3.6.1 The Swallowing Process: An overview

Swallowing, also commonly referred to as ‘deglutition’, is a complex process that involves the coordinated movement of saliva, food or liquid from the mouth to the stomach (Logemann, 1998). It is essential for life, allowing for the intake of nutrients and fluids. This action involves the coordination of multiple muscles in the mouth, pharynx (throat), and oesophagus (food pipe) and is primarily controlled by the central nervous system.

The process of swallowing can be divided into four main stages (also referred to as ‘phases’), each with specific functions:

1. Oral preparatory;
2. Oral;
3. Pharyngeal; and
4. Oesophageal.

Each stage involves a combination of voluntary and involuntary actions that require coordination between various muscles, nerves, and anatomical structures.  In the context of swallowing, the terms voluntary and involuntary refer to the conscious control of the different stages of the swallowing process.

Voluntary stages: The oral preparatory and oral stages of swallowing are both voluntary, where a person has conscious control over chewing and moving the bolus to the back of the mouth, and a person can stop this at any time.

Involuntary stages: The pharyngeal and oesophageal stages are both involuntary, where swallowing is controlled by automatic processes that do not require conscious input.  Once the swallow is initiated and the pharyngeal stage commences, the swallow is no longer under voluntary control and cannot be stopped by the person.

3.6.2 Stages of swallowing

1. Oral preparatory stage: This is the first phase of the swallowing process, responsible for preparing food or liquid in the mouth to be swallowed. This stage is voluntary and involves both sensory and motor functions to ensure that food or liquid is adequately prepared and made safe for the subsequent stages of swallowing. The primary functions of this stage are mastication (chewing) and the formation of a bolus (a ball of chewed food mixed with saliva), which will be moved to the back of the mouth during the oral stage.
2. Oral stage: This is a voluntary phase of swallowing, and follows on from the oral preparatory stage.  Once food is chewed and mixed with saliva to form a bolus, the tongue then controls and pushes it against the hard palate (roof of the mouth) to the back of the mouth, and once the swallow is triggered, the pharyngeal stage commences.
3. Pharyngeal stage: This is an involuntary phase where the bolus is propelled through the pharynx (throat) toward the oesophagus (food pipe). During this phase, breathing pauses while the airway is temporarily closed off by the vocal folds to prevent food from entering the trachea (windpipe), while the soft palate rises to prevent food from entering the nasal cavity.  Muscle contractions in the pharynx then propel the bolus downwards, ready for the oesophageal stage.
4. Oesophageal stage: This is the final stage of swallowing, and is also involuntary.  The bolus enters the oesophagus, where peristalsis (a wave-like muscle contraction) moves the food downward towards the stomach. The lower oesophageal sphincter (a ring-shaped muscle) relaxes to allow the food to enter the stomach.

The video below provides a descriptive animation of the swallowing processes including the 4 stages of swallowing.

^{The 4 Stages of Swallowing: Biomechanics and Bolus Movement by Fauquier ENT}

3.6.3 Dysphagia: definition, causes, assessment and treatment

Dysphagia refers to an impairment of the swallowing mechanism that may result in penetration or aspiration of saliva, food or fluid into the airway (McCarty & Chao, 2021).

• Penetration – this is where part or all of the bolus enters the airway to the level of the vocal folds, but not beyond.
• Aspiration – this is where part or all of the bolus enters the airway below the level of the vocal folds.

Ultimately, dysphagia can be a socially debilitating or even life-threatening disorder, and the person with dysphagia may experience emotions such as anxiety, isolation, frustration, and depression (Newman, 2012).  Dysphagia can be caused by a range of conditions affecting the muscles, nerves, or structures involved in the swallowing process. This condition can present as difficulty initiating swallowing, a sensation of food ‘sticking’ in the throat or chest, coughing or choking while eating and drinking, excessive throat clearing after swallowing, or pain during swallowing. Dysphagia can be classified into two main types: oropharyngeal dysphagia (difficulty in the oral preparatory, oral, and pharyngeal stages) and oesophageal dysphagia (difficulty in the oesophageal stage).  Speech pathologists are involved in the assessment and treatment of oropharyngeal dysphagia, but for someone with oesophageal dysphagia, care is usually transferred to another professional, such as a gastroenterologist.

