H.N. Medved, C.L. Chapman, S.M. Holt, C.T. O’Connell, S.C. Brazelton, W.A.B. Howells, E.L. Reed, K. Wiedenfeld Needham, J.R. Halliwill, FACSM, C.T. Minson, FACSM

University of Oregon, Eugene, OR

Females have attenuated increases in blood pressure to the exercise pressor reflex (EPR) compared to males. Mild hypohydration (~2% body mass loss) alters blood pressure regulation but increases in blood pressure to EPR are not modified by very mild hypohydration (~0.5% body mass loss). It is unknown whether mild hypohydration modulates the differential blood pressure responses to EPR. PURPOSE: To test the hypothesis that increases in blood pressure during EPR remain attenuated in females compared to males during mild hypohydration. METHODS: In a block-randomized crossover design, twenty-two healthy adults [11 females (F), 11 males (M); 21 (3) years] completed 24 hours of fluid deprivation (HYPO) or 24 hours of normal fluid consumption (EUHY). Participants underwent 2 min static handgrip exercise at 30% of maximum voluntary isometric contraction (HG) and 2 min arterial occlusion of the right arm (OCC). Body fluid losses were estimated by the change in body mass (∆BM) over 24 hours. Blood pressure was measured via finger photoplethysmography corrected to brachial artery blood pressure at baseline (electrosphygmomanometer). Data are presented as the change from baseline (∆) as mean with 95% confidence intervals. RESULTS: ∆BM was not different between sexes (P=0.5393) during HYPO [F: -2.2% (-2.9, -1.6); M: -2.8% (-3.4, -2.3)] or EUHY [F: -0.1% (-0.8, 0.5); M: 0.1% (-0.3, 0.6)]. At end HG and OCC, increases in systolic [HG, F: 14 mmHg (6, 21), M: 26 mmHg (16, 36); OCC, F: 7 mmHg (-1, 15), M: 23 mmHg (13, 33), P≤0.0500] and diastolic [HG, F: 14 mmHg (9, 19), M: 23 mmHg (16, 30); OCC, F: 6 mmHg (1, 10), M: 16 mmHg (10, 22), P≤0.0371] blood pressure were attenuated in females during EUHY compared to males. There were no differences between sexes at end HG and OCC in systolic [HG, F: 18 mmHg (12, 24), M: 25 mmHg (15, 35); OCC, F: 12 mmHg (4, 19), M: 16 mmHg (10, 22), P³0.2029] and diastolic [HG, F: 16 mmHg (10, 22), M: 22 mmHg (16, 28); OCC, F: 16 mmHg (10, 22), M: 22 mmHg (16, 28), P³0.1223] blood pressure. CONCLUSION: These findings indicate that mildly hypohydrated females do not retain the attenuated increases in blood pressure during EPR compared to males that is observed in euhydration.

Supported by NIH R01HL144128 and F32HL164021, and the UO Summer Program for Undergraduate Research.

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