[Basic concepts on the assessment of arterial baroreceptor sensitivity with non invasive methods. Estimate of the spontaneous gain of the arterial baroreceptor].
Arterial baroreceptors are sensitive to variation in both blood and pulse pressure. When there is an increase in those pressures, the baroreceptors increase the rhythm in which electric impulses are discharged. The impulses are transmitted by the receptors to the nervous centres of the brainstem. Once processed, these signals turn into sympathetic and vagal impulses. The vagal efferents control heart rate and the sympathetic efferents control heart rate, myocardial contractility and peripheral resistance. If there is an increase in blood pressure, then there will be a reflex decrease in the sympathetic activity and an increase in the parasympathetic one. The cardiac cronotropic response to blood pressure variation is very fast-with a delay of one or two beats. The amplitude of the response is a sigmoidal function. The greatest inclination of the response curve, that is to say, the area of greatest variation of the RR interval per unit of pressure, characterises the gain of the baroreceptors. The traditional method for obtaining the gain of the baroreceptor is a pharmacological one. Generally, the patient is given phenilephrine intravenously, in bolus and then the correlation between heart rate and the increase in intra-arterial blood pressure (reflex bradycardia) is calculated. Lately, it has been used the calculation of the spontaneous gain of the baroreceptor starting from a study carried out on the normal fluctuations in blood pressure and in the pulse interval both in time and frequency domain. The first case deals with the calculation of the gain of the function of transfer between the variations both in blood pressure and the RR intervals in the LF and the HF bands. The second case deals with the analysis of the occurrence of sequences of three beats with successive increases or decreases in blood pressure and in the RR interval. The gain is obtained from the linear regression of all the sequences. The application of these techniques to the recordings of blood pressure obtained by non-invasive methods (Finapress) makes possible that this procedure be followed under real conditions since it requires no previous stimulation of the cardiovascular system, which would probably interfere with the mechanisms to be evaluated, and requires no equipment in the condition which is normally required by experimental methodology.
Costa
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Faculdade de Medicina do Porto.
Lago
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P
Miranda
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F
Freitas
J
J
Puig
J
J
Freitas
A F
AF
D001794:Blood Pressure / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D011311:Pressoreceptors / Q000502:physiology*
Conceitos básicos da avaliação da sensibilidade dos barorreceptores arteriais por métodos não invasivos. Cálculo do ganho espontâneo do barorreceptor arterial.