Aug 10, 2015
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Hey all,
Just reading FA 2015 and it says asthma, obstructive sleep apnea, pericarditis, and croup can all cause pulsus paradoxus (along with the classical cardiac tamponade) on page 299. Just wondering if anyone knows how asthma, sleep apnea, and croup can cause pulsus paradoxus!
Thanks!
 

Jabbed

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Increased intrathoracic pressure + increased venous return on inspiration = ventricular interdependence
 
OP
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Aug 10, 2015
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Increased intrathoracic pressure + increased venous return on inspiration = ventricular interdependence
Hey Jabbed, thanks for replying. I'm not entirely sure what you mean? Ventricular interdependence causing pulsus paradoxus?
 

Jabbed

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Hey Jabbed, thanks for replying. I'm not entirely sure what you mean? Ventricular interdependence causing pulsus paradoxus?
So:
1. Increased intrathoracic pressure limits the overall expansion of the ventricles.
2. Inspiration always increases venous return by decreasing intrathoracic pressure.
3. The combination of increased venous return and increased intrathoracic pressure causes the septal wall of the RV to bulge into the LV, functionally decreasing the volume of the LV.
4. ↓ LVEDV → ↓ SV → ↓ SBP

Overall we have a decrease in systolic blood pressure upon inspiration. If you substitute the underlined parts above with "constriction of the heart by pericardial effusion", this explanation also applies to the mechanism of pulsus paradoxicus in pericardial tamponade.
 

stop2stop

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May 15, 2015
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Could I possibly ask a follow up question here if anyone knows? I notice the above talking about increased intrathoracic pressure during inspiration. I thought negative intrathoracic pressure increases in inspiration. Wouldn't this do the opposite of limiting ventricular expansion? Perhaps I'm just way too confused here, but would love any help someone could provide.
 

walakin25

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Oct 28, 2015
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in the above post, when he says "increased intrathoracic pressure", he effectively means "constriction of the heart due to pericardial effusion." read the above post again and it'll make sense.
 
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stop2stop

2+ Year Member
May 15, 2015
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in the above post, when he says "increased intrathoracic pressure", he effectively means "constriction of the heart due to pericardial effusion." read the above post again and it'll make sense.
Thanks so much for the reply. I guess I am a bit confused by the fact that I don't understand why inspiration increases venous return in cardiac tamponade at all. I thought that the negative intrathoracic pressure seen on inspiration was not translated to the heart in cardiac tamponade (Reason we do not see Kussmaul sign in cardiac tamponade) and thus venous return really shouldn't be increasing more at all. Thus there shouldn't be a pulsus paradoxus in the same way that there shouldn't be a Kussmaul sign, the negative intrathoracic pressure simply cannot make up for the strong compression on the right heart by the accumulated fluid in tamponade. Does this make sense? Thanks so much for your help.