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The effects of hypoxia in the new‐born lamb before and after denervation of the carotid chemoreceptors *
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.sp007972
Subject(s) - hypoxia (environmental) , denervation , ventilation (architecture) , ductus arteriosus , respiration , oxygen tension , medicine , room air distribution , blood pressure , peripheral chemoreceptors , anesthesia , chemistry , chemoreceptor , carotid body , oxygen , anatomy , carotid arteries , mechanical engineering , physics , organic chemistry , engineering , thermodynamics , receptor
1. Twenty‐seven unanaesthetized new‐born lambs, 6 hr‐10 days old, responded to two levels of inspired oxygen, 125 and 110 mm Hg (alveolar CO 2 being controlled) with a sustained increase in minute ventilation ( V̇ ), a small increase in heart rate and a less consistent rise in systemic blood pressure. 2. An increase in V̇ was observed when arterial oxygen tension ( P a , O 2 ) had fallen by 6‐15 mm Hg. There appeared to be no fixed threshold of P a , O 2 at which ventilation started to increase. 3. The increase in ventilation caused by these levels of hypoxia was significantly and directly related to the age of the lamb and to its control alveolar CO 2 . 4. More severe hypoxia caused a progressive increase in V̇ until P a , O 2 was about 25 mm Hg when respiration failed. This increase at P a , O 2 > 25 mm Hg was markedly potentiated when alveolar P CO 2 ( P A , CO 2 ) was increased and abolished after bilateral denervation of the carotid chemoreceptors. 5. Significant (> 10%) left‐to‐right shunts were found in ten out of twelve lambs lightly anaesthetized with pentobarbitone sodium, breathing air. Hypoxia diminished the left‐to‐right pressure gradient largely by its pressor effect on the pulmonary circulation. When inspired O 2 tension ( P I , O 2 ) was 70 mm Hg, all seven lambs studied showed a reversal of the pressure gradient and evidence of right‐to‐left shunts (11‐42%) across the ductus arteriosus. 6. The implications of these findings have been discussed with reference to previous studies of the new‐born response to hypoxia and it is concluded that the peripheral chemoreceptors are fully active at birth and in the new‐born period.