Sensory Aspects of Respiratory Disease

Question 1

Physiologic or Pathological stimulus leading to conscious sensation

Sensory stimulation (e.g. pain from a cut in the skin) activates a sensory …………….. which transmits the signal via excitation of sensory ………….. which lead onto afferent nerves going to the …………

The CNS creates a sensory ………………….. -NEUROPHYSIOLOGY

This sensory impression then leads to the perception of the information

The brain interprets the information coming from the sensory nerves and this evokes a ‘sensation’ - this is ……………………….. PSYCHOLOGY

People react differently to different sensations

Answer 1

Physiologic or Pathological stimulus leading to conscious sensation

Sensory stimulation (e.g. pain from a cut in the skin) activates a sensory transducer which transmits the signal via excitation of sensory nerves which lead onto afferent nerves going to the CNS

The CNS creates a sensory impression -NEUROPHYSIOLOGY

This sensory impression then leads to the perception of the information

The brain interprets the information coming from the sensory nerves and this evokes a ‘sensation’ - this is BEHAVIOURAL PSYCHOLOGY

People react differently to different sensations

Question 2

Cough

A CRUCIAL ……………… MECHANISM protecting the lower respiratory tract from:

Inhaled foreign material

Excessive mucous secretion

Usually secondary to ………………. clearance

Particularly important in lung disease where mucociliary function is impaired and mucous production is increased

Expulsive phase of cough

Once the mucus gets to the large airways it ……………… the cough mechanism

Generates …………… velocity airflow

Expels the mucus or ………………. material

This is facilitated by mucus secretion and ……………………………

Answer 2

Cough

A CRUCIAL DEFENCE MECHANISM protecting the lower respiratory tract from:

Inhaled foreign material

Excessive mucous secretion

Usually secondary to mucociliary clearance

Particularly important in lung disease where mucociliary function is impaired and mucous production is increased

Expulsive phase of cough

Once the mucus gets to the large airways it stimulates the cough mechanism

Generates high velocity airflow

Expels the mucus or foreign material

This is facilitated by mucus secretion and bronchoconstriction

Question 3

Answer 3

Nerve Profiles in Airways

Image on the left shows a nerve terminal on the surface of the epithelium

It is well placed to sense the external environment (e.g. by mechanical stimulation of the nerve terminal by dust)

This nerve terminal could respond by triggering a cough

Question 4

Localisation of Cough Receptors

Rapidly adapting irritant receptors found within the …………………. epithelium

They are MOST NUMEROUS on the ……………… WALL of the trachea

They are also found at the main ………………..

Less numerous in more ………….. airways

ABSENT beyond the ………………….

Cough receptors are found MAINLY IN THE ………………. AIRWAYS

Commonly found at ……………… points of large airways

Cough receptors are also found in the larynx, pharynx and the external auditory meatus

Can also be found in the diaphragm, pleura, pericardium and stomach

Answer 4

Localisation of Cough Receptors

Rapidly adapting irritant receptors found within the airway epithelium

They are MOST NUMEROUS on the POSTERIOR WALL of the trachea

They are also found at the main carina

Less numerous in more distal airways

ABSENT beyond the bronchioles

Cough receptors are found MAINLY IN THE PROXIMAL AIRWAYS

Commonly found at branching points of large airways

Cough receptors are also found in the larynx, pharynx and the external auditory meatus

Can also be found in the diaphragm, pleura, pericardium and stomach

Question 5

Sensory Receptors in the Lungs and Airways

Can be divided into THREE main types:

list them

Answer 5

Sensory Receptors in the Lungs and Airways

Can be divided into THREE main types:

SLOW adapting stretch receptors

RAPIDLY adapting stretch receptors

C-fibre receptors

Question 6

C-fibre receptors

Name 4 places where they are located?

Are they myelinated or unmyelinated?

What do they respond to?

List 3 things they release?

Answer 6

C-fibre receptors

Free nerve endings

Present in the upper airways - larynx, trachea, bronchi and lungs

They are small UNMYELINATED fibres - so conduction is SLOW

Responds to chemical irritant stimuli and inflammatory mediators - C FOR CHEMICAL

Release neuropeptide inflammatory mediators:

Substance P

Neurokinin A

Calcitonin Gene Related Peptide

Question 7

Rapidly adapting stretch receptors

Are they myelinated or unmyelinated?

List 4 Places where they are found?

List 3 thing that stimulate these receptors?

Answer 7

Rapidly adapting stretch receptors

MYELINATED - so conduct very quickly

Present in the naso-pharynx, larynx, trachea and bronchi

Mechanical, chemical irritant stimuli, inflammatory mediators

If you stimulate them with hyperinflation there is a rapid response (rapid silencing of the receptor)

Question 8

Slowly adapting stretch receptors

Where are they located?

