Respiratory  and circulatory effects of breathing 100 per cent oxygen in the new-born lamb before and after denervation of the carotid chemoreceptors.
1. Methods are described for measuring tidal volume and frequency, end-tidal CO(2), blood pressure and heart rate, and arterial gas tensions in the unanaesthetized new-born lamb.2. The resting values of minute ventilation (V)/kg body wt. and arterial oxygen and carbon dioxide tension, (P(a, o2)) and (P(a, CO2)) were similar to those which have been reported in the new-born baby. There was a direct and significant relation between P(a, o2) and P(a, CO2) and the age of the lamb.3. Thirty-five unanaesthetized lambs aged 40 min to 10 days breathed 100% oxygen; minute ventilation fell by an average of 19% of control, end-tidal CO(2) increased and the ratio of change in tidal volume (DeltaV(T)) to change in pressure (DeltaP) (DeltaV(T)/DeltaP) remained constant. In a proportion of lambs, a small decrease in blood pressure and heart rate was observed. The effect of breathing 100% O(2) on lung compliance was variable.4. These changes in ventilation were virtually abolished after both sinus nerves had been cut.5. The results therefore suggest that a significant hypoxic drive to ventilation exists in the new-born lamb and that this drive is mediated by functioning and mature peripheral chemoreceptors.6. Preliminary evidence suggested that, on 100% O(2), the sensitivity of new-born lambs to inhaled CO(2) was reduced.
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology*; D002245:Carbon Dioxide / Q000097:blood; D002344:Carotid Body / Q000502:physiology*; D003714:Denervation; D006339:Heart Rate / Q000502:physiology*; D009538:Nicotine / Q000494:pharmacology; D010100:Oxygen / Q000097:blood; D010991:Plethysmography; D011343:Procaine / Q000494:pharmacology; D012119:Respiration / Q000502:physiology*; D012756:Sheep
D002245:Carbon Dioxide; D011343:Procaine; D009538:Nicotine; D010100:Oxygen