Frequency of stage II oral transport cycles in healthy human

Stage II transport (St2Tr) is propulsion of triturated food into the pharynx for storage before swallowing via tongue squeeze-back against the palate. To clarify the phenomenology of St2Tr, we examined the effects of food consistency and the number of chewing cycles on the number of St2Tr cycles in a chew-swallow sequence. We recorded chew-swallow sequences in lateral projection with videofluoroscopy of 13 healthy volunteers eating 6 g of hard (shortbread cookie), and soft foods (ripe banana and tofu) with barium. We counted the number of chewing and St2Tr cycles from food intake to terminal swallow. We used the Friedman test for bivariate analyses and negative binomial regression for multivariable analyses. On bivariate analysis, food consistency had a positive association with the number of chewing cycles (P = 0.013), but not with the number of St2Tr cycles (P = 0.27). Multivariable analysis, however, revealed a greater number of St2Tr cycles with hard than soft food (≤ 0.01) and a trend toward negative correlation between the numbers of St2Tr and chewing cycles (P = 0.083). The number of chewing cycles needed to clear the mouth differs among food consistencies as demonstrated previously. Greater numbers of both St2Tr and chewing cycles were elicited with the hard than with the soft foods. Given the trend toward negative correlation, the association between the number of St2Tr cycles and that of chewing cycles deserves further study.