Bedside Rounds #1: Why is a pulsus paradoxus not a paradox?

February 1, 2007

Welcome to our inaugural Bedside Rounds a new regular feature of Clinical Correlations.  Here you will learn not only practical physical diagnosis pearls, but also the historical context in which these findings were discovered.

Commentary By: Judith Brenner MD, Associate Program Director, NYU Internal Medicine Residency Program

When you take a deep breath in, what happens? Because of an increase in the negative intrathoracic pressure, blood is sucked into the right side of the heart. Temporarily, a filled right ventricle can bulge into the left ventricle and thus, result in a momentary decrease in left ventricular filling. Blood also pours into the pulmonary vasculature and can result in a momentary decrease in left ventricular filling and thus, our systolic blood pressure drops. You can even test this on yourself by feeling your radial pulse and continuing to feel it during a deep inspiration. There is a subtle, but definite decrease in the amplitude of the pulsation.

What is “pulsus paradoxus”?

In fact, pulsus paradoxus is an exaggeration of normal physiology. It is an inspiratory fall in the systolic blood pressure greater than 10 mm Hg that occurs in the setting of:

  • Acute Pericardial tamponade (nearly 100% of the time)
  • Asthma with FEV1 <0.7L.
  • Shock (approximately 50% of the time)
  • PE (approximately 30% of the time)

With pericardial tamponade, the total pericardial space is constrained due to the effusion. Thus, the normal bulging of the RV into the LV is exaggerated and limits left sided filling even more. In addition, there is probably more filling and pooling of blood in the pulmonary vasculature since it is more distensible. Again, this is an exaggeration of normal physiology and systolic blood pressure declines.

How do you determine the pulsus?
Inflate your BP cuff above the systolic. Lower the pressure very slowly until you hear your first Korotkoff sound; this first sound will only be heard during expiration. Continue to lower the cuff pressure to the highest value at which you hear Korotkoff sounds with each beat; this means that you are hearing sounds with inspiration and expiration. Find the difference between the two numbers and this is the pulsus. Remember, a pulsus greater than 10 mm Hg is abnormal.

Why the paradox?
In fact, to be true to Kussmaul’s original description in 1873, he recognized that “pulsus paradoxus” was not a “paradox” but an exaggeration of normal physiology. The “paradox” that he refers to was that the peripheral pulse went away when the central heartbeat continued. “The pulse was simultaneously slight and irregular, disappearing during inspiration and returning upon expiration.”

Kussmaul’s other signs include:

  • Kussmaul’s sign: neck vein engorgement during inspiration seen in constrictive pericarditis and in fact, a true paradox!
  • Kussmaul breathing: seen in diabetic ketoacidosis

Image: Dr. Adolf Kussmaul 1822-1902, courtesy  of The Anesthesia Education Website

http://www.anaesthesiamcq.com/AcidBaseBook/AB5_4Kussmaul.php

3 Responses to Bedside Rounds #1: Why is a pulsus paradoxus not a paradox?

  1. Barry Rosenzweig on February 8, 2007 at 4:23 pm

    A very important point to remember when searching for a “paradoxical pulse” is that the blood pressure should be obtained during the slow fall of the column of mercury while the patient is breathing NORMALLY. The patient should not be instructed to breathe deeply; wide swings in intrathoracic pressure will exaggerate the normal pulsus (

  2. Greg Mints on February 9, 2007 at 2:07 am

    Several comments:

    1. Any condition in which results in exaggerated drop in intrathoracic pressure on inspiration can result in pulsus paradoxus. Examples include both deep breathing during exam and respiratory distress of any etiology (asthma, COPD, PE etc.)
    2. Hypovolemia can result in pulsus paradoxus in the absence of tamponade.
    3. Conditions resulting in unusually low inspiratory changes in intrathoracic pressure can result in absence of pulsus paradoxus in tamponade, as seen in patients with diseases of respiratory muscles.
    4. Other conditions may result in false negative pulsus in tamponade: severe hypotension and large ASD. The latter was described by Dr. Kronzon in the ‘70s. http://www.strong-mints.com/gregdocs/Hemodynamics%20and%20circ/Paradoxical%20Pulse/Winer1979.pdf
    5. Paradoxical Pulse originally referred to the absent blood pressure (decrease to zero) in the presence of pulse on inspiration seen in patients with severe tamponade. I imagine these patients were not alive for long after that original paradoxical pulse sign.
    6. An interesting difference between pulsus paradoxus seen in tamponade and the one seen in most cases of exaggerated intrathoracic pressure is that in the former diastolic pressure does not change, while in the latter both systolic and diastolic pressure change equally.
    7. This difference can be observed only while examining invasive monitoring tracings.
    8. There is good data showing that respiratory variation in the amplitude of Pulse Ox tracing correlates well with changes in arterial pressure, and therefore is a measure of pulsus paradoxus. In appropriate clinical setting this may indicate hypovolemia or “volume-responsiveness”.

  3. Asad Kundi on August 19, 2009 at 11:55 am

    The explanation given above for the reduction in pressure during inspiration is increase in right ventricle (RV volume which bulges into Left ventricle(LV)

    I think RV (interventicle septum )will bulge into LV if RV pressure is higher or at least equal to LV.

    How can it bulge,push and impair LV filling, due to increase in volume of blood during inspiration ,if the RV pressure is < 30 mm Hg ?

    Can some one comment
    Thanks
    Asad kundi

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