1461 DETERMINANTS OF ORAL BREATHING IN PREMATURE INFANTS

Abstract

We have previously demonstrated that 40% of term neonates may exhibit effective oral ventilation during nasal occlusion. To evaluate the influence of postnatal maturation on oral breathing (OB), we measured nasal and oral ventilation in response to 15 sec nasal occlusions(10/study) in 11 sleeping preterm infants (gest.age 29±1wk, BW 1.3±0.2kg). When OB occurred, nasal occlusion was maintained for up to 1 min. Studies were performed at 31-32, 33-34 and 35-36 wk post-conceptual age. Nasal and oral airflow(via 2 resistance matched pneumotachometers), TcPO2 and esophageal pressure(via fluid filled catheter) were recorded. Frequency of OB in response to nasal occlusion increased with advancing postconceptual age from 8±8% at 31-32wk to 26±18 at 33-34wk (n=9,p<0.04) and 29±29% at 35-36wk (n=7). Unlike term infants, OB in preterm infants is characterized by intermittent airway obstruction and respiratory pauses, resulting in a fall in minute ventilation from 447±95 to 229±88cc/min/kg (p<0.01) and TcPO2 from 64±8 to 56±6 (p<0.01). Inspir.(RI) and expir.(RE) total airway resistances were calculated from the ratio of flow resistive pressure to flow at half maximal volume. On switching from nasal to oral breathing, RI increased from 41±30 to 234±228 (p<0.004) and RE increased from 62±16 to 145±43 cmH2O·L−1·sec (p<0.004). We conclude that oral breathing becomes more frequent and effective with increasing postnatal maturation. High oral airway resistance appears to be the critical factor which limits oral ventilation in preterm infants. Supp. by NHL 25830 and 31173.