Background: The baroreflex pathway is composed of vascular and cerebral segments, which are individually affected by variations in blood pressure. Baroreceptor sensitivity (BRS) is conventionally derived from spectral relationship between changes in peripheral blood pressure and heart-rate (R-R), and recently from carotid artery (CA) diameter and R-R, within the spectral frequency band of 0.05–0.15 Hz.

Objective: To discriminate the contribution of distinct segments to the overall BRS value calculated, in response to blood pressure variations induced by posture changes.

Methods: The common CA was visualised in B/M-mode with an ultrasound system. Processing of received signal resulted in beat to beat changes in diameter characteristics as a function of time, over 10min. To reveal the segmental response to local changes in transmural pressure, the BRS mean amplitudes were computed for 20 young subjects in supine and uprightseated postures.

Results: Correlation analysis revealed variation in the transfer function of the cerebral segment, has a dominant contribution to the overall BRS value. Paired t-test revealed that the pressure-based BRS value is significantly lower in sitting than supine position (p < 0.01), while the strain-based BRS value did not change.

Conclusions: Shifting to an upright posture results in a lower CA transmural pressure, causing a larger change in diameter for a given blood pressure stimulus, thus enhancing the pressure-based BRS. The arterial pressure to CA diameter transfer function has the largest contribution to the change in the pressure-based BRS value, in response to the variation in pressure by posture.