Causes of dysphagia

There are many causes of dysphagia, some of which can include the following:

• Neurological disorders: Conditions such as stroke, traumatic brain injury, Parkinson’s disease, multiple sclerosis, and motor neuron disease (MND) which can impact the strength and accuracy of movement involved in swallowing.
• Muscle disorders: Diseases such as muscular dystrophy can affect muscle movement responsible for safe swallowing.
• Structural abnormalities: Conditions such as narrowing caused by tissue swelling or tumours can cause obstructions in the pharynx or oesophagus, making swallowing difficult.
• Aging: As people age, the muscles and nerves involved in swallowing may weaken or become less efficient, leading to age-related dysphagia.
• Dementia: This occurs as cognitive decline impacts the brain’s ability to coordinate the complex processes involved in swallowing. As the disease progresses, it can impair a person’s ability to recognise food, and also causes deterioration of oral control and the ability to initiate or complete the swallowing process, leading to an increased risk of choking, aspiration, and malnutrition.

Dysphagia can have significant impacts on the wellbeing, nutritional intake, hydration, and quality of life, not only for the person with dysphagia, but also their close social networks. The video below provides insights into what it is like to live with dysphagia.

^{Swallow: A documentary – Dysphagia, by NFOSD Team}

Diagnosis of dysphagia

To understand dysphagia, it is important to understand the biomechanics of normal swallowing.  The biomechanics of swallowing refers to the study of the physical movements and forces involved in the process of swallowing, and includes the coordinated actions of muscles and tissues in the mouth, pharynx, and oesophagus, as well as the mechanics of bolus formation in the mouth, and bolus propulsion from the mouth to the stomach.

A diagnosis of dysphagia typically involves a detailed clinical evaluation, including a medical history, an oromotor examination, and sometimes imaging studies like a videofluoroscopic swallow study (VFSS), or a fibreoptic endoscopic evaluation of swallowing (FEES).

A swallowing study or a videofluoroscopic swallow study (VFSS) can help identify the exact stage at which swallowing dysfunction occurs. Treatment depends on the underlying cause and may include speech therapy to strengthen swallowing muscles, changes in diet or food texture, medications, or surgical interventions if there are structural causes.

• Medical history: a detailed record of a patient’s past and present health, including information about previous illnesses, surgeries, medications, lifestyle factors, family health history, and any ongoing or recent symptoms. Obtaining a comprehensive history helps a SLP assess risk factors, diagnose conditions, and plan appropriate assessment, treatment or management strategies.
• Oro-motor examination (OME): a clinical assessment that evaluates the strength, coordination, and function of the muscles involved in movements of the mouth and face, including those used for chewing, swallowing, and speaking. Asking a person to move certain parts of the mouth and face can help to identify impairments that may affect swallowing and speech.
• Oral trials: the process of testing a patient’s ability to swallow food or fluids safely during a bedside swallowing assessment. Oral trials involve offering the patient small amounts of food or drink, often in different textures or viscosities, to observe their swallowing ability, identify signs of aspiration or choking, and determine either further assessments, dietary modifications or other treatments needed to ensure safe swallowing.
• Videofluoroscopic Swallowing Study (VFSS): an imaging procedure that uses real-time x-ray technology to evaluate the process of swallowing. During a VFSS, the patient swallows food or liquid mixed with a contrast material (typically barium) to enable it to be visualised while x-ray images are taken, allowing speech pathologists to observe the movement of the bolus through the mouth, pharynx, and oesophagus to identify any swallowing dysfunction, and consider what treatment options are available.
• Fibreoptic Endoscopic Evaluation of Swallowing (FEES): a procedure where a flexible endoscope (a long, flexible tube with a light and camera at the end) is inserted through the nose to visualise the throat and larynx during swallowing. It provides real-time images of the swallow, helping to assess for aspiration or other swallowing difficulties.

