Normal Nocturnal Dipping
Normal nocturnal dipping is defined as a ≥10% reduction in both systolic and diastolic blood pressure from daytime to nighttime during sleep, as measured by 24-hour ambulatory blood pressure monitoring. 1, 2, 3
Quantitative Definition
The standard threshold for normal dipping is a 10% or greater decline in blood pressure from daytime (awake) to nighttime (asleep) periods 1, 2, 3
This can be calculated as: ([mean daytime BP - mean nighttime BP] / mean daytime BP) × 100 ≥ 10% 1
In healthy individuals, nighttime blood pressure typically drops by 10-20% from daytime levels 2, 3
Normal Blood Pressure Values During Sleep
The night/day pressure ratio averages 0.87 for systolic and 0.83 for diastolic pressure in individuals with normal dipping 2, 3
For hypertensive individuals with normal dipping: daytime pressure averages approximately 135/85 mmHg, dropping to 120/75 mmHg during sleep 2, 3
The European Society of Cardiology defines normal nighttime BP as <110/60 mmHg 3
In normotensive subjects, daytime pressure averages 122/77 mmHg 3
Clinical Classification
Dippers: Individuals who achieve ≥10% nocturnal BP reduction and have normal circadian rhythm 1, 2
Non-dippers: Individuals who fail to achieve the 10% reduction threshold, representing approximately 10-25% of patients with essential hypertension 1, 2
Extreme dippers: Those with nighttime reduction ≥20% in systolic and/or diastolic BP 4
Clinical Significance of Normal Dipping
Individuals with preserved dipping patterns (≥10% reduction) have lower cardiovascular risk compared to non-dippers 2, 3
Non-dippers face significantly increased cardiovascular risk and target organ damage independent of their average 24-hour blood pressure levels 2
Nighttime blood pressure may be the best independent predictor of cardiovascular risk, even surpassing daytime values in prognostic importance 2, 3
Blunted nocturnal dipping has been specifically associated with nephropathy in patients with types 1 and 2 diabetes mellitus 1, 2
Physiologic Mechanisms
Blood pressure normally follows a circadian pattern with highest levels during morning hours, gradually decreasing throughout the day to reach lowest levels at night 1
The sympathetic nervous system plays a key role: normal dipping requires appropriate reduction in sympathetic activity during sleep 5
Non-dipping is associated with blunted nighttime reduction in systemic vascular resistance (7.8% vs. 16.1% in dippers) 6
Important Caveats
Racial differences exist: African American youth show elevated nighttime pressures compared to white youth, with blunted dipping patterns more common 1, 2, 6
Reproducibility is modest: Only 67-70% of patients classified as dippers or non-dippers on initial monitoring maintain the same classification on subsequent recordings 7
At least 70% of blood pressure readings during nighttime periods must be satisfactory for valid interpretation, with preferably seven nocturnal readings obtained 3
Day-to-day variability exists in the day-night blood pressure profile, particularly among hemodialysis patients 1