks of cilazapril treatment, the LF component of SAP variability during standing was significantly lower than prior to treatment, while the increase in the LF component of R-R variability was left unchanged. These findings suggest an inhibitory effect of chronic ACE inhibition upon vasomotor sympathetic control, as assessed non-invasively by this technique.