Results from this pilot study provide evidence that a surprisingly high number of asymptomatic healthy adult subjects exhibit esophageal bolus movement patterns that are often considered to be abnormal clinically, with 96% of this sample exhibiting IES and 60% exhibiting IER at least once during a videofluoroscopic esophagram. The rates of IES and IER were potentially higher given that the time between swallows was 10 seconds rather than 20–30 seconds described in prior protocols investigating dysphagia [18
]. Additionally, the power to detect differences between age and gender groups was limited given the modest sample size of this cohort. However, these data provide a framework for further studies of a larger magnitude to assess for possible differences in swallowing of normal order individuals
Healthy individuals are by definition not symptomatic, although they might display inefficient esophageal bolus transport as measured with radiography. Normal subjects may have variation in esophageal bolus transport displayed by the occurrence of inefficient bolus progression; however it may be at a less frequent rate than in dysphagic persons thus highlighting the correlation of the frequency of inefficient bolus progression to symptoms. Symptomatic patients also may demonstrate increased sensitivity to distension of the esophagus or chronicity of abnormal esophageal bolus transport.
The rates of IES with liquid barium (16%) were similar to those described in normal individuals by Imam et al. [19
] who reported a 10% rate of stasis with liquid barium. However, these results are in contrast to those reported by Ott et al. [18
], in which no normal controls had ineffective esophageal bolus transport as viewed with fluoroscopy. There are probably multiple factors that lead to the different results from the present compared with Ott et al. [18
]: the use of different barium materials comprising only liquids; the systematic swallowing protocol followed for the videofluoroscopic esophagram, including the simultaneous performance of manometry in the upright position only; and the use of broad criteria for defining abnormal esophageal swallowing (a disruption in the peristaltic wave) [20
Our results also differed from the results in normal individuals seen by Tutuian et al., who reported on combined results of multichannel intraluminal impedance and manometry in normal individuals [21
]. Videofluoroscopic esophagram was not used in the protocol. In the study by Tutuian et al., more than 93% of normal individuals had at least 80% complete liquid or at least 70% complete viscous bolus transit. These results were in a younger population with a mean age of 38 (range 21–72 years) whereas our cohort was of older adults aged 45 and older. (REF- Tutuian et al.)
Gravity is thought to play a significant role in aiding the swallow mechanism for those with dysphagia [22
]. In our cohort of normal individuals, gravity did not affect the occurrence of IES or IER. Notably, when IES did occur in the cervical region, it occurred in the prone position and was more likely manifest with semisolid as compared to liquid. Therefore, gravity may influence swallowing to a greater degree in those who do display IES with semisolid barium, and may play a role in determining the location where the bolus arrests in its path. Such deviations in esophageal bolus clearance patterns may be important markers for identifying individuals potentially susceptible to developing symptoms in response to minor insults to the swallowing mechanism.
The only gender or age-related effect observed was a trend of increased IER in males age 65 and older. This is an important consideration as IER and IES could be risk factors for the development of esophagitis and aspiration pneumonia. Additionally, significantly more stasis emerged in the aortic esophagus with semisolid as compared to liquid barium. The finding of stasis at the level of the aortic arch can also be accounted for by the presence of a transition zone where there is a delay and/or spatial gap between the terminus of the proximal esophageal contraction and initiation of the distal esophageal contraction as described by Ghosh et al. [23
]. Additionally, the natural tendency for esophageal contents to remain in the aortic esophagus might be worsened if there was any ectasia or tortuosity at the aortic arch. Cardiac disease, which may be associated with aortic arch prominence, is the second most common associated comorbidity with aspiration pneumonia [24
]. The next step would be to assess if pathology affecting aortic size affects barium retention and if patients are indeed more symptomatic when boluses are retained around the aortic arch.
The short interval between swallows is a potential limitation of the study because of the second bolus arriving prior to the conclusion of the refractory period from the first. However, given the rapid rate of eating in our fast-paced society, it also could be considered a more accurate representation of mealtime behavior. Patient positioning prevents the comparison of outcomes with some esophageal motility studies in that patients in this study were evaluated in the prone position (standard for videofluoroscopic studies) while traditional esophageal motility studies are completed with the patient in a supine position.