10.3.1 Selection of Study Participants

Τhe selection of appropriate study participants is one of the most important methodological issues in clinical hypertension research. HBPM is a valuable diagnostic tool that accurately defines hypertension phenotypes in studies aiming to investigate the prevalence, characteristics, determinants, and prognostic significance of a specific BP pattern. In addition, isolation of BP patterns such as white-coat and masked hypertension that may exhibit heterogenous behavior and distort findings of a study is needed by out-of-office monitoring. For example, in study participants with white-coat hypertension, there is often minimal ambulatory BP response to antihypertensive drug therapy compared to those subjects with sustained hypertension [9]. Studies in patients with resistant hypertension also have demonstrated the importance of using HBPM for the reliable diagnosis and the exclusion of the white-coat hypertension phenomenon, which is common even among treated and moderately to severely hypertensive subjects [10, 11].

10.3.2 Improvement of Study Power and Reduction of Sample Size

The reproducibility of a BP measurement method, expressed as the standard deviation of differences between repeated measurements, plays a major role in the calculation of the sample size required for a clinical trial. As has been observed with ABPM, HBPM also has superior reproducibility to OBPM which makes it useful for clinical trials that compare the efficacy of antihypertensive drugs since it allows the same antihypertensive effect size to be identified with higher precision [3]. In other words, HBPM allows a smaller sample size to be recruited in order to identify a difference in the BP lowering effect of two drugs with the same study power [3, 12].

Based on power curves of a randomized crossover clinical trial comparing the antihypertensive efficacy of two drugs using clinic, ambulatory, or home BP measurements, for a trial aiming to detect a difference in the hypotensive effect of 10 mmHg for systolic BP, 5 mmHg for diastolic BP, or 3 mmHg for pulse pressure, the statistical power is much higher with HBPM and ABPM than with OBPM (Fig. 10.1) [13].

10.3.3 Evaluation of the Effects of Antihypertensive Drugs

10.3.3.1 Evaluation of the Magnitude of BP Lowering Effect

Because of its superior reproducibility to OBPM, HBPM provides a more accurate classification of the true baseline BP and improves the precision for the determination of antihypertensive drug treatment-induced BP changes. These benefits are also related to the absence of the placebo effect, regression dilution bias (regression to the mean), and observer bias (when electronic devices with automated memory are used), which typically affect clinical trials when OBPM is employed.

In a randomized controlled parallel-group design study which evaluated the antihypertensive efficacy of the angiotensin-converting enzyme inhibitor trandolapril versus placebo, HBPM, but not OBPM, determined the expected antihypertensive effect of trandolapril versus placebo [14]. Another clinical trial comparing the 24-h efficacy of beta-blocker bisoprolol with the calcium channel blocker nitrendipine found no difference in the antihypertensive effect of the two drugs when clinic or daytime ABP were used, whereas home and nighttime ambulatory BP measurements detected a greater systolic BP fall with bisoprolol [12]. Furthermore, a randomized crossover clinical trial comparing the BP lowering effect of the angiotensin-converting enzyme inhibitor lisinopril with the angiotensin receptor blocker losartan reported that all the BP measurement methods (clinic, ambulatory, and home) demonstrated greater efficacy with lisinopril (Fig. 10.2) with HBPM providing the greatest precision (p < 0.001 versus p < 0.01 for 24-hour ABPM and p < 0.05 for OBPM) [13]. Home and ambulatory BP, but not office BP, detected the antihypertensive effect of lisinopril on pulse pressure (Fig. 10.2) [13]. Regarding comparative assessment of the antihypertensive effect of drug combinations versus monotherapy, a study by Mancia et al. showed that a calcium channel blocker/angiotensin-converting enzyme inhibitor combination was more effective in lowering home BP vs. monotherapy with these drugs or placebo [15].