Are they myelinated?

Predominantly in the ………….. and …………. ……………….

Slowly and rapidly adapting stretch receptors are ………………………………….

They respond to lung ………………………..

Answer 8

Slowly adapting stretch receptors

Located in airway smooth muscle

Also MYELINATED - so conduct very quickly

Predominantly in the trachea and main bronchi

Slowly and rapidly adapting stretch receptors are mechanoreceptors

They respond to lung inflation

Question 9

Sensory Receptors in the Lungs and Airways

This is a recording from airway vagal afferent nerves in an experiment using anaesthetised rats

The vagus is the 10th Cranial Nerve through which ALL sensory nerves from the airways pass through to the brain

The above image shows measurements of the action potential, tracheal pressure (P) and arterial blood pressure (ABP)

Caspaicin has been given which is a stimulus to the sensory nerves

C-fibres are stimulated by CHEMICALS

The C-fibre is stimulated when the caspaicin is injected intravenously

The caspaicin has NO EFFECT on the rapidly and slow adapting stretch receptors

The MAIN STIMULUS for the rapidly and slow adapting stretch receptors is INFLATION

INCREASE in tracheal pressure = rapidly adapting stretch receptors STOP firing + slow adapting stretch receptors are STIMULATED to fire

These receptors are most likely to be involved in coughing

Answer 9

Sensory Receptors in the Lungs and Airways

This is a recording from airway vagal afferent nerves in an experiment using anaesthetised rats

The vagus is the 10th Cranial Nerve through which ALL sensory nerves from the airways pass through to the brain

The above image shows measurements of the action potential, tracheal pressure (P) and arterial blood pressure (ABP)

Caspaicin has been given which is a stimulus to the sensory nerves

C-fibres are stimulated by CHEMICALS

The C-fibre is stimulated when the caspaicin is injected intravenously

The caspaicin has NO EFFECT on the rapidly and slow adapting stretch receptors

The MAIN STIMULUS for the rapidly and slow adapting stretch receptors is INFLATION

INCREASE in tracheal pressure = rapidly adapting stretch receptors STOP firing + slow adapting stretch receptors are STIMULATED to fire

These receptors are most likely to be involved in coughing

Question 10

There are TWO types of sensors that will lead to cough: name them

Answer 10

Vagal Afferent Innervation of Guinea Pig Trachea

There are TWO types of sensors that will lead to cough: Mechanoreceptors and Nociceptors

MECHANOSENSORS are activated by:

Mechanical Displacement

CITRIC ACID

NOCICEPTORS are activated by:

Caspaicin

Bradykinin

Citric Acid

Cinnamaldehyde

Mechanosensors look a bit like a tree

TRPV1, TRPA1 and B2 are present on nociceptors

Question 11

Afferent Neural Pathways for Cough

Stimulation of mechanical or chemical receptors leads to impulses going up the …………… nerve, through the ………………….. to the ……………….. centre

Some signal goes to the ………………… ……………………

Answer 11

Afferent Neural Pathways for Cough

Stimulation of mechanical or chemical receptors leads to impulses going up the vagus nerve, through the brainstem to the cough centre

Some signal goes to the cerebral cortex

Question 12

Efferent Neural Pathways for Cough

The efferent pathways involve the stimulation of various muscles leading to the closure of the ………….. and the production of sound

Answer 12

Efferent Neural Pathways for Cough

The efferent pathways involve the stimulation of various muscles leading to the closure of the glottis and the production of sound

Question 13

Mechanics of Cough

There are THREE main phases:

List them

The …………….. phase opens up the trachea

During the act of coughing there is an ……………… in intrapulmonary pressure that compresses the ………………… membrane of the trachea which pushes through and narrows the trachea into a ……………….. shape

This increases flow and contributes to the sound produced

Answer 13

Mechanics of Cough

There are THREE main phases:

Inspiratory Phase

Glottic Closure

Expiratory Phase

The inspiratory phase opens up the trachea

The inspiratory phase opens up the trachea

During the act of coughing there is an increase in intrapulmonary pressure that compresses the posterior membrane of the trachea which pushes through and narrows the trachea into a crescent shape

This increases flow and contributes to the sound produced

Question 14

The Complete Cough Pathway

Sensory information goes via the …………… nerve and through the ……………….. to the …………… centre

The ………………. centre consists of the ……………… ………………. …………….. - a collection of neurons that are connected to the ……………….. ………………….. ………………. …………………….

The reflex is probably a …………………. reflex

From the ………………. …………….. ………………… ……………….. you get stimulation of various muscles needed to produce the cough

The complete cough pathways also includes the ……………… ………………….

