Accurate assessment and diagnosis of swallowing disorders is key to providing appropriate intervention. Selection of treatment relies on our diagnostic methodology. If incorrect treatment is selected, then swallowing disorders may not improve. Pre-swallow pooling is a feature of dysphagia that can cause aspiration before or during swallowing. It is presumed to be caused by two different pathophysiological impairments. One is presumed to be a motor impairment, which causes poor bolus containment as a result of oral weakness. This leads to some or all of the bolus entering the pharynx prior to purposeful propulsion of the bolus in the mouth. The other is presumed to be a sensory impairment whereby reduced sensation in the mouth causes a delay or absence of the pharyngeal swallowing response, after the bolus is propelled into the pharynx. However, assessment and diagnosis of pre-swallow pooling is poorly defined in the literature. In clinical practice, observations on videofluoroscopic swallowing studies are used to distinguish between poor bolus containment and delayed pharyngeal swallowing. However, videofluoroscopic swallowing studies allow for observation of biomechanics and cannot provide information regarding a sensory or motor impairment. Therefore, this PhD program investigated the phenomenon of pre-swallow pooling in stroke, to understand how it is differentiated into either poor bolus containment or delayed pharyngeal swallowing and whether a sensory and motor cause of pre-swallow pooling can be established.

This PhD program of research involved four studies and a scoping review. The scoping review findings were included within the literature review for continuity. This identified a large variation of the terms used to describe pre-swallow pooling, the measurement methods, and the methods by which to differentiate poor bolus containment from delayed pharyngeal swallowing. Study one was a normative study on 60 healthy participants. This study evaluated normative and reliability data of a novel oral sensory threshold measurement, and posterior lingual-palatal pressure measurement and the relationship between them. Electrical stimulation was used to establish sensory thresholds in the mouth including the lips, tongue and faucial palate. Whilst lingual-palatal pressure norms have previously been reported, there is scant data on the posterior position that includes both isometric lingual-palatal pressure and lingual-palatal pressure during swallowing. The relationship between both physiological measures has not previously been investigated. Results suggest that there is some preliminary evidence that these tools can be used to determine a motor or sensory cause of pre-swallow pooling.

Study two was the first study to evaluate the agreement of speech pathologists’ current methods for distinguishing poor bolus containment from delayed pharyngeal swallowing. This study evaluated inter- and intra-rater reliability of speech pathologist’s current practice in the diagnosis of poor bolus containment and delayed pharyngeal swallowing using videofluoroscopic swallowing studies. Thirty videofluoroscopic thin fluid swallows with five of those appearing twice, were presented via an online survey to examine agreement both between and within raters. Definitions of poor bolus containment and delayed pharyngeal swallowing were provided to one of two groups to evaluate whether this information increased reliability. Reliability was poor for inter and intra-rater reliability for both the group with, and the group without, definitions. This indicated that our current methodology for determining poor bolus containment from delayed pharyngeal swallowing is unreliable. Further, the addition of definitions to guide speech pathologists in determining one from the other did not increase agreement, suggesting that the application or interpretation of measures is too subjective.

Study three was an exploratory study to determine whether distinct groups could be formed based on the physiological data obtained by the oral sensory threshold and posterior lingual-palatal pressure measurements. As there is no “gold-standard” for determining the difference between poor bolus containment and delayed pharyngeal swallowing, cluster analysis methodology was used to identify clusters that could be differentiated into one of potentially 3 groups. The groups were proposed to include a sensory group, a motor group, and a sensory-motor group. The aim was then to evaluate these groups against speech pathologists’ diagnosis of poor bolus containment and delayed pharyngeal swallowing in an attempt to determine whether a sensory and motor cause of pre-swallow pooling could be differentiated by clinicians. However, due to inconsistencies in speech pathologists’ diagnosis of poor bolus containment and delayed pharyngeal swallowing, this could not be completed. Since distinct groups could be established via cluster analysis, it is likely that evidence for a sensory and motor cause of pre-swallow pooling exists, however, our current methods for determining this is flawed.

The final study evaluated the groups identified by the cluster analysis against common swallowing measures including oral transit time (OTT), stage transition duration (STD) and the Penetration-Aspiration Scale (PAS). Due to small numbers, most of the statistical methodology could not be applied, and results were presented descriptively.

This research addressed the need for more consistent terminology to describe the two causes of pre-swallow pooling and improved methods for distinguishing between poor bolus containment and delayed pharyngeal swallowing. There is evidence that subjects who have pre-swallow pooling following a stroke can be separated into those who have both a sensory and motor impairment and those who have a motor impairment alone. However, there remains no evidence for linking poor bolus containment with a motor impairment and delayed pharyngeal swallowing with a sensory impairment. New methodologies for determining the cause of pre-swallow pooling are required to ensure correct selection of dysphagia intervention and optimise rehabilitation outcomes.