Methodology of baroreflex testing

Recent clinical data have generated fresh interest in the assessment of baroreflex sensitivity, largely because of the relationship between this parameter and prognosis after a myocardial infarction. The present article reviews and discusses some of the methodologies currently used for the determination of baroreflex sensitivity. The Neck Chamber involves stimulation of the carotid baroreceptors by either augmenting or decreasing pressure at the level of the neck. The main advantage of this technique is to allow the simultaneous measurement of changes in heart rate and in the peripheral resistances. Another advantage is represented by the fact that no drugs are necessary for this type of study. On the other hand, this procedure modifies autonomic influences in several receptors areas while the stimulus is acting only at the carotid level; as a result of the baroreceptor activation or deactivation, this will produce complex and not uniform afferent information from receptors that are exposed to mechanical stimuli of opposite direction. In addition, it is difficult to quantify the pressure transmitted to the baroreceptors located in the carotid wall. The use of vasoactive substances, usually phenylephrine or nitroglycerin, produces a brisk change in pressure which is then linearly correlated with the attendant changes in the R-R interval to obtain a "baroreflex slope". The first concern with vasoactive drugs is that they act also on smooth muscle in the carotid sinus wall and might thereby interfere with the mechanical effects on the baroreceptors. The second is that peripheral resistance cannot be calculated at the same time.(ABSTRACT TRUNCATED AT 250 WORDS)