Impact of Nipple Properties on Coordination of Respiration and Swallowing in Infant Pigs

Abstract

Coordination of respiration and swallowing in mammalian feeding is a tightly regulated process necessary for survival. It is particularly critical in infants owing to their immature development and associated elevation aspiration risk. Infant swallowing disorders are associated with abnormal swallow‐breathe patterns. Commercial nipples are often marketed as being able to regulate swallow‐respiration coordination to manage infant swallowing problems, however, a systematic analysis of what aspects of nipple design affect aerodigestive coordination has not been undertaken. We tested the impact of varying two parameters of nipple design, stiffness and nipple opening diameter, on the coordination of respiration and swallowing. We hypothesized that parameters associated with easier feeding (lower stiffness, larger hole diameter), would lead to more variable swallow respiration coordination as a result of increased frequency of swallowing. We designed and manufactured four test nipples representing all combinations of two stiffnesses and two diameters. Six infant pigs were trained to drink milk replacement formula mixed with barium on a nipple of intermediate stiffness and diameter to the experimental nipples. At six days of age, pigs were recorded using high speed (100 fps) videofluoroscopy suckling from each of the experimental nipples. We randomized the order in which the pigs drank from the nipples. We measured respiration using a plethysmograph placed around the thorax to record thoracic expansion and contraction, synchronized with the fluoroscope recording. We collected twenty swallows per nipple for each pig. We identified the time of each swallow from the videofluoroscopy, and the onset of each inspiration and expiration cycle from the plethysmograph trace. For each swallow, we calculated the delay between the swallow and the closest onset of inspiration. For each breath cycle, we calculated length of the breath cycle as well as the number of swallows occurring the cycle. We used linear mixed models, with individual as a random factor, for all analyses. We tested the effect of stiffness, diameter, and their interaction on swallow‐inspiration delay, and the effect of nipple type and number of swallows during a respiration cycle on duration of respiratory phases. Swallow inspiration delay was lower for large diameter nipples than small diameter nipples regardless of stiffness (diameter F(1,351)=7.6, p=0.006). Both nipple type (F(3,644.02)=4.8, p=0.003) and swallow number (F(3,656.31)=19.5, p<0.001) had a significant effect on respiratory duration length. Larger diameter nipples resulted in shorter respiratory cycle lengths, but the more swallows in a respiratory cycle, the longer that cycle was. Both coordination of individual swallows with respiration, and overall respiratory patterns during feeding, changed in response to changing nipple diameter, but not stiffness. However, this was strongly linked to the number of swallows occurring in a respiratory cycle, suggesting that understanding how nipple properties affect frequency and distribution of swallows in the feeding sequence may be key to understanding how milk delivery affects aerodigestive coordination in infant feeding.