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Dyspnea

by Noah Lechtzin, MD, MHS

Dyspnea is unpleasant or uncomfortable breathing. It is experienced and described differently by patients depending on the cause.

Pathophysiology

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 recent 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 CNS. Some authors have described the imbalance between neurologic stimulation and mechanical changes in the lungs and chest wall as neuromechanical uncoupling.

Etiology

Dyspnea has many pulmonary, cardiac, and other causes, which vary by acuity of onset (see Table: Some Causes of Acute* Dyspnea, see Table: Some Causes of Subacute* Dyspnea, and see Table: Some Causes of Chronic* Dyspnea).

The most common causes include

  • Asthma

  • Pneumonia

  • COPD

  • Myocardial ischemia

  • Deconditioning

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 an MI, a patient with chronic heart failure may develop pneumonia).

Some Causes of Acute* Dyspnea

Cause

Suggestive Findings

Diagnostic Approach

Pulmonary causes

Pneumothorax

Abrupt onset of sharp chest pain, tachypnea, diminished breath sounds, and hyperresonance to percussion

May follow injury or occur spontaneously (especially in tall, thin patients and in patients with COPD)

Chest x-ray

Pulmonary embolism

Abrupt onset of sharp chest pain, tachypnea, and tachycardia

Often risk factors for pulmonary embolism (eg, cancer, immobilization, DVT, pregnancy, use of oral contraceptives or other estrogen-containing drugs, recent surgery or hospitalization, family history)

CT angiography Less often, V/Q scanning and possibly pulmonary arteriography

Asthma, bronchospasm, or reactive airway disease

Wheezing and poor air exchange that arise spontaneously or after exposure to specific stimuli (eg, allergen, URI, cold, exercise)

Possibly pulsus paradoxus

Often a preexisting history of reactive airway disease

Clinical evaluation

Sometimes pulmonary function testing or peak flow measurement

Foreign body inhalation

Sudden onset of cough or stridor in a patient (typically an infant or young child) without URI or constitutional symptoms

Inspiratory and expiratory chest x-rays

Sometimes bronchoscopy

Toxin-induced airway damage (eg, due to inhalation of chlorine or hydrogen sulfide)

Sudden onset after occupational exposure or inappropriate use of cleaning agents

Inhalation usually obvious by history

Chest x-ray

Sometimes ABGs and observation to determine severity

Cardiac causes

Acute myocardial ischemia or infarction

Substernal chest pressure or pain that may or may not radiate to the arm or jaw, particularly in patients with risk factors for CAD

ECG

Cardiac enzyme testing

Papillary muscle dysfunction or rupture

Sudden onset of chest pain, new or loud holosystolic murmur, and signs of heart failure, particularly in patients with recent MI

Auscultation

Echocardiography

Heart failure

Crackles, S 3 gallop, and signs of central or peripheral volume overload (eg, elevated neck veins, peripheral edema)

Dyspnea while lying flat (orthopnea) or appearing 1–2 h after falling asleep (paroxysmal nocturnal dyspnea)

Auscultation

Chest x-ray

BNP measurement

Echocardiography

Other causes

Diaphragmatic paralysis

Sudden onset after trauma affecting the phrenic nerve

Frequent orthopnea

Chest x-ray

Fluoroscopic sniff test

Anxiety disorder causing hyperventilation

Situational dyspnea often accompanied by psychomotor agitation and paresthesias in the fingers or around the mouth

Normal examination findings and pulse oximetry measurements

Clinical evaluation

Diagnosis of exclusion

*Acute dyspnea occurs within minutes of triggering event.

Most patients should have pulse oximetry and, unless symptoms are clearly a mild exacerbation of known chronic disease, chest x-ray.

BNP = brain (B-type) natriuretic peptide; DVT = deep venous thrombosis; S 3 = 3rd heart sound; V/Q =ventilation/perfusion.

Some Causes of Subacute* Dyspnea

Cause

Suggestive Findings

Diagnostic Approach

Pulmonary causes

Pneumonia

Fever, productive cough, dyspnea, sometimes pleuritic chest pain

Focal lung findings, including crackles, decreased breath sounds, and egophony

Chest x-ray

Sometimes blood and sputum cultures

WBC count

COPD exacerbation

Cough, productive or nonproductive

Poor air movement

Accessory muscle use or pursed lip breathing

Clinical evaluation

Sometimes chest x-ray and ABGs

Cardiac causes

Angina or CAD

Substernal chest pressure with or without radiation to the arm or jaw, often provoked by physical exertion, particularly in patients with risk factors for CAD

ECG

Cardiac stress testing

Cardiac catheterization

Pericardial effusion or tamponade

Muffled heart sounds or enlarged cardiac silhouette in patients with risk factors for pericardial effusion (eg, cancer, pericarditis, SLE)

Possibly pulsus paradoxus

Echocardiography

*Subacute dyspnea occurs within hours or days.

Most patients should have pulse oximetry and, unless symptoms are clearly a mild exacerbation of known chronic disease, chest x-ray.

CAD = coronary artery disease.

