Submental and Diaphragmatic Muscle Activity during and at Resolution of Mixed and Obstructive Apneas and Cardiorespiratory Arousal in Preterm Infants

Abstract

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).

Late-developing rostral ventrolateral medullary surface responses to cardiovascular challenges during sleep

“…The onset of the latedeveloping response was identified by an abrupt increase in heart rate, subsequent to the initial baroreflex-mediated heart rate effects of a drug (> 5 s), as in other studies [6,18,43]. These late-developing events were examined for effects on RVLMS activity and blood pressure.…”

“…Since we found no differences in blood pressure between trials with or without EEG arousal, it appears that arousal is not a necessary component for homeostatic control of blood pressure in this experimental design. The latter issue is of some clinical importance, since several studies report that different cardiopulmonary challenges (e.g., pressor response or obstructive apnea) resolve as effectively without, as with, EEG arousal [27,32,43].…”

“…Common features of these late responses are sudden increases in heart rate and blood pressure, regardless of the presence or absence of accompanying EEG arousal [6,18,43]. The RVLMS may contribute to those lateemerging responses, just as the early RVLMS neural responses participate in the baroreflex action to the challenge.…”

“…Blood pressure manipulations can also, after a few seconds, lead to activation of the electroencephalogram (EEG) and arousal, presumably recruiting more-rostral brain areas to assist in stabilization of blood delivery, or enhancing the responsiveness of mechanisms that compensate for a perceived error signal between baroreceptor input and cardiovascular or respiratory output [7,16,18,20]. Furthermore, a later-developing compensatory response which may or may not accompany arousal can act to further modulate changes in blood pressure or other cardiopulmonary changes [6,18,43]. These late-developing responses are not found in the anesthetized preparation [13].…”

Apnea of prematurity: pathogenesis and management strategies

“…As electroencephalogram (EEG) recordings were not performed as a part of this study, EEG arousal could not be excluded. The relationship between apnea termination and EEG arousal in preterm infants was investigated in a subsequent study by Wulbrand et al 66 These investigators studied 10 preterm infants longitudinally and observed no EEG changes at apnea termination. McNamara et al 67 observed EEG changes indicative of cortical arousal in only <10% of apneic events among term infants studied at a mean age of 9.5 weeks.…”