The maturation of the process of spontaneous recovery from hypoxic
apnea by gasping (autoresuscitation) was characterized in adult, weanling (18-22 d), and infant (5 and 10 d) BALB/c mice. ECG and respiration were recorded and hypoxic
apnea was induced with 97% N2-3% CO2. Administration of 21% O2 at onset of hypoxic
apnea resulted in successful autoresuscitation in all 63 animals tested. In all mice, three sequential stages occurred: 1) gasping with marked
bradycardia, 2) rapid increase in heart rate (cardiac
resuscitation), and 3) increase in respiratory rate (respiratory
resuscitation). Despite these similar stages, marked maturational differences were apparent. The times to cardiac and respiratory
resuscitation were longer in the pups than in the older mice, whereas the gasp frequency before cardiac
resuscitation was lower in the infants.
Resuscitation time correlated with gasp interval (1/gasp frequency). In addition, the initial
bradycardia at onset of gasping was more pronounced in the pups. A 30- or 60-s delay in
oxygen administration after onset of hypoxic
apnea caused a marked decrease in the adults' ability to autoresuscitate, without affecting that of the pups. A comparison of gasp frequency in 21% O2 versus 97% N2-3% CO2 showed that the presence of
oxygen increased gasp frequency in the pups, but had no effect on gasp frequency in the weanlings or adults. We conclude that autoresuscitation is equally effective in both infant and adult BALB/c mice but only when
oxygen is available before the onset of hypoxic gasping.(ABSTRACT TRUNCATED AT 250 WORDS)