Blood Pressure at Night is Higher Than Previously Thought

Scientists at University College London in the United Kingdom have developed new technology that reveals that blood pressure measured close to the heart is much higher during sleep than previously thought. The research, published in the June edition of the journal Hypertension, could have significant implications for the evaluation of future therapies as drugs used to treat high blood pressure can have markedly different effects on pressure close to the heart, compared to that traditionally measured in the arm.

The team, led by Professor Bryan Williams at UCL’s Institute of Cardiovascular Science, and supported by the National Institute for Health Research (NIHR), worked with a Singaporean technology company (Healthstats International). They developed a portable wristwatch-based device containing a sensor in the strap that detects the pulse wave at the wrist, rather than measuring the pressure directly. By mathematically modeling the pulse wave, the team was able to accurately measure pressure at the aortic root over a full 24-hour period, without disturbing the person being monitored.

Lead author Professor Bryan Williams, who is also Director of the NIHR University College London Hospitals Biomedical Research Centre, says: “This study provides the first-ever description of the natural variation in blood pressure throughout the day and night in which measurements have been taken close to the heart. What we have shown is that pressures by the heart do not dip as much during sleep as we previously thought based upon conventional pressure measurements taken from the arm.”

By simultaneously measuring the patterns of brachial blood pressures and central aortic pressures, the team found that despite similarities in the circadian rhythms of brachial and central aortic pressures, there was a significantly reduced night-time dip in central aortic pressure relative to the corresponding night-time dip in brachial pressure. These novel findings suggest that nocturnal aortic pressures are disproportionately higher than brachial pressures during sleep; potentially crucial information for clinicians investigating the damage high blood pressure can cause the brain and heart.

Dr. Peter Lacy (UCL Institute of Cardiovascular Science), a co-author on the paper, said: “The fact that the watch can be worn continuously means that we can program the device to sample the pulse wave day and night, and obtain measurements of the aortic pressure over a 24-hour period. This allows us to accurately measure aortic pressure in a non-invasive way.”

 The research was supported by the NIHR University College London Hospitals Biomedical Research Centre.