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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/14371 |
| Date | 28 March 2014 |
| Creators | Maseko, Joseph Muzi |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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