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 (i.e. coffee drinking). The aim of this study was to investigate the effect of caffeine on indices expressing the “chaotic”, nonlinear characteristics of BP variability.

Methods: Fourteen healthy subjects consumed 240mg of caffeine or placebo according to a randomized, double-blind, crossover design. Radial pressure waveforms were recorded by applanation tonometry of the radial artery at baseline and 30, 60, 90 and 120 min after ingestion of caffeine or placebo. Detrended fluctuation analysis was used to quantify the fractal correlation properties of the BP data by estimating the scaling (self-similarity) exponent α. Approximate entropy (ApEn) was also determined to assess BP irregularity. Analysis of variance for repeated measurements was used to assess changes in the measured variables over time.

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 α 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 (figure).

Conclusions: Caffeine induced greater “randomness” in BP fluctuations. This caffeine effect might be considered to be beneficial but it should be further investigated.