Pulmonary vasoconstriction and changes in heart rate during asphyxia in immature foetal lambs

Abstract

SUMMARY1. The effect of changing the composition of pulmonary arterial blood on the pulmonary vasoconstrictor response to asphyxia was studied in immature foetal lambs of 90 days gestation age.2. When normal foetal carotid arterial blood (withdrawn before asphyxia) was introduced during asphyxia, the pulmonary vasoconstriction was rapidly and wholly relieved as soon as this blood reached the lung. This did not happen when blood was used which had been withdrawn during asphyxia.3. Conversely introduction into a pulmonary artery of a foetal lamb during recovery, of arterial blood withdrawn during asphyxia, caused an immediate return of pulmonary vasoconstriction.4. These phenomena could not be explained by the generation of vasodilator agents such as bradykinin, acetylcholine, histamine or isoprenaline.5. During asphyxia injection of normal foetal arterial blood into the left atrium did not cause pulmonary vasodilatation, but did elicit a large increase in heart rate.6. Neither the pulmonary vasoconstriction during asphyxia, nor its relief by normal foetal arterial blood, nor the changes in heart rate were affected by previous bilateral vagotomy or administration of atropine or hexamethonium.7. It was concluded that, in immature foetal lambs, the effect of asphyxia in causing pulmonary vasoconstriction was mainly, if not exclusively, by a local action within the lungs, and that the bradycardia during asphyxia was mainly due to the fall in Po2 acting locally upon the heart.

Pulmonary vasoconstriction in asphyxia during cross‐circulation between twin foetal lambs

“…It was not practicable to attempt bilateral thoracic sympathectomy after completion of the preparation. However, it had been observed that stimulation of the post-ganglionic sympathetic fibres arising from the third to fifth ganglia on the left side, as they run across the posterior thoracic wall to reach the left hemiazygos vein, causes left pulmonary vasoconstriction in both mature (Colebatch, Dawes, Goodwin & Nadeau, 1965) and immature foetal lambs (Campbell et at. 1967).…”

“…In the preceding paper (Campbell, Dawes, Fishman & Hyman, 1967) it was concluded that, in immature foetal lambs, the effect of asphyxia in causing pulmonary vasoconstriction was mainly, if not exclusively, due to a local action within the lungs. The following experiments were designed to determine whether asphyxia would still cause pulmonary vasoconstric -112 A.…”

“…Blood samples (0-4 ml.) were analysed at once for P02, PCO2 and pH using small electrodes (Radiometer) as in the preceding paper (Campbell et al 1967). …”

“…Left pulmonary arterial pressure-flow diagrams were recorded as in the preceding paper (Campbell et al 1967) Asphyxia was produced in either recipient or donor lamb by firm compression of the umbilical cord with thick string against a soft plastic tube for 2-3 min. Subsequently, in seven lambs of more than 120 days gestation age, the lungs were ventilated via a tracheal tube, using intermittent positive pressure from a Starling Ideal pump.…”

“…At the end of the experiment the right and left lungs were removed and weighed; any infarcted area in the left lung was dissected out and weighed separately. Pulmonary arterial and venous pressures and flows were recorded as already described on the Schwarzer polygraph (Campbell et al 1967). A. G. M. CAMPBELL AND OTHERS Blood gas analysis.…”