Keywords: Caffeine; heart rate variability; healthy volunteers.
Introduction. The caffeine is one of the most widely used pharmacologically active substances. It has many different physiological effects on the cardiovascular function. Also
the cardiac autonomic control could be altered by caffeine consumption. However, findings regarding the effect of caffeine consumption on cardiac autonomic nervous system (ANS) activity are controversial. The aim of the present study was to assess the effects of caffeine on cardiac ANS in young healthy subjects.
Methods and Materials. In sixteen healthy volunteers (7 women), age 24-35, the electrocardiogram (ECG) was recorded continuously at rest before as well as 30 min and 60
min after caffeine ingestion (200 mg of caffeine in 50 ml of water). Before each the beginning of ECG registration the arterial blood pressure was measured. As assessment of cardiac ANS activity the power spectral analysis (autoregressive spectra) and the Poincaré plot analysis of
the heart rate variability (HRV) were used. Autoregressive spectra were evaluated on intervals of 512 points. The powers of low (LF: 0.04-0.15 Hz) and high (HF: 0.15–0.40 Hz)
spectral bands were determined. In Poincaré plot analysis SD1 and SD2 indexes were used as marker of vagal and sympathetic activities, respectively.
Results. The heart rate did not change significantly after caffeine ingestion. The Poincaré plot SD1 index significantly increased (p<0.05) 30 min after caffeine consumption, whereas SD2 significantly increased (p<0.05) after 60 min. No significant modification of LF and HF spectral parameters was detected. The total spectral power significantly augmented after 30 min. The systolic and diastolic blood pressure significantly increased 30 and 60 min compared to values before ingestion.
Conclusions. These results indicate an effect of caffeine on the cardiac ANS activity. It is likely that single moderate caffeine dose can increase vagal and sympathetic function, as well as total vago-sympathetic activity in the myocardium.
