Pathomechanisms involved in obstructive apneas remain obscure. Apnea arousal failure has been proposed as a cause for sudden death during sleep. The present study hypothesizes an interdependency between upper airway dilating submental muscle electromyogram (EMG) activity (EMGsub), diaphragmatic muscle activity (EMGdia), incidence of bradycardia, and transcutaneous measured Po, (tcpO,) upon termination of apnea. Polygraphic recordings, including surface EMG (EMGsub, EMGdia), EEG, ECG, and transcutaneous Po,/Pco, (tcpO,/ tcpCO,) were performed on 10 preterm infants at 36, 40, 44, and 52 wk of conceptional age. EMGsub increased initially, then decreased in 28 of 33 non-rapid eye movement (N-REM) sleep apneas (REM: 35 of 69 events). This correlated with a decrease of tcpO2 during N-REM sleep ( y < 0.05). A parallel decrease of EMGsub and EMGdia was correlated with the occurrence of bradycardia (REM and N-REM: p < 0.01). Concomitant termination of apnea and bradycardia (n = 22), occurred in the presence of a phasic, simultaneous activation of EMGsub and EMGdia in 64% of REM sleep and in 79% of N-REM sleeprelated event, was characterized by a deep inspiration preceded by a short expiration, and correlated with the extent of tcp0,-Prolonged apneas accompanied by hypoxemia frequently occur in preterm infants (1-3) especially in those recovering from respiratory distress syndrome (4) during the first months of life, A loss of balance between submental E M G activity (representing mainly the protruding and thus upper airway dilating muscle force of m. genioglossus) and diaphragmatic E M G has been proposed as playing a leading role in the incidence of obstructive apneas (5-7). In contrast to adults (8), in children no significant decrease of EMGsub was found at onset of apneas (9), but a preferential activation of EMGsub accompanied termination of apneas in both adults and children (8, 9). Bradycardia during apnea is a common finding (10).
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