Modifications of cardiac autonomic profile associated with a shift schedule of work.

BACKGROUND: Shift work is associated with an increased rate of cardiovascular diseases and accidents. Discordance between circadian rhythms of stress-related biological variables and the work-sleep schedule might explain the reduced efficiency of work. It is not clear whether a shift schedule of work may induce similar discordance in the 24-hour oscillatory pattern of the cardiac autonomic control in respect to the work-sleep periods. METHODS AND RESULTS: Twenty-two healthy male blue-collar shift workers underwent 24-hour ECG recordings during each of the 3 different shifts (first, 6 AM to 2 PM; second, 2 to 10 PM; third, 10 PM to 6 AM). Spectral analysis of heart rate variability over 24 hours provided the normalized markers of cardiac sympathetic (LF(nu)) and vagal (HF(nu)) modulation of the sinoatrial node activity and of the sympathovagal balance (LF/HF). LF(nu) and LF/HF exhibited 24-hour oscillations with different times of maximum and minimum in accordance with the working and sleeping periods, respectively. Lower values of LF(nu) and LF/HF suggestive of a reduced cardiac sympathetic modulation were present when the job task was performed at night compared with the values observed when the work was performed during morning and evening. CONCLUSIONS: Continuous weekly changes of time of maximum and minimum in the cardiac sympathetic and vagal autonomic control may play a role in the excessive rate of cardiovascular diseases in shift workers. The reduced values of the indexes of cardiac sympathetic modulation during night work might be related to the presence of sleepiness or diminished alertness, which in turn could facilitate errors and accidents.

Oscillatory patterns in sympathetic neural discharge and cardiovascular variables during orthostatic stimulus.

BACKGROUND: We tested the hypothesis that a common oscillatory pattern might characterize the rhythmic discharge of muscle sympathetic nerve activity (MSNA) and the spontaneous variability of heart rate and systolic arterial pressure (SAP) during a physiological increase of sympathetic activity induced by the head-up tilt maneuver. METHODS AND RESULTS: Ten healthy subjects underwent continuous recordings of ECG, intra-arterial pressure, respiratory activity, central venous pressure, and MSNA, both in the recumbent position and during 75 degrees head-up tilt. Venous samplings for catecholamine assessment were obtained at rest and during the fifth minute of tilt. Spectrum and cross-spectrum analyses of R-R interval, SAP, and MSNA variabilities and of respiratory activity provided the low (LF, 0.1 Hz) and high frequency (HF, 0.27 Hz) rhythmic components of each signal and assessed their linear relationships. Compared with the recumbent position, tilt reduced central venous pressure, but blood pressure was unchanged. Heart rate, MSNA, and plasma epinephrine and norepinephrine levels increased, suggesting a marked enhancement of overall sympathetic activity. During tilt, LF(MSNA) increased compared with the level in the supine position; this mirrored similar changes observed in the LF components of R-R interval and SAP variabilities. The increase of LF(MSNA) was proportional to the amount of the sympathetic discharge. The coupling between LF components of MSNA and R-R interval and SAP variabilities was enhanced during tilt compared with rest. CONCLUSIONS: During the sympathetic activation induced by tilt, a similar oscillatory pattern based on an increased LF rhythmicity characterized the spontaneous variability of neural sympathetic discharge, R-R interval, and arterial pressure.

Sequential modulation of cardiac autonomic control induced by cardiopulmonary and arterial baroreflex mechanisms.

