Haematologic changes in rabbits during acclimatisation, deacclimatisation, and reinduction to hypoxia.

Haematologic changes were studied in 16 albino rabbits during acclimatisation, deacclimatisation, and reinduction to hypobaric hypoxia. Of these, four animals died during reinduction. Haemoglobin, haematocrit, and red blood cell count attained maximum values by the 15th day during acclimatisation and by the 10th day during reinduction. Reticulocyte count reached maximum level by the fifth day, both during acclimatisation and reinduction. All these parameters returned to initial control levels by the 10th day of deacclimatisation. The erythrocytes became macrocytic during acclimatisation and remained so during deacclimatisation and reinduction. Blood volume increased on acclimatisation, returned to control values during deacclimatisation, and remained low at this level on reinduction. Red cell mass increased both during acclimatisation and reinduction and returned to control levels on deacclimatisation. Plasma volume did not change on acclimatisation and deacclimatisation, but was reduced on reinduction. The erythrocyte life span and erythrocyte glutamic oxaloacetic transaminase (EGOT) decreased during acclimatisation and reinduction. There was no change in RBC osmotic fragility, indicating no change in the integrity of the red cell wall. The deaths during reinduction were possibly due to haemoconcentration and increased blood viscosity as a result of reduction in plasma volume. It has been concluded that reinduction to hypoxia after a phase of deacclimatisation imposes a more severe stress than experienced during acclimatisation.