Sensory aspects of respiratory disease Flashcards
Outline the prevalence of different respiratory symptoms
Cough Third most common complaint heard by GP 10-38% of patients in respiratory outpatients complain of cough Chest pain Most common pain for which patient seeks medical attention (35%), including acute chest pain Shortness of breath (SOB, dyspnea) 6-27% of general population 3% of visits to A&E
What is meant by symptoms of respiratory disease
SYMPTOMS
An abnormal or worrying sensation that leads the
person to seek medical attention
e.g. Cough
Chest pain
Shortness of breathWhat is meant by a physical sign of respiratory disease
PHYSICAL SIGN
An observable feature on physical examination
e.g. Hyperinflation of chest wall
Dullness on percussion of chest wall
Increased respiratory rate
Reduced movement of chest wall
Describe conscious sensation production
- The sensory stimulation (e.g. a cut) activates sensory transducers which transmit the signal via excitation of sensory nerves (afferent nerves into the CNS).
- CNS creates a sensory impression – neurophysiology.
a. This impression leads to the perception of information. - The brain interprets the information coming from sensory nerves and evokes a ‘sensation’ – behavioural psychology.
Describe the function of cough
A crucial defence mechanism protecting the lower respiratory tract from
inhaled foreign material
excessive mucous secretion
Usually secondary to mucociliary clearance
but important in lung disease when mucociliary function is impaired and mucous production is increased
Mucous reaches large airways- then you cough
Describe the expulsive phase of coughing
Inhaled material and material brought up the broncho-pulmonary tree to the trachea and larynx by mucocilliray clearance can trigger a cough reflex
This is caused by a reflex deep inspiration that increases intrathoracic pressure whilst the larynx is closed
The larynx is suddenly opened, producing a high-velocity jet of air, which ejects unwanted material at a high speed through the mouth
facilitated by bronchoconstriction and mucous secretion.
Describe the nerve profile in the 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
Some on goblet cells- sensitive to mucus
Summarise the localisation of cough receptors
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.
Also in the pharynx. Possibly also in the external auditory meatus, eardrums, paranasal sinuses, pharynx, diaphragm, pleura, pericardium, and stomach.
Stimuli: laryngeal and tracheobronchial receptors respond to chemical and mechanical stimuli.
Describe the different nerves involved
Vagus- stomach, trachea, bronchi, ear drums
Trigemminal- para nasal sinuses
Glossopharyngeal- larynx
Describe the different types of nerve fibres
§ Slow adapting stretch receptors. o Main stimulus is inflation. § Rapidly adapting stretch receptors. o Main stimulus is inflation. § C-fibre receptors. o Main stimulator is chemicals like capsaicin.
Describe C-fibres
C – fibre receptors
“free” nerve endings
Larynx, trachea, bronchi, lungs
Small unmyelinated fibres (C)
Chemical irritant stimuli, inflammatory mediators
Release neuropeptide inflammatory mediators Substance P, Neurokinin A, Calcitonin Gene Related peptide
Describe rapidly adapting stretch receptors
Rapidly adapting stretch receptors
Naso-pharynx, larynx, trachea, bronchi
Small, myelinated nerve fibres (A)
Mechanical, chemical irritant stimuli, inflammatory mediators
Describe slowly adapting stretch receptors
Slowly adapting stretch receptors Located in airways smooth muscle Myelinated nerve fibres Predominantly in trachea and main bronchi Mechanoreceptors Respond to lung inflation
What do all the sensory nerves in the airways pass through to reach the brain
ALL sensory nerves from the airway pass through the 10th cranial nerve, AKA the Vagus nerve.
Describe the experiments which demonstrated the functions of the different nerve fibres
• 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 coughin
Distinguish between the stimuli for rapidly and slow adapting stretch receptors
o Hyperinflation (mechanical) stimulates a rapid response. o Hyperinflation (mechanical) stimulates a slow response.
Describe mechanoreceptors
o Activated by mechanical displacement and citric acid.
o Look like a tree.
Transmit vagus nerve afferents through nodose ganglion via myelinated A alpha fibres
Describe noicireceptors
o Activated by capsaicin, bradykinin, citric acid and cinnamaldehyde.
o TRPV1, TRPA1 and B2 channels are present.
Transmit vagus nerve afferents via unmyelinatec C-fibres through nodose ganglion
List some receptors involved in sensing mechanical and chemical changes
TRPV1: Transient receptor potential vanniloid-1 receptor
TRPA1: Transient receptor potential cation channel, subfamily A1
ASIC: Acid-sensing ion channel
B2: Bradykinin receptor B2
Describe the afferent neural pathways for cough
Stimulation of irritant receptors (RARs)/ Or cough receptor Mechanical (e.g. dust, mucous, food/drink)
Chemical
(e.g. noxious, intrinsic inflammatory agents)
stimulation of irritant receptors leads to firing down Vagus nerve to cough centre in medulla- superior laryngeal nerve joins from larynx
Some also sent to other parts of the cerebral cortex
Describe the efferent neural pathways for cough
Cerebral cortex communicates with medullary cough centre
Efferents sent to glottis (to close it)
Diaphragm, external intercostals and the accessory muscles of inspiration
Summarise the full neural pathway for cough
• 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 Laz’s Notes Respiratory 108 • 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
Outline the mechanics of coughing
• Inspiratory phase with negative flow during inhalation Glottic pressure in the minimum flow phase (glottis closes to generate pressure) Glottis opening Expiratory phase • 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 • NOTE: the brain is really active when you feel the need to cough
Describe the cough sound waveforms
2 phases with an initial explosive phase that is the first cough sound, followed by an intermediate phase with decreasing sound.
an additional third phase called voiced or glottal phase which gives rise to a second cough sound.
