cough Flashcards
what is a cough?
a cough is a useful physiological mechanism that serves to clear the respiratory passage of foreign materials and excess secretions
what triggers a cough?
Cough is triggered by stimulation of airway cough receptors, either by irritants or by conditions that cause airway distortion.
is a cough voluntary or involuntary?
can be either- usuallty involuntray
should a cough be suppressed?
no but it may be difficult to live with- give treatment then
what is the role of the skin in a cough?
top layer of the skin has airways- cilia to help clear mucous from airways
layer of epithelia and goblet cells which help produce mucous
mast cells important for defence
how do we clasify a cough?
the length of time someone has a cough
less than 3 weeks- acute
3-8weeks -subacute
8+ weeks- chronic
what are the types of acute cough?
infectious- viral/acute bronchitis/ penumonia/ covid 19
non-infectious-chf/ exacerbations of COPD
what would be seen in a sub- acute cough?
post infectious
acei
what would cause a chronic cough?
UACS -Upper airway cough syndrome (post-nasal drip)
•Asthma/COPD
•NAEB –Non-asthmatic eosinophilic bronchitis
•GORD
•Smoking
what are the 3 components of a cough reflex?
afferent sensory limb (of the vagusnerve)
–central processing centre(the medulla)
–efferent limb
what do the stimuli that stimulate cough reflex do?
stimulate sensory nerve fibres that have been divided broadly into three main groups:
–Aδ-fibres (rapidly adapting stretch receptors (RARs)
–C-fibres
–slowly adapting stretch receptors (SARs)
what are Aδfibres?
Rapidly adapting receptors (RARs) are myelinated fibres that terminate within the epithelium throughout the intrapulmonary airways
what do Ad fibres respond to?
They respond to changes in airway mechanics to regulate normal breathing
•These fibres fire in response to most ‘tussive’ stimuli and their stimulation is of key importance in the elicitation of the cough reflex
what are Ad fibres activity increased by?
In general, their activity is increased by mechanical stimuli such as mucus secretion or oedema
what do C-fibers do?
They are unmyelinated and respond to chemical stimuli egirritation such as acid, chemicals you inhale, or inflammation from prostaglandins, bradykinin, histamines
•They also respond to mechanical stimuli
what do SARS do?
Slowly Adapting Receptor activity is not altered by stimuli that evoke cough, and these fibres are not believed to be directly involved in the cough reflex
•However, they might facilitate the cough reflex via interneurons, which are believed to either permit or augment the cough reflex as a result of RAR activity
how does a central integration of a cough reflex work?
Many sensory afferent fibre types contribute to/modulate the cough reflex
•Their signals integrate at the nucleus tractus solitarius (NTS) found in the dorsal medulla
•Here, both pulmonary and extrapulmonary (from other vagally innervated organs) afferent fibres terminate and send polysynaptic input to second-order neurons
•These second-order neurons probably alter the activity of the respiratory neurons responsible for normal breathing to produce cough
•Each of these synapses in this ‘cough network’ is a potential target for centrally acting antitussives
what happens in the motor phase of coughing?
inspiration phase
compression phase
expiration phase
what happens when airway receptors are irritated?
Irritation of airways receptors may cause a cough reflex via the brainstem
.Sensation of irritation can also cause cough via higher centres such as the cerebral cortex.
how does a voluntary cough work?
Voluntary cough can be initiated and inhibited via the cerebral cortex that influences cough by two pathways: the brainstem and the spinal cord.
how can we inhibit coughs?
We can also inhibit cough by the use of opioids.Cough associated with a common cold may be a mixture of both reflex and voluntary cough
what is a chronic cough associated with?
Associated with many inflammatory airways diseases -asthma, COPD, pulmonary fibrosis, and bronchiectasis (permanent enlargement of airways in lung)
what drugs can be used to inhibit the underlying inflammatory processes that can cause cough?
corticosteroids for asthma or COPD, PPIs for gastro-oesophageal reflux
Some patients do not respond to treatments directed at the cause, and there are patients in whom there is no identifiable cause to treat
why are compounds targeted in a cough?
n theory compounds that are targeted to inhibit sensory nerve activity directly (by blocking peripheral or central mechanisms), should inhibit cough of any aetiology
how do ACEI cause a cough?
Airway Inhibit peptidase enzymes in the airways •Bradykinin and tachykinins can then accumulate
•Stimulate sensory nerves leading to cough
what is another name for a cough suppressant?
antitussives
- peripheral or centrally acting drugs
what are the peropheral acting cough suppressants?
local anasthetics
Tachykinin receptor antagonists
Leukotriene receptor antagonists
Bradykinin receptor antagonists
how do local anasthetics work?
The mechanism of action is believed to be through use-dependent inhibition of voltage-gated Na+channels, thereby reducing action potential generation and transmission in afferent nerves
lidocaine
how do Tachykinin receptor antagonists work?
Implicated in cough because they are released from C-fibres via and can stimulate RARs therefore enhancing the cough reflex
not used clinically
how do Leukotriene receptor antagonists work?
E.g. Zafirlukast (POM)
•Used in the treatment of asthma
•Cysteinyl leukotriene receptor antagonist, has shown therapeutic efficacy in cough-variant asthma even in patients who are unresponsive to inhaled bronchodilators and corticosteroids
how do Bradykinin receptor antagonists work?
Bradykinin activates C-fibres and can induce coughing in asthmatic subjects
not used clinically
what are centrally acting cough suppressants usually used to treat?
Generally used clinically to treat an acute dry cough
Can and do cause addiction, respiratory depression and nausea
which is better codiene l or codiene p?
Codeine Linctus (P) has a better side-effect profile than the others •Pholcodine Linctus (P) tends to show very few side effects
what is Dextromethorphan?
It is thought the opioid dextromethorphan acts on sigma receptors (centrally and peripherally) rather than at classic opioid receptors
what is an other potential drug target?
GABA receptors- but not clinically useful as it crosses BBB
what is used to treat a cough in pallative care?
Methadone (CD-POM) and diamorphine (CD-POM) have been used previously to treat distressing cough in terminal lung cancer
morphine is first line
what is Mucolytics?
Help in expectoration by liquefying the viscous tracheobronchial secretions
what kind of drug is Carbocisteine(POM) and what does it do?
it is a mucolytics and works by
works by breaking sulphydrylbonds and directly thinning the sputum–Used clinically in patients with COPD
what role do antihistamines play in a cough?
Competitively inhibit the effects of histamine stimulation at receptor sites
what extra actions do antihistamines show ?
Primarily anti-allergy drugs but H1-receptor antagonists often have anti-emetic, sedative and anticholinergic properties
may act indirectly on cough by reducing postnasal drip
what do Expectorants do?
Act peripherally •Increase bronchial secretion OR•Decrease its viscosity → facilitates its removal by coughing•Loosen mucus → less tiring &more productive
what are the two classifications of expectorants?
Directly acting •Guaifenesin(P) (glyceryl guaiacolate)–Reflexlyacting
•Ammonium salts
what is the worry with combination products?
- check they do not have conflicting products inside
Combination products containing topical anaesthetic agents, mucolytic drugs, antihistamines, oral nasal decongestants, antitussives and anticholinergics should be avoided in young children
what is the role of Demulcents (Linctus) ?
Coat the throat and soothe irritated mucous membranes •May help reduce cough associated with a dry throat and are soothing to many patients
