Cerebral blood flow in rats under immersion cooling and mechanical ventilation

The work objective is to study the changes in the cerebral blood flow rate in rats under cold respiratory arrest and mechanical ventilation. Materials and Methods. The experiments were carried out on anesthetized Wistar male rats (n=8). Animals were connected to artificial respirator via tracheal cannula. Intravital microscopy of blood flow in pial microvessels was observed under LUMAM-1 microscope. Respiration and heart rates were registered by analog-to-digital convertor L-Card. Rectal temperature and the temperature of medulla oblongata were also measured. During the experiment rats were placed in cold water (8-10 °C). Artificial pulmonary ventilation was initiated 1.5 minutes after cold respiratory arrest. A total of 150 microvenules (12 to 40 jum in diameter) were observed. The rate of blood flow was measured at respiratory arrest, in 1, 3, 10, 30 and 60 minutes and at almost full cessation of blood flow in venules. Results and Dicussion. Respiratory arrest occurred when the animal body temperature was reduced to 19.40+0.54 °C, and the temperature of medulla oblongata - to 21.80+0.72 °C. At the same time the heart rate decreased to 36.30+8.27 beats per minute. Cerebral blood flow decreased as well. Within 1 min after artificial respiration the heart rate of rats increased to 50-70 beats per minute. The rate of cerebral blood flow gained 20 %. Such a level of blood flow was maintained for 10 minutes. Then its gradual slowdown was observed along with decrease in temperature and heart rate. Cessation of blood flow occurred 90 minutes after artificial pulmonary ventilation. The temperature of the animal's body was 11.30+0.77 °C, and the brain temperature was 16.70+0.48 °C. Conclusion. Under deep hypothermia causing respiratory arrest artificial pulmonary ventilation significantly increases effective heart function, thus maintaining the cerebral blood flow.