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Nonlinear Dynamics of Blood Pressure Variability After Caffeine Consumption

Theodore G. Papaioannou, PhD, Unit of Biomedical Engineering, First Department of Cardiology, Hippocration Hospital, Medical School, National and Kapodistrian University of Athens, Greece
Charalambos Vlachopoulos, MD, Unit of Biomedical Engineering, First Department of Cardiology, Hippocration Hospital, Medical School, National and Kapodistrian University of Athens, Greece
Nikolaos Ioakeimidis, MD, Unit of Biomedical Engineering, First Department of Cardiology, Hippocration Hospital, Medical School, National and Kapodistrian University of Athens, Greece
Nikolaos Alexopoulos, MD, Unit of Biomedical Engineering, First Department of Cardiology, Hippocration Hospital, Medical School, National and Kapodistrian University of Athens, Greece
Christodoulos Stefanadis, MD, Unit of Biomedical Engineering, First Department of Cardiology, Hippocration Hospital, Medical School, National and Kapodistrian University of Athens, Greece

Reprint Requests: Theodore G. Papaioannou, PhD; Iak. Patatsou 13, Nea Kipseli, 113 63 Athens, Greece, Fax: 3 210 7485 039, Email: theopap{at}hippocratio.gr

Objectives: The occurrence of continuous blood pressure (BP) fluctuations is an intrinsic feature of the cardiovascular system and is related to complex cardiovascular mechanisms and environmental stimulations or daily habits such as coffee drinking. The aim of this study was to investigate the effect of caffeine on indices expressing the complex and "chaotic" nonlinear characteristics of BP variability.

Design: Fourteen healthy subjects consumed 240 mg of caffeine or placebo according to a randomized, double-blind, crossover design. Continuous radial pressure waveforms were recorded by applanation tonometry at baseline and at 30, 60, 90 and 120 minutes after ingestion of caffeine or placebo.

Methods: Approximate entropy (ApEn) was determined to assess BP irregularity. Detrended fluctuation analysis was also used to quantify the fractal correlation properties of the BP data by estimating the scaling (self-similarity) exponent . Analysis of variance for repeated measurements was used to detect significant changes in the measured variables at 30, 60, 90 and 120 minutes after ingestion of caffeine or placebo.

Results: BP fluctuations demonstrated high regularity and predictability as indicated by the low values of ApEn (0.2 ± 0.3), and they remained unchanged after caffeine ingestion. In contrast, the long-term scaling exponent of the BP time series was significantly increased from 0.99 to 1.04 (p=0.01) after caffeine ingestion, while the placebo induced no significant change.

Conclusions: Caffeine induced greater "randomness" in BP fluctuations, possibly by triggering cardiovascular mechanisms that could not be directly specified but should be investigated in future studies.

Key Words: Applanation tonometry • Approximate entropy • Caffeine • Chaos • Coffee • Detrended fluctuation analysis • Fractal • Nonlinear dynamics • Pressure waveform • Variability