HBPM has been shown to be useful in predicting target organ damage, cardiovascular (CVD) mortality and CVD events. In a small study conducted in Italy, Mule compared office, ambulatory and home BP measurements and their relationship to various indices of target organ damage (94
). Subjects underwent electrocardiographic (ECG) recordings, echocardiographic studies, and microalbuminuria assays. Neither systolic nor diastolic BP recorded in the office showed a significant correlation with left ventricular mass (LVM) or albumin excretion rate (AER.) However, HBP, especially during the second day of monitoring, correlated significantly with LVM, AER, and global target organ damage.
Several other cross-sectional studies have shown that BP measured at home correlates with hypertensive target organ damage. Kleinert et al. found the degree of left ventricular hypertrophy determined by echocardiography was more strongly correlated to multiple self-measurements than to office BP (23
). Abe et al. (95
) found the correlation between BP levels and target organ damage for self-measured readings at home and office readings were similar. Hypertensive complications were equally related to home and office BPs (95
). Jula et al. compared multiple office and HBPs and ABPs in the clinical evaluation of hypertension using a sample of 239 untreated hypertensive adults (96
). They found that office and HBPs predicted albuminuria and left ventricular hypertrophy at least equally to ABPM. Left ventricular mass index correlated slightly more strongly with morning home systolic BP/diastolic BPs than evening readings (r = .46/.43, p<.001 and r = .41/.37, p < .001 for morning and evening BPs)
Other investigators have used cross-sectional designs to evaluate the usefulness of HBPM in diabetics. Researchers examined whether BP elevations in the morning detected by HBPM were more predictive than office BP for microvascular (nephropathy and retinopathy) and macrovascular complications (coronary heart disease and cerebral vascular disease) in type 2 and type 1 diabetic patients (69
). In both groups, home BP but not office BP was strongly related to nephropathy. There were no significant differences between the groups for the other measures of target organ damage.
Five prospective studies (all with several publications) have compared the prediction of morbid events using both conventional office BP and HBP (). Three were based on population samples, while two recruited hypertensive patients. Four found that HBP was the stronger predictor of risk. The fifth (Didima) reported that both HBP and OBP predicted risk equally well (98
Prospective studies relating HBP and OBP to cardiovascular events and mortality
The first was the population-based Ohasama study, which was conducted in 1,789 subjects over 40 years of age who were followed for a mean of 6.6 years (81
). Subjects were asked to measure their BP at home within one hour of waking over a four-week period. The mean number of measures recorded was 20.8+8.3. As part of annual screening visits two consecutive measures of BP were recorded by a nurse or technician after two minutes of rest. When HBPM and BPs taken during annual screening were included in a Cox regression model, only home systolic BPs were significantly related to cardiovascular mortality risk. (multiple home systolic BP RH=1.012, p=0.048; screening systolic BP RH=1.000. p=0.972; multiple diastolic BP RH=1.013, p=0.414; screening diastolic BP RH=1.006, p=0.642.) Moreover, the average of two home BP measures showed a stronger relationship to mortality than the screening BPs taken by nurses and technicians.
More recently, the Ohasama data have been examined to determine the predictive value of HBPM on the risk of TIA, and hemorrhagic and ischemic stroke. (101
). Of the 1,789 patients in the original study, mean duration of follow-up was 10.6 years. Home BP values were linearly related to risks for total, hemorrhagic, and ischemic stroke. A 10 mmHg elevation in home systolic BP was associated with 29%, 32%, and 30% increases in the risk of total, hemorrhagic, and ischemic strokes, respectively. Finally, home BP values showed a significantly greater relation to the risk of both hemorrhagic and ischemic stroke than screening BP values. (p<0.02). In another analysis Ohkubo and colleagues found that the predictive value of stroke risk increased for all measures of home BP but was greatest when at least 14 measurements were obtained (102
). The original reports were based on readings taken in the morning, but a later analysis included evening readings, and found that both measures predicted strokes, but morning readings were superior in patients taking antihypertensive medications (68
). The Ohasama study also included ABPM, and has reported that the average BP during the first 2 hours after waking is an independent predictor of risk (103
). These findings emphasize the importance of taking BP readings first thing in the morning.