The video below provides an example of an oro-motor examination.

^{Clinical Examination for Dysphagia by Medbridge}

The video below provides an example of a bedside swallow screen that includes and oro-motor examination and oral trials.

^{Bedside Swallow Screen, by Stanford Medicine 25}

The video below provides an example of a VFSS.

^{VFSS Swallowing Study: Videofluoroscopic Swallowing Study by Mayo Clinic}

The video below provides an example of a FEES.

^{FEES Swallowing Study: Fibreoptic Endoscopic Evaluation of Swallowing by Mayo Clinic}

treatment of dysphagia

Dysphagia can be treated in various ways depending on its cause, severity, and the specific stage of swallowing that is affected. Treatment typically involves a combination of strategies aimed at improving the ability to swallow safely and efficiently. Here are the common approaches to managing dysphagia:

Swallowing therapy

• Swallowing exercises: Speech pathologists may teach exercises to strengthen the muscles involved in swallowing, improve coordination, and reduce the risk of aspiration.
• Swallowing techniques: Speech pathologists may train patients in certain techniques which help improve swallowing safety and efficiency by modifying head position or breathing patterns.

Dietary modifications:

• Bolus modification: Foods and fluids can be altered to a safer consistency, such as pureeing solid foods to eliminate the need for chewing, or offering thickened liquids, proven to slow fluids down and make them easier and safer to swallow (Newman et al, 2016).
  • International Dysphagia Diet Standardisation Initiative (IDDSI).  IDDSI is an international collaboration of professionals who developed a standardised framework for labelling texture-modified foods and thickened liquids.
  • The framework is designed to avoid the confusion created by variable terminology and definitions to describe modified diets around the world.
• Dietary restrictions: In some cases, certain foods may be restricted altogether, or a patient may be instructed to avoid foods that are difficult to swallow or may pose a risk for aspiration.

Feeding support

• Assistive devices: Special tools or adaptive equipment, such as modified utensils, cups, or feeding devices, can help individuals manage dysphagia more easily.
• Tube feeding: In severe cases where swallowing is unsafe and eating and drinking orally would pose a risk to the patient, tube feeding may be recommended to ensure nutritional intake. This is usually a temporary solution until the swallowing function improves, but it also may be long-term for patients with chronic or progressive conditions.
  • Nasogastric Tube (NGT): a thin flexible tube that is inserted through the nose, down the oesophagus, and into the stomach. It is used to provide short term nutrition for patients who are unable to swallow food and fluids orally.
  • Percutaneous Endoscopic Gastrostomy (PEG): a medical procedure in which a feeding tube is inserted directly into the stomach through the abdominal wall. It is commonly used for long-term nutritional support in patients who are unable to swallow safely.

Addressing underlying conditions:

• Neurological rehabilitation: If dysphagia is due to neurological conditions (e.g., stroke, Parkinson’s disease, or MND), treatment may focus on managing the underlying disorder and improving swallowing through targeted therapy.
• Occupational therapy / physiotherapy: In some cases, physiotherapy may be recommended to address posture or coordination issues that affect swallowing function.

Behavioural and compensatory strategies:

• Postural adjustments: Adjusting the patient’s posture while eating, such as sitting upright or leaning slightly forward, can help facilitate safer swallowing and reduce the risk of aspiration.
• Compensatory techniques: These may include strategies to slow down the eating process, such as taking smaller bites or sips, chewing more thoroughly, or swallowing multiple times to clear food from the mouth and throat.

The treatment of dysphagia needs to be individualised, and based on the underlying cause, the specific difficulties a patient experiences, and their overall health. It often involves a multidisciplinary approach, including input from speech-language pathologists, dietitians, doctors, and other healthcare providers to ensure safe swallowing and adequate nutrition and hydration.