PHYSIOLOGY OF DEGLUTITION

BY,DR. ASHWIN MENON

DEGLUTITION

Deglutition is the act of swallowing, through which a food or liquid bolus is transported from the mouth through the pharynx and esophagus into the stomach.

Normal deglutition is a smooth coordinated process that involves a complex series of voluntary and involuntary neuromuscular contractions and typically is divided into three distinct phases: Oral Pharyngeal Esophageal

ORAL PHASE

1. ORAL PREPARATORY PHASE

2. ORAL PHASE PROPER

ORAL PREPARATORY PHASE This phase is where the food is readied for swallowing

by reducing & mixing it with saliva, by the muscles of jaw and oral cavity.

Jaw is closed by jaw elevator muscles ( temporalis, masseter & medial pterygoid).

Lips maintain a seal under the action of Orbicularis oris.

Food is returned from the vestibule by contraction of buccinators.

Through out this phase, the soft palate is lowered & Ant and Post pillars approx. under the action of palatoglossus & palato pharyngeus muscles.

Thus, the oral cavity is sealed post. & the airway remains open.

Bolus is progressively accumulated on the posterior surface of the tongue, by several cycles of upward and downward movement on the tongue surface.

When the bolus consistency ( sensed by mechano-receptors in the oral cavity) is suitable for swallowing, the oral phase proper begins.

ORAL PHASE PROPER The first event is mandibular elevation

Although the mouth does not have to be completely closed, it is hard to swallow with an open mouth.

Mandibular elevation assists the suprahyoid muscles in raising the hyoid bone

Next, the tip of the tongue is elevated towards the hard palate by the action of genioglossus muscle

Blade of the tongue then moves up due to contraction of intrinsic muscles.

These movements are accompanied by lifting the floor of the mouth under the action of stylohyoid.

As the bolus reaches the back of the tongue ,the soft palate is elevated by tensor and levator veli palatini to protect the nasopharynx.

PHARYNGEAL PHASE As the bolus enters the oropharynx, it makes

contact with faucial pillars or with the mucosa overlying the posterior pharynx, the region which is sensory innervated by glossopharyngeal nerve.

Hereafter swallowing becomes reflexive

Pharyngeal phase consists of a sequence of events that ensures that the airway is protected during bolus transport.

Diaphragmatic contraction is inhibited making simultaneous breathing and swallowing impossible.

Soft palate is elevated to ensure closure of the nasopharynx.

Vocal cords start to close to protect the airway, either do the vestibular folds.

The larynx is closed by the contraction of muscles of laryngeal inlet(AEF, interarytenoid and thyro epiglottic) resembling a draw string purse.

The larynx is closed under the contraction of suprahyoid muscles, in order to narrow the laryngeal inlet and moving it towards the pharyngeal surface of epiglottis.

As the bolus moves in to oropharynx, the epiglottis moves downwards.

This downward movement occurs in 2 distinct stages.1.movement from vertical to horizontal position 2.movement from horizontal to below horizontal in order to cover the narrow laryngeal inlet.

The first epiglottis movement is passive, due to the forces generated by compression of the pre epiglottic adipose fat and ligamentous attachment of epiglottis.

The second movement occurs by a combination of passive and active(contraction of thyroepiglottic and hyoepiglottic) components.

The bolus enters the pharynx which is widened, resembling the engulfing of prey by a snake. Widening is partly due to relaxation of constrictor muscles and partly due to anterior movement. Of the pharynx under the action of suprahyoid muscles.

As the food passes over the post. Part of the epiglottis, it is diverted into the pyriform fossae. Solids tend to go straight over the epiglottis, whereas liquids are diverted laterally.

OESOPHAGEAL PHASE The crico pharyngeus muscle relaxes so the

upper oesophageal sphincter opens, bolus is passed on into & through the sphincter & oesophagus by peristalsis.

Tensor & Levator veli palatini relax, lowering the soft palate, laryngeal inlet & vestibule open-> hyoid & larynx drops -> at the very end stage of swallowing, the glottis open.

NEURAL CONTROL

Neural control of swallowing involves a number of different regions of the CNS, extending from the motor nuclei within the brainstem, up to the cortex. The act of swallowing is regulated by sensory feedback.

The initiation of swallowing can either be as a voluntary act, or a reflex as the result of stimulation of the mucosa in the oral cavity. The latter may occur during saliva accumulation or by presence of food or liquid.

Due to anatomical & physiological close relationship between swallowing, ventilation & mastication, there is extensive overlap in the brainstem areas controlling these functions.