BACKGROUND: Nonhypotensive lower body negative pressure (LBNP) induces a reflex increase in forearm vascular resistance and muscle sympathetic neural discharge without affecting mean heart rate. We tested the hypothesis that a reflex change of the autonomic modulation of heartbeat might arise during low intensity LBNP without changes of mean heart rate. METHODS AND RESULTS: Ten healthy volunteers underwent plasma catecholamine evaluation and a continuous recording of ECG, finger blood pressure, respiratory activity, and central venous pressure (CVP) during increasing levels of LBNP up to -40 mm Hg. Spectrum and cross-spectrum analyses assessed the changes in the spontaneous variability of R-R interval, respiration, systolic arterial pressure (SAP), and CVP and in the gain (alpha(LF)) of arterial baroreflex control of heart rate. Baroreceptor sensitivity was also evaluated by the SAP/R-R spontaneous sequences technique. LBNP began decreasing significantly: CVP at -10, R-R interval at -20, SAP at -40, and the indexes alpha(LF) and baroreceptor sensitivity at -30 and -20 mm Hg, compared with baseline conditions. Plasma norepinephrine increased significantly at -20 mm Hg. The normalized low-frequency component of R-R variability (LF(R-R)) progressively increased and was significantly higher than in the control condition at -15 mm Hg. CONCLUSIONS: Nonhypotensive LBNP elicits a reflex increase of cardiac sympathetic modulation, as evaluated by LF(R-R), which precedes the changes in the hemodynamics and in the indexes of arterial baroreflex control.

[Syncope and work. STePS study (Short Term Prognosis of Syncope)]. / La sincope in età lavorativa. Studio multicentrico prospettico STePS.

BACKGROUND: Recurrent syncope is a common medical problem responsible for 3-5% of emergency department (ED) accesses and 1-6% of hospital admissions. If syncope occurs in a subject working in a critical safety task, the consequences of this event might be very dangerous for the worker, colleagues, others or for the environment. Therefore, syncope management is a major problem for occupational medicine, converning the general safety at work. AIMS: To evaluate the syncope events in a group of potential workers aged 18 to 65 years; to evaluate the symptoms preceding syncope and the presence of associated illnesses and recurrent events. POPULATION AND RESULTS: This study is part of the prospective study STePS (Short Term Prognosis of Syncope), and included 305 consecutive patients (aged 18-65 years, female 56%) who had syncope as a main symptom and presented at ED of four general hospitals in the Milan area, Italy, between the 23rd of January and 30th of June 2004. The 24% of subjects were hospitalized. In 21% the syncope occurs suddenly without any preceding symptom. The 67% of subjects didn't have any important illness at the time. 50% of subjects had recurrent syncope. In four subjects another syncope occurred in a 10 day follow-up. CONCLUSIONS: occupational medicine should consider syncope scrupulously. Proper diagnostic management is important to permit a correct evaluation of work safety issues.

Premature ventricular contractions and reflex sympathetic activation in cats.

In 27 decerebrate cats under various experimental conditions, we studied the effects of programmed premature ventricular contractions on the impulse activity of preganglionic sympathetic fibres isolated from the third left thoracic ramus. Single extrastimuli increased the sympathetic discharge by 319(SEM 43)% [from 10.3(1.7) to 36(3.7) imp.s-1, p less than 0.05]. The neural response was significantly enhanced after bilateral vagotomy by 394(34)% [from 12(2.6) to 53.3(9.8) imp.s-1, p less than 0.05], but abolished when the stimuli were delivered during bilateral carotid artery occlusion. No sympathetic reflex response was observed in cats with chronic sino-aortic denervation. In eight cats, during occlusion of the left anterior descending coronary artery, the control sympathetic response was progressively and reversibly attenuated from 239(28)% to 36(14)%, at 90 s from the beginning of the occlusion. After bilateral vagotomy, this inhibitory interaction was no longer present and the sympathetic neural response to programmed stimulation was maintained throughout the occlusion period. The data indicate that the sympathetic reflex response initiated by baroreceptive deactivation could be attenuated by cardiac vagal afferent activity induced by coronary occlusion.

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.

Early and late effects of exercise and athletic training on neural mechanisms controlling heart rate.