When you go to SLEEP, this reflex is ………………….. so you need to be awake to a certain extent to be able to cough

Under general anaesthetic this is also suppressed

Answer 14

The Complete Cough Pathway

Sensory information goes via the vagus nerve and through the brainstem to the cough centre

The cough centre consists of the nucleus tractus solitarius - a collection of neurons that are connected to the medullary cough pattern generator

The reflex is probably a brainstem reflex

From the medullary cough pattern generator you get stimulation of various muscles needed to produce the cough

The complete cough pathways also includes the cerebral cortex

When you go to SLEEP, this reflex is INHIBITED so you need to be awake to a certain extent to be able to cough

Under general anaesthetic this is also suppressed

Question 15

Common Causes of Cough

Answer 15

Question 16

ACUTE Cough (<3 weeks)

The most common cause of a cough is an acute cough caused by ……………..

By ……………. weeks most people would have lost their symptoms

Answer 16

ACUTE Cough (<3 weeks)

The most common cause of a cough is an acute cough caused by rhinovirus

By two weeks most people would have lost their symptoms

Question 17

What makes a cough chronic?

Answer 17

CHRONIC Persistent Cough (>3 weeks)

Causes in order of frequency:

Asthma and eosinophilic-associated - 25%

Gastro-oesophageal reflux - 25%

Rhinosinusitis (post-nasal drip) - 20%

Chronic Bronchitis - 8%

Bronchiectasis - 5%

Drugs (e.g. ACE inhibitors) - 1%

Post-viral - 3%

Idiopathic - 10%

Other causes - 3%

When there is an infection, the mucus might change colour and become yellowish

Gastro-oesophageal reflux - the protons coming up from the stomach can activate the cough receptors which, in turn, activate brainstem cough receptors

Question 18

Chronic Cough: Indication of Increased Cough Reflex

Also known as …………….. ………………. …………………….

Cough paroxysms that are difficult to control (not just throat clearing)

Triggers include: deep breath, laughing, talking too much, vigorous exercise, smells, cigarette smoke, eating crumbs, cold air, changing temperatures, lying flat

Sensitivity of the cough reflex can be measured using ……………….

………………… is the thing in chilies that give them their hotness

You initially give a dilute solution of caspaicin and then increase the concentration until the participant coughs

Chronic coughers are particularly sensitive to caspaicin

Caspaicin an activate ……………………. through ………………… receptors

Answer 18

Chronic Cough: Indication of Increased Cough Reflex

Also known as Cough Hypersensitivity Syndrome

Cough paroxysms that are difficult to control (not just throat clearing)

Triggers include: deep breath, laughing, talking too much, vigorous exercise, smells, cigarette smoke, eating crumbs, cold air, changing temperatures, lying flat

Sensitivity of the cough reflex can be measured using caspaicin

Caspaicin is the thing in chilies that give them their hotness

You initially give a dilute solution of caspaicin and then increase the concentration until the participant coughs

Chronic coughers are particularly sensitive to caspaicin

Caspaicin an activate nociceptors through TRPV1 receptors

Question 19

Plasticity of neural mechanisms

This is the mechanism by which you get hypersensitivity

List 4 mechanisms

Answer 19

Plasticity of neural mechanisms

This is the mechanism by which you get hypersensitivity

Increased excitability of the afferent nerves by chemical mediators e.g. prostaglandin E2

Increase in receptor numbers e.g. TRPV1

Increase in neurotransmitter in the brainstem e.g. neurokinins

There may also be an increase in inflammatory mediators, which damage or change the reactivity of the nerves to various stimuli like caspaicin

Question 20

Answer 20

this diagram shows that smooth muscle hypertrophy in asthma could affect the slowly adapting receptors that could contribute to enhanced hypersensitivity

Question 21

Current Antitussives

If you are coughing excessively then you might want to suppress it but not completely eliminate the cough response because then you’d be getting rid of its defensive capabilities

Opiates can act as an antitussive but they are not particularly effective as they work at doses where there are a lot of side-effects (e.g. morphine and codeine)

Answer 21

Question 22

Which of the following is insensitive to pain: parietal or visceral plueral?

Answer 22

Visceral pluera

The patient would not feel pain from inflammation of the visceral pleura because it is insensitive to pain – its afferent fibers relay stretch sensations only. However, the parietal pleura is very sensitive to pain due to the somatic afferent fibers that innervate it.

Question 23

What nerve supplies the Nose, Pharynx, larync, Lungs, Chest wall?

Answer 23

Question 24

Anatomical Pathways of Touch and Pain

We need to distinguish between touch and pain because the anatomical pathways are slightly different, as are the sensory receptors

Touch travels via ……………. and …………… fibres via the …………….. …………..

The MAIN DIFFERENCE between the two pathways is really at ……………………………………………………………………………………………………………

TOUCH - goes to the …………………. …………….. at the level of the ……………….. ………………… (……………..)

