Sensory aspects of respiratory disease Flashcards
what is a symptom?
An abnormal or worrying sensation that leads the person to seek medical attention
Describe the pathway from stimulus to evoked sensation? What are the names for the two main parts of this?
Stimulus - transducer - excitation of sensory nerves - integration of CNS - sensory impression
This is NEUROPHYSIOLOGY
Sensory impression - perception - evoked sensation
This is BEHAVIOURAL PSYCHOLOGY
- 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 - 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
why do we cough?
It is a crucial defence mechanism protecting lower respiratory tract from:
- inhaled foreign material
- excessive mucous secretion
what is usually the primary defence mechanism against lower respiratory infections?
-Mucociliary clearance
how does cough expel foreign material and what else is also involved?
- Once the mucus gets to the large airways it stimulates the cough mechanism
- Generates high-velocity airflow
- Expels the mucus or foreign material
- This is facilitated by mucus secretion and bronchoconstriction
Describe the distribution of rapidly adapting irritant receptors within the airway epithelium.
- 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.
What are the three main types of sensory receptors in the lungs and airways?
C-fibre receptor
Slow adapting stretch receptors
Rapidly adapting stretch receptors
which cranial nerve does the vagus come from and what comes from this?
It is the 10th cranial nerve.
-all sensory nerves from the airways pass through to the brain.
Which nerve do all the sensory receptors in the lungs and airways pass through?
Vagus nerve
What is used as a stimulus for the C-fibres?
what is a stimulus to the sensory nerves?
Caspaicin
What stimulates C-fibres?
Chemicals
describe the process in which the c-fibre is stimulated?
C-fibre is stimulated when the caspaicin is injected intravenously.
what effect does caspaicin have on the rapidly and slow adapting stretch receptors
NO EFFECT
What do the rapidly and slowly adapting stretch receptors respond to?
Inflation (increase in tracheal pressure)
Describe the differences between the three types of sensory receptor.
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.
What are the two broad types of sensory receptor in the airways that lead to cough?
- Mechanoreceptor/sensor (mechanical displacement, citric acid)
- 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
what activates the mechanoreceptors and what do they look like?
- Citric acid
- mechanical displacement
Looks like a tree
TRPV1, TRPA1 and B2 are present on nociceptors
what are nociceptors activated by?
- Caspaicin
- Bradykinin
- Citric Acid
- Cinnamaldehyde
What is the collection of neurons in the cough centre called?
Nucleus tractus solitarius
What is the role of the cerebral cortex in the complete cough pathway?
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.
describe the complete cough pathway?
- 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
what is the afferent and efferent pathway?
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.
What are the three phases of cough?
Inspiratory phase
Glottic closure
Expiratory phase
what does the inspiratory phase do?
Opens up the trachea
What happens during when you cough?
- 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
What is acute cough and what is it usually caused by?
Cough that lasts less than 3 weeks
It is commonly caused by rhinovirus
What are the causes of chronic cough?
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%
What is another name for chronic cough? How can the sensitivity be tested?
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
What drugs can inhibit the cortical control of the cough reflex?
Opiates: work at doses when there are a lot of side-effects
describe the plasticity of neural mechanisms?
- 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
Sensory perception from the nose and the pharynx goes through which nerves?
Nose - trigeminal (V) Pharynx - glossopharyngeal (IX) and vagus (X) Larynx- Vagus (X) Lungs - Vagus (X) Chest wall- spinal nerves
Describe the anatomical pathways of touch and pain.
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.
What is the clinical significance of this?
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.
What’s the difference between somatic and visceral pain?
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.
what type of respiratory stuff can give you chest pain?
- Pleuropulmonary Disorders:
Pleural inflammation e.g. infection, pulmonary embolism, pneumothorax, malignancy (mesothelioma) - Tracheobronchitis:
Infections, inhalation of irritants - Inflammation or Trauma to Chest Wall:
Rib fracture, muscle injury, malignancy, Herpes Zoster Virus (intercostal nerve pain) - Referred Pain:
Shoulder-tip pain of diaphragmatic irritation
What scale is used to grade dyspnoea?
Modified Borg Scale
What are the three types of dyspnoea?
Air Hunger
Tightness
Work/Effort of breathing
Describe different typical patterns of chest pain that can help in diagnosing the cause of pain
- Musculoskeletal disorders
- injury to ribs or thoracic muscles - Cardiovascular disorders
- MI, dissecting aortic aneurysm - Gastrointestinal disorders
- gastro-oesophageal reflux
Discuss the approach to management of shortness of breath
- Treat the cause e.g. lung or cardiac
- Treatment of dyspnoea itself
- 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)
