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The respiratory response of the new‐born lamb to inhaled CO 2 with and without accompanying hypoxia *
Author(s) -
Purves M. J.
Publication year - 1966
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1966.sp007973
Subject(s) - respiratory acidosis , arterial ph , hypoxia (environmental) , acidosis , pco2 , respiratory system , bicarbonate , chemistry , anesthesia , respiration , ventilation (architecture) , alkalosis , respiratory alkalosis , metabolic acidosis , medicine , oxygen , anatomy , mechanical engineering , organic chemistry , engineering
1. The respiratory response to inhaled CO 2 was measured in twenty unanaesthetized new‐born lambs aged 4 hr‐10 days. Measurement of resting arterial pH, P CO 2 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 CO 2 was added to the inspired gases and resting arterial oxygen tension ( P a , O 2 ) was controlled, the average increase in minute ventilation ( V̇ ) was 0·075 l.min −1 .kg −1 .mm Hg, P a , CO 2 −1 and duplicate responses in the same lamb differed by 6‐22·5%. 3. The slope of the V̇ / P a , CO 2 line (S) varied inversely with P a , O 2 . In one lamb, severe hypoxia ( P a , O 2 = 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 [HCO 3 − ] 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 CO 2 was similar to that of man acclimatized to a P a , O 2 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% CO 2 in air, an increase in the respiratory lag and a reduction in the rate at which V̇ increased. 6. It was concluded that, in the new‐born lamb, the carotid chemo‐receptors are involved in the response to inhaled CO 2 and that hypoxia potentiates this response.