A review of swallow timing in the elderly

Tongue Force Training Induces Plasticity of the Lingual Motor Cortex in Young Adult and Aged Rats

Tongue exercise programs are used clinically for dysphagia in aged individuals and have been shown to improve lingual strength. However, the neural mechanisms of age-related decline in swallowing function and its association with lingual strength are not well understood. Using an established rat model of aging and tongue exercise, we hypothesized that the motor cortex of aged rats would have a smaller lingual motor map area than young adult rats and would increase in size as a function of tongue exercise. Over 8 weeks, rats either underwent a progressive resistance tongue exercise program (TE), learned the task but did not exercise (trained controls, TC), or were naïve untrained controls (UC). Cortical motor map areas for tongue and jaw were determined using intracortical microstimulation (ICMS). Rats in the TE and TC groups had a significantly larger motor cortex region for the tongue than the UC group. Lingual cortical motor area was not correlated with protrusive tongue force gains and did not differ significantly with age. These results suggest that learning a novel tongue force skill was sufficient to induce plasticity of the lingual motor cortex yet increasing tongue strength with progressive resistance exercise did not significantly expand the lingual motor area beyond the gains that occurred through the skilled learning component.

The Importance of Extensional Rheology in Bolus Control during Swallowing

Thickened fluids are commonly used in the medical management of individuals who suffer swallowing difficulty (known as dysphagia). Previous studies have shown that the rheological properties of a liquid affect the flow behavior of the bolus in swallowing, such as pharyngeal transit time. While there is no doubt that shear rheology is a highly important factor for bolus flow, it is suspected that extensional properties of a liquid bolus also plays an important role in swallowing, due to elongation of the bolus as it flows through the oropharynx. Our aim in this work was to observe the effect of extensional viscosity on pharyngeal transit time and elongation of the bolus during swallowing. Eight samples of thickened liquid barium that were shear-controlled, but varied in extensional viscosity and two samples that were extensional-controlled, but varied in shear viscosity were swallowed by eight healthy individuals. Data were collected under lateral view of videofluoroscopy swallow study (VFSS); measures of pharyngeal transit time and the ratio of the length to the width of the bolus on the frame of Upper Esophageal Sphincter (UES) opening were taken from the VFSS recordings. It was observed that the pharyngeal transit time generally increases when the fluids are thickened to higher IDDSI consistency. Additionally, higher extensional viscosity fluids reduced the elongation of the bolus during swallowing, thus potentially reducing the risk of post-swallow residue due to bolus breakage. This study confirmed the relevance of the extensional viscosity of the bolus in swallowing.

A Systematic Review of Physiological Changes in Swallowing in the Oldest Old

Age-related swallowing changes are well-researched in deglutology, usually distinguishing those over 60 years as older aged. World-wide, older adults are healthier and forecast to live longer: many over 85 years. It is necessary for clinicians to understand healthy swallowing changes in this 'oldest old' in order to appropriately manage swallowing complaints in older patients. This systematic review collated and critically appraised studies investigating swallowing changes in adults over 85 years using instrumental assessment. Criteria for inclusion were healthy subjects over 85 years. Exclusion criteria included studies focused on anatomy and oral processing. Studies published until December 2018 were retrieved from BIOSIS, CINAHL, Embase, Medline, and Scopus, totaling 2125 articles. During data screening, 64% of studies investigating age-related swallowing changes were excluded, as the oldest old were not recruited. After PRISMA screening, 44 articles met criteria. These were further reviewed for data extraction, bias and quality. Main quantitative age-related changes in swallowing included increases in delay in swallow onset, bolus transit times, duration of UES opening, pressure above the UES and UES relaxation pressure, and reduction in pressure at the UES. Few studies detected increased residue or airway compromise in the form of aspiration. Results were not easily comparable due to differences in age ranges, methods for deeming participants 'healthy', measures used to define swallowing physiology, and swallowing tasks. Age-related swallowing changes are identified that do not compromise safety. The oldest old are underrepresented in normative deglutition research. It is essential future studies plan accordingly to recruit those over 85 years.

