Dyspnea

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.

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

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)

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.