Evaluation du systeme nerveux autonome dans l'hypertension arterielle essentielle

The spectral analysis of the heart rate, the systolic blood pressure, the diastolic blood pressure and the respiration with the Fast Fourier Transform, is considered as a non-invasive technique for the determination of the autonomic nervous system activity. In a population of normal volunteer subjects, we obtained in the basal state, low-frequency oscillations related to the sympathetic autonomous nervous system (0.05-0.15Hz) and the high-frequency oscillations (0.2Hz), which represent, on RR intervals, the respiratory sinus arrhythmia corresponding to vagal activity. We compared the sympathetic nervous system stimulation tests triggered by the transition from resting to voluntary orthostatic positions and the transition from resting to orthostatic position using tilt table at 60o. We also compared a normal blood pressure group to a hypertensive group which were both subject to the transition from resting to voluntary orthostation and for whom we evaluated the baroreflex sensitivity and the sympathetic response by measuring circulating catecholamines. In a group of subjects having an essential arterial hypertension, we have evaluated the effect of hypotensive therapy, by the Trandolapril which is an Angiotensin Converting Enzyme Inhibitor. In the hypertensive group, we evaluated the sympathetic stimulation using the voluntary orthostation, and we have also proceeded to a 3 minutes isometric exercise at 30% of maximum force. We have also completed our evaluation by measuring both the ß2 adrenergic receptor density on isolated lymphocytes and the contractility index using the echocardiography in M mode. In both sympathetic nervous system stimulation types by orthostatic position, the results have shown, for normal blood pressure volunteer subject groups, a significant increase in concentration of plasma catecholamines with an increase of heart rate (HR) and the low frequency RR, confirming therefore that we are in the presence of a sympathetic stimulation state. At the same time, we observed a significant decrease of high frequency of RR, suggesting a vagal withdrawal during the stimulation. We observed six cases of orthostatic hypotension from the tilt table test. We compared the voluntary orthostatic position between normal and hypertension subject groups. The results with combined spectral analysis of RR and the systolic blood pressure allowed to evaluate in the essential high blood pressure a reduced baroreflex sensitivity along with a reduced vagal reactivity in presence of increased sympathetic activity and reactivity suggesting a sympatho-vagal alteration in essential arterial hypertension. In hypertensive subjects treated with Trandolapril 2mg/day, we have identified a group responding to Trandolapril treatment and a group of non-responders to this type of anti-hypertensive therapy. The responding group has an hyper-adrenergic profile with higher sympathetic reactivity, heart rate and arterial diastolic and systolic pressures at rest. In the total group treated with Trandolapril, the ß2 adrenergic receptor density has doubled after therapy, while the reactivity of low frequencies obtained from spectral analysis has increased. We have shown in this study that Angiotensin Converting Enzyme Inhibitor could inhibit the facilitatory mechanism of angII on sympathetic nerve terminals and therefore allowed the reduction of the sympathetic hyperactivity and the cause of a beta2 adrenergic “down regulation”. Thus it allowed us to obtain an increased density of the receptors and the expression of more effective influence of post synaptic Sympathetic nervous system. In all of our clinical protocols, using spectral analysis of RR, systolic blood pressure, diastolic blood pressure and breathing signals, we have shown that this non-invasive technique has helped to describe and to better understand the physiological and pharmacological mechanisms related to the autonomic nervous system in normotensive and hypertensive subjects.

Keyphrases: RR variability, Blood pressure variability, Autonomic nervous system, Baroreceptor sensitivity, Essential hypertension, Angiotensin-converting Enzyme inhibitors