Etiology
The most common causes of acute dyspnea in patients attending the emergency department are:[6]
Asthma
COPD
Heart failure
Pneumonia (or other infection)
Five main etiologic categories account for most cases of chronic dyspnea (duration >1 month):[7][8]
Pulmonary disease
Cardiovascular disease
Respiratory muscle dysfunction
Psychogenic dyspnea
Deconditioning/obesity.
A useful approach in the diagnosis of dyspnea is to envision the etiologies and diagnostic workup as a checklist of the physiologic processes that move oxygen from the atmosphere into the mitochondria. Respiratory (including pulmonary) causes of dyspnea may affect any level of the respiratory tract, from the nares and mouth to the pulmonary alveoli. A respiratory pump (affected in neurologic 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 (anemia and hemoglobinopathy) 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 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 dyspnea, presyncope, and syncope.
It should be stressed that dyspnea does not equate to hypoxemia; many dyspneic patients are not hypoxemic and, similarly, chronic hypoxemia may not produce dyspnea.
Deconditioning leads to chronic dyspnea and may result from immobilization after medical illness, surgery (especially orthopedic procedures), trauma, a sedentary lifestyle, or discontinuing an aerobic program. Patients with dyspnea may avoid activity as a way of reducing their symptoms. Long term, this exacerbates skeletal muscle deconditioning, which worsens chronic dyspnea. The etiology of dyspnea 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, dyspnea, 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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