Pulsus Paradoxus

Normal person exhibit a 10 mmHg drop in systolic pressure during normal inspiration. A greater decline in systolic pressure accompanied by marked decrease in pulse amplitude during inspiration results in pulsus paradoxus. Thus it is an exaggeration of normal physiological response when additional pathological factors contribute to the drop in left ventricular stroke volume during inspiration. The paradox is that while cardiac auscultation with a stethoscope would reveal the central pulse, it cannot be felt peripherally by palpating the radial artery due to the drop in pulse amplitude during inspiration.  In short traditionally it is the inspiratory disappearance of the radial pulse but modern medicine has an object criteria based on fall in systolic pressure to diagnose pulsus paradoxus. This sign was first reported by Kussmaul(1).



Several physiological and pathological factors play simultaneously to bring about pulsus paradoxus during the inspiratory phase.

1) In conditions like cardiac tamponade, the high intrapericardial pressure decreases the filling capacity of the heart resulting in low LV ejection fraction

2) During inspiration the venous return to the right heart increases. Since the pressure surrounding heart in these conditions is high, the increased filling of right side, results in inter ventricular septum bulging into the left ventricle and limiting the filling in the left side and hence low LV ejection fraction during inspiration(2).

3) The decreased intrathoracic pressure during inspiration favors the pooling of blood in the pulmonary venous system rather than draining into the left atrium. Thus sufficient blood doesn’t flow into the left side of heart resulting in low LV ejection volume.

4) The negative intrathoracic pressure during inspiration increases the afterload and hence decreases the stroke volume and LV ejection fraction (3)(4).

5) In obstructive airway disease different mechanism may be causing pulsus paradoxus. Due to the hyperinflation, the intrapleural pressures are increased and there is increased impedance to right ventricular outflow which reduces the volume of blood passing to left heart resulting in impaired left ventricular stroke output(5).



The pulsus paradoxus can be diagnosed using sphygmomanometer. The patient should breathe normally without any exaggeration of inspiratory effort (6).  The pressure difference between the first discernible korotkoff sound on expiration and the korotkoff sounds that are heard in all phases of respiration is measured (7). This difference is less than 10 mmHg physiologically. A difference greater than 10 mmHg is indicative of pulsus paradoxus. Currently pulse oximetry plethysmographic waveform (POPW) can be used to calculate the pulsus paradoxus with better accuracy by measuring the reduced plethysmographicpeak with inspiration (8). If invasive arterial line is present pulsus paradoxus can be measured in the arterial wave form



Pulsus paradoxus is seen in the following conditions

Cardiac Causes

  1. Acute Cardiac Tamponade (9)(10)
  2. Pericardial effusion (11)(12)
  3. Constrictive Pericarditis(12)(13)
  4. Restrictive Cardiomyopathy(14)
  5. Superior Vena Caval Syndrome
  6. Cardiogenic Shock
  7. Right ventricular infarct
  8. Tricuspid Atresia

Pulmonary Causes

  1. Severe Obstructive Lung Disease
  2. Tension Pneumothorax(15)
  3. Obstructive Sleep Apnea (16)
  4. Pulmonary Embolism
  5. Croup (17)
  6. Bilateral pleural effusion (15)
  7. Tracheal compression (15)


  1. Shock (18)
  2. Hypovolumia
  3. Extra pericardial tamponade due to hiatus hernia(19)
  4. Compression of inferior vena cava in severe pectus excavatum(20)

The leftward shift of the interventricular septum during sleep in individuals with obstructive sleep apnea is attributed as a cause  of pulsus paradoxus. In addition treatment with nasal CPAP decreased the leftward shift of interventricular septum and pulsus paradoxus(16). The severity of the acute asthma can also be measured by the degree of pulsus paradoxus using a pulse oximeter wave tracing (21).


Influence of other Cardiac diseases on Pulsus paradoxus

Some co-existing cardiac conditions may interfere with the mechanisms causing pulsus paradoxus and can obliterate it or counteracting mechanisms may decrease the magnitude of the pulsus paradoxus. Some of them are as follows

  1. Severe LV dysfunction
  2. Cardiac tamponade with accompanying atrial fibrillation
  3. High left ventricular diastolic pressure
  4. Atrial septal defect
  5. Positive pressure breathing
  6. Pulmonary arterial obstruction
  7. Severe aortic regurgitation
  8. Regional right atrial effusion (22)
  9. More advanced restrictive cardiomyopathy as result of non compliant septum (1)
  10. Ventricular hypertrophy
  11. Heart failure
  12. Cardiac adhesions
  13. Acute left ventricular myocardial infarction


Reversed Pulsus Paradoxus

In reversed pulsus paradoxus there is an inspiratory rise of the arterial systolic pressure by greater than 15mmHg. This may be related to an inspiratory increase in left ventricular stroke output due to changes in intra-thoracic pressure secondary to positive pressure ventilation(23). The positive pressure acts differently in the right and left heart. In the left side it squeezes the pulmonary veins to drain into the left heart and compresses the left ventricle, thereby increasing the stroke volume and systolic blood pressure. In the right side it compresses the inferior vena cava and decreases the inflow into the right heart. With less blood the interventricular septum does not bulge into the left ventricle thereby allowing more blood to fill in the left ventricle. (Note – One of the mechanisms of pulsus paradoxus is the interventricular septum bulging into the left ventricle decreasing the volume available for ventricular filling). Reverse pulsus paradoxus can occur in the following conditions.