OBJECTIVE: This study addresses the long term and short term effects of heavy dynamic exercise on neural control of heart rate. METHODS: A group of healthy controls was compared with (1) a group of trained athletes during a period of yearly rest (detrained) and (2) a group of trained athletes at the peak of their training routine. Additionally, a group of 10 controls was studied 1, 24, and 48 h after a single bout of maximal dynamic exercise. Spectral analysis of RR interval variability provided markers of sympathetic (low frequency, LF, 0.10 Hz) and vagal (high frequency, HF, 0.25 Hz) modulation of the sinoatrial node. RESULTS: (1) In detrained athletes resting bradycardia was accompanied by a predominant HF rhythmic component suggestive of a prevailing vagal tone. (2) Trained athletes showed a resting bradycardia together with high LF values, thus suggesting a more complex neural interaction modulating heart rate. An additional longitudinal part of the study, performed on a group of detrained athletes who were examined for the second time after resuming training, confirmed the finding of a prevailing LF component in resting conditions. (3) In the 10 control subjects maximal dynamic exercise induced an increase in LF which outlasted the cessation of exercise up to 24 h, suggesting a persistent sympathetic activation. (4) Passive tilt, a manoeuvre which enhances sympathetic drive, produced a greater enhancement of the LF component in trained athletes than in control subjects. CONCLUSIONS: The cardiac sympathetic excitation outlasting heavy dynamic exercise may explain the coexistence of training bradycardia with signs of enhanced sympathetic activity in trained champion athletes.

Non-linear dynamics and chaotic indices in heart rate variability of normal subjects and heart-transplanted patients.

OBJECTIVES: Heart rate variability (HRV) is characterised by a variety of linear, non-linear, periodical and non-periodical oscillations. The aim of the present study was mainly to investigate the role played by neural mechanisms in determining non-linear and non-periodical components. METHODS: Analysis was performed in 7 recently heart transplanted patients and in 7 controls of similar age whose HRV signal was collected during 24 h. Parameters that quantify non-linear dynamic behaviour, in a time series, were calculated. We first assessed the specific non-linear nature of the time series by a test on surrogate data after Fourier phase randomization. Furthermore, the D2 correlation dimension, K2 Kolmogorov entropy, and H self-similarity exponent of the signal were estimated. From this last parameter, the dimension D = 1/H can be obtained. In order to assess whether the dynamics of the system are compatible with chaotic characteristics, the entire spectrum of Lyapunov exponents was calculated. We used return maps to graphically represent the non-linear and non-periodical behaviours in patients and controls. RESULTS: Surrogate data suggest that the HRV time courses have unique non-linear characteristics. D2, K2 and 1/H parameters were significantly lower in transplanted subjects than in controls. Positivity of the first Lyapunov exponent indicates divergence of trajectories in state-space. Furthermore, the display of return maps on projections obtained after Singular Value Decomposition, especially in low-complexity data (as in transplanted patients), shows a structure which is suggestive of a strange attractor. These findings support the hypothesis that chaotic dynamics underlie HRV. CONCLUSION: These results indicate that non-linear dynamics are likely to be present in HRV control mechanisms, giving rise to complex and qualitatively different behaviours. System complexity decreases in transplanted patients and this may be related to loss of the neural modulation of heart rate.

Global versus regional myocardial ischaemia: differences in cardiovascular and sympathetic responses in cats.

The cardiovascular and sympathetic responses to occlusions of the left main ("global" ischaemia) or distal left anterior descending ("regional" ischaemia) coronary artery were studied in 19 anaesthetised cats with chronic sinoaortic baroreceptor denervation. "Global" ischaemia, before vagotomy, resulted in a significant reduction of mean arterial pressure (MAP), left ventricular pressure (LVP), and LVdP/dtmax while sympathetic efferent impulse activity was significantly augmented during the initial 15 +/- 2 s of occlusion (early phase) and, vice versa inhibited during the subsequent 20 +/- 2 s of occlusion (late phase). Vagotomy did not modify the haemodynamic responses, however, a significant increase in sympathetic discharge was detectable during the whole occlusion period (early and late phases). "Regional" ischaemia, before vagotomy, resulted in a significant increase in sympathetic neural discharge and MAP, with no changes in left ventricular function. After vagotomy the occlusion elicited a significant increase in MAP, LVP, LVdP/dtmax and efferent sympathetic neural activity. These excitatory responses were abolished after the interruption of a large part of the cardiac sympathetic afferents. Thus coronary artery occlusion induced haemodynamic and sympathetic reflex responses that were dependent upon the interaction of opposite influences mediated by the simultaneous activation of cardiac vagal and sympathetic afferents. The extent of "ischaemic myocardium" represented a determinant factor for the prevailing type of neural response.

