52. Dyspnoea

Last updated on December 13, 2018 at 14:48

Dyspnoea is defined as the subjective feeling of difficulty to breathe. Patients usually complain about an unpleasant feeling of awareness of respiratory efforts, shortness of breath and angina-like thoracic pressure.

Dyspnoea isn’t always accompanied by respiratory failure, however they often occur together. It always involves an increased work of breathing.

It can be caused by:

  • Exercise (not pathological)
  • Increased respiratory drive
    • Hypoxaemia
    • Metabolic acidosis
    • Stimulation of J-receptors
      • Pulmonary infiltration by cancer
      • Pulmonary hypertension
      • Pulmonary oedema
  • Impaired ventilation
    • Airway obstruction
      • Bronchial asthma
      • Emphysema
      • Bronchitis
      • Trachea or larynx obstruction
    • Impaired lung compliance
      • Pulmonary fibrosis
      • Left ventricular failure
    • Impaired compliance of the chest
      • Kyphoscoliosis
      • Obesity
      • Pregnancy
  • Weakness of ventilatory muscles
    • Neurological disorders
  • Enhanced dead-space ventilation (increased V/Q ratio)
    • Capillary destruction
      • Emphysema
      • Interstitial lung diseases
    • Obstruction of pulmonary vessels (embolism)
  • Anxiety

J-receptors (or C-fibre receptors) are receptors located in the alveolar wall. They’re activated by the factors listed above and are innervated by vagus. Stimulation of these receptors causes a reflex increase in respiratory drive (increased breathing rate). The reflex is also part of the sensation of dyspnoea.

Types of dyspnoea

Dyspnoea of cardiac origin and dyspnoea of pulmonary origin have different symptoms, so we can look at them as two different types.

Cardiac dyspnoea occurs due to pulmonary congestion or oedema and induces alveolar hyperventilation, which causes hypocapnia and hypoxaemia. The hypocapnia can cause cerebral vasoconstriction which may lead to psychosomatic symptoms, a disorder called hyperventilation syndrome.

Pulmonary dyspnoea occurs in most lung diseases. Hypoxaemia can be caused by many things, like V/Q mismatching or diffusion abnormalities. Global respiratory failure usually develops, causing hypercapnia rather than hypocapnia.

In both types can pulmonary hypertension develop due to widespread vasoconstriction in the lungs due to hypoxia.

Pathomechanism of dyspnoea

Dyspnoea develops when the brain understands that there is a mismatch between how ventilation should be and how the ventilation currently is. The brain compares the afferent signals from chemoreceptors, J-receptors, muscle spindles in respiratory muscles, proprioceptors and other peripheral and central receptors and the efferent signals going from the respiratory centre to the respiratory muscles. When there’s a mismatch between the respiratory drive and the actual ventilation will the sensory cortex induce the sensation that “something’s wrong with the respiration”.

 


Previous page:
51. Partial or complete respiratory failure

Next page:
53. Forms, general pathophysiology and consequences of anaemia

2 thoughts on “52. Dyspnoea”

  1. Are you gonna take pathology exam first ?
    Can you please upload more notes for pathophysio if you finished them ?
    Thank you very much. I really appreciate your great work
    Good luck for the exams 😍

    1. Yes, I’m planning on doing pathology the 10th, which is why I’m rushing to finish the patho topics first. After that I’ll continue with the pathophys topics, hopefully I’ll finish before the 19th. I’ll upload them as I do them.

      I appreciate the kind words, good luck for your exams too! ❤

Leave a Reply

Only the "Comment" field must be filled in. It is not compulsory to fill out your name; you can remain anonymous. Do not fill out e-mail or website; if you do, your comment will not be published.