Sleep apneas and cardiac arrhythmias in freely moving rats

We studied the mechanisms of occurrences of apneas and bradyarrhythmias during sleep in five Wistar-Kyoto rats. We recorded electroencephalograms, electrocardiograms, chest wall movement, and diaphragmatic electromyograms (EMGdi) for three continuous days in each freely moving rat and demonstrated that: 1) 99% of the apneas and 99% of the bradyarrhythmias occurred during paradoxical sleep (PS), 2) 98% of the apneas were due to spontaneous cessations of respiratory drive, 3) the percentages among apneas accompanied with bradyarrhythmias were only about 30% and independent of the apneic durations, 4) every autoregressive power spectrum contained two significant components in the ranges of 50-80 and 110-140 Hz, which would be analogous to high-frequency oscillations postulated to originate in the synaptic input to the phrenic motoneurons from respiratory centers, and 5) spectral patterns of EMGdi signals varied with sleep states. These results suggest that "PS-related" neural activity modulating central respiratory output is important in inducing apneas and promoting bradyarrhythmias.