Contribution of vascular and neural segments to baroreflex sensitivity in response to postural stress.

BACKGROUND/AIMS The baroreflex pathway has a vascular and a neural segment, both being modulated by variations in peripheral blood pressure (BP). Besides overall baroreceptor sensitivity (BRS), defined as the spectral relationship between changes in peripheral BP and R-R interval within the frequency band of 0.05-0.15 Hz, vascular and neural segment contributions to the overall BRS can be distinguished. We test the hypothesis that changes in overall BRS following a postural maneuver mainly originate from the vascular (peripheral pressure to carotid artery diameter) rather than the neural segment (carotid artery diameter to R-R interval). METHODS Peripheral pressure (Finapress), carotid artery diameter (ultrasound in B-/M-mode) and electrocardiogram values of 20 young subjects in supine and upright-seated postures were recorded simultaneously. Transfer gains were computed for the segmental and overall responses. RESULTS Postural change significantly increases peripheral BP and carotid artery diameter. The vascular segment has a uniform spectral distribution. Statistical analyses revealed that postural change decreased overall (p < 0.004) and vascular (p < 0.0001) transfer gains, but did not modify neural gain. CONCLUSIONS Unlike the neural segment, the vascular segment is frequency non-specific. The decrease in overall BRS due to a postural change is mainly explained by the reduced transfer gain of the vascular segment.