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Nocturnal Blood Pressure and Cardiovascular Risk.

Detection and effective treatment for high blood pressure (hypertension) remains a major challenge for improvement of cardiovascular health. In recent years, strategies for both reducing the false-positive diagnosis of hypertension (white coat hypertension) and detecting true hypertension when clinic pressures are normal (masked hypertension) have become an important addition to the this effort. Twentyfour-hour ambulatory blood pressure monitoring (ABPM) and home blood pressure monitoring (HBPM) are becoming widely implemented with important reclassification for those suspected of high blood pressure on the basis of inadequate or erroneous clinic measurement. Both ABPM and HBPM provide out-of-office blood pressure measurement from the real world in which patients spend >99% of their time when compared with very brief intervals for clinic assessment, often <1 to 2 hours per year. ABPM reveals variation within the full day, so that pressures can be compared for day and night. Several large surveys indicate that nocturnal pressures are superior to daytime measurement for prediction of long-term cardiovascular disease. Furthermore, the nocturnal blood pressure pattern has independent prognostic significance reflecting the normal 10% to 20% fall during sleep (dipping) versus nondipping, reverse dipping, or extreme dipping. ABPM has, in the past, been necessary for measuring nocturnal pressures, but this method has limitations due to lack of availability in underserved areas, practicality, and acceptance compared with HBPM. Can the convenience and acceptability of HBPM be merged with the value of ABPM for nocturnal blood pressure assessment? Kario et al have developed a program implementing home blood pressure devices with a protocol for nocturnal pressure measurement. Their initial publication described use of a modified home blood pressure device, placed on the upper arm at bedtime and programed to take 3 pressures at 2 AM, 3 AM, and 4 AM each night for several days. Two thousand five hundred forty-five participants were enrolled. After an average follow-up of ≈5 years, there was a significant positive correlation between home nocturnal blood systolic pressure and the occurrence of 152 cardiovascular events. In this issue of Hypertension, a follow-up survey of 1005 participants compares the nocturnal home pressures and the average nighttime pressures calculated from the single baseline ABPM recordings. The average duration for follow-up was 7.1 years. There were a total 80 events for analysis. Whereas nocturnal HBPM systolic pressures were significantly associated with cardiovascular events, nocturnal ABPM systolic pressures were not. Average systolic pressures were ≈3 mm Hg higher for nocturnal HBPM compared with nocturnal ABPM. Also, the average number of observations per participant were ≈25 for nocturnal HBPM and ≈14 for nocturnal ABPM. It may be that the difference in apparent cardiovascular risk for the 2 methods is due to statistical differences alone. However, it is possible that increased blood pressure during the early morning hours, 2 to 4 AM, when pressure was higher as detected by nocturnal HBPM, reflects underlying mechanisms linked to increased cardiovascular risk. Sleep is not a uniform period of somnolence but varies with regard to brain activity and physical activity that includes respiratory patterns. Obstructive sleep apnea is linked to hypertension and to increased cardiovascular risk. Treatment of obstructive sleep apnea with positive pressure devices reduces symptoms but also lowers blood pressure, more so in nondipping participants than those with normal nocturnal dipping. Other patterns of disturbed sleep architecture might be studied for patterns of nocturnal pressure and cardiovascular risk as well. More research combining measurement of nocturnal blood pressure patterns with polysomnography might unmask new links that explain why blood pressure during sleep is such an important predictor for cardiovascular disease.