Assessment of the condition of conditioned reflex activity in the process of liquid respiration

Introduction. Liquid respiration is the ability of mammalian lungs to receive oxygen dissolved in a liquid for respiration and release carbon dioxide into it. A promising field of application is the provision of marine operations. For the use of liquid respiration during deep-sea operations, the technology must ensure the normal functioning of all organs and systems of the body, prevent decompression sickness, and allow conscious activity.

The study aims to assess the safety of conditioned reflex activity during independent liquid respiration in laboratory animals in normobaric conditions.

Materials and methods. We performed the study on male Syrian hamsters aged four months, weighing 120-140 g. Researchers have developed a stand with an eight-level maze with a lock. We immersed the labyrinth in an aquarium. The scientists carried out the study in two stages. At the first stage, we have developed in animals a conditioned reflex of actively avoiding drowning in conditions of breathing air. The researchers placed the animal on the lower level, then immersed the maze in an aquarium filled with water at a speed that only the animal's head was above the water level. The threat of drowning prompted the animal to search for a passage to a higher level. The training was three times a day for ten days. At the second stage, scientists studied the influence of various conditions of liquid respiration on the state of the conditioned reflex activity of animals. We used two respiratory fluids — perfluorohexane (PFH) and perfluorodecalin (PFD) in three temperature regimes: 22.0, 27.0, and 32.0°C. The researchers filled the aquarium with two oxygenated respiratory fluids of the required temperature instead of water. We have entirely immersed the maze with the animal fixed at the lower level in the aquarium. After switching to liquid respiration, scientists removed the animal from fixation. From the moment of removal from fixation, the countdown of the passage of the maze began. First, we assessed the condition of conditioned reflex activity by the number of animals in the group that successfully passed the maze and the average time of its passage.

Results. Animals on liquid respiration in perfluorohexane successfully passed the labyrinth in all temperature conditions. The average transit time at 22.0°C was 323±94 s; 27.0°C — 45±12 s; 32.0°C — 147±101 s. Animals on liquid respiration in perfluorodecalin successfully passed the labyrinth at a temperature of 27.0°C; the average passage time is 131±79 s; at a temperature of 32.0°C, 20% of animals successfully passed the labyrinth, the average time is 32.5 s; at a temperature of 22.0°C, none of the animals passed the maze.

Conclusions. Conditioned reflex activity during independent liquid respiration in small laboratory animals in normobaric conditions persists and depends on the physico-chemical properties and temperature of the respiratory fluid.

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