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Objective: To examine venous partial pressure of oxygen (PvO 2 ), transcutaneous oxygen tension (tcPO 2 ), and VO 2 MAX in a normobaric environment after a single hyperbaric oxygen (HBO 2 ) treatment. Methods: This was a prospective study of conditions after the intervention compared with baseline. The participants were 10 moderately trained (VO 2 MAX = 57.6 ml/kg/min) men. Two HBO 2 treatments consisting of breathing 95% oxygen at 2.5 atmospheres absolute (ATA) for 90 minutes were administered on non-consecutive days. Baseline testing included measures of VO 2 MAX, tcPO 2 , and anthropometry. At 6.0 (1.0) minutes after the first HBO 2 treatment, a VO 2 MAX test was performed. After the second HBO 2 treatment, leg and chest tcPO 2 and PvO 2 were monitored for 60 minutes. Results: VO 2 MAX, running time, and peak blood lactate were not altered after the HBO 2 treatment. Leg tcPO 2 was lower (p = 0.003) and chest tcPO 2 was unchanged after the HBO 2 treatment compared with baseline values. PvO 2 was significantly (p,0.001) lower in the first three minutes after treatment than subsequent values, but no other differences were found. Conclusions: A single HBO 2 treatment at 2.5 ATA for 90 minutes does not raise PvO 2 , tcPO 2 , or VO 2 MAX in a normobaric, normoxic environment.

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To investigate splenic erythrocyte volume after exercise and the effect on hematocrit- and hemoglobin-based plasma volume equations, nine men cycled at an intensity of 60% maximal O(2) uptake for 5-, 10-, or 15-min duration, followed by an incremental ride to exhaustion. The reduction in spleen volume, calculated using (99m)Tc-labeled erythrocytes, was not significantly different among the three submaximal rides (5 min = 28%, 10 min = 30%, 15 min = 36%; P = 0.26). The incremental ride to exhaustion resulted in a 56% reduction in spleen volume, which recovered to baseline levels within 20 min. Plasma catecholamines were inversely related to spleen volume after exercise (r = 0.70-0.84; P< 0.0001). There were no differences in red cell or total blood volume pre- to postexercise; however, a significant reduction in plasma volume was observed (18.9%; P < 0.01). There was no difference between the iodinated albumin and the hematocrit and hemoglobin methods of assessing plasma volume changes. These results suggest that the spleen regulates its volume in response to an intensity-dependent signal, and plasma catecholamines appear partially responsible. Splenic release of erythrocytes has no effect on indirect measures of plasma volume.