Dyspnea is unpleasant or uncomfortable breathing. It is experienced and described differently by patients depending on the cause.
Pathophysiology of Dyspnea
Although dyspnea is a relatively common problem, the pathophysiology of the uncomfortable sensation of breathing is poorly understood. Unlike those for other types of noxious stimuli, there are no specialized dyspnea receptors (although MRI studies have identified a few specific areas in the midbrain that may mediate perception of dyspnea).
The experience of dyspnea likely results from a complex interaction between chemoreceptor stimulation, mechanical abnormalities in breathing, and the perception of those abnormalities by the central nervous system. Some authors have described the imbalance between neurologic stimulation and mechanical changes in the lungs and chest wall as neuromechanical uncoupling.
Etiology of Dyspnea
Dyspnea has many pulmonary, cardiac, and other causes (1 Etiology reference Dyspnea is unpleasant or uncomfortable breathing. It is experienced and described differently by patients depending on the cause. Although dyspnea is a relatively common problem, the pathophysiology... read more ), which vary by acuity of onset (see tables Some Causes of Acute Dyspnea Some Causes of Acute* Dyspnea , Some Causes of Subacute Dyspnea Some Causes of Subacute* Dyspnea , and Some Causes of Chronic Dyspnea Some Causes of Chronic* Dyspnea ).
The most common causes include
COPD Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more (chronic obstructive pulmonary disease)
The most common cause of dyspnea in patients with chronic pulmonary or cardiac disorders is
Exacerbation of their disease
However, such patients may also acutely develop another condition (eg, a patient with long-standing asthma may have a myocardial infarction, a patient with chronic heart failure may develop pneumonia).
Evaluation of Dyspnea
History of present illness should cover the duration, temporal onset (eg, abrupt, insidious), and provoking or exacerbating factors (eg, allergen exposure, cold, exertion, supine position). Severity can be determined by assessing the activity level required to cause dyspnea (eg, dyspnea at rest is more severe than dyspnea only when climbing stairs). Physicians should note how much dyspnea has changed from the patient’s usual state.
Review of systems should seek symptoms of possible causes, including chest pain or pressure (pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more , myocardial ischemia, pneumonia Overview of Pneumonia Pneumonia is acute inflammation of the lungs caused by infection. Initial diagnosis is usually based on chest x-ray and clinical findings. Causes, symptoms, treatment, preventive measures, and... read more ); dependent edema, orthopnea, and paroxysmal nocturnal dyspnea (heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular (LV) failure causes shortness of breath and fatigue, and right ventricular (RV) failure causes peripheral and abdominal... read more ); fever, chills, cough, and sputum production (pneumonia); black, tarry stools or heavy menses (occult bleeding, possibly causing anemia Etiology of Anemia Anemia is a decrease in the number of red blood cells (RBCs), which leads to a decrease in hematocrit and hemoglobin content. (See also Red Blood Cell Production.) The RBC mass represents the... read more ); and weight loss or night sweats (cancer or chronic lung infection).
Past medical history should cover disorders known to cause dyspnea, including asthma Asthma Asthma is a disease of diffuse airway inflammation caused by a variety of triggering stimuli resulting in partially or completely reversible bronchoconstriction. Symptoms and signs include dyspnea... read more , COPD Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more , and heart disease, as well as risk factors for the different etiologies:
Smoking history—for cancer, COPD, some interstitial lung diseases Overview of Interstitial Lung Disease Interstitial lung diseases are a heterogeneous group of disorders characterized by alveolar septal thickening, fibroblast proliferation, collagen deposition, and, if the process remains unchecked... read more , and heart disease
Family history, hypertension, and high cholesterol levels—for coronary artery disease Overview of Coronary Artery Disease Coronary artery disease (CAD) involves impairment of blood flow through the coronary arteries, most commonly by atheromas. Clinical presentations include silent ischemia, angina pectoris, acute... read more
Recent immobilization or surgery, recent long-distance travel, cancer or risk factors for or signs of occult cancer, prior or family history of clotting, pregnancy, oral contraceptive use, calf pain, leg swelling, and known deep venous thrombosis—for pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more
Occupational exposures (eg, gases, smoke, asbestos) should be investigated.
Vital signs are reviewed for fever, tachycardia, and tachypnea.
Examination focuses on the cardiovascular and pulmonary systems.
A full lung examination is done, particularly including adequacy of air entry and exit, symmetry of breath sounds, and presence of crackles, rhonchi, stridor, and wheezing. Signs of consolidation (eg, egophony, dullness to percussion) should be sought. The cervical, supraclavicular, and inguinal areas should be inspected and palpated for lymphadenopathy.
Neck veins should be inspected for distention, and the legs and presacral area should be palpated for pitting edema (both suggesting heart failure).
Heart sounds should be auscultated with notation of any extra heart sounds, muffled heart sounds, or murmur. Testing for pulsus paradoxus Pulsus paradoxus Complete examination of all systems is essential to detect peripheral and systemic effects of cardiac disorders and evidence of noncardiac disorders that might affect the heart. Examination... read more (a > 12-mm Hg drop of systolic blood pressure during inspiration) can be done by inflating a blood pressure cuff to 20 mm Hg above the systolic pressure and then slowly deflating until the first Korotkoff sound is heard only during expiration. As the cuff is further deflated, the point at which the first Korotkoff sound is audible during both inspiration and expiration is recorded. If the difference between the first and second measurement is > 12 mm Hg, then pulsus paradoxus is present.
