Hemoglobin concentration maintained despite reduced erythrocyte count and hematocrit during exercise under hyperbaric oxygen conditions in healthy adult males: A randomized crossover trial

Hyperbaric oxygen (HBO), physical exercise, and eicosapentaenoic acid (EPA) intake combined may have beneficial effects on blood components and vascular endothelial function. To test this hypothesis, we conducted a randomized crossover trial involving healthy adult male participants. Participants were assigned to three groups: two performed exercise under HBO or normobaric normoxia (NN) conditions while taking EPA (HBO + Ex + EPA and NN + Ex + EPA), and one received EPA without exercise (EPA control). Each exercise-based intervention lasted for 4 weeks, with a 1-week washout period before crossover into the other environment. Blood parameters and endothelial function were measured before and after the interventions. In the HBO + Ex + EPA group, hemoglobin (Hb) levels remained unchanged despite reductions in the red blood cell (RBC) count and hematocrit (Ht). No significant changes were observed in the RBC or Ht in the NN + Ex + EPA or EPA control groups, suggesting that the reductions were likely attributable to exercise performed under HBO conditions. No significant changes were observed in other blood parameters (blood sugar, glutamate oxaloacetate transaminase, glutamate pyruvate transaminase, and gamma-glutamyl transpeptidase concentrations), blood lipid concentrations (triglycerides and high- and low-density lipoprotein cholesterol), or indicators of vascular endothelial function (baseline brachial artery diameter, maximum brachial artery diameter, flow-mediated dilation percentage, and vascular wall shear rate) in either of the exercise groups. In the EPA control group, triglyceride levels significantly decreased and high-density lipoprotein cholesterol levels increased, whereas no significant changes were observed in other blood markers or indicators of vascular endothelial function. In the current study, Hb levels were maintained despite reductions in the RBC count and Ht during exercise under HBO conditions. This study provides valuable fundamental insights into the effects of exercise performed in extreme physiological environments, such as HBO conditions, on blood homeostasis and vascular function.