Sensory aspects of respiratory disease Flashcards
Physiologic or pathologic stimulus leading to
conscious sensation diagram
(slide 5, lecture 10)
Conscious Sensation Production
1. The sensory stimulation (e.g. a cut) activates sensory
transducers which transmit the signal via excitation of
sensory nerves (afferent nerves into the CNS).
2. CNS creates a sensory impression – neurophysiology.
a. This impression leads to the perception of
information.
3. The brain interprets the information coming from
sensory nerves and evokes a ‘sensation’ – behavioural
psychology.
Difference between symptom and sign
▪ Symptom – an abnormal or worrying SENSATION
that leads a person to seek medical attention.
▪ Sign – an OBSERVABLE feature on physical
examination.
Prevalence of Respiratory Symptoms
Cough
Chest pain
Dyspnoea
▪ Cough:
o 3rd most common complaint in GP practice.
o 10-38% patients in respiratory outpatients
complain of a cough.
▪ Chest pain:
o Most common trigger for consultation (35%).
▪ Dyspnoea:
o 6-27% of general population, 3% A&E visits.
Location of cough receptors
Cough Receptors – Rapidly adapting irritant receptors
Location:
▪ Within the epithelium and most numerous on the
posterior wall of the trachea.
▪ Main carina (and other branching points).
▪ Less numerous in the distal airways.
▪ Absent beyond the bronchioles.
▪ Also found in the diaphragm, pleura, pericardium
and stomach.
Types of cough receptors
Stimuli of each type
Forms of Cough Receptor
Can be divided into three main types of receptor:
▪ Slow adapting stretch receptors.
▪ Rapidly adapting stretch receptors.
▪ C-fibre receptors.
ALL sensory nerves from the airway pass through
the 10th cranial nerve, AKA the Vagus nerve.
C-Fibre Receptors Stimulator? Structure? Location? Respond to? Examples?
Main stimulator =chemicals like capsaicin.
Structure= “free” nerve endings that are small and unmyelinated – conduction is therefore slow.
Located in the larynx, trachea, bronchi and lungs.
They respond to chemical stimuli and inflammatory mediators. Inflammatory mediators include:
o Substance P.
o Neurokinin A.
o Calcitonin Gene Related Peptide.
Rapidly Adapting Stretch Receptors Type of receptor? Stimulus? Structure? Located in?
mechanoreceptor.
Main stimulus is inflation. They respond to mechanical, chemical and inflammatory mediators’ stimuli. o Hyperinflation (mechanical) stimulates a rapid response.
They are small myelinated fibres – conduction is therefore fast.
Located in the naso-pharynx, larynx, trachea and bronchi.
Slowly Adapting Stretch Receptors Type of receptor? Structure? Located in? Respond to?
a mechanoreceptor.
They are myelinated fibres – conduction is therefore fast.
Located in the airways smooth muscle (primarily trachea and main bronchi).
Main stimulus is inflation. They respond to mechanical, chemical and inflammatory mediators’ stimuli. o Hyperinflation (mechanical) stimulates a slow response.
2 types of receptor lead to a cough:
Activated by?
1) Mechanoreceptors.
o Activated by mechanical displacement and
citric acid.
o Look like a tree (picture on slide 15, lecture 10)
2) Nocireceptors.
o Activated by capsaicin, bradykinin, citric acid
and cinnamaldehyde.
o TRPV1, TRPA1 and B2 channels are present.
Afferent neural pathways for cough
slide 17, lecture 10
Stimulation of irritant receptors (RARs)/ Or cough receptor by mechanical or chemical triggers
Goes down Vagus (X) nerve and Superior laryngeal nerve which combine to ‘cough centre’ in medulla which goes to cerebral cortex
Efferent neural pathways for cough
slide 18, lecture 10
Cerebral cortex goes to “Cough Centre” in medulla
3 outputs to Glottis muscle, diaphragm, expiratory muscles
Cerebral cortex also goes directly to neurone from cough centre to glottis muscle
Mechanics of cough draw graph
(slide 19, lecture 10)
Phases?
