The ventilatory response to acute hypoxia is mediated mainly by the carotid body (CB) chemoreceptors. These are active in the last trimester of the fetal lamb. The normal rise in PaO2 occurring at birth silences the CB during the first postnatal days before the postnatal reset of O2 sensitivity has occurred. We hypothesized that the postnatal reset mechanism of the CB oxygen sensitivity can be reversed by longterm exposure to hypoxia. Minute ventilation (Vmin) was studied in 6 lambs at 2 weeks of age during normoxia and during hypoxia (FiO2 0.14). The results were compared to Vmin after 8 days in chronic hypoxia (FiO2 0.14). Vmin decreased 53% during chronic hypoxic exposure compared to Vmin prior to hypoxia. The acute hypoxic ventilatory response to a change in FiO2 from 0.21 to 0.14 was decreased compared to that prior to chronic hypoxia (+3% vs +53%, p 0.002). The hypoxic ventilatory response after chronic hypoxia corresponds to our previously reported hypoxic ventilatory response to CB denervated lambs. We conclude that the decreased hypoxic ventilatory response demonstrated is due to a reversal of the CB oxygen sensitivity. This finding might have implications for the ability to abort apnea in infants at a time period when CB is an important factor in the control of breathing.
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Grógaard, J., Selstam, U., Hascoet, J. et al. 112: POSTNATAL CHRONIC HYPOXIA CHANGES THE OXYGEN SENSITIVITY IN THE CAROTID BODIES. Pediatr Res 24, 279 (1988). https://doi.org/10.1203/00006450-198808000-00137