EXAMPLE: the sensation of touch from the leg will run up along the same side as the leg it is coming from and then cross onto the other side at the brainstem

PAIN - goes to the ………………. ……………… at the ………… anatomical level (it crosses right away)

Both touch and pain information goes to the ………….. ………………. ………………

CLINICAL IMPORTANCE: …………………-……………….. Syndrome (hemisection of the spinal cord)

If you have hemisection on the LEFT SIDE of the spinal cord, the …………. sensation will be fine on the opposite side but the …………… sensation on the other side will be affected

Answer 24

Anatomical Pathways of Touch and Pain

We need to distinguish between touch and pain because the anatomical pathways are slightly different, as are the sensory receptors

Touch travels via Aalpha and Abeta fibres via the dorsal horn

The MAIN DIFFERENCE between the two pathways is really at the level at which the pathways cross through to the contralateral side

TOUCH - goes to the contralateral side at the level of the caudal medulla (brainstem)

EXAMPLE: the sensation of touch from the leg will run up along the same side as the leg it is coming from and then cross onto the other side at the brainstem

PAIN - goes to the contralateral side at the same anatomical level (it crosses right away)

Both touch and pain information goes to the primary somatosensory cortex

CLINICAL IMPORTANCE: Brown-Sequard Syndrome (hemisection of the spinal cord)

If you have hemisection on the LEFT SIDE of the spinal cord, the touch sensation will be fine on the opposite side but the pain sensation on the other side will be affected

Question 25

Different types of pain: somatic vs visceral

–Visceral pain (from visceral organs eg heart, gi tract, bronchial wall) is not the same as somatic pain (from skin).

–Visceral pain is difficult to localise( patients find it hard to distinguish pain from left lung or right lung), diffuse in character and is referred to somatic structures.

–Number of visceral afferents is ……….. than number of somatic afferents

–Pain arising from various viscera in the thoracic cavity and from the chest wall is often qualitatively similar and exhibits overlapping patterns of referral, localisation and quality, leading to difficulties in diagnosis.

Answer 25

Different types of pain: somatic vs visceral

–Visceral pain (from visceral organs eg heart, gi tract, bronchial wall) is not the same as somatic pain (from skin).

–Visceral pain is difficult to localise( patients find it hard to distinguish pain from left lung or right lung), diffuse in character and is referred to somatic structures.

–Number of visceral afferents is less than number of somatic afferents

–Pain arising from various viscera in the thoracic cavity and from the chest wall is often qualitatively similar and exhibits overlapping patterns of referral, localisation and quality, leading to difficulties in diagnosis.

Question 26

Different Types of Pain: Somatic and Visceral

NOTE: there is also a third type of pain called ……………….

Visceral pain comes from the ……………. (internal organs)

This is NOT the same as somatic (which comes from the skin and subcutaneous tissue)

Somatic is VERY ……………. - we know exactly where the pain is coming from

Visceral is ……………. to localise, diffuse in character and is referred to somatic structures

The number of visceral afferents is FEWER than the number of somatic afferents

Pain arising from various viscera in the thoracic cavity and from the chest wall is often qualitatively similar and exhibits overlapping patterns of referral, localisation and quality leading to difficulties in diagnosis

Answer 26

Different Types of Pain: Somatic and Visceral

NOTE: there is also a third type of pain called neuropathic

Visceral pain comes from the viscera (internal organs)

This is NOT the same as somatic (which comes from the skin and subcutaneous tissue)

Somatic is VERY localised - we know exactly where the pain is coming from

Visceral is DIFFICULT to localise, diffuse in character and is referred to somatic structures

The number of visceral afferents is FEWER than the number of somatic afferents

Pain arising from various viscera in the thoracic cavity and from the chest wall is often qualitatively similar and exhibits overlapping patterns of referral, localisation and quality leading to difficulties in diagnosis

Question 27

Chest pain from non-respiratory disorders

Cardiovascular Disorders:

Myocardial ischaemia/infarction

Pericarditis

Dissecting aneurysm

Aortic valve disease

Gastrointestinal Disorders:

Oesophageal rupture

Gastro-oesophageal reflux

Cholecystitis

Pancreatitis

Psychiatric Disorders:

Panic disorder

Self-inflicted

Answer 27

Question 28

What is dyspnea or shortness of breath?

Answer 28

• Troublesome shortness of breath reported by a patient
• Occurs at inappropriately low levels of exertion, and limits exercise tolerance
• Unpleasant and frightening experience. Can be associated with feelings of impending suffocation
• Poor perception of respiratory symptoms and dyspnea may be life-threatening

Question 29

Clinical Dyspnoea Scale (American Thoracic Society)

Answer 29

Question 30

Answer 30

Question 31

Answer 31