title: Age-related changes in vasomotor reflex control of calf venous capacitance response to lower body negative pressure in humans.
abstract: The present study was performed to test the hypothesis that calf venous capacitance would be reduced by mild gravitational stress through a vasomotor reflex in humans, and this response could be diminished with advancing age. Nine young (31 +/- 1 years, mean +/- SE) and 9 elderly (69 +/- 1 years) healthy males were exposed to a lower body negative pressure (LBNP) of 15 mmHg. Venous occlusion plethysmography was used to measure calf venous capacitance and calf blood flow. Muscle sympathetic nerve activity (MSNA) was recorded microneurographically from the tibial nerve along with cardiovascular variables. It was found that baseline MSNA was higher [21 +/- 4 (mean +/- SE) vs. 37 +/- 5 bursts x min(-1), young vs. elderly; p < 0.05] and calf venous capacitance was lower (1.71 +/- 0.12 vs. 1.44 +/- 0.10, ml x 100 ml(-1), young vs. elderly; p < 0.05) in the elderly group. At 15 mmHg-LBNP, heart rate and mean arterial pressure both remained unchanged, MSNA was enhanced, and calf blood flow was reduced in all subjects. Calf venous capacitance during LBNP decreased in the young, but did not change in the elderly. A significant negative correlation between percent changes in MSNA and percent changes in calf venous capacitance existed in the young group (y = 20.171x-11.863, r = 20.682; p = 0.0432), but disappeared in the elderly group. The ratio of percent changes in calf venous capacitance to percent changes in MSNA was markedly lower in the elderly (p < 0.01). In conclusion, these results substantiate our hypothesis that calf venous capacitance is reduced by mild LBNP through the vasomotor reflex, and this response is diminished in the elderly.
authors.affiliation: Department of Neuroimmunology, Research Institute of Environmental Medicine, Nagoya University, Nagoya, 464-8601 Japan.
authors.forename: Qi
authors.initials: Q
authors.lastname: Fu
authors.forename: Satoshi
authors.initials: S
authors.lastname: Iwase
authors.forename: Yuki
authors.initials: Y
authors.lastname: Niimi
authors.forename: Astunori
authors.initials: A
authors.lastname: Kamiya
authors.forename: Daisaku
authors.initials: D
authors.lastname: Michikami
authors.forename: Tadaaki
authors.initials: T
authors.lastname: Mano
authors.forename: Akio
authors.initials: A
authors.lastname: Suzumura
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D017704:Baroreflex / Q000502:physiology*; D006112:Gravitation; D006801:Humans; D007866:Leg / Q000098:blood supply*; D008150:Lower Body Negative Pressure; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation; D012146:Rest; D013564:Sympathetic Nervous System / Q000502:physiology; D018924:Vascular Capacitance; D014666:Vasomotor System / Q000502:physiology*; D014680:Veins / Q000502:physiology