Measurement of force applied by infant tongue to the nipple during sucking and investigation of the mechanism of tongue movement.

In order to clarify the dynamic mechanisms involved in sucking by infants, we developed an artificial nipple with built-in force sensors and have measured the contact force between the tongue and the artificial nipple in infants including healthy, premature and low birth weight. In this study, we measured the force applied by the tongue on the artificial nipple in 10 healthy infants and in 10 infants who were also tube-fed and investigated the differences in dynamic actions between the two groups to extract factors involved in satisfactory sucking. The results showed that differences in the maximum force applied and in the time to reach the maximum force were found between infants with and without established oral feeding. For an infant to suck satisfactorily, 1) the time for the force to propagate from the tongue tip to the tongue root needs to constitute at least 8 % of the sucking period and 2) the force applied at the tongue tip needs to be at least 50% of the force at the tongue root.

Measurement of tongue-artificial nipple contact force in infants with sucking difficulties.

Infants are known to suckle and ingest breast milk by wrapping the tongue around a nipple, writhing the tongue, and pressing the nipple. However, the dynamic mechanisms of tongue movement are still obscure, and factors related to sucking difficulties of infants are not well understood. We developed an artificial nipple installed with small cantilever-type sensors and directly measured the force applied on the nipple by the tongue. Small force sensors were arranged within the artificial nipple in a two-dimensional matrix of 3 × 2 to measure the force at 6 points. Subjects were 20 healthy infants (Group A) and 5 infants who had difficulty sucking (Group B). The latter could not breastfeed well and were fed from bottles or tubes. Informed consent was provided by the parents or guardians. The measured maximum force at the tip of the nipple was 1.4 ± 0.4 N and 1.2 ± 0.3 N (mean ± SD) in Groups A and B, respectively. At the base of the nipple, the maximum force recorded was 0.8 ± 0.5 N and 0.3 ± 0.3 N (mean ± SD), respectively, showing a statistically significant difference (p<0.05). The sucking period was 0.6 ± 0.1 s (mean ± SD) in both groups. The difference in time necessary to reach the maximum forces between the sensors at the tip and base was 39.7 ± 28.8 ms (mean ± SD) and 37.2 ± 75.9 ms in Groups A and B, respectively.