Spontaneous baroreflex sensitivity in young and older people during voluntary and electrically evoked isometric exercise

Abstract

Background: In young people, cardiovagal baroreflex sensitivity, alters during isometric exercise. We investigated whether the reduced resting baroreflex sensitivity seen with increasing age is similarly altered during exercise. Methods: Cardiovagal baroreflex sensitivity was examined in 8 young (age±SEM, 25±1.7 vears) and 9 older (61±3.0 years) subjects, using sequence analysis during voluntary and electrically evoked isometric exercise (at 30% maximum voluntary strength) and during subsequent post-exercise circulatory occlusion. Results: In all phases of both conditions, baroreflex sensitivity was significantly reduced in the older group compared with the young group. (Median (interquartile range), voluntary 7.0 (4.4) vs 3.6 (3.8) ms.mmHg-1, post-exercise circulatory occlusion 9.0 (8.2) vs 4.6 (4.0) ms.mmHg-1; electrically evoked 6.6 (10.6) vs 3.2 (3.6) ms. mmHg-1, post-exercise circulatory occlusion 8.3 (7.7) vs 2.9 (2.2) ms.mmHg-1, young vs older respectively; P<0.05.) There was a marked rightward shift (resetting) of the baroreflex during exercise with the exception of electrically evoked in the older group. Conclusion: Our data demonstrate that the reduction in baroreflex sensitivity in older people is maintained during exercise and during post-excrcise circulatory occlusion. Resetting of the baroreflex in the older subjects during moderate voluntary isometric calf exercise is largely the result of central command.