Detailed Study Notes on Swallowing Phases

Overview of Swallowing Phases

• Swallowing involves multiple distinct phases, commonly categorized as:

  • Oral Prep

  • Oral Transport

  • Pharyngeal

  • Esophageal

• Terminology may vary; sometimes referred to as:

  • Oral Prep and Oral Transport vs. Oral Pharyngeal and Esophageal

• Importance of differentiating these stages in clinical settings, such as:

  • Pediatric feeding

  • Nursing homes

  • Head and neck cancer rehabilitation

Importance of Phases

• Oral Preparation vs. Oral Transport:

  • Distinction made for patients with conditions affecting swallowing, such as:

  • Head and neck cancer

  • Cognitive deficits

  • Loss of teeth

• Laryngeal Phase:

  • Not considered a stage of swallowing; food should not enter the laryngeal area.

  • Aspiration represents an abnormality, not a normal stage of swallowing.

Phases of Swallowing

1. Oral Prep Phase

• Function: Prepare food for swallowing.

• Muscle Control:

  • Mandibular Depressors - Open the jaw (pulling down).

  • Tongue positions:

  • Tip is up to block the larynx.

  • Back part of the tongue against the velum to prevent food from entering the pharynx.

• Chewing Mechanics:

  • Maintenance of tone in buccal (cheek) muscles to prevent spillage.

• Bolus Formation:

  • The bolus is held anteriorly and laterally by the tongue against the hard palate.

  • Velum (soft palate) is forward against the back of the tongue to maintain closure.

• Voluntary Control:

  • The oral prep phase is under voluntary control and can be bypassed.

2. Oral Transport Phase

• Function: Move bolus to the back of the throat.

• Tongue Action:

  • Moves the food from anterior to posterior in a rolling or stripping motion.

  • Tongue position changes as it prepares to transport the bolus to the pharynx.

• Transition Trigger:

  • Oral phase transitions to pharyngeal when the bolus passes the anterior facial arches or the ramus of the mandible.

• Velum moves up and back to prevent nasal entry.

• Some voluntary control persists until the bolus is near the back of the throat.

3. Pharyngeal Phase

• Importance: This phase requires utmost coordination and involves the greatest risk for aspiration.

• Muscle Coordination:

  • The base of the tongue drops, creating pressure to push the bolus down.

  • The epiglottis inverts to protect the airway.

  • Upper esophageal sphincter (cricopharyngeus) relaxes to allow passage into the esophagus.

  • Timing: The pharyngeal swallow takes approximately 0.8 seconds.

  • Involuntary once initiated.

• Aspiration vs. Obstruction:

  • Aspiration: Inhalation of food or liquid past the vocal folds.

  • Obstruction: Physical blockage preventing airflow or food passage.

4. Esophageal Phase

• Initiation follows the food's passage through the upper esophageal sphincter.

• Control Mechanisms:

  • The esophagus is pulled open by muscular contractions rather than pushed.

• Involuntary control; person cannot consciously affect this process.

Key Concepts for Clinical Application

• Muscle Groups Used in Swallowing:

  • Approximately 36 muscles contribute to swallowing, paired on left and right sides.

• Reflex vs. Response:

  • Swallowing is a response to stimuli (e.g., saliva, food) rather than a reflex.

• Aspiration and Aspiration Pneumonia:

  • Aspiration can lead to pneumonia, particularly with poor chewing techniques or large food pieces.

Practical Applications in Patient Care

• Utilize awareness of the phases in assessing and treating swallowing disorders.

• Tailor interventions to individual patient needs, understanding their physical and cognitive abilities.

Summary and Takeaways

• Mastering the phases of swallowing provides the groundwork for identifying and treating dysphagia.

• Knowledge is crucial for understanding developmental stages in pediatric feeding and adjustments required for aging adults.

• Developing a comprehensive understanding of normal swallowing is fundamental for effective clinical practice in dysphagia management.

