Carotid diameter variations as a non-invasive tool to examine cardiac baroreceptor sensitivity.

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Abstract
Objective and design Recently we developed a non-invasive ultrasound technique, enabling the determination of end-diastolic diameter and distension (increase in diameter during cardiac cycle) over a long time period. Using this technique we test the hypothesis that low-frequency variations derived from non-invasively determined common carotid artery diameter signals are superior to those derived from non-invasively determined arterial pressure to predict heart rate variability, a method used to assess baroreceptor sensitivity. Moreover, we investigate whether the reduced baroreflex sensitivity in the elderly persists after eliminating the influence of the stiffness of the vessel wall and can be attributed to an impairment of the neural baroreflex pathways. Results The main finding of the present study is that variability in distension rate, i.e. increase in diameter during the cardiac cycle per systolic time interval, of the common carotid artery is a considerably more accurate predictor of R–R interval variability than variability in systolic arterial finger pressure. Moreover, distension rate variability is a more accurate predictor of R–R interval variability than distension and diameter variability. The reduced baroreflex sensitivity in the elderly persists in spite of the elimination of the influence of the stiffness of the vessel wall. Conclusions We conclude that: (1) in the evaluation of baroreceptor sensitivity the assessment of variations in parameters derived from carotid arterial diameter is superior to the assessment of parameters derived from peripheral arterial finger pressure; and (2) conduction by the neural baroreflex pathways deteriorates with age.