Lecture 19: Pharmacology of cough and breathing problems Flashcards
What happens with a cough?
Deep inspiration followed by a build up of intra-thoracic pressure against a closed glottis - glottis opens and you have a rapid expulsion of air and the sound
What are the receptors for a cough reflex?
- Laryngeal and tracheobronchial
- Diaphragm
- Pleura
- Oesophagus
- Non myelinated c fibres
What is the cough centre?
Integration of afferent fibres in the medulla, separate to centres which control breathing
What are the afferent nerves of the cough reflex?
- Ipsilateral vagus nerve
- Glossopharyngeal, Phrenic
What are the efferent nerves of the cough reflex?
- Phrenic and sponimotor nerves
- Recurrent laryngeal
- Vagal efferents to bronchial tree
What are the effector masculatures of the cough reflex?
- Expiratory muscles
- Diaphragm
- Larynx
- Bronchial smooth muscle
What is a productive cough?
Usually gets rid of secretions and foreign objects
What is an unprodcutive cough?
A dry cough that is persistent and served no useful purpose
What are common causes of persistent coughs?
- Asthma
- Rhinosinusitis (with post nasal drip)
- oesophageal reflux (GERD)
- Lung cancer
- Chronic infections like TB and bronchitis
- Medication - ACE inhibitors
- Sleep apnea
- Vocal cord dysfunction
- COVID
What causes a wet cough?
- Cold
- Flu
- Lung infection
- Cystic fibrosis
- COPD
- Acute bronchitis
- Bronchiectasis
How do you treat coughs above the larynx?
- Application of a medication that forms a soothing coat over the inflamed membranous tissue - this is called a demulcent
- Honey, thick sugar based syrups (with or without a central cough suppressant) and lozenges are useful for this purpose. Useful for about 30 minutes or so.
How do you treat coughs below the larynx?
- Steam inhalation or water aerosol inhalations
- Menthol, eucalyptus and benzoin tincture can help by stimulating the secretion of a thin layer of mucus to protect the inflamed area.
- Menthol can block TRPV1 channels
What can suppress a cough centrally?
Opioids can suppress neauronal activity in the cough centre in the medulla
What opiods are used to suppress a cough?
- Codeine and methadone
- Dextromethorphan and pholcodeine
Describe codeine and methadone for suppressing coughs
Activates µ-opioid receptors. Methadone and diamorphine linctus is sometimes helpful to lung cancer patients – they can help with pain relief (analgesia) and better sleep (sedation).
Describe dextromethorphan and pholcodeine for suppressing coughs
act via o-opioid receptors. They are anti-tussive without offering pain relief. Dextromethorphan is common in OTC cough medicines.
Describe ATP as a key modulator of the cough reflex
ATP is released from damaged or inflamed cells and acts on specific receptors, cactivates the P2X3 and P2X2/3 receptors on sensory neurones within the airway mucosa. Activation of these receptors by ATP has been shown to enhance the cough reflex
What is mucus made up of?
- Water (98%)
- salts (1%)
- mucin glycoproteins (0.5%)
What is the function of mucus?
Protective and clears foreign particles, trapped pathogens and lysed material from immune cells from the lungs
What is the role of bronchial cilia?
Play a key role in moving the mucus upwards and out of the lungs- so the mucus has to be the correct thickness
Name mucolytics
N-acetylcysteine (NAC) and carbocysteine
What do mucolytic do?
Break apart the di-sulphide bonds in the mucins. This decreases the viscosity of mucus.
What is dornase alpha?
Mucolytic enzyme - used in patients with cystic fibrosis
How does dornase alpha work?
Breaks down DNA polymers found in the thickened mucus and so makes it less viscous