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

Ten men were exposed to hyperbaric oxygen (HBO2), and their tissue oxygen levels were monitored after they drank either placebo or caffeine beverages. Transcutaneous tissue oxygen (PtcO2) monitor measurements in a normobaric 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 pressurized 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 administration of the experimental beverage, and continued for 30 min, after which the final chest and foot PtcO2 measurements were recorded (1 h after ingestion of the test drink). Each subject underwent a second hyperbaric exposure during which the alternate drink was administered (either the placebo or the caffeine), and PtcO2 measurements were again obtained. The increase in right foot PtcO2 values during HBO2 exposure was significantly smaller after caffeine consumption than after placebo (P = 0.0018).