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 24 h 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.