The Prognostic Value of Self‐Assessed Nocturnal Blood Pressure

The predictive value for cardiovascular risk of nocturnal or sleep blood pressure (BP) levels as well as the absence of nocturnal dipping has long been established and is superior to clinic or even out-of-office daytime BP measurements. This finding has been made possible largely by the widespread use of ambulatory BP monitoring (ABPM) involving lightweight portable devices introduced in the 1980s with sufficient memory and battery power to make possible multiple measurements per hour (usually two or three) over 24 hours or even several days. ABPM is not only the gold standard for BP measurement but has been adopted by the National Institute for Health and Clinical Excellence in the United Kingdom as the preferred technique for the diagnosis of hypertension. A strong case is being made that ABPM is now ready to replace clinic BP for the diagnosis and management of hypertension although there are counter arguments. The superior prognostic capability of ABPM over clinic BP was perhaps thought to be the result of the accuracy of the large number of recordings during the active and sleep periods, but recent studies suggest that this is not so straightforward. Generally fewer measurements are made during the night to limit the disturbance to sleep and yet the best prediction of cardiovascular outcomes appears to be from the nocturnal measurement. Thus, one of the strongest arguments for ABPM over other techniques has been the ability to determine nocturnal asleep BP, which is particularly important for high-risk patients such as those with diabetes or chronic kidney disease. A recent finding from the Korean Ambulatory Blood Pressure multicenter observational study suggests that the nocturnal BP level rather than the presence of nondipping predicts left ventricular hypertrophy. By contrast, analysis of the Spanish ABPM Registry suggests that nondipping is associated with more advanced disease. This discussion is somewhat parallel to the controversy of whether it is the morning BP surge or extreme nocturnal dipping that accounts for the greater number of strokes in the morning, as outlined in a recent article in this Journal. These studies highlight the confounding issue that the relatedness of each measure of BP, whether it’s a change in BP at a particular time or a peak or trough makes it very difficult to separate the contribution that each value makes to cardiovascular risk. Thus, the very large population studies that are sufficiently powered to distinguish the exact contribution of all the interrelated day and night measures of systolic and diastolic BP would be very expensive and perhaps prohibitively so using ABPM. While the Spanish ABPM Registry has more than 37,000 patients, others have used a meta-analysis approach to combine international databases. An example is the Hansen study reported in 2007 with more than 7000 patients. By comparison, epidemiological studies in specific cancers can contain hundreds of thousands of patients. What is limiting the size of hypertension studies in predicting cardiovascular events related to sleep or nocturnal levels is that, currently, ABPM devices are expensive and not widely available. Further, a considerable investment has to be made to implement the skills in general practice required to operate the device and to extract and interpret the findings. While technology with apps and smartphones is advancing and simplifying the procedures and reducing training, the high cost of the ABPM device has remained due to robustness of the device required for its continual use in clinical practice. Cost is particularly relevant to underdeveloped countries where such outlays may be prohibitive. Thus, there appears to be a need for a low-cost device such as those used for home BP measurement that will also measure sleep BP sufficiently accurately to be able to provide the full prognostic information currently provided for by ABPM. A major recent development by Ishikawa and colleagues has been to develop a home BP measurement (HBPM) device that can be programmed to record multiple measurements during sleep. The device can be programmed to take measurements at 2 AM, 3 AM, and 4 AM, which were considered by the investigators to be the most likely to represent sleep given the differing nocturnal habits of patients. Importantly, the patients were required to do this on as many nights as possible during a 2-week period (average 9). The major contribution of this study was to use recordings from 854 patients enrolled in the Japan Morning Surge Home Blood Pressure (J-HOP) trial to show for the first time that nighttime systolic BP measured using a patientcontrolled home device is associated with target organ damage and is a better predictor than even ambulatory nighttime BP. In addition, they found that adding sleep BP to other measures such as clinic or ambulatory BP improved the correlation with target organ damage. A new study by Kario and colleagues featured in this issue of The Journal of Clinical Hypertension has considerably extended this work with a new larger analysis of more than 2500 participants also from the J-HOP study. The major findings were that sleepmeasured home systolic BP correlated with all measures Address for correspondence: Geoffrey A. Head, BSc, PhD, Baker IDI Heart and Diabetes Institute, PO Box 6492, St Kilda Road, Central, Melbourne, Victoria 8008, Australia E-mail: geoff.head@baker.edu. au