From the Guidelines
Yes, there is a significant diurnal variation in blood pressure, with the most recent and highest quality study confirming this pattern 1. Blood pressure typically follows a 24-hour pattern where it rises during the day, peaks in the mid-afternoon, and then decreases during the night, reaching its lowest point during sleep. This pattern is controlled by the body's circadian rhythm, which influences hormonal secretion, sympathetic nervous system activity, and other physiological processes that regulate blood pressure. Some key points to consider include:
- The morning surge in blood pressure, which occurs upon awakening, is a natural phenomenon but can be a vulnerable period for cardiovascular events in some individuals.
- Some people don't experience the normal nighttime blood pressure dip (called "non-dippers"), which is associated with increased cardiovascular risk.
- Ambulatory blood pressure monitoring (ABPM) can help identify individual patterns and optimize treatment timing, as it provides estimates of mean BP over the entire monitoring period and separately during nighttime and daytime 1.
- ABPM can also determine the daytime-to-nighttime BP ratio to identify the extent of nocturnal “dipping,” identify the early-morning BP surge pattern, estimate BP variability, and allow for recognition of symptomatic hypotension. The diurnal variation in blood pressure is important for timing blood pressure medications, with some regimens specifically designed to target high-risk periods like the early morning surge. Home and ambulatory blood pressure monitoring can help identify individual patterns and optimize treatment timing, with the goal of reducing morbidity, mortality, and improving quality of life. It is generally recommended that patients should take readings both in the early morning and at night to account for the diurnal variation in blood pressure 1.
From the Research
Diurnal Variation in Blood Pressure
- Diurnal variation in blood pressure refers to the natural fluctuations in blood pressure that occur throughout the day, typically characterized by higher blood pressure during the day and lower blood pressure at night 2, 3, 4.
- Studies have shown that the magnitude of this diurnal variation can be influenced by various factors, including physical activity level, age, and the use of antihypertensive medications 2, 4.
- The nocturnal dip in blood pressure, which is the decrease in blood pressure that occurs at night, is an important aspect of diurnal variation, and its magnitude can be used to predict cardiovascular risk 2, 3.
Factors Influencing Diurnal Variation
- Physical activity level has been shown to be an independent predictor of the diurnal variation in blood pressure, with higher daytime activity levels associated with a greater nocturnal dip 4.
- Age is also a significant factor, with older patients tend to have a smaller nocturnal dip 4.
- The use of antihypertensive medications can also influence diurnal variation, with some medications affecting the magnitude of the nocturnal dip 2, 4.
Measurement and Definition
- The definition of daytime and night-time blood pressure is crucial for assessing diurnal variation, and various methods have been proposed, including clock-time-independent and clock-time-dependent methods 3.
- The optimal definition of daytime and night-time blood pressure is provided by the narrow clock-time-dependent method, which excludes data from morning and evening transition periods 3.
Clinical Implications
- Diurnal variation in blood pressure has important clinical implications, as it can be used to predict cardiovascular risk and guide antihypertensive treatment 2, 5.
- The choice of antihypertensive medication and the timing of its administration can influence diurnal variation, and should be taken into account when treating patients with hypertension 2, 5.