Improvement of left ventricular function and cardiovascular neural control after endoventriculoplasty and myocardial revascularization.

OBJECTIVE: To investigate the effects of endoventriculoplasty (EVP) and myocardial revascularization on left ventricular function and on sympathovagal balance modulating sinus node and vasomotor activity, we studied patients with left anterior, septal or anteroseptal ventricular aneurysm, before and after surgery. It has been demonstrated that, compared to the standard aneurismectomy, EVP associated with coronary grafting has a lower operative mortality and improves ventricular function, clinical status and prognosis. METHODS: We collected pre- and post-operative echocardiographic and angiographic data to determine morphological and hemodynamic changes. The pre- and post-operative neural cardiovascular control was assessed by power spectrum analysis of heart rate and systolic arterial pressure (SAP) variabilities during rest and tilt. RESULTS: As expected, post-operative ventricular function improved significantly: ejection fraction increased from 33 +/- 2 to 46 +/- 3% (p < 0.01) when assessed by echocardiography and from 40 +/- 4 to 55 +/- 5% (p < 0.01) when assessed by angiography; left ventricular end-diastolic pressure fell from 22 +/- 3 to 13 +/- 2 mmHg (p < 0.05). Pre-operatively sympathovagal balance responsiveness was blunted: tilt test did not induce, in respect to resting values, any significant change in low frequency (LFRR) and high frequency (HFRR) components of RR variability (in normalized units, n.u.) and in LFSAP. Post-operatively, tilt induced significant changes in LFRR and HFRR (in n.u.), in LF/HF ratio and LFSAP in respect to resting values. The pre- and post-operative percent differences--delta%--, from rest to tilt, of LFRR, HFRR, LF/HF and LFSAP were also significantly different (p < 0.01, p < 0.05, p < 0.05, p < 0.05). In addition, we compared data obtained from survivors and non-survivors (6 out of 19 patients died within 4 months because of heart failure). Non-survivors were characterized by significantly lower RR variance (184 +/- 80 vs. 1193 +/- 309 ms2 at rest, 196 +/- 87 vs. 546 +/- 104 ms2 during tilt, p < 0.05) and lower LFRR (15 +/- 7 vs. 61 +/- 6 at rest, 23 +/- 10 vs. 58 +/- 6 during tilt, in n.u., p < 0.01). CONCLUSIONS: (1) The improvement of ventricular function induced by EVP and myocardial revascularization is accompanied by a restored capability to oscillate of cardiovascular neural regulatory mechanisms; (2) the drastic reduction of variance and LF component from RR variability seems to be associated with an ominous outcome.

Continuous recording of direct high fidelity arterial pressure and electrocardiogram in ambulant patients.

A system providing high quality direct arterial blood pressure recordings and electrocardiograms in ambulatory patients was devised using a modified commercially available Holter type magnetic tape recorder together with a microminiature Millar (3F) tip transducer. This system did not require a perfusion line and solved the major drawbacks of other available systems. Pressure and electrocardiographic data were fed directly from the playback unit into a minicomputer for automatic beat to beat waveform analysis. Thus the blood pressure and RR interval variability signals could be simultaneously analysed with autoregressive modelling techniques to provide a quantitative estimate of sympathovagal balance in ambulant patients. The system was reliable, simple, and safe to use.

Effects of propranolol on the impulse activity of cardiovascular sympathetic afferent fibers.

