Dyspnea

Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychologic exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). The medical history and physical exam of a patient presenting with dyspnea should be used to rule out certain conditions or suggest the most likely cause of the respiratory discomfort. Management focuses on treating the underlying condition.

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Definition and Epidemiology

Definition

Dyspnea is the subjective sensation of breathing discomfort that derives from interactions among multiple physiologic, psychologic, social, and environmental factors. 

  • Also referred to as chest tightness or shortness of breath
  • Experienced and described differently among patients depending on the cause
  • Types:
    • Acute dyspnea: occurring within minutes of the triggering event
    • Chronic dyspnea: lasting longer than 1 month

Epidemiology

  • Very common symptom, present in: 
    • 50% of inpatients
    • 25% of ambulatory patients
    • 9%–13% of the entire population
    • 37% of people aged ≥ 70 years
  • In chronic obstructive pulmonary disease (COPD) and other pathologic lung and heart conditions, dyspnea may be a better predictor of outcome than traditional assessments.

Etiology

There are 5 basic categories of causes that can lead to dyspnea. The causes can present individually or as a combination:

  1. Respiratory conditions
  2. Cardiac conditions
  3. Neuromuscular conditions
  4. Psychogenic conditions
  5. Systemic illnesses

General causes of dyspnea

Table: Pulmonary causes of dyspnea
EtiologyClinical presentationAssociated conditions
Obstructive lung disease Characterized by air trapping in the lungs:
  • ↑ FRC and TLC
  • ↓↓ FEV₁
  • ↓ FVC
  • ↓ FEV₁/FVC
Findings:
  • Wheezing
  • Dyspnea is not worsened by a change in body position.
  • COPD
  • Chronic bronchitis
  • Bronchiectasis
  • Emphysema
  • Asthma
Restrictive lung disease Characterized by decreased lung compliance:
  • FVC and TLC
  • FEV₁/FVC ≥ 80%
  • Short, shallow breaths
Findings:
  • Short, shallow breaths
Poor breathing mechanics:
  • Polio
  • Kyphoscoliosis
  • Morbid obesity

ILDs:
  • Pneumoconiosis
  • Sarcoidosis
  • Idiopathic pulmonary fibrosis
  • Drug toxicity:
    • Bleomycin
    • Amiodarone
    • Methotrexate
Upper airway obstruction Findings:
  • Usually causes acute onset of dyspnea
  • Associated with stridor
  • Epiglottitis
  • Foreign body obstruction
  • Croup
Others Clinical presentation and findings vary with the cause.
  • Pulmonary embolism
  • Pneumothorax
  • Pleural effusions
  • Metastatic disease
  • Pulmonary edema
FRC: functional residual capacity
TLC: total lung capacity
FEV₁: forced expiratory capacity in 1 second
FVC: forced vital capacity
ILD: interstitial lung disease
Table: Extrapulmonary causes of dyspnea
EtiologyClinical presentationAssociated conditions
Cardiac Often a complication of left-sided heart failure
Findings:
  • Dyspnea varies with body position.
  • Orthopnea
  • Paroxysmal nocturnal dyspnea
  • Bibasilar crackles
  • Hypertensive or valvular heart disease
  • Cardiomyopathy
  • Ischemic heart disease:
    • Stable/unstable angina
    • Acute MI
    • Coronary heart disease
  • Heart failure with a reduced or preserved EF
  • Pericarditis
  • Arrhythmia
Anemia Due to impaired tissue oxygenation
Findings:
  • Dyspnea, persistent or on exertion
  • Pale skin and conjunctivae
  • Tachycardia
  • Hypovolemic shock
  • Acute hemorrhage
Psychogenic Hyperventilation may lead to acute respiratory alkalosis manifested as:
  • Paresthesias in the fingertips and around the mouth
  • Tetanic cramps in severe cases
  • Panic disorder
  • Anxiety
  • Intense pain
  • Somatization disorder
Endocrine Changes in pH and PaCO₂ stimulate the brainstem:
  • Alveolar hyperventilation
  • Deep breathing
  • Compensates acidosis by dilating cerebral arterioles, to increase “washout” of CO₂ from the brainstem
Metabolic acidosis:
  • Ketoacidosis in diabetes
  • Acidosis in renal insufficiency
Medications:
  • Salicylate overdose
Central dyspnea Clinical presentation and findings vary with the cause. Neuromuscular disease
  • Myasthenia gravis
  • Guillain-Barré
  • Amyotrophic lateral sclerosis
MI: myocardial infarction
EF: ejection fraction

Acute dyspnea

Common causes per affected organ system:

