Shortness of breath
Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity", and recommends evaluating dyspnea by assessing the intensity of its distinct sensations, the degree of distress and discomfort involved, and its burden or impact on the patient's activities of daily living. Distinct sensations include effort/work to breathe, chest tightness or pain, and "air hunger" (the feeling of not enough oxygen).[1] The tripod position is often assumed to be a sign.
Shortness of breath
Dyspnea, dyspnoea, breathlessness, difficulty (in/of) breathing; respiratory distress
- Dyspnea: /dɪspˈniːə/; see also § Etymology and pronunciation
Dyspnea is a normal symptom of heavy physical exertion but becomes pathological if it occurs in unexpected situations,[2] when resting or during light exertion. In 85% of cases it is due to asthma, pneumonia, cardiac ischemia, COVID-19, interstitial lung disease, congestive heart failure, chronic obstructive pulmonary disease, or psychogenic causes,[2][3] such as panic disorder and anxiety .[4] The best treatment to relieve or even remove shortness of breath[5] typically depends on the underlying cause.[6]
Definition[edit]
Dyspnea, in medical terms, is "shortness of breath". The American Thoracic Society defines dyspnea as: "A subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity."[7] Other definitions also describe it as "difficulty in breathing",[8] "disordered or inadequate breathing",[9] "uncomfortable awareness of breathing",[3] and as the experience of "breathlessness" (which may be either acute or chronic).[2][6][10]
Pathophysiology[edit]
Different physiological pathways may lead to shortness of breath including via ASIC chemoreceptors, mechanoreceptors, and lung receptors.[15]
It is thought that three main components contribute to dyspnea: afferent signals, efferent signals, and central information processing. It is believed the central processing in the brain compares the afferent and efferent signals; and dyspnea results when a "mismatch" occurs between the two: such as when the need for ventilation (afferent signaling) is not being met by physical breathing (efferent signaling).[23]
Afferent signals are sensory neuronal signals that ascend to the brain. Afferent neurons significant in dyspnea arise from a large number of sources including the carotid bodies, medulla, lungs, and chest wall. Chemoreceptors in the carotid bodies and medulla supply information regarding the blood gas levels of O2, CO2 and H+.[24] In the lungs, juxtacapillary (J) receptors are sensitive to pulmonary interstitial edema, while stretch receptors signal bronchoconstriction. Muscle spindles in the chest wall signal the stretch and tension of the respiratory muscles. Thus, poor ventilation leading to hypercapnia, left heart failure leading to interstitial edema (impairing gas exchange), asthma causing bronchoconstriction (limiting airflow) and muscle fatigue leading to ineffective respiratory muscle action could all contribute to a feeling of dyspnea.[23]
Efferent signals are the motor neuronal signals descending to the respiratory muscles. The most important respiratory muscle is the diaphragm. Other respiratory muscles include the external and internal intercostal muscles, the abdominal muscles and the accessory breathing muscles.[25]
As the brain receives its plentiful supply of afferent information relating to ventilation, it is able to compare it to the current level of respiration as determined by the efferent signals. If the level of respiration is inappropriate for the body's status then dyspnea might occur. There is also a psychological component to dyspnea, as some people may become aware of their breathing in such circumstances but not experience the typical distress of dyspnea.[23]
Epidemiology[edit]
Shortness of breath is the primary reason 3.5% of people present to the emergency department in the United States. Of these individuals, approximately 51% are admitted to the hospital and 13% are dead within a year.[41] Some studies have suggested that up to 27% of hospitalized people develop dyspnea,[42] while in dying patients 75% will experience it.[23] Acute shortness of breath is the most common reason people requiring palliative care visit an emergency department.[3] Up to 70% of adults with advanced cancer also experience dyspnoea.[19]