**2. Physiological aspects of the swallowing process**

Swallowing is a sequence of coordinated voluntary and involuntary (reflex) movements that push contents of the oral cavity into the esophagus and the stomach. It is a complex process consisting of coordinated movements of the jaw, the soft palate, and the esophagus muscles. The process involves the olivary nuclei and the cerebral cortex [2]. A person swallows approximately 600 times per day. Nearly 200 times while eating, 50 times while sleeping, and 350 times in all other cases. In most cases, swallowing is performed unconsciously [3].

The process of swallowing can be divided into four phases: oral, oropharyngeal, pharyngeal, and esophagopharyngeal. During the first (oral) phase, food is delivered into the oral cavity. Food is chewed, it is moistened with saliva, and a food bolus is formed [3, 4].

During the second (oropharyngeal) phase, the food is accumulated at the back of the tongue, chewing is stopped, and the tongue lifts up and pushes the food bolus through the pharynx into the middle portion of the pharynx (oropharynx). At the same time, the longitudinal muscles of the tongue and the mylohyoid muscles contract and press down the tip, back, and root of the tongue sequentially to the hard palate. The tongue is pushed backwards. The soft palate lifts up as to close down the nasopharynx. The pharynx and the hyoid bone move forward and up. The epiglottis moves back and down as to close down the entrance to the trachea. Breathing stops. The pharynx contracts [5].

During the third (pharyngeal) phase, the food bolus moves down into the middle portion of the pharynx, where the middle pharyngeal constrictor and the inferior pharyngeal constrictor contract, ensuring the bolus is squeezed and pushed downwards. At the same time, the larynx and the hyoid bone lifts up, enabling faster food bolus passing through the middle portion of the pharynx to the inferior portion. At the moment of swallowing, the reflex response enables expansion of the esophageal entrance, and the pharyngeal constrictors push the food bolus through the pyriform sinuses into the esophagus [5, 6].

During the fourth (esophagopharyngeal) phase, the upper esophageal sphincter relaxes. The food bolus enters the esophagus. The esophagus contracts sequentially. The inferior esophageal sphincter opens. The food bolus enters the stomach [6].

The first phase is voluntary, while the others are involuntary. Cranial nerves IX, X, XI are involved at all stages of swallowing [7].

Dysphagia (from dys- + Greek "phagein" meaning to eat, to swallow) is a clinical symptom of swallowing dysfunction: difficulty or painful passage of a food bolus from the oral cavity to the stomach [8]. Dysphagia can occur both as an independent condition or as a part of complex syndrome. Thus, dysphagia is the most important element of a bulbar or pseudobulbar palsy. Dysphagia is a subjective perception of difficulty swallowing.

Swallowing disorders are signs of various diseases. It is one of the key problems in diffuse and focal brain injuries [9]. Dysphagia occurs in 27.2% of elderly, who can take care of themselves; in 47.4% of elderly patients in intensive care units; in 51% of persons needing assistance. Dysphagia develops in 13–57% of patients suffering from dementia, in 19–81% of patients with Parkinson's disease, in 44–60% of patients with neurodegenerative diseases. Neurogenic dysphagia occurs in 25–65% of patients after stroke, provided that mortality rates among tube-fed patients with post-stroke dysphagia vary from 20 to 24% [2, 10]. In 15–17% of cases, difficulty swallowing develops after posterior fossa brain tumor surgeries and represents one of dangerous postoperative complications. Nearly 60% of patients experience difficulty swallowing after extubation [11, 12].

**93**

*Dysphagia Associated with Neurological Disorders DOI: http://dx.doi.org/10.5772/intechopen.96165*

development of aspiration pneumonia [13].

**3. Dysphagia classification**

• neurogenic (motor, high)

• organic or mechanical

• psychogenic

• acute

• chronic

• intermittent

• persistent

(**Tables 1** and **2**).

classified into:

Dysphagia has a negative impact on the quality of life. It leads to severe respiratory complications; it becomes the cause of dehydration, metabolic disorders, and cachexia. Dysphagia increases disability, significantly worsens prognosis, and complicates patient rehabilitation. Dysphagia is a significant risk factor for the

Dysphagia is commonly divided into esophageal and oropharyngeal. Based on the functional mechanisms of disease development, dysphagia is

In addition, all types of dysphagia can be divided into:

Based on the disease course, dysphagia can be:

• progressive, with increasing clinical symptoms

In most cases, neurogenic dysphagia is oropharyngeal [14]. Neurogenic dysphagia is characterized by problems with neural control of swallowing caused by

On rare occasions, neurogenic dysphagia can be the sole manifestation. However, in most cases it is a component of bulbar or pseudobulbar palsy

Bulbar palsy occurs in case of bilateral or unilateral injury of cranial nerve nuclei IX, X, and XII and their roots. Isolated nuclear palsy is not common due to close proximity of anatomical structures of the caudal part of the medulla. Bulbar palsy elements are also included in some alternating syndromes. By its nature, bulbar palsy is peripheral paralysis of the pharynx. In addition to dysphagia, bulbar palsy is

The most common cause of neurogenic dysphagia development is a stroke [9–10, 15, 16]. Dysphagia can also occur in case of traumatic brain injury, brain tumors, encephalitis, botulism, and rabies. This type of pathology is observed at late stages of Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, other neurodegenerative diseases, severe myasthenia gravis, multiple sclerosis, Guillain–

**4. Pathogenesis of neurogenic dysphagia**

various neurological diseases.

Barré syndrome, and other disorders.

*Dysphagia Associated with Neurological Disorders DOI: http://dx.doi.org/10.5772/intechopen.96165*

Dysphagia has a negative impact on the quality of life. It leads to severe respiratory complications; it becomes the cause of dehydration, metabolic disorders, and cachexia. Dysphagia increases disability, significantly worsens prognosis, and complicates patient rehabilitation. Dysphagia is a significant risk factor for the development of aspiration pneumonia [13].