  • Conditions affecting the cardiovascular system:
    • Acute myocardial ischemia
    • Heart failure
    • Cardiac tamponade
  • Conditions affecting the respiratory system:
    • Asthma 
    • Pulmonary infection/bronchitis
    • Pulmonary embolism
    • Pneumothorax
    • Upper airway obstruction

Chronic or recurrent dyspnea

The 5 most common causes:

  • Asthma
  • COPD
  • Interstitial lung disease (ILD)
  • Myocardial dysfunction 
  • Obesity/physical deconditioning 

Pulmonary causes of chronic dyspnea can originate from disturbances in any of the following:

  • Central respiratory controller: the efferent signals from the brain to the ventilatory muscles, which produce “air hunger” when stimulated
  • Ventilatory pump: the muscles, peripheral nerves, airways, and chest wall used to move air into and out of the lungs
  • Gas exchange: the alveolar membranes:
    • Affected in conditions with hypoxemia +/- hypercapnia
    • Leads to stimulation of the central controller

Extrapulmonary causes of chronic dyspnea:

  • Heart failure
  • Anemia
  • Physical deconditioning

Pathophysiology

  • Dyspnea is a poorly understood phenomenon. 
  • Appears to be a mismatch of afferent and efferent signaling between the respiratory and central nervous system (CNS) (“neuromechanical uncoupling”): 
    • Afferent signals from:
      • Chemoreceptors activated by hypoxemia, hypercapnia, and acidosis
      • Mechano-, biochemical, and irritant receptors
    • Efferent signals from the CNS (motor cortex, brainstem) to the following: 
      • Respiratory muscles
      • Sensory cortex (by corollary discharge), which cause sensation of work of breathing and air hunger 
    • Autonomic input by fear and anxiety contribute to the dyspneic state.
  • Changes in lung physiology can also contribute to the sensation of dyspnea:
    • Increased airway resistance
    • Increased dead space
    • Ventilation-perfusion mismatch
    • Decrease in lung/chest wall compliance
    • Impaired oxygen delivery/utilization:
      • Reduced oxygen-carrying capacity of the blood
      • Physical deconditioning

Diagnosis

Important elements in the clinical history

  • Features of the dyspnea:
    • Duration
    • Onset
    • Severity
    • Progression
  • Triggers:
    • Exertion
    • Body position
    • Cold air
    • Allergy to animal dander or other allergens
    • Stress/anxiety
  • Associated symptoms:
    • Cough
    • Sputum production
    • Orthopnea
    • Paroxysmal nocturnal dyspnea
    • Chest pain
    • Peripheral edema
    • Palpitations
  • Effects of medications (e.g., albuterol, beta blockers)
  • Tobacco history
  • Thrombosis risk factors
Table: Important elements in the physical exam
Elements of the physical examImportant signsRed-flag signs
Vital signs
  • Stable versus unstable
  • Is the respiratory rate increasing?
  • Is the work of breathing increasing?
Red-flag vital signs:
  • Heart rate > 120/min
  • Respiratory rate > 30/min
  • Pulse oximetry < 90%
  • Hypotension
Pulmonary
  • Stridor
  • Wheezing
  • Crackles
  • Rales
Red-flag exam findings:
  • Stridor or airway obstruction
  • Periods of apnea
  • Use of accessory muscles, chest retractions, or tracheal deviation
  • Cyanosis
  • Altered mental status
  • Fatigue
  • Reduced or asymmetric breath sounds
Cardiovascular
  • Jugular venous distention
  • Distant heart sounds
  • Tachycardia
  • Arrhythmia
  • Murmurs
  • Gallops
  • Peripheral edema
Abdominal
  • Protruding abdomen
Musculoskeletal
  • Muscle weakness
  • Clubbing

Labs

  • Complete blood count and basic metabolic profile, especially if patients present with fever, sputum production, or anemia
  • Brain natriuretic peptide (BNP) levels to assist in the diagnosis of heart failure 
  • D-dimer, in conjunction with Well’s criteria, to evaluate for pulmonary embolism
  • Troponin to assist in the diagnosis of MI
  • Arterial blood gas

Imaging and other tests

  • Chest X-ray to evaluate the presence of cardiopulmonary disease (e.g., congestive heart failure, COPD, cor pulmonale, pulmonary hypertension)
  • Lateral neck radiography and direct visualization by endoscopy, if upper airway obstruction is suspected 
  • Electrocardiogram (ECG) may detect ischemia/infarction, arrhythmia, or ventricular hypertrophy.
  • Computed tomography (CT) pulmonary angiogram or ventilation-perfusion (VQ) lung scan if pulmonary embolism is suspected 
  • Spirometry can differentiate the following:
    • Obstructive versus restrictive lung disease
    • Upper versus lower airway obstruction
    • Asthma versus COPD, if used with a bronchodilator 
  • Echocardiography and cardiac stress testing if cardiac conditions are suspected (e.g., MI, heart failure)

