Blood Pressure Measurement outside Medical Settings

The utility of measurement of blood pressure (BP) outside medical settings, such as home BP (HBP) or ambulatory BP (ABP) measurement has been recognized, and the practice has been adopted widely [1,2]. The Ohasama study has provided clear evidence on the superiority of HBP measurement versus casual or clinic BP (CBP) measurement to predict the risk of events [3,4]. Some studies also have shown that the target organ damage of hypertension correlates more closely with HBP values than with CBP values [5]. These beneficial characteristics of HBP measurement may be derived from an increase in the number of measurements taken [3,4]. Furthermore, HBP measurements are usually taken under more controlled conditions than CBP measurements, which can produce high reproducibility and reliability of the BP information obtained without biases, such as the white-coat effect, regression dilution biases, observer bias, and environmental influences [3,4]. It is clinically difficult to exclude such biases using CBP measurements.

White-Coat Hypertension and Masked Hypertension

HBP measurement and ABP monitoring have identified a subgroup of individuals with white-coat hypertension (WCHT) [6] who have persistently increased CBP but normal HBP or ABP, and a subgroup of individuals with masked hypertension (MHT) [7] who have normal CBP but increased HBP or ABP. The prevalence of WCHT and MHT has been estimated to occur in approximately 15-40% and MHT in 10-30% of individuals [8]. Several longitudinal studies have established the existence of WCHT, but controversy remains as to whether it is a benign condition [9] or is linked with an increased risk of target organ damage and a worse prognosis [10,11]. With respect to MHT, some data support the hypothesis that individuals with this condition may have a high risk of cardiovascular diseases [12,13].

Carotid Atherosclerosis in White-Coat Hypertension and Masked Hypertension

In hypertensive patients, the presence and degree of target-organ damage have been proven to be useful in predicting prognosis. Thus, carotid ultrasonography, which can detect intima-media thickness (IMT) and atherosclerotic plaques, has been used to noninvasively assess markers of early atherosclerosis [14]. Carotid IMT and plaques more accurately predict the risk of future myocardial infarction and stroke than traditional risk factors [15].
Although several studies have reported an association between WCHT and carotid atherosclerosis, the association still remains controversial [16,17]. Some investigators [16] have noted that carotid IMT was greater in individuals with sustained hypertension (SHT) than in those with WCHT or SNBP, while others [17] suggested that carotid IMT was similar in WCHT and SHT patients. However, since these results are based on a small series, a large population sample has not yet been studied. With respect to MHT and carotid atherosclerosis, only limited data are available [18]. In a study of 295 clinically normotensive adults and 64 patients with SHT, Liu et al. showed that patients with MHT (defined by ABP monitoring) have a greater frequency of carotid atherosclerosis. They demonstrated that carotid atherosclerotic changes were similar in patients with MHT and in patients with SHT. After adjustment for cardiovascular risk factors, however, these significant differences disappeared.

Carotid Atherosclerosis in White-Coat Hypertension and Masked Hypertension: Findings from the Ohasama Study

We obtained HBP and CBP values on 812 subjects ? 55-years-old (mean age, 66.4 years) from the general Japanese population in Ohasama, Hanamaki, Japan, and compared carotid atherosclerosis in subjects with WCHT, MHT, SHT, and sustained normal BP (SNBP) [19]. Carotid IMT of the near and far wall of both common carotid arteries was measured and averaged. The common carotid artery, carotid bifurcation, internal carotid artery, and external carotid artery were examined on both sides for the presence of plaques.
Subjects were classified into 4 groups on the basis of their HBP and CBP levels: 1) SNBP (n = 283, 35%), displaying CBP < 140/90 mmHg and HBP < 135/85 mm Hg; 2) WCHT (n = 262, 32%), displaying CBP ? 140/90 mmHg and HBP < 135/85 mm Hg; 3) MHT (n = 54, 7%), displaying CBP < 140/90 mmHg and HBP ? 135/85 mmHg; and 4) SHT (n = 213, 26%), displaying CBP ? 140/90 mmHg and HBP ? 135/85 mm Hg. The carotid atherosclerotic indices, mean IMT and plaque, among the 4 groups were compared by analyses of covariance or a logistic regression model adjust for cardiovascular risk factors.
Adjusted mean IMT in subjects with sustained hypertension (0.77 mm; 95% confidence interval [CI] 0.75 to 0.79 mm) and MHT (0.77mm; 95% CI 0.73 to 0.80 mm) was significantly greater than in those with sustained normal BP (0.71 mm; 95% CI 0.69 to 0.72 mm) and WCHT (0.72 mm; 95% CI 0.71 to 0.74 mm) (p < 0.0001). The adjusted odds ratios for the presence of plaques in the 4 groups by multiple logistic regression analysis were similar to the trend in the mean IMT, but did not differ significantly among the 4 groups. Use of antihypertensive medication did not significantly interact with any of the above results (all p for interaction > 0.5).

Comments

To our knowledge, this study is the first to establish the significance of mean IMT in subjects with MHT. Significant association of MHT with carotid IMT remained even after adjustment for cardiovascular risk factors.

Carotid IMT in WCHT subjects was thinner than in SHT and MHT subjects, and equal to that in SNBP subjects. However, some long-term studies have shown that WCHT is not a benign condition [10,11]. Our 8-year follow-up study demonstrated that WCHT was a significant predictor for the development of sustained hypertension at home [10]. Moreover, Verdecchia et al. reported that there was a trend towards an increased incidence of stroke in the WCHT group by the ninth follow-up year [11]. Thus, the risk of carotid atherosclerosis in WCHT patients might increase over the long term, indicating that WCHT remains a condition that warrants careful follow-up.

CBP measurements alone are insufficient to distinguish individuals at high risk from those at low risk of carotid atherosclerosis. However, these individuals do have distinct HBP measurements. HBP measurement has the potential of becoming a valuable tool for predicting carotid atherosclerosis.