Sensory Aspects of Respiratory Disease Flashcards
What is a cough
Complex defence mechanism that protects the respiratory tract from inhaled foreign material or excessive mucous secretion
Usually secondary to mucociliary clearance
Vagus nerve most important
Where are the nerve terminals for cough found
Next to mucous goblet cells
Allows recognition of mucous secretion to induce a cough
What are the three types of sensory receptors for cough
C-fibre receptors
Rapidly adapting stretch receptors
Slowly adapting stretch receptors
Describe the C-fibre receptors and where are they found
Free nerve endings
Unmyelinated
Larynx, trachea, bronchi, lungs
What are the c-fibre receptors irritated by and what do they release
Chemicals and inflammatory mediators e.g. histamine, leukotrienes, capsaicin
Releases neuropeptide inflammatory mediators e.g. substance P, neurokinin A to stimulate RARs
Describe the rapidly adapting stretch receptors and where are they found
Small, myelinated nerve fibres
Pharynx, larynx, trachea, bronchi
What are the rapidly adapting stretch receptors stimulated by
Mechanical and chemical irritants and inflammatory mediators
What can the vagal afferent nerve be activated by
Acid-sensing ion channels
Bradykinin receptor B2
Transient receptor potential vanniloid-1 receptor
What are the mechanical and chemical stimulants of the afferent neural pathway for cough
Mechanical - dust, mucous, food/drink, citric acid (mechanosensor)
Chemical - noxious, intrinsic inflammatory agent, bradykinin, capsaicin, citric acid (nociceptor)
Outline the neural pathway for cough (afferent and efferent)
- Cough/irritant receptors are stimulated chemically or mechanically
- Vagus nerve
- Superior laryngeal nerve
- Impulses integrated in the cough centre in the medulla
- Activated suppression from the medial prefrontal cortex
- Cough centre in the medulla
- Glottis, diaphragm, expiratory muscles
What happens to the airways during cough
Airways narrow to increase pressure and increase airflow out (trachea forms crescent)
Give some common causes of cough
Asthma + eosinophilic related Gastro-oesophageal reflux Rhinosinusitis Chronic bronchitis Drugs
What is cough hypersensitivity syndrome
Increased expression of TRPV-1 (Calcium-permeable channel)
Activated by capsaicin, endocannabinoid, noxious heat and metabolites
Expressed in sensory neurones of dorsal root and trigeminal ganglia
What are the symptomatic antitussives
Central - opiates e.g. codeine, morphine
peripheral e.g. moguistine, levodopropizine
What are the disease-specific antitussives
Corticosteroids
Histamine H2 antagonists
Proton pump inhibitors
Post nasal drip
What is the sensory input for the following: nose pharynx larynx lungs chest wall
nose - trigeminal pharynx - glossopharyngeal, vagus larynx - vagus lungs - vagus chest wall - spinal nerves
What is the neural pathway for touch
- A𝛼 and Aβ via the dorsal horn which travel up to the medulla on the same side
- Switches onto the other side of the spinal cord at the medulla
- Link in the mid-brain in the primary somato-sensory cortex
What is the neural pathway for pain
- Aẟ and C-fibres recognise pain via the dorsal horn
- Aẟ and C-fibres will cross at the same level of entry
- Travels up the spinothalamic tract
- Thalamus
- Primary somato-sensory cortex
What are the types of pain
Visceral - visceral organs, chronic-feeling, grumbling pain (lower number of afferents)
Somatic - pain from the skin, deep structures, bone (herpes zoster)
Referred - shoulder-tip pain of diaphragmatic irritation
Give some respiratory causes of chest pain
Pneumonia
Malignancy
pneumothorax
Pulmonary embolism
Give some non-respiratory causes of chest pain
MI
Pericarditis
GORD - heart burn
Costochondritis - patient can localise the pain
What is dyspnoea
Shortness of breath reported by a patient
Occurs at inappropriately low levels of exertion, and limits exercise tolerance
Describe the assessment of dyspnoea
Subjective rating scales
Questionnaires e.g. baseline dyspnoea test index, shortness of breath questionnaire
Exercise testing e.g. 6-minute walk test, shuttle test
Clinical dyspnoea scale (grade 0-4)
Modified Borg scale
What can cause dypsnoea
Asthma COPD MI Hypoxia Metabolic acidosis Anaemia Pregnancy
What are some treatments for dyspnoea
Bronchodilators e.g. anticholinergics
Drugs that affect the brain e.g morphine, diazepam
Lung resection e.g. long volume reduction
Pulmonary rehabilitation (improve general fitness)
What are some drugs used to treat dyspnoea
Amitryptiline
Gabapentin
Opiates
Describe the slowly adapting stretch receptors (where they are found and what they are sensitive to)
Myelinated nerve fibres
Mechanoreceptors
Airways smooth muscle: trachea and main bronchi
Mechanical stimuli only (inflation)
What are the effects of the cerebral cortex and cough centre on coughing
cerebral cortex - negative effect
Cough centre - Positive effect
Explain the concept of sensitised cough reflex in disease
Irritation in the throat or upper chest
Cough difficult to control
Triggered by deep breath, laughing, smells, smoke, crumbly food, cold air etc.
Describe the motor response of cough
Diaphragm, intercostals and laryngeal muscles involved
- Inspiration
- Compression as the laryngeal muscles close the glottis
- Expulsion as the laryngeal muscles relax and air is expelled
