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HYPERREACTIVITY TO STANDING IS ASSOCIATED WITH INCREASED AMBULATORY BP A RELATIONSHIP AMPLIFIED BY ENHANCED SYMPATHOADRENERGIC ACTIVITY

Objective: Previous research showed that elevated systolic blood pressure (SBP) reaction to standing (RS), a condition that may be accompanied by sympathoadrenergic hyperactivity, is a predictor of cardiovascular events. This might be due to the influence of RS on ambulatory BP (ABP). Thus, we investigated whether RS is a determinant of ABP and if this putative relationship is stronger in a milieu of hyperadrenergic activity. Design and method: We studied 630 young-to-middle-age (mean age 33.6 ± 8.5 years), stage I untreated hypertensives from the HARVEST study. RS was defined as the difference between 6 SBP measurements in the orthostatic and the supine posture. Participants were divided into tertiles of SBP RS (<-5.34, -5.34–0.30 and > 0.30 mmHg, respectively) and of 24 h urinary epinephrine (UE) (<8.3, 8.3–14 and > 14 mcg/24 h, respectively). The relationship with 24 h average SBP was tested in a two-way ANCOVA adjusting for age, sex and office SBP. Results: Mean office SBP was 145.8 ± 10.5/93.9 ± 5.2 mmg, mean RS -3.0 ± 7.4 mmHg and median UE 10.5 (IQR, 7.0–16.0) mcg/24 h, in the entire group. Subjects in the highest UE tertile had a higher (mean ± SEM) 24 h SBP (132.2 ± 0.8 mmHg) than the lower tertiles (129.9 ± 0.7 mmHg and 129.8 ± 0.7 mmHg, p = 0.041). The same trend was observed for the RS tertiles, as 24 h SBP was 134.3 ± 0.7 mmHg in the highest tertile vs 129.5 ± 0.7 in the intermediate and 128.3 ± 0.7 mmHg in the lowest tertile (p < 0.001). 24 h SBP was positively and significantly correlated with both RS (r = 0.16 p < 0.001) and UE (r = 0.10 p = 0.028). In a two-way ANCOVA analysis a significant interaction was observed between RS and UE (p = 0.033): average 24 h SBP was 136.5 ± 1.2 mmHg in the group with the highest RS and UE levels and was 127.2 ± 1.2 mmHg in the group with the lowest RS and UE levels. Conclusions: Our data show that RS is a significant determinant of average 24 h SBP and that this association is amplified by sympathoadrenergic hyperactivity. This can account for the increased risk of cardiovascular events found in hypertensive subjects with hyperreactivity to standing.