Abstract 285: The Ratio Between Heart Period and Diastolic Decay Time Derived From 24-hour Ambulatory Blood Pressure Monitoring is Associated With Cardiovascular Risk.

The ratio between the heart period (T) and the time constant (τ), characterizing the arterial pressure decay during the diastole, is a known ventriculo-arterial coupling factor, which is constant in mammals. Previously we have shown T/τ can be determined using standard ambulatory blood pressure(BP) monitoring (ABPM) records and when increased ,predicts all-cause mortality. Here we evaluated the association between increased T/τ and risk-related variation in some continuous clinical and demographic characteristics. We analyzed ABPM records of 2823 hypertensive patients (age 56±16, 54% women, 58% medicated and 9% with diabetes). T/τ was determined using its model expression, as the ratio between T coefficient of variation (SD/mean) and ln(SBP/DBP) variability (SD), where SBP and DBP are the systolic and diastolic BP and T (in sec) is 60/heart rate (HR). One-way ANOVA was applied to T/τ (dependent variable) using as a factor one of the following characteristics after grouping at constant intervals: age [in 5-yr intervals], body mass index (BMI) [5 kg/m 2 ], mean SBP, DBP and pulse pressure (PP) [5 mmHg]; the corresponding dipping [5%], and hear rate (HR) [5 bpm]. End groups with size<50 were eliminated. T, τ and T/τ were 0.88±0.13 sec, 1.18±0.48 sec and 0.88±0.42, respectively. T/τ was greater than 0.9, 1.0 and 1.1, respectively, for 37%, 29% and 16% of the patients (1048, 829 and 647 of 2823). T/τ variation with the tested factors was monotonous and highly significant (p<10 -6 for all). T/τ increased with older age, higher BMI, SBP, PP, and lower DBP, HR, and their dipping: T/τ was greater than 1.03 for age>77 yr; >1.06 for BMI>32 kg/m 2 ; >1.06 for (mean) SBP>162 mmHg; >1.07 for DBP<68 mmHg; >1.07 for HR<57 beat/min; >1.05, >0.96 and >1.11 for SBP- DBP- and HR dipping smaller than 2.5%, 2.5% and 7.5%, respectively. The finding that T/τ values greater than a relatively narrow threshold (1.05±0.04) corresponds to risk factors level, and tendency tendency of the tested characteristics supports the view that T/τ that deviates from sucha threshold may signify autonomic cardiovascular dysregulation.