The influence of beta-adrenergic receptor blockade on the impulse activity of 21 cardiovascular sympathetic afferent nerve fibers (11 from the thoracic aorta, 10 from the pulmonary veins), isolated from the left sympathetic rami communicantes T-3 and T-4 was studied in anesthetized, vagotomized cats. Aortic pressure, heart rate, and neural discharge were recorded during control conditions and during brief aortic occlusions of comparable amplitude and duration. Administration of dl-propranolol (0.2-0-4 mg/kg) did not modify aortic pressure or neural discharge of the fibers during control conditions, although, as expected, heart rate was diminished. dl-Propranolol administration did change the response of cardiovascular sympathetic afferents to similar aortic pressure increases. Before drug administration, aortic occlusion caused a significant increase in neural discharge of both aortic and pulmonary vein sympathetic afferent fibers, from 0.52 +/- 0.12 to 1.64 +/- 0.31 and from 0.67 +/- 0.10 to 2.08 +/- 0.25 impulses/sec, respectively (p less than 0.05). After dl-propranolol administration, comparable increases in aortic pressure resulted in slight but not significant increases in neural discharge of aortic and pulmonary vein fibers. Administration of d-propranolol (0.4-0.6 mg/kg), which possesses only membrane-stabilizing properties, did not modify the firing rate of four pulmonary sympathetic afferents, which subsequently decreased their response to pressure rises after administration of dl-propranolol. These results indicate that beta-adrenergic receptor blockade reduces the responsiveness to hemodynamic stimuli of sympathetic cardiovascular afferent fibers that are capable of mediating excitatory pressor reflexes.

Changes in autonomic regulation induced by physical training in mild hypertension.

The adaptive effects of physical training on cardiovascular control mechanisms were studied in 11 subjects with mild hypertension. In these subjects we assessed the gain of the heart period-systolic arterial pressure relationship in the unfit and the fit state by using 1) an open loop approach, whereby the gain is expressed by the slope of the regression of heart period as a function of systolic arterial pressure, during a phenylephrine-induced pressure rise and 2) a closed loop approach with proper simplification, whereby the gain is expressed by the index alpha, obtained through simultaneous spectral analysis of the spontaneous variabilities of heart period and systolic arterial pressure. Both methods indicated that training significantly increased the gain of the relationship between heart period and systolic arterial pressure at rest and reduced arterial pressure and increased heart period significantly. This gain was drastically reduced during bicycle exercise both in the unfit and fit state. In a second group of normotensive (n = 7; systolic pressure, 133 +/- 3 mm Hg) and hypertensive (n = 7; systolic pressure, 180 +/- 10 mm Hg) subjects undergoing 24-hour diagnostic continuous electrocardiographic and high fidelity arterial pressure monitoring, the index alpha was significantly reduced in the hypertensive group at rest. Furthermore, when analyzed continuously over the entire 24-hour period, this index underwent minute-to-minute changes with lower values during the day and higher values during the night. We propose the index alpha as a quantitative indicator of the changes in the gain of baroreceptor mechanisms occurring with physical training in mild hypertension and during a 24-hour period in ambulatory subjects.

Interpreting oscillations of muscle sympathetic nerve activity and heart rate variability.

Computer analysis of spontaneous cardiovascular beat-by-beat variability has gained wide credibility as a means of inferring disturbances of autonomic cardiovascular regulation in a variety of cardiovascular conditions, including hypertension, myocardial infarction and heart failure. Recent applications of spectral analysis to muscle sympathetic nerve activity (MSNA) offer a new approach to a better understanding of the relationship between cardiovascular oscillations and autonomic regulation. However, areas of uncertainty and unresolved debates remain, mostly concerning different methodologies and interpretative models that we will consider in this article. Perusal of all available literature suggests that average sympathetic nerve activity and its oscillatory components, although correlated to some extent, are likely to provide different types of information. In addition, the specific experimental context is of paramount importance, as the rules that seem to govern the relationship between average and oscillatory properties of MSNA appear to be different in usual conditions and in conditions of extremes of activation or disease. In general, dynamic experiments, such as with graded tilt or with vasoactive drugs, are more suited to investigations of the complexity of autonomic regulation than are static comparisons. In addition, because the information is spread across variables and is affected by a potentially large error, it appears that several different techniques should be perceived as complementary rather than as mutually exclusive. Available evidence suggests that low-frequency and high-frequency oscillations in peripheral signals of variability might have a predominantly central, rather than a peripheral, origin and that this applies in particular to low-frequency oscillations. A crucial point in the assessment of the meaning of spectral components relates to consideration of the varying level of very-low-frequency noise, and the mathematical manipulation of derived indices, particularly using a normalization procedure. This appears easier to obtain with auto-regressive than with fast Fourier techniques. With this approach, discrepant interpretations seem to be resolved, provided adequate care is taken in separating direct physiological data from derived meaning, which relates to hidden information and neural codes; in the case of sympathetic discharge, the latter display greater complexity than simple average spike activity per unit time. Accordingly we believe, in conclusion, that the judicious use of spectral methodology, in addition to other techniques, might provide unprecedented, useful insights into autonomic cardiovascular regulation, in both physiopathological and clinical circumstances.