Conjunctiva should be examined for pallor.
The following findings are of particular concern:
Dyspnea at rest during examination
Decreased level of consciousness or agitation or confusion
Accessory muscle use and poor air excursion
Interpretation of findings
The history and physical examination often suggest a cause and guide further testing (1 Evaluation reference Dyspnea is unpleasant or uncomfortable breathing. It is experienced and described differently by patients depending on the cause. Although dyspnea is a relatively common problem, the pathophysiology... read more —see tables Some Causes of Acute Dyspnea Some Causes of Acute* Dyspnea , Some Causes of Subacute Dyspnea Some Causes of Subacute* Dyspnea , and Some Causes of Chronic Dyspnea Some Causes of Chronic* Dyspnea ). Several findings are of note:
Stridor Stridor Stridor is a high-pitched, predominantly inspiratory sound. It is most commonly associated with acute disorders, such as foreign body aspiration, but can be due to more chronic disorders, such... read more suggests extrathoracic airway obstruction (eg, foreign body, epiglottitis, vocal cord dysfunction).
Crackles suggest left heart failure, interstitial lung disease, or, if accompanied by signs of consolidation, pneumonia.
However, the symptoms and signs of life-threatening conditions such as myocardial ischemia and pulmonary embolism can be nonspecific. Furthermore, the severity of symptoms is not always proportional to the severity of the cause (eg, pulmonary embolism in a fit, healthy person may cause only mild dyspnea). Thus, a high degree of suspicion for these common conditions is prudent. It is often appropriate to rule out these conditions before attributing dyspnea to a less serious etiology.
A clinical prediction rule can help estimate the risk of pulmonary embolism. Note that normal oxygen saturation does not exclude pulmonary embolism.
Hyperventilation syndrome Hyperventilation Syndrome Hyperventilation syndrome is anxiety-related dyspnea and tachypnea often accompanied by systemic symptoms. Hyperventilation syndrome most commonly occurs among young women but can affect either... read more is a diagnosis of exclusion. Because hypoxia may cause tachypnea and agitation, it is unwise to assume every rapidly breathing, anxious young person merely has hyperventilation syndrome.
Pulse oximetry should be done in all patients, and a chest x-ray should be done as well unless symptoms are clearly caused by a mild or moderate exacerbation of a known condition. For example, patients with asthma or heart failure do not require an x-ray for each flare-up, unless clinical findings suggest another cause or an unusually severe attack.
Most adults should have an ECG to detect myocardial ischemia (and serum cardiac marker testing if suspicion is high) unless myocardial ischemia can be excluded clinically.
In patients with severe or deteriorating respiratory status, arterial blood gases (ABGs) should be measured to more precisely quantify hypoxemia, measure PaCO2, diagnose any acid-base disorders Acid-Base Disorders Acid-base disorders are pathologic changes in carbon dioxide partial pressure (Pco2) or serum bicarbonate (HCO3−) that typically produce abnormal arterial pH values. Acidemia is serum... read more stimulating hyperventilation, and calculate the alveolar-arterial gradient.
Patients who have no clear diagnosis after chest x-ray and ECG and are at moderate or high risk of having pulmonary embolism (from a clinical prediction rule) should undergo CT angiography or ventilation/perfusion scanning. Patients who are at low risk may have D-dimer testing (a normal D-dimer level effectively rules out pulmonary embolism in a low-risk patient).
Chronic dyspnea may warrant additional tests, such as CT, pulmonary function tests, echocardiography, and bronchoscopy.
1. Parshall MB, Schwartzstein RM, Adams L, et al: An Official American Thoracic Society Statement: Update on the mechanisms, assessment, and management of dyspnea. Am J Respir Crit Care Med 185:435–452, 2012.
Treatment of Dyspnea
Treatment is correction of the underlying disorder.
Hypoxemia (in the absence of compensatory hyperventilation) is treated with supplemental oxygen as needed to maintain oxygen saturation > 88% or PaO2 > 55 mm Hg (> 7.3 kPa) because levels above these thresholds provide adequate oxygen delivery to tissues. Levels below these thresholds are on the steep portion of the oxygen–hemoglobin dissociation curve, where even a small decline in arterial oxygen tension can result in a large decline in hemoglobin saturation. Oxygen saturation should be maintained at > 93% if myocardial or cerebral ischemia is a concern, although data suggest that supplemental oxygen is not beneficial in the treatment of acute myocardial infarction unless the patient has hypoxia.
Morphine 0.5 to 5 mg IV helps reduce anxiety and the discomfort of dyspnea in various conditions, including myocardial infarction, pulmonary embolism, and the dyspnea that commonly accompanies terminal illness. However, opioids can be deleterious in patients with acute airflow limitation (eg, asthma, COPD) because they suppress the ventilatory drive and can worsen respiratory acidemia.
Pulse oximetry is a key component of the examination.
Low oxygen saturation (< 90%) indicates a serious problem, but normal saturation does not rule one out.
Accessory muscle use, a sudden decrease in oxygen saturation, or a decreased level of consciousness requires emergency evaluation and hospitalization.
Myocardial ischemia and pulmonary embolism are relatively common, but symptoms and signs can be nonspecific.
Exacerbation of known conditions (eg, asthma, chronic obstructive pulmonary disease, heart failure) is common, but patients may also develop new problems.
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