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Study: Blood Pressure at Night Is Higher Than Previously Thought

‘Wrist watch’ device detects pulse wave (June 11)

Scientists at University College London have found that blood pressure (BP) measured close to the heart is much higher during sleep than previously thought. Nocturnal BP is a strong predictor of both heart disease and stroke, with previous studies establishing that BP measured over the arm falls at night during sleep. However, the new data indicate that the night-time drop in blood pressure may be less extensive than previously thought.

The research, published in the June issue of Hypertension, could have significant implications for the evaluation of future therapies as drugs used to treat hypertension can have markedly different effects on BP close to the heart, compared with that traditionally measured in the arm.

The researchers developed a portable wrist watch-based device containing a sensor in the strap, which detects the pulse wave at the wrist, rather than measuring BP directly. By mathematically modeling the pulse wave, the team was able to accurately measure BP at the aortic root (i.e., close to the heart) over a 24-hour period without disturbing the person being monitored.

“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,” said lead author Professor Bryan Williams. “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.

“We hope our findings will highlight the importance of reducing blood pressure at night, potentially rethinking our approaches both to measuring and treating high blood pressure.”

By simultaneously measuring the patterns of brachial BPs (in the arm) and central aortic pressures (where blood exits the heart), 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 new findings suggest that nocturnal aortic pressures are disproportionately higher than brachial pressures during sleep — potentially crucial information for clinicians investigating the damage that hypertension can cause to the brain and heart.

Co-author Dr. Peter Lacy 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.”

Source: University College London; June 11, 2013.

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