Aetiology
The most common causes of acute dyspnoea in patients attending the accident and emergency department are:[6]
Asthma
COPD
Heart failure
Pneumonia (or other infection)
Five main aetiological categories account for most cases of chronic dyspnoea (duration >1 month):[7][8]
Pulmonary disease
Cardiovascular disease
Respiratory muscle dysfunction
Psychogenic dyspnoea
Deconditioning/obesity.
A useful approach in the diagnosis of dyspnoea is to envision the aetiologies and diagnostic work-up as a checklist of the physiological processes that move oxygen from the atmosphere into the mitochondria. Respiratory (including pulmonary) causes of dyspnoea may affect any level of the respiratory tract, from the nares and mouth to the pulmonary alveoli. A respiratory pump (affected in neurological and musculoskeletal disease) to generate negative pleural pressure (pleural disease) and expand the compliant lung parenchyma (parenchymal lung disease) requires an open conducting airway system (laryngeal and tracheobronchial disease) to conduct adequately oxygenated ambient air (high altitude) and allow the extraction of oxygen. The distributory circulatory system requires an adequate amount of oxygen carriers (anaemia and haemoglobinopathy) and an intact series of unidirectional priming (atrial and valvular disease) and main pumps (diastolic and systolic dysfunction), as well as an open vascular distributory network (pulmonary and systemic vascular disease) to deliver the oxygen to the lungs and end users, such as muscles. The heart has to expand to receive (pericardial disease and restrictive cardiomyopathy) and send blood into the lungs (pulmonary embolism and pulmonary hypertension) and distribute it into aerated exchange units (ventilation-perfusion mismatching and shunts, unresponsive to oxygen supplementation) before it is received into the left atrium (pulmonary veno-occlusive disease and atrial arrhythmias). The priming and main left pump deliver this blood to the systemic circulation through a series of vascular conduits (atherosclerosis and other obstructive vasculopathy). The oxygen finally diffuses from the capillaries to the mitochondria (myopathy and mitochondrial disease).
Paget's disease, atrioventricular malformation, hereditary telangiectasia, patent ductus arteriosus, and patent foramen ovale may cause intra- and extracardiac shunting.
Use of medications that slow atrioventricular conduction may lead to the heart not meeting the increased cardiac output demand at the time of physical exercise (chronotropic deficiency). This can manifest as dyspnoea, presyncope, and syncope.
It should be stressed that dyspnoea does not equate to hypoxaemia; many dyspnoeic patients are not hypoxaemic and, similarly, chronic hypoxaemia may not produce dyspnoea.
Deconditioning leads to chronic dyspnoea and may result from immobilisation after medical illness, surgery (especially orthopaedic procedures), trauma, a sedentary lifestyle, or discontinuing an aerobic programme. Patients with dyspnoea may avoid activity as a way of reducing their symptoms. Long term, this exacerbates skeletal muscle deconditioning, which worsens chronic dyspnoea. The aetiology of dyspnoea is often multifactorial.[9][10][11]
Coronavirus disease 2019 (COVID-19)
COVID-19 is a potentially severe acute respiratory infection. The clinical presentation is that of a respiratory infection with fever, cough, dyspnoea, and/or fatigue. Symptom severity ranges from a mild common cold-like illness, to a severe viral pneumonia leading to acute respiratory distress syndrome that is potentially fatal. Severe illness is associated with older age and the presence of underlying health conditions.
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