Definition of pulsus paradoxus

A drop in systolic blood pressure (BP) of greater than 10 mmHg during inspiration

Causes of pulsus paradoxus

Conditions that intensify negative intrathoracic pressure during inspiration, conditions that increase pulmonary arterial pressure, and conditions that constrict the heart can all cause pulsus paradoxus.

Pulmonary

  • Chronic obstructive pulmonary disease (COPD)
  • Obstructive sleep apnea (OSA)
  • Pulmonary embolism (PE)
  • Pulmonary hypertension
  • Exarcebation of asthma
  • Tension pneumothorax

Cardiac

  • Cardiac tamponade
  • Constrictive pericarditis
  • Superior vena cava obstruction

Other

  • Anaphylaxis
  • Pregnancy
  • Obesity

Physiology of pulsus paradoxus

Most clinicians believe that pulsus paradoxus has a singular physiology, something to do with “bowing of the interventricular septum”. In reality, the physiology can differ depending on the aetiology.

Intense negative intrathoracic pressure during inspiration

Certain conditions such as asthma exarcebation can lead to more intense negative intrathoracic pressure during inspiration. This negative pressure increases venous return to the right atrium and ventricle, as well as decreases left atrial and ventricular filling. The engorged right ventricle results in bowing of the interventricular septum and impingement of the left ventricle. All this results in reduced left ventricular filling, reduced left ventricular output, and a drop in systolic BP during inspiration.

Increased pulmonary arterial pressures

Conditions such as a pulmonary embolism and pulmonary hypertension can result in right ventricular distension. In the setting of chronically elevated pulmonary pressures, right ventricular hypertrophy develops. These situations can lead to bowing of the interventricular septum, reduced left ventricular filling, reduced left ventricular output, and a drop in systolic BP during inspiration.

Constriction of the heart

Conditions such as cardiac tamponade and constrictive pericarditis limits the heart’s ability to fill during diastole. During inspiration, the negative intrathoracic pressure leads to increased right ventricular filling, decreased left ventricular filling, bowing of the interventricular septum, reduced left ventricular output, and a drop in systolic BP.