A new method for assessing 24-h blood pressure variability after excluding the contribution of nocturnal blood pressure fall.
OBJECTIVE
To assess quantitatively the relationship between nocturnal blood pressure (BP) fall and 24-h BP variability; to propose a new method for computing 24-h BP variability, devoid of the contribution from nocturnal BP fall; and to verify the clinical value of this method.


RESULTS
We analysed 3863 ambulatory BP recordings, and computed: (1) the standard deviation (SD) of 24-h BP directly from all individual readings and as a weighted mean of daytime and night-time SD (wSD); and (2) the size of nocturnal BP fall. Left ventricular mass index (LVMI) was assessed by echocardiography in 339 of the patients. The 24-h SD of BP was significantly greater than the 24-h wSD. Nocturnal BP fall was strongly and directly related to 24-h SD, the relationship with 24-h wSD being much weaker and inverse. The difference between SD and wSD was almost exclusively determined by the size of nocturnal BP fall. wSD of systolic BP was significantly related to LVMI, while 24-h SD was not.


CONCLUSIONS
Conventional 24-h SD of BP is markedly influenced by nocturnal BP fall. The weighted 24-h SD of BP removes the mathematical interference from night-time BP fall and correlates better with end-organ damage, therefore it may be considered as a simple index of 24-h BP variability superior to conventional 24-h SD.
Bilo
Grzegorz
G
Department of Clinical Medicine and Prevention, University of Milano-Bicocca, Italy.
Giglio
Alessia
A
Styczkiewicz
Katarzyna
K
Caldara
Gianluca
G
Maronati
Alberto
A
Kawecka-Jaszcz
Kalina
K
Mancia
Giuseppe
G
Parati
Gianfranco
G
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001794:Blood Pressure / Q000502:physiology*; D018660:Blood Pressure Monitoring, Ambulatory / Q000706:statistics & numerical data*; D002940:Circadian Rhythm / Q000502:physiology; D004452:Echocardiography; D005260:Female; D006352:Heart Ventricles / Q000000981:diagnostic imaging; D006801:Humans; D006973:Hypertension / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged