Effects of Age and Fitness on Tolerance to Lower Body Negative Pressure

Abstract

0177 Orthostatic hypotension has and has not been reported among the elderly and endurance athletes may or may not have reduced tolerance to orthostatic stress. One of the limitations of many of the aging studies is in the use of submaximal rather than maximal orthostatic stress and a focus on either aging or fitness, not both. Purpose: The purpose of this investigation was to determine the effects of age and fitness on tolerance to maximal lower body negative pressure. Methods: Ten older fit (OF; 73.9 + 2 yo; 39.0 + 2 ml·kg-1·min-1), ten older unfit (OU; 70.9 + 1 yo; 27.1 + 2 ml·kg-1·min-1), ten young fit (YF; 22.6 + 0.5 yo; 57.1 + 2 ml·kg-1·min-1) and ten young unfit (YU; 23.1 + 1 yo; 41.1 + 2 ml·kg-1·min-1) participants underwent graded LBNP to either presyncope or −100 mmHg. Results: Compared to the other groups, YF had an earlier increase in HR (−40 mmHg vs the last stage, p<0.05) and decline in stroke volume (−20 mmHg vs −40 mmHg, p<0.05). OU had a higher resting mean arterial pressure; this difference was maintained until the last stage (p<0.05). OF had an earlier decline in total peripheral conductance than the other groups (−20 mmHg vs −40 mmHg, p<0.05). Tolerance to maximal LBNP did not differ between the groups. Conclusion: Despite differences in the responses to submaximal LBNP, which suggest that mechanisms to maintain blood pressure are different, neither age nor cardiovascular fitness affect tolerance to LBNP.