The voluntary initiation of swallowing involves b/l areas of frontal, pre-frontal & parietal cortices. Frontal swallowing centre is associated with motor control of swallowing. This centre includes- Lower pre-central & post inferior frontal gyri

- oral phase Middle frontal & anterior inferior frontal gyri

- pharyngeal & oesophageal

Voluntary sensory control of swallowing is mediated by the parietal cortex.

Swallowing control is asymmetrical with projections from one hemisphere being larger than the other, independent of handedness.

This explains why damage to the hemisphere that is

source of greater projection to the swallowing centres in the brain stem will cause initial difficulty, and recovery the occurs as the intact projection from the undamaged hemisphere is re organized.

Descending pathways project from the frontal swallowing areas of cortex to the medullary swallowing centers within the medulla

There are a number of nucleus in the medulla ,involved in control of swallowing.

Swallowing is initiated by the touch or pressure sensation from the posterior part of the oral cavity or oropharynx.

The nuclei receiving afferent input include -Nucleus tractus solitariesSpinal trigeminal nucleus

The efferent pathways from the medulla and pons to the swallowing muscles include –

1.nucleus ambigus->for muscles of the palate, pharynx and the larynx.

2.motor nuclei of hypoglossal->tongue3.motor nuclei of trigeminal -> jaw4.motor nuclei of facial->lips

THANK YOU…

ESOPHAGEAL MANOMETRY A test to assess motor function of the upper

oesophageal sphincter (UES), oesophageal body and lower oesophageal sphincter (LES).

When does it help?

Functional disorder is suspected Unrevealing morphological studies Part of pre-operative evaluation

OESOPHAGEAL MOTILITY

All GI manometry setups consist of two hardwarecomponents: A pressure sensor/transducer, which isable to sense changes in intra luminal pressure andconvert what is detected into an electrical signal. A recording device that amplifies the signal and stores it.

Two types of sensing/transducer devices are currentlyused for oesophageal manometry- water-perfused catheters coupled to volume-displacement

transducers. solid-state strain gauge transducers

WATER-PERFUSED CATHETERS COUPLED TO VOLUME-DISPLACEMENTTRANSDUCERS This type of catheter comprises a bundle of thin plastic tubes

each with an outward facing side-hole. There are typically 3-8pressure-sensing side holes spaced along the length of the

catheter and radially orientated, thereby allowing simultaneous measurement of pressures at multiple locations. The

tubes are continuously perfused with bubble-free water as anon-compressible medium and the pressure in each tube is

monitored by a volume-displacement transducer. Water flowthrough the side holes is impeded by oesophageal contraction

WATER PERFUSED SYSTEM

SOLID-STATE STRAIN GAUGES This type of catheter is composed of a linear arrangement of

miniature, solid-state strain gauges spatially and radially orientated along a flexible tube. The signal from each straingauge provides a direct measure of intra luminal pressure.

These catheters are technically easier to use and less cumbersome than traditional water-perfused systems, but are more

expensive both to buy and repair. There have been no studiesto compare the relative running costs of the two alternative

systems. Absolute pressure values and normal rangesobtained with water-perfused versus solid state systems arenot identical and the choice of laboratory reference range

should reflect the type of catheter assembly

SOLID STATE CATHETERS

HIGH RESOLUTION MANOMETRY (HRM)

Miniaturisation of solid state pressure sensors has allowed the

development of high resolution manometry (HRM), employing catheters with multiple sensors (up to 36)

distributedlongitudinally and radially.(3,4) This allows topographical

analyses with the generation of 2- and 3-dimensional contour

plots based on simultaneous pressure readings taken at multiple sensors within the sphincters and oesophageal

body.These catheters have the potential to reduce the need for

repositioning, thereby shortening the duration of the procedure.

Simultaneous assessment of sphincters and body with a single series of swallows is possible with the catheter in a single, fixed position. The increased resolution and better radial information promised by HRM should reduce the problems of asymmetry and artefact inherent in existing systems.(3,4).

This type of equipment is not widely available in the UK and the present guidance relates to traditional water-perfused and solid state catheters

INDICATIONS FOR OESOPHAGEALMANOMETRY

1) To diagnose suspected primary oesophageal motilitydisorders (eg. achalasia and diffuse oesophageal spasm)

2) To diagnose suspected secondary oesophageal motilitydisorders occurring in association with systemicdiseases (eg. systemic sclerosis)

3) To guide the accurate placement of pH electrodes forambulatory pH monitoring studies.

(B) Equipment preparation (1) Calibrate the equipment and document it

on recording (2) Record the catheter type and

configuration (3) Check to assure functioning of the

recording device prior to intubation (a) Are the recording devices turned on? (b) Are all of the appropriate connections

made and documented?