There are THREE main phases:
o Inspiratory phase.
o Glottic closure.
o Expiratory phase.
▪ High brain activity when you have the need to cough.
Causes of cough
▪ Acute infection – e.g. bronchopneumonia, rhinovirus.
▪ Chronic infection – e.g. CF or TB.
▪ Airways disease – e.g. Asthma.
▪ Parenchymal disease – e.g. Emphysema.
▪ Tumours.
▪ Foreign bodies.
▪ Cardiovascular problems – e.g. Left ventricular failure.
▪ Other disease – e.g. Recurrent aspiration, GERD.
▪ Drugs – e.g. ACE inhibitors.
Causes of chronic cough (>3 weeks)
Most common?
Second most common?
Other cause?
1) Most common= Asthma and eosinophilic-associated (25%)
2) Second= acid reflux (25%)
In gastro-oesophageal reflux, protons from the stomach can activate cough receptors.
3) Other cause= drugs such as ACE inhibitors only contribute ~1% of the cause.
Cough hypersensitivity syndrome=?
Triggers?
Sensitivity measured with? Mechanism?
Possible causes of condition?
Increased sensitivity of the cough receptors.
Triggers=deep breathing, laughing, talking, exercise etc.
Sensitivity is measured using capsaicin with increasing dosages of capsaicin. Capsaicin activates nocireceptors through the TRPV1 receptors.
Possible causes?
▪ Increased excitability of the afferent nerves by chemical mediators (e.g. prostaglandin E2).
▪ Increase in receptor number (e.g. TRPV1).
▪ Increase in NT in the brainstem (e.g. neurokinins).
Treatment
General name for all drugs?
Symptomatic suppressant therapy?
Disease-specific therapy:
Antitussives
Symptomatic suppressant therapy: o Narcotics: Codeine, dihydrocodiene, pholcodiene. Morphine, diamorphine, methadone. o Non-narcotics: Dextromethorphan (derivative of morphine), levopropoxyphene.
Disease specific therapy:
Eosinophil-associated – e.g. corticosteroids.
GERD – e.g. Proton pump inhibitors.
Post-nasal drip – e.g. antihistamines or topical steroids.
Bronchiectasis – e.g. antibiotics.
Which nerve contributes to sensory input from nose?
Trigeminal (V)
Which nerve contributes to sensory input from pharynx?
Glossopharyngeal (IX)
Vagus (X)
Which nerve contributes to sensory input from larynx?
Vagus (X)
Which nerve contributes to sensory input from lungs?
Vagus (X)
Which nerve contributes to sensory input from chest wall?
Spinal nerves
Chest pain can be felt in:
o Chest wall. o Skin. o Pleural pain. o Deep-seated, poorly-localised. o Nerve root pain. o Referred pain (pain that occurs at a different site from where the issue is)
Difference between touch and pain pathways
The main difference is at which level the pathways
cross to the contra-lateral side:
o Touch – crosses at the caudal medulla.
o Pain – crosses at the same anatomical level, i.e. straight away
Brown-Sequard Syndrome
hemisection of the left side of the spinal cord means touch will be fine but pain will be felt on the other side of the body.
3 types of pain:
Somatic, visceral and neuropathic.
o Somatic is localised while visceral is from the
organs and isn’t very specific
Causes of chest Pain from RESPIRATORY Disease
▪ Pleuropulmonary Disorders.
▪ Tracheobronchitis.
▪ Inflammation or trauma.
▪ Referred pain (shoulder-tip pain).
Causes of chest Pain from NON-RESPIRATORY Disease
▪ Cardiovascular disorders – e.g. MI or pericarditis.
▪ Gastrointestinal disorders – e.g. GERD.
▪ Psychiatric disorders – e.g. panic disorder.
Dyspnoea meaning
troublesome shortness of breath
Treatment of Dyspnoea
Therapeutic options?
Treat the cause. Therapeutic options (difficult) include: bronchodilators, lung resections, pulmonary rehabilitation.
