MD Notes

creation date: 2025-07-11 02:16
tags: Workups

Dyspnea

Background

Also referred to as breathing discomfort, dyspnea is a common manifestation of pulmonary disease as well as a number of other disorders ranging from myocardial ischemia to deconditioning.

Considered acute if develops over hours to days and chronic when it occurs more than 4-8 weeks. Chronic dyspnea can be acutely worsened.

Dyspnea can be classified as respiratory system dyspnea which relate to the central controller, ventilatory pump, and gas exchanger or cardiovascular system dyspnea, which relate to cardiac diseases (eg. ischemia, systolic dysfunction, pericardial diseases), anemia, and deconditioning.

Note that the physiology of dyspnea does not always adhere to one type or the other.

Pathophysiology

Respiratory
Controller: determines rate and depth of breathing via efferent signals sent to ventilatory muscles. Ventilation and breathing discomfort may be induced through stimulation by:

  • Hypoxia or hypercapnia, such as due to ventilation/perfusion mismatch
  • Stimulation of pulmonary receptors (eg. interstitial inflammation or edema)
  • Drugs (eg. aspirin overdose, progesterone)
  • Conditions (eg. pregnancy, DKA)
    Ventilatory pump: consisting of ventilatory muscles, peripheral nerves, chest wall bones, the pleura, and airways. Actions of the pump translate to the flow of gas between the atmosphere and the alveoli. Derangements include:
  • Neuromuscular weakness (eg. myasthenia gravis, Guillain-Barre syndrome)
  • Reduced compliance of chest wall (eg. kyphoscoliosis)
  • Reduced compliance of lungs (eg. interstitial fibrosis)
  • Hyperinflation (eg. obstructive lung disease) resulting in combination of above
    Gas exchanger: consisting of the alveoli and pulmonary capillaries. Possible derangements include:
  • Destruction of diffusing membrane (eg. emphysema)
  • Addition of fluid or inflammatory material reducing ventilation region
  • Increased diffusion distance

Cardiovascular
Heart failure: causes dyspnea through increased venous pressure and fluid accumulation and reduced cardiac output (and thus issue metabolism and waste from anaerobic energy generation stimulating metaboreceptors)
Anemia: impairs oxygen delivery; possible similar mechanism to heart failure
Deconditioning: exertionary “discomfort” which may be due to underlying cardiopulmonary disease or poor cardiovascular fitness

Differential Diagnosis

Acute dyspnea
Cardiovascular

Chronic dyspnea
The differential for chronic dyspnea without a clear etiology is broad but is most commonly one of the following five:

Initial Evaluation

History

Pertinent positives/negatives include:

  • Positional (ie. orthopnea)
  • Timing (ie. PND)
  • Exertional (to what degree, new-onset worsening)
  • Cough
  • Sputum production (volume and characteristic)
  • Hemoptysis
  • Risk factors for PE (see Well’s score)
  • Lower extremity edema
  • Recent infection, sick contacts

Relevant PMHx include:

  • DVT/PE
  • COPD
  • CHF

Physical Exam

O/E should include:

  • Respiratory exam
  • Cardiovascular exam
  • Examination of lower extremities
  • ENT exam

Investigations

References

Tools / Guidelines

Additional Reading

Backlinks