10. Sensory Aspects of Respiratory Disease Flashcards
What is the difference between a symptom and a sign?
- Symptom - abnormal or worrying sensation that leads the person to seek medical attention
- Sign - an observable feature on physical examination of the patient
How do people interpret sensations?
- Sensory stimulation
- Sensory transducer
- Excitation of sensory nerve
- CNS creates a sensory impression (neurophysiology)
- Brain interprets the information - sensation (behavioural psychology)
What is a cough?
• Crucial defence mechanism protecting the lower respiratory tract from
- inhaled foreign material
- excessive mucus secretion
• Secondary to mucociliary clearance (important when this function is impaired)
Describe the expulsive phase of cough?
- Mucus gets to large airways
- High velocity airflow generated
- Expels mucus or foreign material
- Facilitated by mucus secretion and bronchoconstriction
Where are nerve terminals located in the lungs at a microscopic level?
- Surface of the epithelium
* Well placed to sense the external environment
Where are cough receptors located throughout the lungs?
- Most - posterior wall of the trachea
- Main carina (ridge between division of bronchi)
- Common at branching points
- Larynx, pharynx and external auditory meatus
- Diaphragm, pleura, pericardium, stomach
- Absent beyond the bronchioles
What are the 3 main types of cough receptors?
- Slow adapting stretch receptors
- Rapidly adapting stretch receptors
- C-fibre receptors (stimulated by chemicals)
Which nerve do all sensory nerves from the airways pass through to get to the brain?
- Vagus nerve
* Cranial Nerve X
What is capsaicin?
- Stimulus to sensory nerves (activate nociceptors through TRPV1 receptors)
- Burning sensation
- No affect on stretch receptors
What is the main stimulus for the stretch receptors?
Inflation
What affect does an increase in tracheal pressure have on cough receptors?
- Slow adapting stretch receptors are stimulated
- Rapidly adapting stretch receptors stop firing
(most likely to be involved in coughing)
Describe the C-fibre receptors and how they work
• Free nerve endings
• Small unmyelinated fibres - slow conduction
• Present in upper airways (down to bronchi)
• Responds to chemical irritant stimuli and inflammatory mediators
• Release neuropeptide inflammatory mediators:
- Substance P
- Neurokinin A
- Calcitonin Gene Related Peptide
Describe the rapidly adapting stretch receptors and how they work
- Mechanoreceptor
- Myelinated - conduct quickly
- Present in upper airways (down to bronchi)
- Mechanical, chemical irritant stimuli, inflammatory mediators
- Rapid response to hyperinflation
Describe the slowly adapting stretch receptors and how they work
- Mechanoreceptor
- Myelinated - conduct quickly
- In airway smooth muscle
- Predominantly in the trachea and main bronchi
- Slowly and rapidly adapting s
What are mechanosensors activated by?
- Mechanical displacement
* Citric acid
What are nociceptors activated by?
- Capsaicin
- Bradykinin
- Citric Acid
- Cinnamaldehyde
What is TRPV1, TRPA1 and B2 present on?
Nociceptors
How is the sensory information from a cough stimulus processed?
- Vagus nerve => brainstem => cough centre
- Consists of nucleus tractus solitarius - neurones connected to the medullar cough pattern generator
- This stimulates various muscles to produce the cough
- Cerebral cortex also involved
What happens to the brainstem cough reflex when asleep?
Inhibited
also under general anaesthetic
What are the 3 phases of a cough?
- Inspiratory phase - trachea opens
- Glottic closure - increase in intrapulmonary pressure compresses the posterior membrane of the trachea which pushes through and narrows it into a crescent shape
- Expiratory phase - Pressure in lungs released when glottis opens
What is the most common cause of a cough?
- Rhinovirus
* Acute cough (< 3 weeks)
What are the most common chronic persistent coughs (>3 weeks)?
- Asthma and eosinophilic-associated
- Gastro-oesophageal reflux
- Rhinosinusitis (post-nasal drip)
- Chronic Bronchitis
- Bronchiectasis
- Drugs
How can a gastro-oesophageal reflux cause a cough?
