Aging and chronic exercise training influence leg venous compliance. Venous compliance affects responses to an orthostatic stress; its effect on tolerance to maximal lower body negative pressure (LBNP) in the elderly is unknown. The purpose of this study was to determine the influence of age and fitness, a surrogate measure of exercise training, on calf venous compliance and tolerance to maximal LBNP in men and women. Forty participants, 10 young fit (YF; age = 22.6 +/- 0.5 yr, peak oxygen uptake = 57.1 +/- 2.0 ml.kg(-1).min(-1)), 10 young unfit (YU; 23.1 +/- 1.0 yr, 41.1 +/- 2.0 ml.kg(-1).min(-1)), 10 older fit (OF; 73.9 +/- 2.0 yr, 39.0 +/- 2.0 ml.kg(-1).min(-1)), and 10 older unfit (OU; 70.9 +/- 1.6 yr, 27.1 +/- 2.0 ml.kg(-1).min(-1)), underwent graded LBNP to presyncope or 4 min at -100 mmHg. By utilizing venous occlusion plethysmography, calf venous compliance was determined by using the first derivative of the pressure-volume relation during cuff pressure reduction. We found that the more fit groups had greater venous compliance than their unfit peers (P < 0.05) as did the young groups compared with their older peers (P < 0.05) such that OU < YU = OF < YF. LBNP tolerance did not differ between groups. In conclusion, these data suggest that aging reduces, and chronic exercise increases, venous compliance. However, these data do not support a significant influence of venous compliance on LBNP tolerance.

Despite the decrease in the size of fast twitch motor units associated with aging, bilateral deficits exist in older adults, do not differ from those observed for younger adults, and remain larger for submaximal intensities.

. Effects of a 6-mo endurance-training program on venous compliance and maximal lower body negative pressure in older men and women. J Appl Physiol 99: 1070 -1077, 2005. First published April 14, 2005 doi:10.1152/japplphysiol.01169.2004.-Aging and chronic exercise training influence leg venous compliance. Venous compliance affects responses to an orthostatic stress. The extent to which exercise training in a previously sedentary older population will affect venous compliance and tolerance to the simulated orthostatic stress of maximal lower body negative pressure (LBNP) is unknown. The purpose of this investigation is to determine the influence of a 6-mo endurance-training program on calf venous compliance and responses and tolerance to maximal LBNP in older men and women. Twenty participants (exercise group: n ϭ 10, 5 men, 5 women; control group: n ϭ 10, 6 men, 4 women; all Ͼ60 yr) underwent graded LBNP to presyncope or 4 min at Ϫ100 mmHg before and after a 6-mo endurance-training program. Utilizing venous occlusion plethysmography, calf venous compliance was determined in both groups using the first derivative of the pressure-volume relation during cuff pressure reduction before training, at 3 mo, and at the end of the training program. The exercise group improved their fitness with the 6-mo endurance-training program, whereas the control group did not change (14 Ϯ 3 vs. Ͻ1 Ϯ 2%; P Ͻ 0.05). LBNP tolerance did not differ between groups or across trials (P ϭ 0.47). Venous compliance was not different between groups or trials, either initially or after 3 mo of endurance training, but tended to be greater in the exercise group after 6 mo of training (P ϭ 0.08). These data suggest that a 6-mo endurance-training program may improve venous compliance without affecting tolerance to maximal LBNP in older participants. orthostatic tolerance; peripheral circulation; baroreceptor sensitivity DESPITE EXTENSIVE investigation, the effects of either cardiovascular fitness or age on orthostatic tolerance remain uncertain. In younger people, some cross-sectional investigations have shown that endurance-trained participants have lower tolerance to head-up tilt or lower body negative pressure (LBNP) (6, 27), whereas others have found no fitness-related differences in tolerance (10, 16). Longitudinal investigations have shown that exercise training has improved (5, 13), had no effect on orthostatic tolerance (4, 33), or diminished tolerance to head-up tilt (26) and LBNP (28,36).Much less attention has been given to the effects of exercise training on orthostatic tolerance in older adults. Aging has been associated with a higher incidence of orthostatic hypotension (21, 30), which might increase the risk of falls in this population. A greater predisposition to orthostatic hypotension as a result of endurance training in an older population would be undesirable. On the other hand, if endurance training improved blood pressure regulation, then it would further support the inclusion of this type of exercise training in current recomm...

