Sensory aspects of respiratory disease

Question 1

what is a symptom?

Answer 1

An abnormal or worrying sensation that leads the person to seek medical attention

Question 2

Describe the pathway from stimulus to evoked sensation? What are the names for the two main parts of this?

Answer 2

Stimulus - transducer - excitation of sensory nerves - integration of CNS - sensory impression
This is NEUROPHYSIOLOGY

Sensory impression - perception - evoked sensation
This is BEHAVIOURAL PSYCHOLOGY

1. Neurophysiology
   - 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
2. Behavioural psychology
   - The CNS creates a sensory impression
   - 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

Question 3

why do we cough?

Answer 3

It is a crucial defence mechanism protecting lower respiratory tract from:

• inhaled foreign material
• excessive mucous secretion

Question 4

what is usually the primary defence mechanism against lower respiratory infections?

Answer 4

-Mucociliary clearance

Question 5

how does cough expel foreign material and what else is also involved?

Answer 5

1. Once the mucus gets to the large airways it stimulates the cough mechanism
2. Generates high-velocity airflow
3. Expels the mucus or foreign material
4. This is facilitated by mucus secretion and bronchoconstriction

Question 6

Describe the distribution of rapidly adapting irritant receptors within the airway epithelium.

Answer 6

• Rapidly adapting irritant receptors which are located within airway
  epithelium.
• Most numerous on posterior wall of trachea, at main carina, and branching points of large airways, less numerous in more distal airways.
• Absent beyond the respiratory bronchioles.
• Possibly also in the external auditory meatus, eardrums, paranasal sinuses, pharynx, diaphragm, pleura, pericardium, and stomach
  They are also found in the diaphragm, pleura, pericardium and stomach.

Question 7

What are the three main types of sensory receptors in the lungs and airways?

Answer 7

C-fibre receptor
Slow adapting stretch receptors
Rapidly adapting stretch receptors

Question 8

which cranial nerve does the vagus come from and what comes from this?

Answer 8

It is the 10th cranial nerve.

-all sensory nerves from the airways pass through to the brain.

Question 9

Which nerve do all the sensory receptors in the lungs and airways pass through?

Answer 9

Vagus nerve

Question 10

What is used as a stimulus for the C-fibres?

what is a stimulus to the sensory nerves?

Answer 10

Caspaicin

Question 11

What stimulates C-fibres?

Answer 11

Chemicals

Question 12

describe the process in which the c-fibre is stimulated?

Answer 12

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

Question 13

what effect does caspaicin have on the rapidly and slow adapting stretch receptors

Answer 13

NO EFFECT

Question 14

What do the rapidly and slowly adapting stretch receptors respond to?

Answer 14

Inflation (increase in tracheal pressure)

Question 15

Describe the differences between the three types of sensory receptor.

Answer 15

C-fibre receptors:
-Unmyelinated fibres so conduction is slow
-responds to chemical irritant stimuli and inflammatory mediators
Sensitive to chemical irritant stimuli, inflammatory mediators and capsaicin
- Free nerve endings
-C-fibres are found in the larynx, trachea, bronchi and lungs
-release neuropeptide inflammatory mediators:
-Substance P
-Neurokinin A
-Calcitonin Gene Related Peptide

Rapidly adapting stretch receptors are found in the naso-pharynx, larynx, trachea and bronchi.
-if stimulate them with hyperinflation there is a rapid response (rapid silencing of the receptor)
Mechanical, chemical irritant stimuli, inflammatory mediators
*can respond to chemical stimuli but does not involve TRPV1 channels

Slowly adapting stretch receptors are located on airway smooth muscle, mainly in the trachea and main bronchi. Respond to lung inflation.
Slowly adapting stretch receptors are mechanoreceptors - respond to lung inflation

Both are myelinated.

Question 16

What are the two broad types of sensory receptor in the airways that lead to cough?

Answer 16

1. Mechanoreceptor/sensor (mechanical displacement, citric acid)
2. Nociceptors (caspaicin, bradykinin, citric acid, cinnamaldehyde)

• (these are the two types of sensors that will lead to cough)
• Mechanosensors look a bit like a tree
• TRPV1, TRPA1 and B2 are present on nociceptors

Question 17

what activates the mechanoreceptors and what do they look like?

Answer 17

• Citric acid
• mechanical displacement

Looks like a tree
TRPV1, TRPA1 and B2 are present on nociceptors

Question 18

what are nociceptors activated by?

Answer 18

• Caspaicin
• Bradykinin
• Citric Acid
• Cinnamaldehyde

Question 19

What is the collection of neurons in the cough centre called?

Answer 19

Nucleus tractus solitarius

Question 20

What is the role of the cerebral cortex in the complete cough pathway?

Answer 20

The cerebral cortex is needed to generate a cough and generate the urge to cough. When asleep, this component of the complete cough pathway is inhibited so a certain degree of wakefulness is needed to cough. General anaesthetic also inhibits this.

