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1. The respiratory response to inhaled CO₂ was measured in twenty unanaesthetized new-born lambs aged 4 hr-10 days. Measurement of resting arterial pH, P_CO2 and plasma bicarbonate showed a non-respiratory acidosis immediately after birth which was corrected in the first 24-28 hr: thereafter, the acid—base pattern was of a compensated respiratory alkalosis.

2. When CO₂ was added to the inspired gases and resting arterial oxygen tension (P_a, _O2) was controlled, the average increase in minute ventilation () was 0·075 l.min^-1.kg^-1.mm Hg, P_a, _CO2^-1 and duplicate responses in the same lamb differed by 6-22·5%.

3. The slope of the /P_a, _CO2 line (S) varied inversely with P_a, _O2. In one lamb, severe hypoxia (P_a, _O2 = 21 mm Hg) caused a marked depression of the slope.

4. Neither the slope S nor the horizontal intercept B of the lines was related to the age of the lamb. B was not related to pH_a and only slightly affected by acute hypoxia. B was related to arterial [HCO₃^-] and values for both were reduced with the acid—base disturbances seen in the first 10 days after birth. Evidence was given which suggested that the response of the new-born lamb to inhaled CO₂ was similar to that of man acclimatized to a P_a, _O2 of 70-75 mm Hg.

5. In the lightly anaesthetized lamb, bilateral section of the sinus nerves caused a small reduction in the sensitivity to inhaled 5% CO₂ in air, an increase in the respiratory lag and a reduction in the rate at which increased.

6. It was concluded that, in the new-born lamb, the carotid chemo-receptors are involved in the response to inhaled CO₂ and that hypoxia potentiates this response.

This article has been cited by other articles:

				K. A. Waters and K. D. Tinworth Depression of ventilatory responses after daily, cyclic hypercapnic hypoxia in piglets J Appl Physiol, March 1, 2001; 90(3): 1065 - 1073. [Abstract] [Full Text] [PDF]