Abstract
Little is known about the pathogenesis of bradycardias in preterm infants. We therefore studied episodes of bradycardia and their relationship with apnoeic pauses and desaturations in overnight tape recordings of arterial oxygen saturation (SaO2, Nellcor N100 in beat to beat mode), breathing movements, nasal airflow and ECG from 80 preterm infants at the time of discharge from hospital (mean gestational age at birth 32.5 wk (SD 2.6 wk), and at the time of study 36.3 wk (SD 2.3 wk). A bradycardia was defined as a fall in heart rate to ≤67% of baseline level for ≥4 s, an apnoeic pause as a cessation of respiration for ≥4 s, and a desaturation as a fall in SaO2 to ≤80%. 196 bradycardias were found in 46 (58%) of the recordings.
There was a close relationship between bradycardias, apnoeic pauses and desaturations: excluding artefact, 83% of the bradycardias were associated with apnoeic pauses, and 87% with desaturations. Where all 3 phenomena occurred in combination (n=117), they commenced almost simultaneously, apnoeic pauses preceded the onset of the bradycardias by a median of +4.6 s (range -4.0 to +11.0 s); desaturations commenced +5.4 s (-2.2 to +12.7) before the bradycardias and +0.5 s (-5.1 to +5.8) before the apnoeic pauses (after correction of the SaO2 values for the response time of the pulse oximeter in each infant (median 6.0 s)).
These observations suggest that a reflex mechanism may be involved in the pathogenesis of some bradycardias in these preterm infants. This reflex can involve an inhibition of respiratory movements, a change in ventilation to perfusion matching (resulting in a fall in SaO2), and a slowing of the heart rate.
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Poets, C., Stebbens, V., Von Der Hardt, H. et al. THE RELATIONSHIP BETWEEN EPISODES OF BRADYCARDIA, APNOEA AND HYPOXAEMIA IN PRETERM INFANTS. Pediatr Res 32, 614 (1992). https://doi.org/10.1203/00006450-199211000-00056
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DOI: https://doi.org/10.1203/00006450-199211000-00056