RELATIONSHIP BETWEEN APNOEA AND BRADYCARDIA IN PRETERM INFANTS

Abstract

Nine studies were carried out on 7 babies who were having repeated episodes of bradycardias without any clinically obvious apnea. Their mean gestational age was 31.7 wk (range 29-36 wk) and the mean birth wt was 1.56 kg (range 1.08-2.16 kg). Investigations were carried out in a total body plethysmograph. Face mask with a pneumotachograph attached to it measured flow. Tidal volume was obtained by integrating these signals. An esophageal balloon measured intrathoracic pressure changes and the heart rate was measured from ECG chest electrodes. A total of 172 episodes of apnea were observed. In 50% of these apneas, the airway was closed as determined by the presence of cardiac artefact on the flow signals. Apnea was associated with bradycardia in just over 25% of all apnea. It tended to occur early (11-14 s). Whether the apnea was central or obstructive had no effect on the pattern, provided the baby did not make any inspiratory efforts. Inspiration against a closed airway produced bradycardia in > 50% of obstructive apnea, the heart rate falling precipitously within 1-2 s. Often bradycardias occur too early in apnea to be due to central hypoxia and must be due to a peripheral mechanism.