- Protons from the stomach can activate the cough receptors
* Activate brainstem cough receptors
What is Cough Hypersensitivity Syndrome?
- Chronic cough
- Cough paroxysms - difficult to control
- Triggered by: deep breath, laughing, talking, cold air etc.
How can you measure the sensitivity of a cough reflex?
- Capsaicin
* Give dilute solution then increase concentration
Describe the mechanism that leads to hypersensitivity
- Increased excitability of the afferent nerves by chemical mediators
- Increase in receptor numbers
- Increase in neurotransmitter in the brainstem
- May be an increase in inflammatory mediators - change the reactivity of nerves
What symptomatic suppressant therapies act centrally?
• Opiates
- codeine
- dihydrocodeine
- pholcodeine
- dextromethorphan
What symptomatic suppressant therapies act peripherally?
- Moguistine
* Levodopropizine
Give examples of disease-specific therapies
- Eosinophil associated - inhaled corticosteroids
- Gastro-oesophageal reflux - proton pump inhibitors, histamine H2 antagonists
- Rhinosinusitis - topical steroids, antihistamines
- Bronchiectasis - postural drainage, antibiotics
Why are opiates not particularly effective?
Work at doses where there are a lot of side-effects (e.g. codeine and morphine)
Which nerves are associated with the nose, pharynx, larynx, lungs and chest wall?
- Nose - Trigeminal (V)
- Pharynx - Glossopharyngeal (IX) and Vagus (X)
- Larynx - Vagus (X)
- Lungs - Vagus (X)
- Chest wall - spinal nerves
How are touch and pain differently transmitted?
Touch
• travels via Aa and Ab fibres to the dorsal horn
• goes to the controlateral side at the level of the caudal medulla (crosses to other half of body at the brainstem)
Pain
• goes to the contralateral side at the same anatomical level (crosses straight away)
• Both go to the primary somatosensory cortex
What is Brown-Sequard Syndrome?
• Hemisection of the spinal cord
• If the hemisection is on the left side:
- touch sensation is fine on the opposite side
- pain sensation affected on the other side
What are the different types of pain?
- Visceral pain - from internal organs, difficult to localise, fewer afferents
- Somatic - from skin and subcutaneous tissue, very localised, more afferents
- Neuropathic
Why is it difficult to diagnose visceral pain in the thoracic cavity and chest wall?
- Qualitatively similar
* Exhibit overlapping patterns of referral, localisation and quality
What can cause chest pain in the respiratory system?
- Pleuropulmonary disorders - pleural inflammatio
- Tracheobronchitis - inhalation of irritants
- Inflammation or trauma to chest wall - rib fracture, muscle injury
- Referred pain - shoulder-tip pain of diaphragmatic irritation
What cardiovascular disorders can cause chest pain?
- MI
- Pericarditis
- Dissecting aneurysm
- Aortic valve disease
What gastrointestinal disorders can cause chest pain?
- Oesophageal rupture
- Gastr-oesophageal reflux
- Cholecytitis
- Pancreatitis
What psychiatric disorders can cause chest pain?
- Panic disorder
* Self-inflicted
What is the clinical dyspnoea scale?
- 0 - breathlessness with strenuous exercise (none)
- 1 - breathlessness when hurrying or walking up a slight hill (slight)
- 2 - walks slower than normal, has to stop for breath when walking (moderate)
- 3 - stops for breath after 100 yards/few minutes on the level (severe)
- 4 - too breathless to leave house and when dressing (very severe)
Briefly describe the Modified Borg Scale
- 0 - 5/6 = nothing to severe
- 7/8 = very severe
- 9 = very, very severe
- 10 = maximal
What is air hunger cluster?
- Hunger for more air
- Suffocation
- Short of breath
- Breath feels too small
What is work/effort cluster?
- Breathing requires effort
- Breathing is uncomfortable
- Breaths feel too large
What is tightness cluster?
- Tightness/constriction in chest
* Heaviness in chest
How can dyspnoea be treated?
- Add bronchodilators
- Drugs affecting CNS
- Lung resection
- Pulmonary rehabilitation (general fitness)
