Dynamic diurnal changes in 24-h ambulatory systolic blood pressure (SBP) are associated with increased cardiovascular risk. We compared ambulatory BP dynamics in Japanese and American black and white populations with treatment-resistant hypertension. Methods and Results: Both HTN-Japan (n=41) and SYMPLICITY HTN-3 (n=384 white and n=140 black patients) enrolled patients with office SBP ≥160 mmHg and 24-h ambulatory SBP ≥135 mmHg while on ≥3 antihypertensive medications. Indices of circadian

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... tion in ambulatory BP, including morning and nighttime dynamic surges, were retrospectively compared. All 3 cohorts had similar baseline office SBP. The Japanese cohort had significantly lower body mass index, less obstructive sleep apnea, and less hypercholesterolemia than the black and white cohorts, but significantly greater morning SBP levels, including moving peak morning SBP (183 vs. 169 vs. 169 mmHg, P<0.001), morning dynamic surge (37.9 vs. 28.6 vs. 24.2 mmHg, P<0.001) and nighttime dynamic surge (24.9 vs. 8.3 vs. 7.7 mmHg, P<0.001). These racial differences in SBP surge parameters persisted despite adjustment for baseline demographic population differences through multivariate regression. Conclusions: Greater diurnal BP variability, including dynamic surges, in Japanese compared with black and white patients may indicate ethnic differences in the underlying BP regulatory mechanism of resistant hypertension. These differences may be important to take into consideration for more specific drug and device-based therapy strategies based on ethnicity.