Is Low Baroreflex Sensitivity only a Consequence of Essential Hypertension or also a Factor Conditioning Its Development?

Baroreflex has several branches: reflex control of the peripheral resistance, of the tone of capacitance vessels, of the heart rate and contractility. Heart rate response to blood pressure variations is studied most intensively. Heart rate changes caused by stimulation of baroreceptors are usually quantified as the index of baroreflex sensitivity (BRS), which corresponds to a prolongation of the cardiac interval due to the increase of blood pressure in ms/mmHg. This mechanism operates beat-by-beat and is evaluated from recordings of blood pressure and inter-beat intervals (IBI) lasting for several minutes or several seconds respectively, depending on the method used. Despite the fact that BRS fluctuates in healthy subjects at rest, it represents a characteristic individual feature. Baroreflex sensitivity decreases with age and in different pathological states. This is of major clinical relevance as a risk factor of sudden cardiac death in patients after myocardial infarction, which is included among complications of hypertension. Therefore, many studies have paid attention to this problem providing evidence that metabolic and sympathetic/parasympathetic changes, especially during obesity, activate mechanisms (for instance thickening of the carotid wall) causing suppression of BRS. On the other hand, some healthy children and adolescents have as low BRS as elderly patients with hypertension. Some genetic studies provided evidence for an inborn disposition to low BRS. This opened the question whether an inborn low BRS could represent an additive factor disposing to blood pressure elevation. This is important with respect to epidemic obesity and to an increased prevalence of hypertension among young people.