Ta'Quoris Newsome, Marshall Dearmon, Kenneth R. Ladner, Barry Faulkner, Hunter Haynes, Ryan Aultman, Jon Stavres. University of Southern Mississippi, Hattiesburg, MS.

BACKGROUND: Resting sympathetic tone has been shown to be elevated in Black and African American (BAA) individuals compared to White individuals, but differences in Baroreflex Sensitivity (BRS) are less clear. Considering that exercise and orthostasis are both known to elicit acute changes in sympathetic tone, evaluating changes in BRS during handgrip exercise or during an orthostatic challenge may unmask any potential differences in BRS between BAA and White individuals. As such, the purpose of this study was to examine the relative influences of isometric handgrip exercise and body position on BRS in a sample of BAA and White participants. METHODS: Cardiac rhythm (via electrocardiography) and beat-by-beat blood pressure (via finger photoplethysmography) were continuously recorded in twenty participants (10 BAA, 10 White) during 3 minutes of rest and 3 minutes of isometric handgrip exercise (35% maximal voluntary isometric contraction) in the supine and seated positions. After manual exclusion of cardiac arrhythmias, BRS was evaluated for each 3-minute period using the sequence method (seq. length > 3, r > 0.8, delay = 0 beats). BRS was quantified as the total baroreflex gain of up-ramping sequences (BRSup), the gain of down-ramping sequences (BRSdown), and total gain (BRStotal). Each value was compared across conditions (supine rest vs. supine handgrip exercise vs. seated rest) and between races using analyses of variance with repeated measures. RESULTS: At baseline, no significant differences were observed for BRSup (-0.12 ± 10.97 ms/mmHg, P=0.99), BRSdown(-2.06 ± 8.24 ms/mmHg, P=0.80), or BRStotal (-3.14 ± 9.35 ms/mmHg, P=0.74) between BAA or White participants. When the influence of handgrip and body position were examined, no significant race by condition interactions were observed for any value (all P>0.31). Instead, significant main effects of condition were observed for the entire sample (F1,32=9.75, P<0.01), which was explained by significant decreases in BRSup (-21.82 ± 5.14 ms/mmHg, P<0.01) and BRStotal (-13.41 ± 4.54 ms/mmHg, P=0.02) during handgrip compared to supine rest. BRSup was also significantly lower during handgrip exercise compared to seated rest (-10.43 ± 3.85 ms/mmHg, P=0.04). CONCLUSIONS: These results suggest that handgrip exercise decreases BRS similarly between BAA and White individuals, supporting the notion that BRS may not be significantly altered in healthy BAA adults.

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