Does reduced vascular stiffening fully explain preserved cardiovagal baroreflex function in older, physically active men?

BACKGROUND: We measured cardiovagal baroreflex gain and its vascular mechanical and neural components during dynamic baroreflex engagement in 10 young untrained men, 6 older untrained men, and 12 older, physically active men. METHODS AND
RESULTS: Our newly developed assessment of beat-to-beat carotid diameters during baroreflex engagement estimates the mechanical transduction of pressure into barosensory stretch (diameter/pressure), the neural transduction of stretch into vagal outflow (R-R interval/diameter), and conventional integrated cardiovagal baroreflex gain (R-R interval/pressure). Integrated gain was lower in older untrained men than in young untrained men (6.8+/-1.2 versus 15.7+/-1.8 ms/mm Hg) due to both lower mechanical (9.1+/-1.0 versus 17.1+/-2.4 mm Hg/microm) and lower neural (0.57+/-0.10 versus 0.90+/-0.10 ms/microm) transduction. Integrated gain in older active men (13.3+/-2.7 ms/mm Hg) was comparable to that in young untrained men. This was achieved through mechanical transduction (12.1+/-1.4 mm Hg/microm) that was modestly higher than that in older untrained men and neural transduction (1.00+/-0.20 ms/microm) comparable to that in young untrained men. Across groups, both mechanical and neural components were related to integrated gain; however, the neural component carried greater predictive weight (beta=0.789 versus 0.588).
CONCLUSIONS: Both vascular and neural deficits contribute to age-related declines in cardiovagal baroreflex gain; however, long-term physical activity attenuates this decline by maintaining neural vagal control.