Pilot Study of Respiratory-Swallow Coordination in Amyotrophic Lateral Sclerosis

How Do Quantitative Videofluoroscopy Measures Differ Between People With Amyotrophic Lateral Sclerosis and Age-Matched Healthy Adults?

PURPOSE

Dysphagia is a leading cause of morbidity in people with amyotrophic lateral sclerosis (PwALS). Previous videofluoroscopic swallowing studies (VFSS) in PwALS do not account for the influence of senescence. We aimed to compare swallowing in PwALS and an age- and sex-matched control group using healthy reference data to define typical and atypical values.

METHOD

We conducted retrospective analysis of VFSS data from 19 PwALS (10 male, Mage = 63 years, range: 47-82) compared to control data from a cohort of healthy adults. Participants swallowed 20% w/v liquid barium from thin to extremely thick consistency. Blinded duplicate VFSS analysis using the ASPEKT (Analysis of Swallowing Physiology: Events, Kinematics and Timing) method yielded descriptive statistics for 16 quantitative VFSS parameters by consistency. Mann-Whitney U tests were used to identify significant cohort differences. Additionally, the frequencies of atypical values (in the 25% tails of the reference distribution) were tabulated by cohort and compared using odds ratios.

RESULTS

PwALS showed increased frequencies of multiple swallows per bolus, incomplete laryngeal vestibule closure, and reduced hyoid speed across consistencies. By contrast, similar frequencies of atypical values for pharyngeal constriction and residue in both cohorts suggest that age-related changes may contribute to the presence of these features in PwALS.

CONCLUSIONS

This analysis builds on previous descriptions of swallowing pathophysiology in amyotrophic lateral sclerosis (ALS) by clarifying the extent to which aging may account for some of the atypical findings seen in this patient population. Longitudinal studies are recommended to further differentiate the effects of ALS from age-related changes in swallowing over the course of disease progression.

Timeline of hypoglossal motor neuron death and intrinsic tongue muscle denervation in high-copy number SOD1G93A mice

In amyotrophic lateral sclerosis (ALS) postmortem tissue and the SOD1 mouse model at mid-disease, death of hypoglossal motor neurons (XII MNs) is evident. These XII MNs innervate the intrinsic and extrinsic tongue muscles, and despite their importance in many oral and lingual motor behaviours that are affected by ALS (e.g., swallowing, speech, and respiratory functions), little is known about the timing and extent of tongue muscle denervation. Here in the well-characterised SOD1G93A (high-copy) mouse model, we evaluated XII MN numbers and intrinsic tongue muscle innervation using standard histopathological approaches, which included stereological evaluation of Nissl-stained brainstem, and the presynaptic and postsynaptic evaluation of neuromuscular junctions (NMJs), using synapsin, neurofilament, and α-bungarotoxin immunolabelling, at presymptomatic, onset, mid-disease, and endstage timepoints. We found that reduction in XII MN size at onset preceded reduced XII MN survival, while the denervation of tongue muscle did not appear until the endstage. Our study suggests that denervation-induced weakness may not be the most pertinent feature of orolingual deficits in ALS. Efforts to preserve oral and respiratory functions of XII MNs are incredibly important if we are to influence patient outcomes.

Dendritic morphology of motor neurons and interneurons within the compact, semicompact, and loose formations of the rat nucleus ambiguus

Introduction

Motor neurons (MNs) within the nucleus ambiguus innervate the skeletal muscles of the larynx, pharynx, and oesophagus. These muscles are activated during vocalisation and swallowing and must be coordinated with several respiratory and other behaviours. Despite many studies evaluating the projections and orientation of MNs within the nucleus ambiguus, there is no quantitative information regarding the dendritic arbours of MNs residing in the compact, and semicompact/loose formations of the nucleus ambiguus..

Methods

In female and male Fischer 344 rats, we evaluated MN number using Nissl staining, and MN and non-MN dendritic morphology using Golgi-Cox impregnation Brightfield imaging of transverse Nissl sections (15 μm) were taken to stereologically assess the number of nucleus ambiguus MNs within the compact and semicompact/loose formations. Pseudo-confocal imaging of Golgi-impregnated neurons within the nucleus ambiguus (sectioned transversely at 180 μm) was traced in 3D to determine dendritic arbourisation.

Results

We found a greater abundance of MNs within the compact than the semicompact/loose formations. Dendritic lengths, complexity, and convex hull surface areas were greatest in MNs of the semicompact/loose formation, with compact formation MNs being smaller. MNs from both regions were larger than non-MNs reconstructed within the nucleus ambiguus.

Conclusion

Adding HBLS to the diet could be a potentially effective strategy to improve horses' health.

Defining Normal Sequential Swallowing Biomechanics

Little is known about the physiology of a common fluid ingestion pattern-sequential swallowing. This study investigated sequential swallowing biomechanics in healthy adults. Archival normative videofluoroscopic swallow studies were analyzed for hyolaryngeal complex (HLC) patterning and biomechanical measures from the first 2 swallows of a 90-mL thin liquid sequential swallow task. The effects of age, sex, HLC type, and swallow order were explored. Eighty-eight participants were included in the primary analyses as they performed sequential swallows. HLC Type I (airway opens, epiglottis approaches baseline) and Type II (airway remains closed, epiglottis remains inverted) most commonly occurred (47% each), followed by Type III (mixed, 6%). Age was significantly associated with Type II and longer hypopharyngeal transit, total pharyngeal transit (TPT), swallow reaction time (SRT), and duration to maximum hyoid elevation. Males demonstrated significantly greater maximum hyoid displacement (Hmax) and longer duration of maximum hyoid displacement. Significantly larger maximum hyoid-to-larynx approximation was linked to the first swallow, while the subsequent swallow had significantly longer oropharyngeal transit, TPT, and SRT. Secondary analyses included an additional 91 participants who performed a series of discrete swallows for the same swallow task. Type II had significantly greater Hmax than Type I and series of discrete swallows. Sequential swallowing biomechanics differ from discrete swallows, and normal variance exists among healthy adults. In vulnerable populations, sequential swallowing may challenge swallow coordination and airway protection. Normative data allow comparison to dysphagic populations. Systematic efforts are needed to further standardize a definition for sequential swallowing.