Diagnostic algorithm for dyspnea

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Management

  • Symptomatic relief can be achieved with supplemental oxygen, but one must identify and correct the underlying condition for long-term treatment:
    • Asthma:
      • Inhaled bronchodilators, corticosteroids, other medications
      • 5-step treatment strategy from the Global Initiative for Asthma Group
    • COPD exacerbations: 
      • Bronchodilator therapy and a course of oral glucocorticoids
      • Possible oral antibiotics (antivirals if there is evidence of influenza)
      • Supplemental oxygen if hypoxic and pulmonary rehabilitation program
    • Heart failure: 
      • Treatment depends on the type of heart failure and severity.
      • Follow published guidelines for treatment.
      • Heart failure and angina medication
    • Pneumonia/infectious causes: 
      • Use the appropriate antibiotic for the causative pathogen.
    • Pulmonary embolism:
      • Thrombolytics (anticoagulants and antiplatelet agents)
      • Embolectomy and/or a vena cava filter if thrombolytics are contraindicated
  • If complete relief of dyspnea is not possible, then attempts at lessening the intensity of dyspnea should follow with other therapy:
    • Oxygen supplementation if O₂ saturation < 88% at rest, with activity, or while sleeping
    • Opioids can reduce air hunger, but one must:
      • Consider the risk-benefit profile.
      • Monitor the patient carefully because of opioids’ ability to cause respiratory depression. 
    • Inhaled furosemide appears to be effective (large-scale studies are pending).

Clinical Relevance

The following conditions are the most common causes of dyspnea by organ system:

Cardiovascular conditions

  • Acute MI: ischemia of the myocardial tissue due to a complete obstruction or drastic constriction of the coronary artery. Acute MI is usually accompanied by an increase in cardiac enzymes, typical ECG changes, and chest pain. 
  • Heart failure: the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Risk factors include hypertension, diabetes mellitus, and coronary artery disease. Echocardiography can confirm the reduced EF. 
  • Cardiac tamponade: the condition of having an abnormal amount of fluid in the pericardial cavity of the heart that restricts cardiac filling and leads to acute heart failure. Treated by pericardiocentesis, removing the fluid with a needle.

Respiratory conditions

  • Asthma: a chronic inflammatory condition characterized by reversible obstruction to airflow in the lower airways. Presents with intermittent or persistent wheezing, cough, and dyspnea. Diagnosis is confirmed with pulmonary function testing that shows a reversible obstructive pattern. 
  • Pneumonia: acute or chronic inflammation of lung tissue caused by infection with bacteria, viruses, or fungi. Pneumonia can also be due to toxic triggers through inhalation of toxic substances, immunologic processes, or radiotherapy.
  • Pulmonary embolism: a potentially fatal clinical condition that occurs as a result of mechanical obstruction of the pulmonary artery or its branches by a thrombus, air, or fat. Diagnosis is established by CT pulmonary angiogram.
  • Pneumothorax: a collection of air in the pleural space that causes the lung to collapse due to the loss of negative pressure. Presents with pleuritic chest pain, dyspnea, tachycardia, and reduced breath sounds on the ipsilateral side.
  • Airway obstruction: a partial or complete blockage of airflow in the respiratory tract, which can be classified into upper or lower airway obstructions. Usually associated with foreign body aspirations, but can be caused by other conditions including mucous plug, epiglottitis, infections, smoke inhalation, goiter, etc.
  • COPD: a spectrum of conditions characterized by irreversible airflow limitation correlated to smoking. Results from obstructive inflammation of the small airways as well as changes in the lung parenchyma and pulmonary vasculature. 
  • ILD: a heterogeneous group of disorders characterized by the inflammation and fibrosis of the lung parenchyma, especially the pulmonary connective tissue in the alveolar walls. May be idiopathic or secondary to connective tissue diseases, medications, malignancies, occupational exposure, or allergens.

References

  1. Parshall, M.B., Schwartzstein, R.M., et al. (2012). American Thoracic Society Committee on Dyspnea. Am J Respir Crit Care Med. 185(4):435. 
  2. Schwartzstein, R.M. (2020). Approach to the patient with dyspnea. UpToDate. Retrieved September 16, 2020, from https://www.uptodate.com/contents/approach-to-the-patient-with-dyspnea?search=dyspnea&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
  3. Baron, R.M. (2018). In Jameson, J.L., et al. (Ed.), Harrison’s Principles of Internal Medicine (20th ed. Vol 1, pp. 226–230 and 1943–1947). 
  4. Pasterkamp, H. (2012). Kendig & Chernick’s Disorders of the Respiratory Tract in Children (8th ed.), pp. 110–130.

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