Overview of Swallowing Phases

• Swallowing, or deglutition, is a complex sensorimotor act involving the coordinated contraction and inhibition of approximately $36$ pairs of muscles. It is typically divided into four distinct stages:

  • Oral Preparatory Phase (Voluntary)

  • Oral Transport Phase (Voluntary)

  • Pharyngeal Phase (Involuntary)

  • Esophageal Phase (Involuntary)

  • Clinical Significance: Precision in identifying the affected phase is critical for diagnosing and treating dysphagia. Mismanagement can lead to severe complications such as malnutrition, dehydration, and aspiration pneumonia.

Detailed Analysis of Phases

1. Oral Preparatory Phase

• Function: The mechanical and chemical breakdown of food to form a cohesive bolus suitable for transport.

• Muscle and Nerve Coordination:

  • Lip Seal: The orbicularis oris muscle (CN $VII$) maintains a tight seal to prevent anterior spillage.

  • Mastication: Revolves around the lateral and vertical movement of the mandible, controlled by the muscles of mastication (masseter, temporalis, pterygoids; CN $V$).

  • Buccal Tone: Muscles in the cheeks (buccinator and risorius) prevent food from accumulating in the lateral sulci.

  • Tongue Control: The tongue manipulates the food, mixing it with saliva (containing salivary amylase) to initiate digestion and create the bolus.

• Protective Positioning: The back of the tongue remains elevated against the velum (soft palate) to prevent the premature entry of liquid or food into the pharynx before the swallow response is triggered.

2. Oral Transport Phase

• Function: Movement of the bolus from the anterior oral cavity to the posterior region for delivery into the pharynx.

• Mechanisms:

  • Stripping Action: The tongue tip elevates to the alveolar ridge while the body of the tongue performs a rolling, posterior-directed motion against the hard palate.

  • Duration: This phase generally lasts approximately $1$ to $1.5$ seconds.

• Pharyngeal Trigger point: The transition occurs when the bolus head passes the anterior faucial arches (or the ramus of the mandible in older adults). This tactile stimulation sends sensory information via CN $IX$ and $X$ to the medulla (deglutition center).

3. Pharyngeal Phase

• Function: The rapid, involuntary passage of the bolus through the pharynx into the esophagus while protecting the airway.

• Critical Physiological Events:

  1. Velopharyngeal Closure: The soft palate (velum) elevates and retracts to seal off the nasopharynx.

  2. Hyolaryngeal Elevation: The hyoid bone and larynx move superiorly and anteriorly. This movement helps open the Upper Esophageal Sphincter (UES) and tilts the epiglottis downward.

  3. Airway Protection: Occurs at three levels:

     • Inversion of the epiglottis over the laryngeal vestibule.

     • Adduction of the false vocal folds.

     • Adduction of the true vocal folds (the primary defense).

  4. Pharyngeal Peristalsis: Progressive contraction of the superior, middle, and inferior pharyngeal constrictors.

• Timing: This phase is extremely fast, taking roughly $0.8$ to $1.0$ second.

4. Esophageal Phase

• Function: Transportation of the bolus through the esophagus to the stomach via peristaltic waves.

• Dynamics:

  • Peristalsis: Sequential muscular contractions that move the bolus downward. Primary peristalsis is triggered by the swallow; secondary peristalsis is triggered by local distension within the esophagus.

  • LES Relaxation: The Lower Esophageal Sphincter relaxes to allow the bolus to enter the stomach and then closes to prevent Gastroesophageal Reflux (GERD).

• Duration: This is the slowest phase, lasting between $8$ and $20$ seconds.

Key Concepts for Clinical Application

• Aspiration vs. Penetration:

  • Penetration: Material enters the laryngeal vestibule but remains above the level of the true vocal folds.

  • Aspiration: Material passes below the level of the true vocal folds into the trachea.

• Reflex vs. Patterned Response: While often called a "reflex," swallowing is more accurately described as a programmed sensory-motor response because it requires a stimulus (bolus/saliva) to initiate and can be modulated by cortical input.

• Safety Mechanisms: The temporary cessation of breathing during the swallow is known as the "swallowing apnea," which typically occurs during the expiratory phase of the respiratory cycle to further protect the airway.