EFFECT OF IMMERSION HYPOTHERMIA ON VELOCITY INDICATORS OF CORTICO-CEREBRAL BLOOD FLOW IN RATS

Highlights The velocity of cortico-cerebral blood flow during general progressive hypothermia of the body, measured by ultrasound Dopplerography in anesthetized rats, changes nonlinearly. The beginning of body cooling (reduction of rectal temperature to 35 °C) is characterized by an increase in peak systolic velocity, mean velocity per cardiac cycle and end diastolic velocity, while the STI index shows a tendency to increase, which together increases the risk of cerebral hemodynamic disorders. A mild stage of hypothermia (rectal temperature 32–35 °C) with stable peak systolic and mean per cardiac cycle velocities and a decrease in the resistance index RI and pulsatility index PI seems to be the most preferable in terms of use in clinical practice. The most significant decrease in the velocity of cortico-cerebral blood flow occurs during severe and deep hypothermia. Abstract Aim. Determination and analysis of linear velocities and indices of blood flow in the cortex and subcortical structures of the cerebral hemispheres during immersion hypothermia of rats using Doppler ultrasound. Methods. Anesthetized (urethane, intraperitoneal, 1 000 mg/kg) Wistar rats weighing 300–320 g (n = 11) underwent craniotomy and removal of the dura mater. While the animals were cooling in water with the addition of ice (the temperature of the mixture was about 10 °C), using Doppler ultrasound the velocity indicators of cerebral blood flow were measured, and the parameters of mean arterial pressure, respiratory rate and heart rate were continuously recorded. Rats were cooled to a rectal temperature of 17 °C in ~80 min with an average cooling rate of 0.25 °C/min. Results. Multidirectional changes in cerebral blood flow velocity parameters were detected. At the beginning of cooling, the perfusion of the frontal and occipital areas of the cerebral hemispheres increases due to an increase in peak systolic velocity (by 15%, p = 0,005) and mean velocity per cardiac cycle (by 41,5%, p = 0,001). In mild to moderate hypothermia, increased perfusion is maintained by maintaining a high peak systolic velocity in the parietal area. At the stages of severe and deep hypothermia of the body, there is a significant decrease in cerebral blood supply, as indicated by a decrease in the values of peak systolic and mean velocity per cardiac cycle, occurring in all studied areas. Conclusion. At various stages of progressive immersion hypothermia in rats, changes in the velocity indicators of cortico-cerebral blood flow are observed, which are nonlinear: at the initial stage of cooling, the blood flow velocity increases, and with further cooling its decrease is observed.