The second prospective study was the SHEAF study, a 3-year prospective cohort study designed to determine the prognostic value of HBPM compared to office measures in an older population (>60 years) with hypertension seen in general practice settings in France (99
). Treated patients with hypertension were followed in two phases: Phase 1 included an evaluation of office and home BP over one month, and Phase 2 included a 3-year observational phase without specific recommendations with regard to the management of hypertension. Phase 1 office measures included triplicate measures on each of two visits. HBPM was done over a four-day period with three consecutive measurements taken in the morning, and repeated in the evening. At the end of follow-up, neither method of measurement was significantly related to CVD events or mortality. However, using a Cox model to control for predictors such as age, CVD history and smoking status, HBPM was predictive of cardiovascular events. Each 10-mmHg increment of systolic BP measured at home increased the risk of a cardiovascular event by 17.2%, and each 5 mmHg increase in diastolic BP increased the risk by 11.7%. Conversely, when the model was applied to office measures controlling for the same predictors, there was no significant increase in CVD events. In patients with masked hypertension (i.e. normal office but raised home BP, who comprised 9% of the total sample), the risk was increased (hazard ratio 2.06), and much higher than in patients with high office and normal home BP (hazard ratio 1.18).
The third study was PAMELA, a population based survey of 2051 Italian subjects who were evaluated with HBPM (2 readings- one in the morning and one in the evening), OBP (3 readings taken with a sphygmomanometer on each of 2 visits), and ABPM (82
). About half of the subjects were hypertensive. Over a 10 year follow-up, there were 186 deaths. All three measures of BP predicted mortality. The steepest association between BP and outcomes was with the nighttime BP, but this may be attributed to the fact that nighttime BP shows much less variation than other measures. The goodness of fit, which is a better measure of the strength of the relationship was strongest for the home BP. In a subsequent publication (78
) it was reported that elevation of any of the three measures of BP was associated with increased risk. Thus a high home BP should not be ignored, even if other measures are normal.
The fourth study was conducted in Belgium, and compared the prognostic significance of office and home BP both measured by a physician (who visited the patients’ homes), and ambulatory BP in a sample of 391 adults at least 60 years of age who were being seen in a primary care setting (100
). Home and office examinations were performed within 2 weeks of one another. Health outcomes (i.e., aggregate of stroke, myocardial infarction and cardiovascular death) were determined after a median follow-up of 10.9 years. Home BP, and daytime and night time ambulatory BP predicted cardiovascular events, independent of office BP. BP measured by the primary care physician in the office was not independently predictive of future cardiovascular events. Diastolic but not systolic home BP added prognostic precision to daytime and night time ambulatory BP. In sum, the prognostic value of BP measured in the patient’s home was at least equal to that of daytime ambulatory BP. This study is of particular interest because it suggests that the relatively poor predictive value of office BP in comparison with home BP is not because of the confounding effects of the physician, but rather to the medical setting itself.
The fifth study is a long-term (8.2 years) follow-up of 662 subjects in the Didima Study (98
), which is a population–based study of the inhabitants of Didima, a village in Greece. The average age was 54 years, and hypertension was diagnosed in 28%, of whom 55% were on antihypertensive drug treatment. Office BP was evaluated on 2 days (3 readings each day) by the village family physician. Home BP was taken as duplicate readings morning and evening for 3 days. The main finding was that both the office and the home BP predicted CVD events, but neither was clearly superior. After adjustment for age and gender the hazard ratio for a 1 mmHg increase of systolic BP was 1.016 (CI 1.004–1.029, p =0.01) for home BP, and 1.021 (CI 1.009–1.034, p= 0.001) for office BP. When fully adjusted (including history of CVD, antihypertensive treatment, diabetes, and smoking) neither measure of systolic BP predicted events. For diastolic pressure the office BP was superior to the home BP, and was the only measure to predict events after fully adjusting for covariates (hazard ratio 1.034, CI 1.008–1.061, p=0.01). The authors concluded that the confidence intervals were too wide to draw firm conclusions about the relative importance of the two methods for predicting risk.
