Blood pressure at night is an important predictor of both stroke and heart disease, with previous research suggesting that blood pressure calculated via the arm decreases at night during sleep. But the current study reveals that night-time reduction in blood pressure may be less significant than originally thought.
The findings, published in the journal Hypertension, reveal important implications for the assessment of future therapies, because drugs used to treat high blood pressure can have widely different effects on pressure near the heart, compared to the historic method of the arm.
The researchers worked with a Singaporean technology company to develop a portable wrist watch-based device that has a sensor in the strap that finds the pulse wave at the wrist, instead of calculating the pressure directly.
By modeling the pulse wave mathematically, the team was able to correctly calculate pressure at the aortic root (near the heart) for a full 24 hours without bothering the people who were being monitored.
Lead author Professor Bryan Williams, who is also Director of the NIHR University College London Hospitals Biomedical Research Centre, says:
"High blood pressure is a major risk factor in the development of cardiovascular disease (heart attack, stroke). It affects over 12 million people in the UK and is the single most important preventable cause of premature death.
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."
The authors hope their results emphasize the importance of decreasing blood pressure at night, possibly changing approaches to treating and measuring high blood pressure.
Previous research suggests that insufficient sleep is associated with high blood pressure. The risk for unhealthy blood pressure levels rise when sleep patterns are irregular.
Prof. Williams and team found that by simultaneously calculating the trends of brachial blood pressure (in the arm) and central aortic pressures (where blood exits the heart), there was a significantly decreased night-time drop in central aortic pressure relative to the corresponding night-time drop in brachial pressure, despite similarities in the circadian rhythms.
The outcomes suggest that night-time aortic pressures are disproportionately higher than brachial pressures during sleep. This could be important information for clinicians examining the negative impact high blood pressure can have on the heart and brain.
Dr Peter Lacy (UCL Institute of Cardiovascular Science), a co-author on the paper, concluded:
"The fact that the watch can be worn continuously means that we can programme 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."
Written by Kelly Fitzgerald