Some Causes of Chronic* Dyspnea

Cause

Suggestive Findings

Diagnostic Approach

Pulmonary causes

Obstructive lung disease

Extensive smoking history, barrel chest, and poor air entry and exit

Chest x-ray

Pulmonary function testing (at initial evaluation)

Restrictive lung disease

Progressive dyspnea in patients with known occupational exposure or neurologic condition

Chest x-ray

Pulmonary function testing (at initial evaluation)

Interstitial lung disease

Fine crackles, frequently accompanied by dry cough

High-resolution chest CT

Pleural effusion

Pleuritic chest pain, lung field that is dull to percussion and has diminished breath sounds

Sometimes history of cancer, heart failure, RA, SLE, or acute pneumonia

Chest x-ray

Often chest CT and thoracentesis

Cardiac causes

Heart failure

Crackles, S 3 gallop, and signs of central or peripheral volume overload (eg, elevated neck veins, peripheral edema)

Orthopnea or paroxysmal nocturnal dyspnea

Auscultation

Chest x-ray

Echocardiography

Stable angina or CAD

Substernal chest pressure with or without radiation to the arm or jaw, often provoked by physical exertion, particularly in patients with risk factors for CAD

ECG

Cardiac stress testing

Sometimes cardiac catheterization

Other causes

Anemia

Dyspnea on exertion progressing to dyspnea at rest

Normal lung examination and pulse oximetry measurement

Sometimes systolic heart murmur due to increased flow

CBC

Physical deconditioning

Dyspnea only on exertion in patients with sedentary lifestyle

Clinical evaluation

*Chronic dyspnea occurs within hours to years.

Most patients should have pulse oximetry and, unless symptoms are clearly a mild exacerbation of known chronic disease, chest x-ray.

CAD = coronary artery disease; S 3 = 3rd heart sound.

Evaluation

History

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 with 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 [PE], myocardial ischemia, pneumonia); dependent edema, orthopnea, and paroxysmal nocturnal dyspnea (heart failure); fever, chills, cough, and sputum production (pneumonia); black, tarry stools or heavy menses (occult bleeding possibly causing anemia); and weight loss or night sweats (cancer or chronic lung infection).

Past medical history should cover disorders known to cause dyspnea, including asthma, COPD, and heart disease, as well as risk factors for the different etiologies:

  • Smoking history—for cancer, COPD, and heart disease

  • Family history, hypertension, and high cholesterol levels—for coronary artery disease

  • 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 PE

Occupational exposures (eg, gases, smoke, asbestos) should be investigated.

Physical examination

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 (a > 12-mm Hg drop of systolic BP during inspiration) can be done by inflating a BP 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. Rectal examination and stool guaiac testing should be done.

Red flags

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

  • Chest pain

  • Crackles

  • Weight loss

  • Night sweats

  • Palpitations

Interpretation of findings

The history and physical examination often suggest a cause and guide further testing (see Table: Some Causes of Acute* Dyspnea, see Table: Some Causes of Subacute* Dyspnea, and see Table: Some Causes of Chronic* Dyspnea). Several findings are of note. Wheezing (see Wheezing) suggests asthma or COPD. Stridor (see Stridor) 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 PE can be nonspecific. Furthermore, the severity of symptoms is not always proportional to the severity of the cause (eg, PE 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 (see Table: Clinical Prediction Rule for Diagnosing Pulmonary Embolism) can help estimate the risk of PE. Note that a normal O 2 saturation does not exclude PE.

Hyperventilation syndrome 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.

Testing

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, ABGs should be measured to more precisely quantify hypoxemia, measure Pa co 2 , diagnose any acid-base disorders 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 PE (from the clinical prediction rule—see Table: Clinical Prediction Rule for Diagnosing Pulmonary Embolism) 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 PE in a low-risk patient).

Chronic dyspnea may warrant additional tests, such as CT, pulmonary function tests, echocardiography, and bronchoscopy.

Treatment

Treatment is correction of the underlying disorder.

Hypoxemia is treated with supplemental O 2 as needed to maintain Sa O 2 > 88% or Pa O 2 > 55 mm Hg because levels above these thresholds provide adequate O 2 delivery to tissues. Levels below these thresholds are on the steep portion of the O 2 –Hb dissociation curve, where even a small decline in arterial O 2 tension can result in a large decline in Hb saturation. O 2 saturation should be maintained at > 93% if myocardial or cerebral ischemia is a concern.

Morphine 0.5 to 5 mg IV helps reduce anxiety and the discomfort of dyspnea in various conditions, including MI, PE, 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.

Key Points

  • Pulse oximetry is a key component of the examination.

  • Low O 2 saturation (< 90%) indicates a serious problem, but normal saturation does not rule one out.

  • Accessory muscle use, a sudden decrease in O 2 saturation, or a decreased level of consciousness requires emergency evaluation and hospitalization.

  • Myocardial ischemia and PE are relatively common, but symptoms and signs can be nonspecific.

  • Exacerbation of known conditions (eg, asthma, COPD, heart failure) is common, but patients may also develop new problems.

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