A sixth study performed in Kahoku, a rural town in Japan, on 1186 elderly people (mean age 74) reported a U-shaped relationship between HBP and mortality (evaluated from death certificates) (104
). There was no comparison with office BP, however, so it is not included in the Table.
Three longitudinal studies have examined the ability of HBPM to predict the progression of renal disease. One found that systolic home BP was a stronger predictor of end-stage renal disease (ESRD) and death than office BP among 217 Veterans with chronic kidney disease who had a median follow-up of 3.5 years (105
). The second followed 77 diabetic patients for 6 years, and concluded that HBP was a better predictor of progression of diabetic nephropathy when compared to office BP measurements (106
). The third used a sample of 113 hypertensive patients with non-diabetic chronic kidney disease who were followed for 3 years, and found that HBP measured in the morning was a better predictor of the decline in glomerular filtration rate (107
These studies thus present a very consistent picture showing that HBPM can give a better prediction of cardiovascular risk than office BP (Class IIa; Level of Evidence A).
Information about BP Control
HPBM has the ability to provide information about BP control outside the office setting. Using data (n = 3400) from the J-Home Study (Japan Home versus Office BP Measurement Evaluation), investigators examined the characteristics of BP control based on home and office measurement (108
). Although 42% of the sample had their BP controlled by office BP criteria (<140/90mmHg), only 34% also had HBP control (<135/85 mmHg). Other investigators have also demonstrated the value of HBPM in determining BP control outside the office (109
). The SHEAF study described above found that the 9% of patients with normal office BP but elevated home BP (i.e. masked hypertension) had twice the risk of CVD events as the group in whom both office and home BP were controlled (99
Use of HBPM to Guide and Evaluate Treatment
HBPM may provide important information about the responsiveness of individuals to anti-hypertensive treatment. In the Study on Ambulatory Monitoring of Blood Pressure and Lisinopril Evaluation (SAMPLE) investigators compared three measures of BP (office, ambulatory, and home) to changes in BP resulting from treatment with an ACE inhibitor on regression of left ventricular hypertrophy (112
). Improvements in left ventricular mass, an intermediate measure of target organ damage, were predicted best by both ambulatory BP and home BP while no changes were correlated with the changes in office BP. Thus, this trial showed the benefit of the use of HBPM to monitor the response to treatment, with important physiologic implications.
Findings about adjusting antihypertensive treatment on the basis of home BPs are mixed. Two studies have compared the effects of treating according to HBP as compared to office BP. In a blinded randomized controlled trial (TOHP- Treatment based on Home or Office blood Pressure) that compared the use of office BP versus HBPM to adjust hypertension treatment, more participants in the home measurement group had their antihypertensive treatment stopped (25.6% vs 11.3% in the office measurement group, p < .001), but had higher final office and 24 hour ambulatory BP compared to the office measurement group (113
). A second study, with a very similar design, was the HOMERUS (Home Versus Office Measurement, Reduction of Unnecessary Treatment Study), in which 430 patients with uncontrolled hypertension were randomized to HBPM or usual care. Their physicians were blinded as to their treatment group, and were provided with the BP levels measured either in the office or by HBPM. In both cases the target BP was <140/90 mmHg. At the end of one year the patients in the HBPM group were on less antihypertensive medications. The office BPs were the same in both groups, but the 24 hour ambulatory BP was significantly higher in the HBPM group.
Thus in both studies, treatment based on HBPM appeared to lead to less intensive drug treatment, and thus less tight BP control. However, the differences between the two groups in both studies can be explained by the fact that home BP tends to be lower than office BP, although the target BP level was the same for both groups. It remains unclear whether the HBPM group was under-treated, but the study did provide evidence for the feasibility of basing treatment on home readings.
Studies of the effects of placebo drugs have found that they have little effect on HBP, in contrast to their much bigger effect on OBP (49
). By having patients take readings both in the early morning and in the evening the adequacy of BP control throughout the day (and the trough: peak ratio) can be assessed (115
). Thus HBPM may be regarded as the method of choice for monitoring the effects of antihypertensive treatment.