This study tested the hypothesis that normotensive black males differ from white males in their autonomic and cardiovascular responses to severe orthostatic stress. College age men (9 blacks, 9 whites) underwent graded lower body negative pressure (LBNP; 10 mmHg steps of 6 min each) to either -100 mmHg or presyncope. LBNP tolerance between the two groups did not differ (LBNP tolerance index: 378 +/- 34 vs 404 +/- 1 9mmHg.min, blacks vs whites). Responses to LBNP common to all subjects (< or = -40 mmHg), including spontaneous baroreflex sensitivity (sequence technique), did not differ between groups except whites experienced an earlier and more pronounced decline in total peripheral conductance than blacks (P < 0.01). At test termination, the heart rate variability measure of low frequency/high frequency ratio increased more in blacks than whites (5.2 +/- 1.1 vs 2.7 +/- 0.7 units; P < 0.05) while cardiac output and total peripheral conductance were lower in whites (both P < 0.05). These data suggest that blacks and whites have similar LBNP tolerances. They maintain blood pressure equally well when exposed to graded LBNP to presyncope, yet they differ in their mechanisms for doing so.

Background. The purpose of this investigation was to determine the effects of age and fitness on tolerance to maximal lower body negative pressure (LBNP).Methods. Ten older fit (OF) [73.9 6 2 years; 39.0 6 2 mlÁkg À1 Ámin À1 (age and estimated VO 2 peak, respectively)], 10 older unfit (OU) (70.9 6 1 years; 27.1 6 2 mlÁkg À1 Ámin À1 ), 10 young fit (YF) (22.6 6 0.5 years; 57.1 6 2 mlÁkg À1 Ámin À1 ), and 10 young unfit (YU) (23.1 6 1 years; 41.1 6 2 mlÁkg À1 Ámin À1 ) participants underwent graded LBNP of À10 mmHg every 4 minutes to either presyncope or À100 mmHg.Results. Compared to the other groups, YF had an earlier increase in heart rate (À40 mmHg vs the last stage; YF vs OF, OU, and YU, respectively) and decline in stroke volume (À20 mmHg vs À40 mmHg; YF vs OF, OU, and YU, respectively). OU had a higher resting mean arterial pressure; this difference was maintained until the last stage. OF had an earlier decline in total peripheral conductance than the other groups (À20 mmHg vs À40 mmHg). Tolerance to maximal LBNP did not differ among the groups.Conclusions. Despite differences in the responses to submaximal LBNP, neither age nor cardiovascular fitness affect tolerance to maximal LBNP.

This study tested the hypotheses that trained swimmers would have greater orthostatic tolerance than runners and, if present, it would be due to differences in their autonomic and hemodynamic responses to graded central hypovolemia. Twenty intercollegiate male athletes [11 runners and 9 swimmers; .VO(2max) =70.0 (1.6) vs 69.5 (2.6) ml.kg(-1).min(-1), respectively] underwent graded lower body negative pressure (LBNP) to presyncope. The swimmers were heavier [80.5 (1.9) vs 70.3 (1.9) kg, P<0.05], with larger resting cardiac [4.44 (0.29) vs 3.68 (0.18) l.min(-1).m(-2)] and total peripheral conductance [0.056 (0.04) vs 0.044 (0.02) units.m(-2)] indices. Neither spontaneous cardiac baroreflex sensitivity (sequence method) nor heart rate variability (spectral analysis) differed significantly between groups at rest. LBNP tolerance did not differ between groups, with an index value of 51 (2) kPa.min for the runners and 54 (4) kPa.min for the swimmers [383 (16) vs 402 (32) mmHg.min], although the swimmers had larger declines in pulse pressure and tended ( P=0.078) to have larger declines in total peripheral conductance index in the last completed stage of LBNP. These responses did not differ between groups in the last 2 min of LBNP. Neither the heart rate, mean arterial pressure nor forearm vascular conductance responses differed between groups throughout. Changes in heart rate variability indices did not differ significantly between groups, with similar declines in the high frequency component and increases in the low frequency/high frequency ratio. These data suggest that swim training does not lead to greater orthostatic tolerance than run training, and responses to maximal LBNP do not differ between swimmers and runners. Moreover, neither heart rate nor the autonomic modulation of the heart rate response to LBNP are affected by training modality.

Despite differences in the responses to submaximal LBNP, neither age nor cardiovascular fitness affect tolerance to maximal LBNP.

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