Respiratory and circulatory effects of breathing 100% oxygen in the new‐born lamb before and after denervation of the carotid chemoreceptors*

Abstract

SUMMARY1. Methods are described for measuring tidal volume and frequency, end-tidal C02, blood pressure and heart rate, and arterial gas tensions in the unanaesthetized new-born lamb.2. The resting values of minute ventilation (J)/kg body wt. and arterial oxygen and carbon dioxide tension, (P.,°s ) and (P., co,) were similar to those which have been reported in the new-born baby. There was a direct and significant relation between Paw 0, and Pa, cO, 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 C02 increased and the ratio of change in tidal volume (AVT) to change in pressure (AP) (AVTIAP) remained constant. In a proportion of lambs, a small decrease in blood pressure and heart rate was observed. The effect of breathing 100 % 02 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 % 02, the sensitivity of new-born lambs to inhaled C02 was reduced.

The respiratory response of the new‐born lamb to inhaled CO2 with and without accompanying hypoxia*

“…The values for resting J", Pa 02 and P'a were within the ranges previously described in the unanaesthetized new-born lamb (Purves, 1966a). The relation between pHa and the age of the lamb is shown in Fig.…”

“…As previously described (Purves, 1966a), to be satisfactory, the records of minute ventilation had to show a variation of no more than 5 % during the control period while there had to be no obvious change in the state of wakefulness during the experimental period which followed. After the 5 min control period during which the lamb breathed an 02/N2 mixture at ambient P02, C02 was added in four increments, approximately 1, 2, 4 and 6 %.…”

The perioperative care of lambs and ewes when the former undergo major experimental (scoliotic) surgery

“…The 'leak' -an adjustable pressure limiting valve incorporated into the inspiratory limbneeded constant adjustment and waste gas scavenging. Despite this, limiting lung inflation pressure to 20 cmH 2 O failed to achieve normocapnia in P1 and P2, even when gas flows exceeded the minute volume of ventilation (VM) calculated for lambs using the Purves' equation, 20 i.e. VM (L/min) ¼ 0.123 þ 0.261 x (where x is the body mass [kg]).…”

Respiratory Effects of Division of the Carotid Sinus Nerve in the Lamb Soon After the Initiation of Breathing

“…Peripheral chemoreceptors other than the carotid glomi have not been shown to be of importance in the young lamb [6,11,12]. Recovery of ventilation after division of the first carotid sinus nerve, therefore, must be attributed to increased activity of the contralateral carotid body and of central chemosensing mechanisms.…”