Premature infant swallowing: patterns of tongue-soft palate coordination based upon videofluoroscopy

Abstract

Coordination between movements of individual tongue points, and between soft palate elevation and tongue movements, were examined in 12 prematurely born infants referred from hospital NICUs for videofluoroscopic swallow study (VFSS) due to poor oral feeding and suspicion of aspiration. Detailed post-evaluation kinematic analysis was conducted by digitizing images of a lateral view of digitally superimposed points on the tongue and soft palate. The primary measure of coordination was continuous relative phase of the time series created by movements of points on the tongue and soft palate over successive frames. Three points on the tongue (anterior, medial, and posterior) were organized around a stable in-phase pattern, with a phase lag that implied an anterior to posterior direction of motion. Coordination between a tongue point and a point on the soft palate during lowering and elevation was close to anti-phase at initiation of the pharyngeal swallow. These findings suggest that anti-phase coordination between tongue and soft palate may reflect the process by which the tongue is timed to pump liquid by moving it into an enclosed space, compressing it, and allowing it to leave by a specific route through the pharynx.

Figure 1

Sequence of video frames during videofluoroscopy of a preterm infant clinically referred due to feeding problems seen in the NICU. The numbered circles indicate points digitally superimposed on successive frames. Point 1 is the tongue tip, point 2 is the medial tongue point, and point 3 is the posterior tongue point. Each circle was placed at the boundary between light regions (the tongue) and dark regions (the bottle nipple filled with barium sulfate) forming the tongue apposition with the nipple. The left panel indicates the tongue rest position during suckling, and the right panel shows the maximum compression of the nipple.

Figure 2

(a) Time series created from the sequence of digitized points over successive frames in Figure 1. Note the increasing phase lag of the points proceeding in an anterior-posterior direction. (b) Plot of the continuous relative phase calculated from the relation between the three points, taken a pair at a time. Note that the posterior point exhibits the largest phase lag, as expected for an anterior-posterior peristaltic wave.

Figure 2

(a) Time series created from the sequence of digitized points over successive frames in Figure 1. Note the increasing phase lag of the points proceeding in an anterior-posterior direction. (b) Plot of the continuous relative phase calculated from the relation between the three points, taken a pair at a time. Note that the posterior point exhibits the largest phase lag, as expected for an anterior-posterior peristaltic wave.

Figure 3

Sequence of video frames as in Figure 1, but now with a fixed line superimposed between a landmark metal sphere taped on the skin and a reference point on a digitally superimposed rectilinear grid. The numbered circle is a point digitized at the light-dark boundary of the soft palate crossing the fixed line. The two panels illustrate the motion of the soft palate as it elevates (left) and lowers (right).

Figure 4

The top panel overlays the time series of the soft palate elevation and the medial tongue point to show that there is a brief moment when the two structures move in opposite directions at the same time (i.e., anti-phase). The bottom panel is a plot of the continuous relative phase of the two time series, indicating that at that brief moment, tongue and soft palate are close to 180 degrees, or anti-phase, and then return to their previous phase relationship.

Figure 5

A circular histogram of the phase angles characterizing tongue-soft palate coordination for the 12 swallows produced by each of the 12 subjects. The line from the radius indicates the mean and standard deviation for all 144 individual swallows.

Figure 6

Mean and standard deviation of continuous relative phase of tongue-soft palate coordination for the 12 infants at each successive swallow, from 1 through 12. Note that the increase of relative phase during the last few swallows is accompanied by a concomitant decrease in SD of relative phase, a measure of coordination stability.