Pulsation of brain tissue increases in response to caffeine: A pilot healthy volunteer study

Objective Caffeine is known to induce cerebral vasoconstriction. We used this effect in a pilot ultrasound-based healthy volunteer study to investigate the directionality of response of brain tissue pulsations (BTPs) with changing middle cerebral artery velocity (MCAv) following caffeine ingestion, as the relationship between BTPs and cerebral circulation has not yet been characterised. Approach BTPs were measured in healthy volunteers using transcranial tissue Doppler ultrasound and MCAv was measured using conventional transcranial Doppler ultrasound. Measurements of blood pressure, heart rate, and end-tidal carbon dioxide (EtCO2) were also recorded. Data were collected at rest and at multiple timepoints over a 60-minute period following ingestion of 250 mg of caffeine. Main results A multivariate multilevel model identified significant decreases in mean MCAv of -0.17 (-0.21, -0.14) (cm/s)/min, ΔMCAv of -0.06 (-0.1, -0.04) (cm/s)/min, and EtCO2 of -0.02 (-0.04, -0.01) mmHg/min. Significant increases in mean arterial pressure of 0.21 (0.15, 0.28) mmHg/min and bulk BTP amplitude of 0.08 (0.02, 0.14) μm/min were also seen. These changes confirm the expected physiological effects of caffeine and provide novel evidence of directionally opposite changes in MCAv and BTP amplitude, suggesting that these variables respond in opposite directions following a vasoconstrictive challenge. Significance We hypothesise that increased bulk BTP amplitude reflects a reduction in intracranial pressure (ICP), driven by caffeine-induced cerebral vasoconstriction, allowing greater brain tissue motion. This interpretation is supported by magnetic resonance imaging studies, which show increased brain tissue motion with lowered ICP.