Kussmaul sign

[Enzymes]

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I'm confused about Kussmaul's sign. I was under the impression that inspiration would increase your venous return. But on p. 295 of first aid 2014, it says that inspiration normally causes JVP to go down. Wouldn't inspiration cause more venous return and increase JVP?

Or is the idea that when we inspire, we have negative pressure in the JVP (causing blood to enter the heart), but ultimately the pressure is still low? Thanks

 

[Psai]

inspiration causes a negative thoracic cavity pressure which brings more blood into the right side of the heart (negative pressure is basically dragging the blood in). so basically you're increasing venous return to the heart but not because there is more blood in the veins themselves but because more of the blood is going into the heart from the veins. so inspiration would cause there to be more blood in the right side of the heart by taking it out of the jugular vein. so jvp goes down

kussmaul sign happens because your heart isn't filling properly because you have fluid in the pericardium that blocks expansion (maybe you have blood or pus in the pericardium around the heart) or the myocardium isn't expanding properly (for example you have fibrosis due to some inflammation from infection or autoimmune disease or there's amyloid or iron from hemochromatosis). when you breathe in, normally blood would go from the veins into the heart but because the heart isn't filling properly there is backflow of blood (like how cirrhosis causes portal hypertension). that's why you get increased jvp on inspiration