17. Breathlessness Flashcards
Define dyspnoea
Difficult or laboured breathing in which the subject is conscious of being short of breath aka. breathlessness
Definition of breathlessness: undue awareness of breathing or awareness of difficulty breathing
What is meant by breathlessness?
Sensations of all or any of the below:
Awareness of breathing normally absent
A sensation of air hunger/requiring more air
Difficulty breathing in
Difficulty breathing out
Feeling that the chest is filled up
Perception of respiratory rate and gasps or sighs
What is the pathophysiology of breathlessness ? (Brief)
Three main components - afferent input, efferent output, central information processing
Central processing in dyspnoea results in mismatch between the afferent and the efferent - so the need for ventilation is not met by the physical breathing
What are the causes of breathlessness?
Hypoxia Metabolic acidosis Hypotension/reduced cardiac output Breathing CO2 Exercise Pregnancy Anxiety Pulmonary oedema Anaemia Obstruction of the pulmonary artery
By what mechanism does hypoxia, metabolic acidosis and hypotension cause dyspnoea/breathlessness?
By a low pO2/altered pH being recognised by the peripheral chemoreceptors
How does the function of the respiratory muscles change when there is airway obstruction?
When there is resistance i.e. airway obstruction, brain activity increases with increased input from the chest wall muscles and their stretch receptors
What are J receptors and how do they function in the lung?
AKA. Pulmonary C-fibre receptors
J receptors are situated next to capillaries in the bronchial wall
These are slow speed C fibres and result in vagal input to the brainstem
Activation of these receptors leads to shortened expiration and increased respiratory frequency
What can activate J receptors?
Local congestion i.e. pneumonia, pulmonary emboli, pulmonary odoema, congestive heart failure - essentially any cause leading to a reduced oxygenation of the lung
What does the activation of J receptors result in?
Activation causes a reflexive increase in breathing rate and so leads to increased rate of ventilation
What neurological factors can lead to breathlessness?
Anxiety Depression Temperature Hormones Hyperventilation Desensitisation and acclimatisation
What different tests can be used to test lung function?
Tests of airflow and resistance Tests of lung volume with measurement of residual volume and air trapping Tests of gas transfer Repeated measurements over time Exercise testing
Why are transplant patients particularly prone to becoming breathless?
These patients have no input via the J receptors or stretch receptors and so have no mechanism to prevent the sensation of breathlessness
What treatments can be used for breathlessness?
Find the cause and treat it (Bronchodilators and steroids Oxygen Morphine Diazepam Retraining and exercise)
How can exercise cause breathlessness?
Increases the pCO2 level
Sensed via afferents from the skeletal muscles
Stimulates the respiratory centre
How does pregnancy lead to breathlessness?
Due to direct effect on the respiratory centre due to increased levels of progesterone
Also results in an increased CO2 production
