Development of respiratory chemoreflexes to hypoxia and CO2 in unanaesthetized kittens

To investigate differences in the postnatal development of the respiratory peripheral chemoreflex response to hypoxia and to CO2, we measured the responses to switching inspired gas on an alternate breath basis between two air lines (control runs), air and 14% oxygen (hypoxia runs) and air and 5% CO2 (CO2 runs) in nine kittens studied sequentially during quiet sleep between 3-7, 11-18, 24-31 and 35-39 days of postnatal age. The response was quantified in terms of the breath-by-breath alternations in respiratory volumes, durations and flows. There was little response to control runs at any age. The hypoxia response was not different from control at days 3-7 but became significantly different at older ages. In contrast, the CO2 response was different from control in each age group. The pattern of response was different between hypoxia runs and CO2 runs until 35-39 days, when the patterns became similar. The results show that chemoreflex responses to CO2 are present even at an age when hypoxia sensitivity is low.