Observations On Heart Rates And Cardiodynamics During Prolonged Weightlessness Simulated By Immersion Method

Abstract

Among the numerous methods proposed for the investigation of physiological effects of weightlessness in laboratory conditions the immersion method seems to be most advantageous. Although no true state of weightlessness is attained, nevertheless long-term observations in subgravity are made possible in this way. Certain human experiments indicate that in such conditions slight disturbances in ECG and blood pressure may become manifest. These results were not confirmed by other authors. The aim of the present work was to investigate the effect of long-term weightlessness simulated by immersion on ECG and blood pressure in rabbits. The animals were under urethane narcosis to eliminate the influence of the central nervous system. The experimental animals were submerged in 1 % solution of NaCl at temperatures ranging from 34 to 35°C. Respiration was made possible by tracheotomy tube connected with respiratory valve. Blood pressure from the carotid artery was registered kymographically using a mercury manometer. ECG electrodes were introduced under the skin of the fore and hind extremities. All incisions were sutured carefully to avoid contact of electrodes with the immersion fluid. The immersion period ranged from 12 to 24 hours.

No apparent changes were seen in the electrocardiograms. The heart rate registered hourly was about 230 per minute and did not change during the whole observation period. No significant changes in ECG were observed. The conduction times remained in the normal range for rabbits. In some instances a slight depression of QRS complexes was noted. Sometimes QRS complexes were elevated even in final stages of the experiments. The arterial blood pressure remained during the whole experiment nearly at a constant level showing only slight deviations.

The above results indicate that 24 hours weightlessness simulated by the immersion method does not induce any significant circulatory disturbances and is fairly well tolerated by rabbits. Supplementary experiments now under way using further physiological tests seem to confirm the foregoing conclusions.