RESPIRATORY AND CARDIOVASCULAR CHANGES DURING ASPHYXIA AND RESUSCITATION OF FTAL AND NEWBORN RABBITS

¹ Department of Physiology, The London Hospital Medical College, London, E.1

A study has been made of the respiratory and circulatory responses to asphyxia and resuscitation of ftal and newborn rabbits. Ftuses were both delivered and maintained under isotonic saline, while newborn animals were asphyxiated in an atmosphere of N₂ after light ether anæsthesia. Both groups were resuscitated by intermittent positive pressure ventilation with 0₂, begun after the last spontaneous gasp of asphyxia.

The response to asphyxia was very similar in the two groups. There was a short initial period of (primary) apna, accompanied by a sudden fall in heart rate and blood pressure. This hypotension and bradycardia during the early part of asphyxia was reduced by vagotomy. Following primary apna, the animals gasped for some 15-20 min. and then again became apnic (secondary apna). The heart rate and blood pressure fell further and, in the absence of external interference, the animals died. Resuscitation was successful, provided the blood pressure was above 5 mm. Hg at the start of I.P.P. ventilation. The heart rate and blood pressure invariably rose before the return of respiration in the successful cases. The Hering-Breuer and paradoxical reflexes were fully active in the newborn rabbit, but were abolished by asphyxia due to a central nervous block. They did not return for several minutes after resuscitation.

Note:

I should like to thank Professor K. W. Cross for his help and advice throughout this work, and Dr. K. B. Roberts for his helpful criticism. Dr. J. H. Green kindly advised me about neurological recording, and Dr. B. R. Simpson lent me a high gain oscilloscope. I should also like to thank Mr. R. M. Hammond and Mr. G. Walter for their help with the photographic reproductions, and Miss K. Newell and Mrs. S. Moonsaffie for their technical assistance. Messrs. Oxygenaire Ltd. helped with finance and equipment, and the work was carried out in association with the M.R.C. Research Group on Respiration and Energy Metabolism in the Newborn.

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