From the Guidelines
Blood pressure typically decreases during sleep when lying flat, with a drop of about 10-20% compared to daytime levels, due to the phenomenon of "nocturnal dipping". When you sleep, your body enters a state of rest where your heart rate slows and your blood vessels relax, causing blood pressure to drop. However, lying flat can sometimes increase blood pressure in certain individuals, particularly those with conditions like sleep apnea or heart failure, as it allows fluid to redistribute from the legs to the central circulation, increasing blood volume in the chest and potentially raising pressure 1.
Key Considerations
- Body position matters, with sleeping on your back potentially worsening sleep apnea and affecting blood pressure differently than sleeping on your side.
- The relationship between sleep position and blood pressure is complex and varies between individuals based on their underlying health conditions.
- If you have concerns about blood pressure during sleep, elevating the head of your bed by 6-8 inches or using a wedge pillow might help manage nighttime blood pressure in some cases.
- It's also important to note that the absence of a night-time drop in blood pressure is associated with target organ involvement, and it may be a useful clue to the presence of secondary hypertension 1.
Important Factors to Consider
- The position of the back and legs can affect blood pressure measurements, with unsupported backs potentially increasing diastolic pressure by 6 mm Hg, and crossing legs potentially raising systolic pressure by 2 to 8 mm Hg 1.
- The arm position is also crucial, with the cuff needing to be at the level of the right atrium for accurate measurements, and the arm being supported with a pillow in the supine position to ensure accurate readings.
From the Research
Effect of Sleep and Body Position on Blood Pressure
- Being asleep and lying flat can have a significant impact on blood pressure, with studies showing a decline in both diastolic and systolic blood pressure during night sleep compared to awake time 2.
- The decline in blood pressure during sleep is more pronounced in untreated hypertensive individuals, with a greater decline observed in this group 2.
- The position of the body during sleep can also affect blood pressure, with different supine body positions influencing blood pressure measurements 3.
- Specifically, blood pressure measurements taken while lying on the back, left side, right side, and abdominal positions can result in significant differences in systolic and diastolic blood pressure 3.
Comparison of Blood Pressure Measurements in Different Positions
- Studies have compared blood pressure measurements taken with patients sitting and supine, finding no significant difference in systolic blood pressure but a higher diastolic blood pressure when sitting 4.
- The difference in diastolic blood pressure between sitting and supine positions decreases with increasing age, and there is no effect of body mass index, hypertension, or medication on this difference 4.
- Another study found that blood pressure tends to drop in the standing position compared to sitting, supine, and supine with crossed legs, with systolic and diastolic blood pressure being highest in the supine position 5.
Clinical Implications
- The findings of these studies have important implications for the measurement and management of blood pressure, highlighting the need to consider the position of the patient during blood pressure measurement 4, 5.
- The use of a standardized position, such as sitting with the arm supported at heart level, is recommended for accurate blood pressure measurement 5.
- Additionally, the effect of sleep and body position on blood pressure should be taken into account when interpreting blood pressure measurements and making clinical decisions 2, 3.