Swallowing function in advanced age

PURPOSE OF REVIEW

To present current literature regarding swallowing function in advanced age, including healthy ageing, dysphagia and trends in multidisciplinary team service delivery.

RECENT FINDINGS

Normative studies support swallowing efficiency but greater variability in healthy advanced age, through to 100 years old. Deviations from normative data and symptoms of dysphagia leading to aspiration or nutritional risk, imply swallowing disorder, rather than simply the ageing process. Quantitative and qualitative studies are emerging that promote management of swallow dysfunction for an ageing society, including innovative assessment, home treatment, swallowing exercise and optimized mealtimes.

SUMMARY

Current literature on swallowing function in advanced age provides multidisciplinary perspectives and initiatives, with clear commitment to improving quality of life for older adults. The diversity of the older population and serious consequences of swallowing difficulties calls for routine screening tools for swallowing impairment and malnutrition risk. Representation of 'oldest old' in future normative studies is essential to guide swallowing management in adults over 85 years old.

Swallow Event Sequencing: Comparing Healthy Older and Younger Adults

Previous research has established that a great deal of variation exists in the temporal sequence of swallowing events for healthy adults. Yet, the impact of aging on swallow event sequence is not well understood. Kendall et al. (Dysphagia 18(2):85-91, 2003) suggested there are 4 obligatory paired-event sequences in swallowing. We directly compared adherence to these sequences, as well as event latencies, and quantified the percentage of unique sequences in two samples of healthy adults: young (< 45) and old (> 65). The 8 swallowing events that contribute to the sequences were reliably identified from videofluoroscopy in a sample of 23 healthy seniors (10 male, mean age 74.7) and 20 healthy young adults (10 male, mean age 31.5) with no evidence of penetration-aspiration or post-swallow residue. Chi-square analyses compared the proportions of obligatory pairs and unique sequences by age group. Compared to the older subjects, younger subjects had significantly lower adherence to two obligatory sequences: Upper Esophageal Sphincter (UES) opening occurs before (or simultaneous with) the bolus arriving at the UES and UES maximum distention occurs before maximum pharyngeal constriction. The associated latencies were significantly different between age groups as well. Further, significantly fewer unique swallow sequences were observed in the older group (61%) compared with the young (82%) (χ2 = 31.8; p < 0.001). Our findings suggest that paired swallow event sequences may not be robust across the age continuum and that variation in swallow sequences appears to decrease with aging. These findings provide normative references for comparisons to older individuals with dysphagia.

Dysphagia Onset in Older Adults during Unrelated Hospital Admission: Quantitative Videofluoroscopic Measures

New-onset swallowing difficulties in older patients during unrelated hospital admissions are well recognized and may result in prolonged hospital stay and increased morbidity. Presbyphagia denotes age-related swallowing changes which do not necessarily result in pathological effects. The trajectory from presbyphagia to dysphagia is not well understood. This retrospective observational study compared quantitative videofluoroscopic measures in hospitalized older adults aged 70-100 years, reporting new dysphagia symptoms during admission (n = 52), to healthy asymptomatic older (n = 56) and younger adults (n = 43). Significant physiological differences seen in hospitalized older adults but not healthy adults, were elevated pharyngeal area (p < 0.001) and pharyngeal constriction ratio (p < 0.001). Significantly increased penetration (p < 0.001), aspiration (p < 0.001) and pharyngeal residue (p < 0.001) were also observed in the hospitalized older cohort. Reasons for onset of new swallow problems during hospitalization are likely multifactorial and complex. Alongside multimorbidity and polypharmacy, a combination of factors during hospitalization, such as fatigue, low levels of alertness, delirium, reduced respiratory support and disuse atrophy, may tip the balance of age-related swallowing adaptations and compensation toward dysfunctional swallowing. To optimize swallowing assessment and management for our aging population, care must be taken not to oversimplify dysphagia complaints as a characteristic of aging.