Inhibitory effects of repeated hyperoxia on breathing in newborn mice

Brief oxygen therapy is commonly used for resuscitation at birth or prevention of hypoxaemia before procedures during the neonatal period. However, O(2) may severely depress breathing, especially when administered repeatedly. The aim of the present study was to test the effects of repeated hyperoxia on breathing control in newborn mice. A total of 97 Swiss mouse pups were assigned to O(2) or air on post-natal day 0, 1 or 2. Each pup in the O(2) group was subjected to four hyperoxic tests (100% O(2) for 3 min followed by 12 min normoxia), whereas pups in the air group were maintained in normoxia. Breathing variables were measured using flow-through barometric plethysmography. O(2) significantly decreased minute ventilation as seen in a decrease in respiratory rate. This decrease became significantly larger with repeated exposure and ranged -17- -26% for all ages combined. Furthermore, hyperoxia increased total apnoea duration, as compared with the baseline value. In newborn mice, repeated hyperoxia increasingly depressed breathing. This finding further supports a need for stringent control of oxygen therapy, most notably repeated oxygen administration in the neonatal period for premature newborn infants and those carried to term.