  1. Mechanical ventilation in a patient with left ventricular failure (24).
  2. Idiopathic hypertrophic subaortic stenosis(25)
  3. Isorhythmic ventricular rhythms(25)
  4. Hypertrophic cardiomyopathy(26)

A reverse pulsus paradoxus in a mechanically ventilated patients can also be sensitive sign of hypovolumia(27). This parameter can be helpful in determining if a patient in critical condition would benefit from fluid therapy (28).



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5.         Blaustein A, Risser T, Weiss J, Parker J, Holman B, McFadden E. Mechanisms of pulsus paradoxus during resistive respiratory loading and asthma [Internet]. J Am Coll Cardiol 1986 Sep;8(3):529-536.[cited 2011 Aug 31] Available from: http://content.onlinejacc.org/cgi/content/abstract/8/3/529

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10.       ScienceDirect - International Journal of Cardiology?: Searching for pulsus paradoxus and correlates in cardiac tamponade [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://www.sciencedirect.com/science/article/pii/S0167527309007402

11.       Arch Intern Med -- Excerpt: OBSERVATIONS ON PULSUS PARADOXUS (WITH SPECIAL REFERENCE TO PERICARDIAL EFFUSIONS) I. CLINICAL, MARCH 1924, GAUCHAT and KATZ 33 (3): 350 [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://archinte.ama-assn.org/cgi/content/summary/33/3/350

12.       Diagnostic Signs in Compressive Cardiac Disorders: Constrictive Pericarditis, Pericardial Effusion, and Tamponade [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://circ.ahajournals.org/content/33/5/763.abstract

13.       ScienceDirect - European Journal of Cardio-Thoracic Surgery?: Constrictive pericarditis, still a diagnostic challenge: comprehensive review of clinical management [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://www.sciencedirect.com/science/article/pii/S1010794009002668

14.       Pulsus Paradoxus [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://priory.com/homol/pulsus.htm

15.       Pulsus paradoxus in cardiac tamponade: A pathophysiologic continuum - Swami - 2006 - Clinical Cardiology - Wiley Online Library [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://onlinelibrary.wiley.com/doi/10.1002/clc.4960260504/abstract

16.       Leftward shift of the interventricular septum and pulsus paradoxus in obstructive sleep apnea syndrome. [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://chestjournal.chestpubs.org/content/100/4/894.short

17.       Pulsus Paradoxus . An Objective Measure of Severity in Croup -- STEELE et al. 157 (1): 331 -- American Journal of Respiratory and Critical Care Medicine [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://ajrccm.atsjournals.org/cgi/content/abstract/157/1/331

18.       Mechanism of Pulsus Paradoxus in Clinical Shock [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC292925/

19.       Outside the Box: Extra-Pericardial Tamponade Due to Acute Recurrence of Hiatus Hernia -- Moore and Fraser 89 (5): 1654 -- The Annals of Thoracic Surgery [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://ats.ctsnetjournals.org/cgi/content/abstract/89/5/1654

20.       Pectus Excavatum with Inspiratory Inferior Vena Cava Compres...?: The American Journal of the Medical Sciences [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://journals.lww.com/amjmedsci/Abstract/2005/01000/Pectus_Excavatum_with_Inspiratory_Inferior_Vena.8.aspx

21.       BioMed Central | Full text | Noninvasive assessment of asthma severity using pulse oximeter plethysmograph estimate of pulsus paradoxus physiology [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://www.biomedcentral.com/1471-2466/10/17

22.       The Eae Textbook of Echocardiography - Google Books [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://books.google.co.in/books?hl=en&lr=&id=esyW-AqN7c4C&oi=fnd&pg=PA345&dq=restrictive+cardiomyopathy+pulsus+paradoxus&ots=-m1BKfmQfN&sig=yRXHkaREkWwHXezvizFH_IhkUe8#v=onepage&q=restrictive%20cardiomyopathy%20pulsus%20paradoxus&f=false

23.       Physiologic and Clinical Principles behind Noninvasive Resuscitation Techniques and Cardiac Output Monitoring [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://www.hindawi.com/journals/crp/2012/531908/

24.       Changes in Arterial Pressure during Mechanical Ventilation?: Anesthesiology [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://journals.lww.com/anesthesiology/Abstract/2005/08000/Changes_in_Arterial_Pressure_during_Mechanical.26.aspx

25.       Reversed Pulsus Paradoxus — NEJM [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://www.nejm.org/doi/pdf/10.1056/NEJM197312132892403

26.       Dynamic respiratory changes in hypertrophic cardiomyopathy [Internet]. [date unknown];[cited 2011 Aug 31] Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1768103/

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