From the Guidelines
Yes, blood pressure can decrease when lying down compared to sitting or standing positions. This phenomenon occurs because gravity no longer forces blood to pool in the lower extremities when lying down, allowing for easier blood flow back to the heart, which in turn results in a slight decrease in blood pressure 1. For most people, this decrease is normal and beneficial, especially during sleep when the body naturally lowers blood pressure as part of the rest and recovery process.
Key Considerations
- When measuring blood pressure, it's essential to be consistent with the position, as different positions can yield different measurements, with diastolic pressure being higher when sitting compared to lying down 1.
- The position of the back and legs can also impact blood pressure readings, with unsupported backs potentially increasing diastolic pressure and crossed legs raising systolic pressure 1.
- Healthcare providers typically recommend sitting upright with back supported, feet flat on the floor, and arm at heart level for standardized readings, but measurements after lying down may be more sensitive for detecting orthostatic hypotension 1.
Clinical Implications
- Individuals with certain medical conditions, such as orthostatic hypotension, may experience a more significant drop in blood pressure when changing positions, which can be detected by measuring blood pressure at 1 min and/or 3 min after standing from a sitting or lying position 1.
- A drop of ≥20/10 mmHg in blood pressure when standing up from lying down or sitting can indicate orthostatic hypotension, and such changes should be discussed with a healthcare provider as they could signify an underlying cardiovascular issue 1.
From the Research
Blood Pressure Changes with Body Position
- Blood pressure can be influenced by body position, with changes occurring when moving from a standing or sitting position to a lying down position 2.
- Studies have shown that blood pressure can decrease when lying down, with one study finding that diastolic blood pressure tends to fall less in hypertensive subjects when moving from a sitting to a lying position 2.
- Another study found that blood pressure measured in a side position at the left arm in hypertensive subjects was lower than when measured in a back position at the same arm, with a mean systolic and diastolic blood pressure difference of -14/-17 mmHg 3.
Orthostatic Hypotension and Blood Pressure
- Orthostatic hypotension is a condition characterized by an excessive fall in blood pressure when standing, and can be influenced by body position 4, 5.
- Management of orthostatic hypotension includes nonpharmacologic measures such as avoiding the supine position and sleeping with the head of the bed elevated, as well as pharmacologic options like fludrocortisone and midodrine 5.
- Fludrocortisone has been used to treat orthostatic hypotension, but its effectiveness and safety are still being studied, with some evidence suggesting that it may not be harmful in the long term for certain conditions 4, 6.
Factors Influencing Blood Pressure Changes
- The distance between the antecubital fossa and sternum can influence blood pressure measurements, with an expected blood pressure difference between the arm of measurement and the right atrium calculated for different body positions 3.
- Body and arm position can both significantly influence ambulatory blood pressure and therefore the day-night difference, which can impact the diagnosis and management of hypertension 3.