Diagnose immediately a foreign body in the airways and anaphylaxis, and as emergencies spontaneous pneumothorax, pulmonary embolism, pulmonary oedema, asthma attack and acute exacerbation of COPD. Identify asthma, COPD, heart failure and unstable angina as causes of recurrent or chronic dyspnoea. Identify psychogenic hyperventilation syndrome and its important differential diagnoses. Dyspnoea is a subjective feeling of difficulty breathing. Acute respiratory failure is a disturbance of blood gas exchange: arterial pO2 < 8.0 or pCO2 > 6.0.