Hypertension is a major cause of morbidity and mortality in communities of African ancestry. The most appropriate method of predicting the risk for blood pressure (BP)-related cardiovascular events is through 24-hour ambulatory BP (ABP) monitoring. Although the cost of monitors precludes the use of 24-hour BP measurement in groups of African descent in Africa, the extent to which BP-related cardiovascular risk may be underestimated by nurse-derived clinic BP measurements, and the current method of BP-related risk assessment in these communities, is uncertain. In this regard, nursederived BP measurement is thought to be superior to other forms of in-office BP measurement. Ambulatory 24-hour, day and night BP (SpaceLabs, model 90207) and nursederived clinic BP (CBP) (mean of 5 values) control rates were determined in 689 randomly selected participants (>16 years) of African ancestry in South Africa. Of the participants 45.7% were hypertensive and 22.6% were receiving antihypertensive medication. More participants had uncontrolled BP at night (34.0%) than during the day (22.6%, p<0.0001). However, uncontrolled CBP was noted in 37.2% of participants, while a much lower proportion had uncontrolled ABP (24.1%)(p<0.0001). These differences were accounted for by a high prevalence of isolated increases in CBP (whitecoat effects)(39.4%). Thus, in communities of African descent, despite a worse BP control at night than during the day, a high prevalence of white-coat effects translates into a striking underestimation of BP control when employing CBP rather than ABP measurements. Nurse-derived BP measurements are often as closely associated with organ damage as ABP. However, the extent to which relationships between nurse-derived BP measurements and organ damage reflect a white-coat effect (isolated increase in inoffice BP) as opposed to the adverse effects of BP per se are unknown. In 750 participants from a community sample, target organ changes were determined from carotid-femoral pulse wave velocity (PWV) (applanation tonometry and SphygmoCor software) (n=662) and left ventricular mass indexed to height2.7 (LVMI) (echocardiography)(n=463). Nurse-derived CBP was associated with organ changes independent of 24-hour BP (LVMI; partial r=0.15, p<0.005, PWV; partial r=0.21, p<0.0001) and day BP. However, in both unadjusted (p<0.0001 for both) and multivariate adjusted models (including adjustments for 24-hour BP)(LVMI; partial r=0.14, p<0.01, PWV; partial r=0.21, p<0.0001) nurse office-day SBP (an index of isolated increases in in-office BP) was associated with target organ changes independent of ambulatory BP and additional confounders. Thus, nurse-elicited whitecoat effects account for a significant proportion of the relationship between nursederived CBP and target organ changes independent of ambulatory BP. Therefore, high quality nurse-derived BP measurements do not approximate the impact of BP effects per se on cardiovascular damage. In 750 participants from a community sample I evaluated whether nurse officeday BP is inversely related to day-night BP (BP dipping) and whether this relationship may in-part explain the independent association between office-day BP and organ damage. Nurse office-day systolic BP (SBP) was correlated with % night/day SBP (r=0.22, p<0.0001) and night SBP (r=0.14, p=0.0001). Although unadjusted and multivariate adjusted (including for day SBP) nurse office-day SBP was associated with LVMI (partial r=0.15, p<0.01) and PWV (partial r=0.22, p<0.0001), neither day-night SBP (LVMI; partial r=-0.01, p=0.88, PWV: partial r=-0.04, p=0.30) nor % night/day SBP (LVMI; partial r=0.01, p=0.91, PWV: partial r=0.04, p=0.37) were independently related to target organ changes. Moreover, the relationships between nurse office-day SBP and target organ changes persisted with adjustments for either day-night SBP (p<0.05- p<0.0001) or night SBP (p<0.01-p=0.0001). Thus, although nurse office-day SBP, an index of an alerting response, is independently associated with an atttenuation of nocturnal decreases in SBP, neither a decreased BP dipping, nor nocturnal BP explain the independent relationship between nurse office-day SBP and target organ changes. Whether nurse office-day BP is affected by antihypertensive therapy, is uncertain. In the present study the effect of antihypertensive therapy on nurse office-day BP was assessed in 173 patients whom, off treatment, had a daytime diastolic BP ranging from 90 to 114 mm Hg. Over the treatment period marked decreases in BP occurred (p<0.0001). However, neither nurse office-day systolic (baseline=16.5±15.8 mm Hg, 4 months=15.3±18.9 mm Hg, p=0.49), nor diastolic (baseline=0.9±9.3 mm Hg, 4 months=4.3±10.7 mm Hg, p<0.005) BP decreased significantly from baseline. Thus, despite producing marked decreases in nurse-derived in-office and out-of-office ambulatory BP, antihypertensive therapy produces no change in nurse-elicited isolated increases in in-office BP (white coat-effects) in a group of African descent. In conclusion, the results of the present thesis indicate that in an urban, developing community of African descent, as compared to 24-hour BP measurements, nurse-derived BP measurements elicit a significant in-office increase in BP which translates into a marked underestimation of BP control at a community level; is strongly associated with organ damage through effects that cannot be attributed to 24-hour BP or to relationships with an attenuated decline in nocturnal BP; and which cannot be treated with antihypertensive therapy. Further work is required to assess the most cost-effective approach to excluding nurse-elicited isolated increases in in-office BP before initiating antihypertensive therapy to groups of African descent.

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Nurse versus ambulatory blood pressure measurement in a community of African descent: prevalence and significant of ``white coat`` responses.	7

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