Acute hyperammonaemia induces a sustained decrease in vigilance, which is modulated by caffeine

Hyperammonaemia is observed after prolonged, intense exercise, or in patients with hepatic failure. In the latter, it isassociatedwith a set of neurological and psychiatric abnormalities termedhepatic encephalopathy. The aimsof our study were: 1. to measure vigilance in a condition of induced hyperammonaemia; 2. to assess whether caffeine modulates the effects of hyperammonaemia on vigilance, if any. Ten healthy volunteers (28.5±5 years; 5 males) underwent three experimental sessions consisting of two-hourly measurements of capillary ammonia, subjective sleepiness (Karolinska Sleepiness Scale) and vigilance (Psychomotor Vigilance Task, PVT), in relation to the intake of breakfast (+/�coffee), an amino acid mixture which induces hyperammonaemia (amino acid challenge; AAC), and AAC+coffee (only for participants who had coffee with their standard breakfast). The AAC resulted in: 1. the expected increase in capillary ammonialevels,withhighest valuesatapproximately4hafter the administration; 2. a significant increase in subjective sleepiness ratings; 3. a sustained increase in PVT-based reaction times. When caffeine was administered after the AAC, both subjective sleepiness and the slowing in RTs were significantly milder than in the AAC-only condi- tion. In conclusion, acute hyperammonaemia induces an increase in subjective sleepiness and a sustained decrease in vigilance, which are attenuated by the administration of as ingle espresso coffee.