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.

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.

Sympathetic predominance in essential hypertension: a study employing spectral analysis of heart rate variability.

In this study on 91 subjects we tested the hypothesis of an enhanced sympathetic activity in uncomplicated essential hypertension employing spectral analysis of heart rate variability. With this technique the tonic sympathetic and vagal activities and their changes are respectively assessed by the power of approximately 0.1 Hz (low frequency, LF) and approximately 0.25 Hz (respiratory linked, high frequency, HF) components of the spectrum of the beat by beat variability of RR interval. When comparing the 40 subjects with diastolic blood pressure consistently greater than 95 mmHg (hypertensives, Ht), with 35 age-matched controls (diastolic arterial pressure less than 90 mmHg, Nt), we observed that LF was greater and HF smaller in Ht as compared to Nt, thus suggesting an enhanced sympathetic activity and a reduce vagal activity in Ht. Additionally, passive tilt, which in Nt enhances LF [delta = 26 +/- 2 normalized units (nu)] and reduces HF (delta = -22 +/- 2, nu), produced smaller (P less than 0.05) changes in Ht (delta LF = 6.3 +/- 2.7 and delta HF = -7.5 +/- 2.3 nu). Furthermore, the values of LF at rest and the altered effects of tilt on LF and HF were significantly correlated with the degree of the hypertensive state. Chronic beta-adrenergic blockade (atenolol 100 mg once daily for 2 weeks, n = 13) reduced heart rate and blood pressure (from 162/103 to 136/88 mmHg) together with a significant diminution of LF and an increase of HF. Thus, spectral analysis of RR variability appears to be a convenient non-invasive technique to follow the progressive alterations in sympatho-vagal balance present in essential hypertension.

Mechanical effects of respiration and stepping on systolic arterial pressure variability during treadmill exercise.

AIM: To evaluate the changes produced by maximal dynamic exercise in the rhythmic components of systolic arterial pressure variability. PATIENTS AND METHODS: We studied seven normotensive subjects during different levels of a modified treadmill test (Bruce protocol, up to stage 4). Arterial pressure was measured directly by a high-fidelity microtip pressure transducer. Spectral analysis provided two main oscillatory components of systolic arterial pressure variability, a low-frequency component related to the sympathetic-mediated neural control of vasomotion and a high-frequency component reflecting the mechanical effects of respiration on blood pressure. RESULTS: The low-frequency component increased at the beginning of exercise and remained stable thereafter, while the high-frequency component increased progressively. A third rhythmic component (very high frequency) with a frequency higher than respiration and synchronous with the rate of the subjects' footsteps, which was undetectable on a visual inspection of analog tracings, became progressively more apparent, reaching its maximum at exercise stage 4. CONCLUSIONS: These findings emphasize the importance of high-fidelity techniques and computer analysis for the evaluation of arterial pressure variability in dynamic conditions.

Altered pattern of circadian neural control of heart period in mild hypertension.

We addressed the problem of the circadian changes in neural control of heart period in ambulant hypertensive subjects. A running spectral analysis of R-R variability from Holter tapes provided markers of sympathetic, i.e. low-frequency component (LF) almost equal to 0.10 Hz, and vagal, i.e. high-frequency component (HF) almost equal to 0.25 Hz, controlling activities for the 24-h period of the recording. Significant circadian differences were observed in LF between the two groups of subjects: during night-time rest (0300-0400 h), LF was greater in hypertensives than in normotensives (56 +/- 2 and 48 +/- 2 nu, respectively; P less than 0.05). Furthermore, the difference between daytime and night-time LF values was progressively reduced with increasing severity of the hypertensive state, as assessed by resting arterial pressure levels. Spectral analysis of R-R variability suggests that essential hypertension may be characterized by a reduced day-night oscillation in sympathetic activity than can be quantified non-invasively using this approach.