Age‐related loss of hysteresis in the spontaneous vascular sympathetic baroreflex is associated with altered neural rather than mechanical control

Figures

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  FIGURE 1. Integrated baroreflex sensitivity slopes separated by responses to falling and rising pressure in a young male participant. Continuous lines represent data obtained during falling pressure; dashed lines represent data obtained during rising pressure. Numbers adjacent to each point indicate the number of cardiac cycles contributing to each pressure bin. Coefficients of determination (r 2) for each relationship are also shown.

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  FIGURE 2. Hysteresis characteristics of mechanical, neural and integrated baroreflex in young and middle‐aged men. Continuous lines represent data obtained during falling pressure; dashed lines represent data obtained during rising pressure. Component operating points (means ± SD) are superimposed on the regression lines as circles in young men and squares for middle‐aged men. YFall, young falling pressure gain; YRise, young rising pressure gain; YFallOP, young falling pressure operating point; YRiseOP, young rising pressure operating point; MAFall, middle‐aged falling pressure gain; MARise, middle‐aged rising pressure gain; MAFallOP, middle‐aged falling pressure operating point; MARiseOP, middle‐aged rising pressure operating point.

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  FIGURE 3. Mechanical, neural, and integrated baroreflex gains derived from spontaneous arterial pressure fluctuations. Mechanical (pressure–diameter), neural (diameter–sympathetic outflow) and integrated baroreflex (pressure–sympathetic outflow) gains are shown for the full baroreflex loop and separately for the falling and rising pressure limbs. Individual values and group means ± SD are presented to illustrate variability and limb‑dependent differences in baroreflex behaviour. Direction dependent response comparisons were performed using two‑way ANOVA (factors: age group × pressure direction). Full baroreflex loop age comparisons were performed using unpaired t‐tests on the integrated burst probability, integrated burst area and mechanical components, and Mann–Whitney tests on the neural burst probability and neural burst area components.