HEMATOLOGICAL ALTERATIONS AFTER ACUTE EXPOSURE TO HYPERBARIC OXYGEN IN RATS

1. Acute exposure to hyperbaric oxygen (HBO) is associated with a significant increase in haematocrit which returns to the control level after 24 h of recovery in room air. In this study we report changes in blood viscosity in Sprague‐Dawley rats after acute exposure to HBO. 2. The rats were divided into three groups: a control group included rats not exposed to HBO (CON), a group studied immediately after acute exposure to HBO at 283.7 kPa for 6 h (HBO), and a group allowed to recover for 24h in room air after HBO exposure (REC). 3. The viscosity of the whole blood, plasma and red blood cells (RBC) suspension was measured in the three groups. A significant increase in whole blood viscosity was detected in HBO and REC groups compared with CON (P<0.05), but no changes in the viscosity of the plasma or RBC suspension were noted. 4. A significant decrease in oxygen delivery index was found in the REC group compared with the CON and HBO groups (P<0.05). 5. In a subgroup of rats, several blood parameters known to influence blood viscosity were evaluated. A significant increase in plasma colloid oncotic pressure was noted in HBO rats compared with CON (P<0.01). A marked increase in platelet count and fibrinogen concentration was detected in HBO and REC rats compared with CON (P<0.05). Furthermore, a significant increase in total leukocytic count was noticed in REC group compared with CON and HBO (P<0.001). 6. We conclude that acute exposure to HBO induces a significant increase in whole blood viscosity which cannot be explained solely by the increase in haematocrit. Alterations in several blood components could lead to this phenomenon.