This study was approved by the Institutional Review Board of the Samsung Medical Center, a tertiary medical center in Seoul, Republic of Korea. A waiver of consent was granted for a chart review without patient contact. Included in the study were 107 infants younger than 1 year with dysphagia who underwent VFSS between March 2010 and March 2011. When infants underwent VFSS more than once during the study period, only the first VFSS findings were analyzed.

Clinical characteristics including sex, gestational age at birth, birth weights, corrected age when the VFSS was performed, height and weight were examined. Chief complaints for which the VFSS was requested and medical conditions associated with dysphagia were also collected.

VFSSs were conducted as described by Logemann [8] with some modifications. To evaluate infants, the fluoroscope table was tilted vertically and a feeder seat was placed on the ledge in a semi-reclined position at approximately 45°. Careful attention was paid to the stability of the positioning of the infant on the chair or footplate. Images of the swallowing process were taken in the lateral view (and occasionally in the anteroposterior view) using fluoroscopic equipment Shimavision 3200 HG (Shimadzu, Kyoto, Japan). In infants who were fed only milk, VFSSs were performed with bottle-feeding by mixing an undiluted liquid barium solution, barium sulfate; Solotop sol 140 (Taejoon Pharm, Seoul, Korea) into the milk. The infants' own bottles and nipples were used. Infants who received weaning food were induced to swallow milk first, followed by ground apples and porridge, in order of precedence by bottle-feeding and spoon-feeding. This was performed as quickly as possible in order to minimize radiation exposure. The results were interpreted by a physiatrist and an experienced speech-language pathologist. These investigations were performed to determine any problems in the following oral and pharyngeal phases: 1) sucking patterns, 2) delayed swallowing reflex, 3) the degrees of epiglottic inversion and laryngeal closure, 4) the presence of residues, 5) the presence of penetration, and 6) the presence of aspiration. Decreased sustained sucking was defined when the infant was unable to engage in long sucking bursts (i.e., more than 5 sucks) without cardiorespiratory compromise or any stress sign. Delayed swallowing reflex was defined as when the swallowing reflex did not occur until the contrast material passed the epiglottic vallecula. Epiglottic inversion was judged to be insufficient if it did not completely invert the larynx. Laryngeal closure was judged to be insufficient if the airway was not completely closed during swallowing. Residue was defined as contrast material remaining in the pharyngeal cavity after swallowing. Penetration was defined as when the contrast material passed above the true vocal cord but not below it. Aspiration was defined as when the contrast material passed below the true vocal cord.

The Mann-Whitney U-test was conducted to determine significant differences with respect to demographic characteristics, associated medical conditions, reasons of referral for VFSS, and VFSS findings between the full-term and preterm infants. The χ² test and Fisher's exact test were conducted to examine the association between the reasons of referral for VFSS and VFSS findings. The level of significance was set at p<0.05. All analyses were performed using SPSS ver. 19.0 (IBM, Armonk, NY, USA).

Of the 107 infants, 63 were boys and 44 were girls. The mean gestational age was 35.1±5.3 weeks. Sixty-seven (62.6%) were full-term infants born at 37 weeks or later, and 40 (37.4%) were preterm infants born earlier than 37 weeks. Thirty-two (29.9%) infants were born earlier than 34 weeks and consequently required steroid administration to prevent respiratory distress syndrome. The mean birth weight was 2,381.0±1,026.3 g and 41.1% of infants had low birth weight (i.e., <2,500 g). The mean corrected age at the time of VFSS was 3.8±3.5 months, mean height was 58.4±8.5 cm and mean weight was 5,330.0±2,071.1 g. When the full-term and preterm infants were compared, significant differences were noted in birth weight as well as corrected age, height, and weight at the time of VFSS (Table 1).

Congenital heart diseases, gastroesophageal reflux, bronchopulmonary dysplasia, clinical genetic syndromes, and neurologic disorders were observed in 47 (43.9%), 28 (26.2%), 21 (19.6%), 11 (10.3%), and 10 (9.3%) infants, respectively. In 15 (14.0%) infants, no particular underlying medical conditions that would cause dysphagia were noted. Except gastroesophageal reflux, there were significant differences in the frequencies between the full-term and preterm infants. Congenital heart disease and clinical genetic syndromes were observed more frequently in full-term infants. Moreover, bronchopulmonary dysplasias and neurologic disorders such as intraventricular hemorrhage were observed more frequently in preterm infants (Table 2).

Among the reasons for referral for VFSS, 'poor sucking' was the most common in 37 cases (34.6%), followed by significant 'desaturation' during feeding in 30 cases (28%), 'coughing' during feeding in 26 cases (24.3%), 'suspected aspiration pneumonia' in 9 cases (8.4%), and 'hoarseness' in 5 cases (4.7%). 'Poor sucking' was the most common reason for VFSS in the full-term infants (40.3%), and significant 'desaturation' during feeding was most common reason for VFSS in the preterm infants (55.0%). 'Desaturation' complaints differed significantly between the 2 groups (Table 3).

VFSS findings revealed 'weak sucking' and 'decreased sustained sucking' in 46 (43.0%) and 48 (44.9%) infants, respectively, in the oral phase. In the pharyngeal phase, 'delayed swallowing reflex,' 'insufficient epiglottic inversion,' and 'insufficient laryngeal closure' were observed in 74 (69.2%), 83 (77.6%), and 60 (56.1%) infants, respectively. 'Residue,' 'penetration only,' and 'aspiration' were observed in 68 (63.6%), 38 (35.5%), and 42 (39.3%) infants, respectively. Of the 42 infants who showed aspiration, 34 (81.0%) had silent aspiration and aspiration occurred without any symptoms in most cases (Table 4). When comparing the VFSS findings between the full-term and preterm infants, only 'decreased sustained sucking' was significantly different (34.3% and 62.5%, respectively). No significant differences were observed with respect to other VFSS findings between the 2 groups (Table 4).

As mentioned above, the χ² test and Fisher's exact test were conducted to determine the associations between reasons for referral for VFSS as well as VFSS findings for oral- and pharyngeal-phase abnormalities. Cases exhibiting 'poor sucking' were significantly associated with 'weak sucking' in VFSS. Cases exhibiting 'desaturation' were significantly associated with 'deceased sustained sucking' in VFSS. In infants with 'coughing,' 'aspiration' was significantly higher than those without coughing (Table 5).