Effect of caffeine consumption on tissue oxygen levels during hyperbaric oxygen treatment

Ten men were exposed to hyperbaric oxygen (HBO2), and their tissue oxygen l evels were monitored after they drank either placebo or caffeine beverages. Transcutaneous tissue oxygen (Ptco(2)) monitor measurements in a normobari c air environment were initially obtained from transducers on the subject's chest and foot. The subjects then consumed either the caffeine (3 mg . kg( -1)) or the placebo beverage, and after 20 min the subjects were pressurize d in a hyperbaric chamber to 2.36 atm abs (1 atm = 101.3250 kPa). The test subjects began breathing 100% oxygen at 2.36 atm abs, 30 min after administ ration of the experimental beverage, and continued for 30 min, after which the final chest and foot Ptco(2) measurements were recorded (1 h after inge stion of the test drink). Each subject underwent a second hyperbaric exposu re during which the alternate drink was administered (either the placebo or the caffeine), and Ptco(2) measurements were again obtained. The increase in right foot Ptco(2) values during HBO2 exposure was significantly smaller after caffeine consumption than after placebo (P = 0.0018).