PRESSURE MEASUREMENTS IN THE LESSER CIRCULATION OF THE NEWBORN RABBIT

¹ Nuffield Institute for Medical Research, University of Oxford, United Kingdom

An attempt is described to investigate whether some of the physiological responses of the pulmonary vascular bed in anæsthetized rabbits aged 0-31 days differ from those observed in other species, and it is shown that accurate measurements of phasic right ventricular pressure can be made in small animals with high heart rates using standard equipment.

A constant relationship of resting peak right ventricular to mean pulmonary arterial pressure is demonstrated in the resting state, but there are indications that the quantitative relationship changes with the circumstances. The variation with age of systemic and peak right ventricular pressure is shown; the latter changes are different from those described in other species and together with results obtained during hypoxia and asphyxia provide indirect evidence of ductus arteriosus closure on day 3. Pulmonary vascular pressor responses comparable to those of other species are never seen in the first 3 weeks and the fall in systemic pressure in response to asphyxia in very young animals is not due to coincident intense pulmonary vasoconstriction but could be explained by hypoxic dilatation of a patent ductus. A systemic response to hypoxia opposite to that to asphyxia is observed in rabbits older than 4 days. There is no evidence that intravenous infusion of acetylcholine in well-oxygenated or hypoxic newborn rabbits has any direct effect on the pulmonary vascular bed.

Note:

I must thank Dr. Joan Mott and Dr. D. G. Wyatt for their advice and supervision during these experiments; Dr. G. S. Dawes who first suggested the problem and advised in the preparation of the manuscript; and Professor Hansen for permission to reproduce fig. 1.