Papaioannou Theodore G, Vlachopoulos Charalambos, Ioakeimidis Nikolaos, Alexopoulos Nikolaos, Stefanadis Christodoulos
First Department of Cardiology, Hippocration Hospital, National and Kapodistrian University of Athens, Greece.
Clin Med Res. 2006 Jun;4(2):114-8. doi: 10.3121/cmr.4.2.114.
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.
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.
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 alpha. 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.
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 alpha 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.
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.
血压（BP）持续波动的发生是心血管系统的一个内在特征，与复杂的心血管机制以及环境刺激或日常习惯（如喝咖啡）有关。本研究的目的是探讨咖啡因对表达血压变异性复杂和“混沌”非线性特征指标的影响。
14名健康受试者按照随机、双盲、交叉设计服用240毫克咖啡因或安慰剂。在摄入咖啡因或安慰剂的基线以及30、60、90和120分钟时，通过压平式眼压测量法记录连续的桡动脉压力波形。
采用近似熵（ApEn）评估血压不规则性。还使用去趋势波动分析通过估计标度（自相似性）指数α来量化血压数据的分形相关特性。采用重复测量方差分析来检测摄入咖啡因或安慰剂后30、60、90和120分钟时测量变量的显著变化。
ApEn值较低（0.2±0.3）表明血压波动具有高度的规律性和可预测性，摄入咖啡因后其保持不变。相比之下，摄入咖啡因后血压时间序列的长期标度指数α从0.99显著增加到1.04（p = 0.01），而安慰剂未引起显著变化。
咖啡因可能通过触发心血管机制，在血压波动中诱导更大的“随机性”，这种机制虽无法直接明确，但应在未来研究中进行探讨。
