Central aortic pressure and assessment of baroreceptor function

Background: Non-invasive assessment of baroreflex sensitivity (BRS) is conventionally performed by relating changes in heart rate (HR) and systolic pressure (SBP), where continuous beat-to-beat changes in blood pressure are measured in a peripheral location (e.g., finger). The pressure pulse is, however, amplified between the aorta and periphery, with amplification depending on HR due to the frequency dependency of the brachial transfer function. In addition, the degree of pulse amplification reduces with increased aortic stiffness as occurs with age. Aim: To assess BRS using changes in SBP and pulse interval (PI) and to compare values of BRS computed from peripheral (finger) SBP (pSPB) and corresponding central aortic SBP (cSBP). Methods: Continuous blood pressure and ECG signal were acquired in 6 adult subjects (mean age 42 ± 16 years) over periods of 5–20 minutes. The spontaneous sequence technique was used for computation of BRS from the slopes of linear relationships of SBP and PI of contiguous cardiac cycles, where SBP and PI change in the same direction. Central aortic pressure was determined from the finger pressure pulse (Finometer) by applying a mathematical transfer function. BRS was computed for a lag of 0, 1, 2 and 3 cardiac cycles between PI and SBP. Results: The relationship between BRS computed from cSBP (y) and from pSBP (x) was y = 0.98x + 0.19 (r²=0.84). However, for all computed BRS values (n=24), BRS using cSBP were higher (by 21.5 ± 28.9SD %) in 62.5% of measurements (15/24) and lower (by 23 ± 12.8 %) in 35.5% (9/24). Across subjects, there was a trend for the difference to be positively related to heart rate (r²=0.21) and negatively related to age (r²=0.24) and mean arterial pressure (r2=0.11). Conclusions: BRS computed from changes in HR and cSBP show a relation to values computed from pSBP. The difference between the two can, however, be positive or negative, and is related to hemodynamic parameters and age. Further studies are required to assess underlying mechanisms of the differences and potential clinical significance.