Question 21

describe the complete cough pathway?

Answer 21

• sensory information goes via the vagus nerve and through the brain-stem 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 pathway also included the cerebral cortex

Question 22

what is the afferent and efferent pathway?

Answer 22

Afferent:

• Stimulation of mechanical or chemical receptors leads to impulses going up the vagus nerve (and superior laryngeal nerve), through the brainstem to the cough centre in the medulla oblongata
• Some signal goes to the cerebral cortex

Efferent neural pathways for cough;
-the efferent pathway involve the stimulation of various muscles leading to the closure of the glottis and the production of sound.

Question 23

What are the three phases of cough?

Answer 23

Inspiratory phase
Glottic closure
Expiratory phase

Question 24

what does the inspiratory phase do?

Answer 24

Opens up the trachea

Question 25

What happens during when you cough?

Answer 25

- 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 26

What is acute cough and what is it usually caused by?

Answer 26

Cough that lasts less than 3 weeks | It is commonly caused by rhinovirus

Question 27

What are the causes of chronic cough?

Answer 27

``` Asthma Gastrooesophageal reflux Rhinosinusitis Chronic bronchitis Bronchiectasis ``` 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%

Question 28

What is another name for chronic cough? How can the sensitivity be tested?

Answer 28

Cough hypersensitivity syndrome Triggers: - deep breath, laughing, talking too much, vigorous exercise, smells, cigarette smoke, eating crumbs, cold air, changing temperatures, lying flat Giving patients increasing concentrations of caspaicin until they cough. People with cough hypersensitivity syndrome will have relatively low tolerance of caspaicin. Chronic coughers are particularly sensitive to caspaicin. -Caspaicin an activate nociceptors through TRPV1 receptors -'Cough Hypersensitivity Syndrome' via INCREASED EXPRESSION OF TRPV-1 - this is a Calcium-permeable channel Activated by capsaicin, endocannabinoid, noxious heat & H+ and 12-lipoxygenase metabolites Expressed in sensory neurones of dorsal root and trigeminal ganglia

Question 29

What drugs can inhibit the cortical control of the cough reflex?

Answer 29

Opiates: work at doses when there are a lot of side-effects

Question 30

describe the plasticity of neural mechanisms?

Answer 30

- 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 brain-stem e.g. neurokinins - may be increase inflammatory mediators, which damage/change the reactivity of the nerves to various stimuli e.g. caspaicin

Question 31

Sensory perception from the nose and the pharynx goes through which nerves?

Answer 31

``` Nose - trigeminal (V) Pharynx - glossopharyngeal (IX) and vagus (X) Larynx- Vagus (X) Lungs - Vagus (X) Chest wall- spinal nerves ```

Question 32

Describe the anatomical pathways of touch and pain.

Answer 32

Touch and pain differ in the level at which they cross to the contralateral side. Touch crosses over at the level of the caudal medulla Pain crosses over immediately.

Question 33

What is the clinical significance of this?

Answer 33

Brown-Sequard Syndrome. 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 34

What’s the difference between somatic and visceral pain?

Answer 34

Visceral pain comes from the viscera (internal organs) Somatic comes from the skin and subcutaneous tissue - Somatic pain is easy to localise - Visceral pain is difficult to localise - There are fewer visceral afferents than somatic afferents Pain arising from various viscera in the thoracic cavity and from the chest wall is often qualitatively similar and both can cause referred pain in similar areas -> difficulties in diagnosis.

Question 35

what type of respiratory stuff can give you chest pain?

Answer 35

1. Pleuropulmonary Disorders: Pleural inflammation e.g. infection, pulmonary embolism, pneumothorax, malignancy (mesothelioma) 2. Tracheobronchitis: Infections, inhalation of irritants 3. Inflammation or Trauma to Chest Wall: Rib fracture, muscle injury, malignancy, Herpes Zoster Virus (intercostal nerve pain) 4. Referred Pain: Shoulder-tip pain of diaphragmatic irritation

Question 36

What scale is used to grade dyspnoea?

Answer 36

Modified Borg Scale

Question 37

What are the three types of dyspnoea?

Answer 37

Air Hunger Tightness Work/Effort of breathing

Question 38

Describe different typical patterns of chest pain that can help in diagnosing the cause of pain

Answer 38

1. Musculoskeletal disorders - injury to ribs or thoracic muscles 2. Cardiovascular disorders - MI, dissecting aortic aneurysm 3. Gastrointestinal disorders - gastro-oesophageal reflux

Question 39

Discuss the approach to management of shortness of breath

Answer 39

1. Treat the cause e.g. lung or cardiac 2. Treatment of dyspnoea itself 3. Therapeutic options e.g. add bronchodilators e.g. anticholinergics or adrenergic agonists ``` Drugs affecting brain e.g. morphine, diazepam Lung resection (e.g. lung volume reduction surgery) Pulmonary rehabilitation (improve general fitness, general health, psychological well being) ```