Swallowing process and its impact on health

Swallowing difficulties (dysphagia) range from mild to severe, can be short or long term in duration, and acute or progressive in nature. Although it is not considered a normal part of ageing, dysphagia can occur due to the physiological ageing process, especially in people over 80. However, it is often a symptom of an underlying disease or condition.

Swallowing is a complex process that relies on many nerves and muscles of the mouth, throat and oesophagus¹. Swallowing difficulties can cause problems with drinking, eating, chewing, controlling saliva, taking medications and protecting the airway². An older adult with swallowing difficulties is at increased risk of pain³, dehydration and malnutrition.

Swallowing problems can mean that food and fluids entering the airway (laryngeal penetration) or the lungs (aspiration) can cause chest infections (aspiration pneumonia), choking or even death.

The swallowing process

The normal adult swallowing process occurs in four stages:

• Oral Preparatory Phase – also known as the pre-oral stage, involves the cognitive response to food and fluid and the ability of the person to think about eating. This is the initial phase, which starts with the mouth closing and chewing the food.
• Oral Transit Phase – is where the tongue works to move the food back towards the throat. Food and liquid is chewed and mixed with saliva, which is then pushed into the pharynx by the tongue.
• Pharyngeal Phase – is where the soft palate elevates and creates pressure within so food doesn’t go back into the nose. The food or fluid reaches the pharynx and triggers the swallow reflex. This acts to protect the airway so that food or fluid pass into the oesophagus and not into the lungs.
• Oesophageal Phase – is the final stage and involves the passage of the food and fluids down the food pipe (the oesophagus) into the stomach⁴.

Dysphagia

Dysphagia occurs when one or more of the four phases of swallowing is disrupted.

There are two main types of dysphagia:

Oropharyngeal dysphagia – trouble with moving food around the mouth and forming a bolus, as well as ‘initiating a swallow’. Patients are often medically unwell, and the most common causes are neurological disorders, such as stroke, Parkinson’s disease and dementia⁵.

Oesophageal dysphagia – the sensation of having food stuck in the throat or chest when swallowing and patients may complain of chest pain. Causes include gastro-oesophageal reflux disease (GORD), cancer, Zenker’s diverticulum, infection, inflammation, motility disorders and certain types of medications⁶. Oesophageal tract changes, which may contribute to swallowing difficulties, are common in people over 80 years.

Causes of dysphagia are varied and patients may present to hospital in the acute or chronic stage with varying symptoms. Patients who are severely ill or have a disability or who have suffered from stroke, brain injury, Parkinson’s disease or dementia, are especially at risk of developing dysphagia⁶.

Impacts of dysphagia

The more unwell an older patient is and the more their overall function is affected, the more vulnerable they are to developing swallowing problems. Critically ill older patients with dysphagia are at higher risk of developing life-threatening conditions, including aspiration and aspiration pneumonia, obstruction, pneumonitis and abscess^7,8.

Aspiration

Aspiration occurs when material is ingested and ends up in the lungs. This may be food particles, fluids, oropharyngeal secretions containing infectious agents⁹ or bacteria, which can cause an inflammatory condition⁸. Patients with dysphagia are at increased risk of developing aspiration, as are patients who are critically ill.

Silent aspiration and silent strokes

Silent aspiration is aspiration without any key clinical symptoms and signs, making it difficult to identify without imaging and assessment¹⁰. However it is common, occurring in more than 50 per cent of patients who aspirate⁵.

Similarly, ‘silent strokes’ are those occurring without symptoms and they are also a common cause of swallowing difficulties.

Aspiration pneumonia and pneumonitis

Dysphagia is also a risk factor for aspiration pneumonia – pneumonia caused by inhaling secretions or food that have been colonised by bacteria. Aspiration pneumonitis is caused by aspirating gastric contents. It is the most common cause of death in patients with dysphagia.

Malnutrition and dehydration

Older adults in hospital who have swallowing difficulties of any type are prone to weight loss and developing malnutrition and dehydration, which can severely impact their ability to recover from illness or surgery and remain independent and can increase the risk of other problems including delirium and falls.

1. Matsuo, K., Palmer, JB, Anatomy and Physiology of Feeding and Swallowing - Normal and Abnormal. Phys Med Rehabilitation 2008. 19(4): p. 16.

2. Australia, S.P., Position Paper, Dysphagia: General, 2004. p. 36.

3. National Stroke Foundation. Clinical Guidelines for Stroke Management, 2010.

4. Nestle Health Sciences. Dysphagia: Mechanisms of dysphagia. 2012.

5. Silverbook Australia, Medical care of older persons in residential aged care facilities, 2006: Tthe Royal Australian College of General Practitioners.

6. Australian and New Zealand Society for Geriatric Medicine, Position statement: dysphagia and aspiration in older people. Australasian Journal on Ageing, 2011. 30(2): p. 5.

7. Marik, P., Aspiration Pneumonitis and Aspiration Pneumonia. New England Journal of Medicine, 2001. 344(9): p. 4.

8. Liantonio, J., Salzman, B, Snyderman, D, Preventing Aspiration Pneumonia by Addressisng Three key risk Factors: Dysphagia, Poor Oral Hygiene and Medication Use. Annals of Internal Medicine, 2014. 22(10): p. 13.

9. Irwin, R., Lilly, C, Rippe, JM, Irwin & Rippe's Manual of Intensive Care Medicine. 6 ed., 2014: Wolters Kluwer Health.

10. Medicine, A.a.N.Z.S.f.G., Dysphagia and Aspiration in Older People, Posiiton Statement 12 2010.