Pulsus paradoxus
"Pulsus paradoxus" refers to an abnormal decrease of over 10mmHg in pulse pressure and subsequently pulse volume on inspiration. It is caused by a decrease in intrathoracic pressure.
- On inspiration the intrathoracic pressure decreases
- The pressure intrathoracically is lower than the pressure extrathoracically which leads to an increased venous return to the right ventricles
- The right ventricles bulges into the left side reducing left ventricular volume.
- Reduced intrathoracic pressure also leads to dialation of the pulmonary vessels
- Blood from the right ventricle pools in the lungs leading to reduced blood returning to the left ventricles
- Reduced blood in the left ventricles leads to a reduced stroke volume according to starling's law.
- Reduced thoracic pressure on the aorta also contributes to the reduced pulse pressure
- Reduction of pulse pressure leads to a weaker or absent pulse volume being felt whist a contraction is heard on auscultation.
Pulsus paradoxus may occur in:
- Cardiac tamponade
- Cardiac effusion
- Restrictive pericarditis
due to reduced left ventricular filling due to increased pericardial pressure without a proportional increase in pulmonary venous pressure, and increased proportional effect of intraventricular septal bulging in a limited space.
- Severe acute asthma
- Severe COPD
due to increased differences in inspiratory and expiratory intrathoracic pressure.
- Massive PE
- Myocardial infarction
due to right ventricular dysfunction and dilation.
Douglas G, Nicol F, Robertson C, Macleod's Clinical Examination, 12th ed, Edinburgh, Churchill Livingstone, 2009.
http://www.jpgmonline.com/article.asp?issn=0022-3859;year=2002;volume=48;issue=1;spage=46;epage=9;aulast=Khasnis
http://en.wikipedia.org/wiki/Pulsus_paradoxus
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