4) As part of the pre-operative assessment of somepatients undergoing anti-reflux procedures.

5) To reassess oesophageal function in patients who have been treated for a primary oesophageal disorder (eg. sub-optimal clinical response to pneumatic balloon dilatation) or undergone anti-reflux surgery (eg. dysphagia following fundoplication).

OUTLINE OF COMPONENTS OF OESOPHAGEAL MANOMETRY

(A) Patient preparation(1) (NPO) >4–6h(2) Ideally, the patient should be off all

medications that may affect oesophageal motor function for 24 h (b-adrenergic antagonists, nitrates, calcium-channel antagonists, anti cholinergic agents, prokinetic agents, nicotine, narcotics and caffeine)

(3) Make a record of medications that the patient is using complete the study. The use of sedation should be documented

(4) Sedation should be used as part of the patient preparation for oesophageal manometry only if it is absolutely needed to

(5) Local anaesthesia may or may not be used. Its use should be documented

(6) Accurate detection of swallowing is desirable, and can be achieved by concurrent, online, intra luminal recording of swallowing

(7) A respiratory monitor is helpful but optional. It allows reliable identification of respiratory artefact

(C) Performing the study(1) The manometry catheter may be placed via the nares

or mouth –document method. Trans-nasal placement of the manometry probe should be used if trans-nasal placement of a pH probe will be carried out subsequently.

(2) The patient should be in the recumbent position after the catheter is passed.

(3) Wait 5–10 min to allow the patient to accommodate to the catheter and the solid-state sensors to reach body temperature

(4) If a perfused catheter system is being used, the patient should be placed so that all of the pressure transducers are at the same level as the mid-axillary line of the recumbent patient

(5) At least the most distal (preferably three of the most distal) recording site(s) should be in the stomach and their intragastric(subdiaphragmatic) location verified. If a Dent sleeve catheter is being used, the sleeve and the recording port just above it should be positioned in the stomach

6) Identification of the high-pressure zone. This part of the study is performed as the catheter is withdrawn in a stepwise fashion,

thestation pull-through technique(Fig. 7). (a) The station pull-through is performed by pulling the catheter

back in 0.5–1.0 cm steps (b) The distances of the recording sites from the incisors or

nares should be documented on the recording as the station pullthrough is being accomplished

(c) At each step swallows and deep inspirations can be used to identify the lower oesophageal sphincter (LES)

(d) The high-pressure zone (HPZ) (Fig. 7) (i) Record the distance of the HPZ from the incisors or nares (ii) The length of the high-pressure zone can be measured (e) The pressure inversion point(PIP) –the location at which

pressure converts from positive to negative deflection on inspiration

(7) The LES –a zone of high pressure at the gastroesophageal junction that normally relaxes with swallowing

(a) Measure LES resting pressure; position the recording port(s) or Dent sleeve within the HPZ and record the mean baseline

LES pressure (i) LES pressure ¼pressure of HPZ)gastric pressure (ii) It is best if pressures in the HPZ and stomach are recorded

simultaneously at least in two sensors or two passes with one sensor (b) Examine LES relaxation (i) Use at least five wet swallows of‡3 cc (preferably 5 cc) of water

at room temperature (ii) At least 20 s should elapse between swallows (iii) Measure the residual LES pressure relative to intragastric

pressure–the minimum LES pressure during LES relaxation produced by swallowing (iv) Recognize pressure overshoot after LES relaxation

(8) The oesophageal body (a) ‡3 pressure sensors positioned 3–5 cm

apart should be located above the LES (b) Both the distal (lower) and proximal (upper)

oesophageal body regions should be examined (c) At least 10 wet swallows should be

performed in the lower and upper oesophagus (d) Swallows should occur at intervals 20–30 s (e) If no peristalsis is seen, have the patient

cough to check the sensors

(9) The upper oesophageal sphincter–measurement of the motor activity of the UES is not part of the minimal study but may be

useful when disorders of the striated muscle segment are possible.

(a) Identify a region of increased resting pressure in the upper oesophagus that relaxes with swallowing

(b) Verify relaxation subjectively (c) Document the position from the nares or

incisors

CLASSIFICATION OF PRIMARY OESOPHAGEALMOTILITY DISORDERS

• Inadequate LOS relaxation Achalasia Atypical disorders of LOS relaxation

• Uncoordinated contraction Diffuse oesophageal spasm

• Hypertensive contraction Nutcracker oesophagus Hypertensive LOS

• Hypotensive contraction Ineffective oesophageal motility Hypotensive LO

COMPLICATIONS