Effects of Food and Liquid Properties on Swallowing Physiology and Function in Adults.

Foods and liquids have properties that are often modified as part of clinical dysphagia management to promote safe and efficient swallowing. However, recent studies have questioned whether this practice is supported by the evidence. To address this, a scoping review was conducted to answer the question: "Can properties of food and liquids modify swallowing physiology and function in adults?" Online search in six databases yielded a set of 4235 non-duplicate articles. Using COVIDENCE software, two independent reviewers screened the articles by title and abstract, and 229 full-text articles were selected for full-text review. One-hundred eleven studies met the inclusion criteria for qualitative synthesis and assessment of risk of bias. Three randomized controlled trials and 108 non-randomized studies were analyzed. Large amounts of variability in instrumental assessment, properties of food and liquids, and swallowing measures were found across studies. Sour, sweet, and salty taste, odor, carbonation, capsaicin, viscosity, hardness, adhesiveness, and cohesiveness were reported to modify the oral and pharyngeal phase of swallowing in both healthy participants and patients with dysphagia. Main swallow measures modified by properties of food and liquids were penetration/aspiration, oral transit time, lingual pressures, submental muscle contraction, oral and pharyngeal residue, hyoid and laryngeal movement, pharyngeal and upper esophageal sphincter pressures, and total swallow duration. The evidence pooled in this review supports the clinical practice of food texture and liquid consistency modification in the management of dysphagia with the caveat that all clinical endeavors must be undertaken with a clear rationale and patient-specific evidence that modifying food or liquid benefits swallow safety and efficiency while maintaining quality of life.

Assays of tongue force, timing, and dynamics in rat and mouse models.

Communication and swallowing are highly complex sensorimotor events that are tightly linked to respiration and vital to health and well-being. The tongue is a complex organ, often described as a muscular hydrostat, that is crucial for maintaining airway patency, preparing and safely transporting food/liquid, and rapidly changing position and shape for speech. As with any complex behavior, tongue function can be compromised with aging, diseases/conditions, trauma, or as a pharmacologic side effect. As such, modeling lingual function and dysfunction for basic and translational research is paramount; understanding how the nervous system controls tongue function for complex behavior is foundational to this work. Non-invasive access to tongue tissues and kinematics during awake behavior has been historically challenging, creating a critical need to measure tongue function in model systems. Germane to this field of study are the instruments and assays of licking/lapping and drinking, including tongue force and timing measures, many of which were designed or modified by Dr. Stephen C. Fowler. The focus of this paper is to review some of the important contributions of measuring tongue behaviors in awake rats and mice and how these have been modified by other researchers to advance translational science.

Rat Models of Vocal Deficits in Parkinson's Disease.

Parkinson's disease (PD) is a progressive, degenerative disorder that affects 10 million people worldwide. More than 90% of individuals with PD develop hypokinetic dysarthria, a motor speech disorder that impairs vocal communication and quality of life. Despite the prevalence of vocal deficits in this population, very little is known about the pathological mechanisms underlying this aspect of disease. As such, effective treatment options are limited. Rat models have provided unique insights into the disease-specific mechanisms of vocal deficits in PD. This review summarizes recent studies investigating vocal deficits in 6-hydroxydopamine (6-OHDA), alpha-synuclein overexpression, DJ1-/-, and Pink1-/- rat models of PD. Model-specific changes to rat ultrasonic vocalization (USV), and the effects of exercise and pharmacologic interventions on USV production in these models are discussed.

Biological and Acoustic Sex Differences in Rat Ultrasonic Vocalization.

The rat model is a useful tool for understanding peripheral and central mechanisms of laryngeal biology. Rats produce ultrasonic vocalizations (USVs) that have communicative intent and are altered by experimental conditions such as social environment, stress, diet, drugs, age, and neurological diseases, validating the rat model's utility for studying communication and related deficits. Sex differences are apparent in both the rat larynx and USV acoustics and are differentially affected by experimental conditions. Therefore, the purpose of this review paper is to highlight the known sex differences in rat USV production, acoustics, and laryngeal biology detailed in the literature across the lifespan.

Pharyngeal Swallowing Pressures in Patients with Radiation-Associated Dysphagia.

Dysphagia associated with radiotherapy for head and neck cancer is complex and can be difficult to treat. Videofluoroscopic swallow studies (VFSS) are the current gold-standard instrumented swallow assessment. High-resolution manometry (HRM) is an additional approach that provides objective measurements of swallowing-related pressures in the pharynx and esophagus. This can provide functional information on the pressure gradients underlying bolus propulsion, and is relevant for this patient population, where radiation-related fibrosis can lead to weakness and impaired pressure generation. The purpose of this preliminary study was to describe pharyngeal swallowing pressures in patients with radiation-associated dysphagia (RAD) and late radiation-associated dysphagia (LRAD) using HRM. RAD occurs during and immediately following treatment, whereas LRAD is a more recently described phenomenon in which the patient experiences an onset of dysphagia at least 5 years post-treatment. We performed a retrospective analysis of pharyngeal swallowing pressures from 21 patients with RAD or LRAD and 21 healthy sex/age-matched controls. Patients with RAD or LRAD exhibited decreased swallowing pressure durations throughout the pharynx (p ≤ 0.002), as well as decreased hypopharynx maximum pressure (p = 0.003) and pharyngeal contractile integral ( p < 0.0001). Understanding how pharyngeal pressure generation is altered in patients with a history of radiotherapy can help clinicians form more precise treatment plans.