Respiratory patterns and strategies during feeding in preterm infants.

Because patterns of integration of respiration into rhythmic suck-swallow efforts are highly variable, we examined the vagaries of respiratory efforts as they evolve from the first tentative attempts at integration through more complex rhythmic interactions, with a focus on several strategies in which breathing and suck-swallow are coordinated. Thirty-four preterm infants (18 males, 16 females) of 26 to 33 weeks gestational age, 32 to 40 weeks postmenstrual age (PMA), and 2 to 12 weeks postnatal age were studied weekly from initiation of bottle feeding (using breast milk or preterm formula, both fed from a bottle) until discharge, with simultaneous digital recordings of pharyngeal pressure, nasal thermistor airflow, and thoraco-abdominal strain-gauge readings. Exceptional patterns of feeding-adapted variations of respiration were noted, including breathing during swallow, alternating blocks of suck-swallow and respiration efforts, narial airflow without thoracic movement, modulation of respiratory phase relationship against swallow rhythm, and paired rhythms with swallow:breath ratios of more than 1:1. Some of these strategies were developmentally regulated. Alternating blocks of suck-swallow and respiratory efforts were only seen in the earliest (PMA 32-33 wks) studies. In contrast, coordination and phase relationships of suck-swallow and breathing stabilized over time, as did the percentage of synchronized narial and thoracic respiratory efforts, which increased significantly after 36 weeks PMA compared with synchronization at 32 to 33.9 and 34 to 35.9 weeks PMA (p<0.05). There was also a significant positive correlation between percentage synchronization and PMA (r=0.58; p<0.001). The strategies and patterns noted here further clarify the developmentally regulated coordination of suck, swallow, and respiration into mature infant feeding, and may be predictive of those infants with short- and long-term feeding or developmental difficulties.