Articles: pressoreceptors-physiology.
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The alpha 2-adrenergic agonist, dexmedetomidine, alters hemodynamics by diminishing sympathetic and/or augmenting parasympathetic neurogenic tone to the heart and peripheral vasculature. However, the specific actions of dexmedetomidine on baroreceptor function are unknown. The purpose of the current investigation was to determine baroreceptor function during an anesthetic state produced by halothane and a similar anesthetic state produced by halothane after dexmedetomidine pretreatment. ⋯ The results indicate that dexmedetomidine alone does not alter baroreflex sensitivity. In addition, possibly through an anesthetic-sparing action, dexmedetomidine preserves baroreflex responses during halothane anesthesia. Such a preservation of the baroreceptor reflex by dexmedetomidine might provide an important mechanism for maintenance of cardiovascular stability by retaining buffer reflexes during general anesthesia.
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J. Auton. Nerv. Syst. · Mar 1994
Role of vagal afferents in the haemodynamic response to acute central hypovolaemia in unanaesthetized rabbits.
In unanaesthetized mammals, including rabbits, the response to acute central hypovolaemia is biphasic. An initial phase of baroreflex-mediated systemic vasoconstriction is succeeded by an abrupt failure of sympathetic vasoconstrictor drive and haemodynamic decompensation. We have tested whether a signal travelling in the cervical vagus nerves is responsible for the second phase. ⋯ Vagotomy had no effect on Phase I, but the onset of Phase II was delayed until CI had fallen by approximately 53% in 6 rabbits. In 1 rabbit, Phase II did not occur, even though CI had fallen by 67%. We conclude that an afferent vagal signal does not contribute to the compensatory Phase I, and is not essential for the occurrence of the decompensatory Phase II, of acute central hypovolaemia in unanaesthetized rabbits.
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The immunocytochemical detection of Fos, the protein product of the immediate-early gene c-fos, was used as a marker for activated neurons to examine whether the C1 neurons in the rat rostral ventrolateral medulla (RVLM) respond to changes in baroreceptor afferent activity. After hydralazine-induced hypotension or sinoaortic denervation, two treatments that reduce baroreceptor afferent activity, numerous Fos-positive neurons were observed in the RVLM. ⋯ Furthermore, in hydralazine-treated rats, the majority of Fluorogold-labeled Fos-positive neurons contained PNMT. These results suggest that C1 neurons are sensitive to baroreceptor afferent input and support a role of these neurons in cardiovascular regulation.
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1. Both electrical and chemical stimulation of the midbrain periaqueductal gray matter (PAG) inhibit baroreflex vagal bradycardia (BVB). The present study was designed to determine the target site of this inhibition about which little is known. ⋯ In addition, unitary recordings revealed that ADN-evoked unitary responses of neurons in the NA region were suppressed by PAG stimulation, whereas NTS baroreceptor neurons, either ADN responsive or nonresponsive, were scarcely inhibited by PAG stimulation. 5. These findings suggest that the PAG inhibited BVB mainly at the vagal preganglionic cell level and not at the NTS interneuron level. The conclusion is in harmony with our previous reports that the target site of hypothalamic inhibition of BVB in rats is also the preganglionic neurons and that hypothalamic inhibition of BVB is mediated predominantly by the PAG.
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Rapid quantification of the human baro-reflex control of heart rate has been achieved on a beat-by-beat basis using a neck-chamber with quick ECG-triggered pressure changes. Referring to recent findings on heart rate and stroke volume, the present study uses this technique to compare cardiac output as well as blood pressure changes in supine and upright position to investigate feedback effects and to confirm postural reflex modifications not revealed by RR-interval changes. A suction profile starting at +40 mmHg and running 7 steps of pressure decrease down to -65 mmHg was examined in 0 degree and 90 degrees tilting position while beat-by-beat recordings were done of heart rate, stroke volume (impedance-cardiography) and blood pressure (Finapres (tm)) (n=16). ⋯ A decrease in all blood pressure values was found during suction, except for systolic values in upright position which increased. Conclusively, (a) it is confirmed that different inotropy accounts for the seen gravitational effect on the cardiac output not represented by heart rate (b) identical suction levels in different positions lead to different stimuli at the carotid receptor. This interference has to be considered in microgravity studies by beat-by-beat measurement of cardiac output and blood pressure.