Sleep apnea in hypoxic and normal kittens

Frequency and characteristics of apneas were studied in 10-, 20-, and 40-day old kittens during several days of exposure to 21%, 10%, or 7% oxygen atmospheres. Ninety-seven percent of all apneas occurred during sleep or at transitions between sleep and waking states. Hypoxic kittens, compared to controls, had greatly decreased apnea frequency, but other characteristics of apneas did not differ significantly. Apneas in both control and hypoxic kittens were normal, stereotyped events and were not considered to represent pathological processes. Evaluation of events preceding apneas indicated that a majority of apneas followed augmented breaths and/or brief arousals. We suggest that apnea, heart rate changes during apnea, and frequently concurrent transitions in sleep-waking state may be causally related to these pre-apnea events. The results of this study and a parallel study of human infants suggest that below-normal apnea frequency may indicate hypoxemia and may be associated with higher risk for Sudden Infant Death Syndrome.