Stridor is a high-pitched sound, heard more loudly over the neck than the chest, in contrast to wheeze. Inspiratory stridor is a feature of laryngeal obstruction; expiratory stridor, of tracheobronchial obstruction; and biphasic stridor, of glottic or subglottic obstruction.

Causes of stridor include upper airway obstruction with a foreign body, angioedema, and vocal cord dysfunction.

Pulsus paradoxus is an exaggeration of the normal inspiratory fall in systolic blood pressure to >10 mmHg. When marked, it may be palpable in the radial artery, with the radial pulse disappearing on inspiration. The ‘paradox’ is that the pulse disappears despite cardiac contraction.

Pulsus paradoxus is a characteristic feature of cardiac tamponade (but may not always occur, e.g. if there is an atrial septal defect or severe aortic regurgitation). It may also be present in acute severe asthma and right ventricular infarction.