Pathophysiology of early and late cyanosis

[Hemichordate]

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Can anyone explain why R->L shunt creates early cyanosis and L -> R shunts create late cyanosis? Also, why does that cause blue babies and blue kids, respectively?

 

[loveoforganic2]

R->L shunt puts deoxygenated blood directly into systemic circulation. L->R shunt increases the volume of blood going through pulmonary vasculature, which causes proliferation of vascular smooth muscle over a long period of time, eventually becoming significant enough to reverse the normal L>R pressure gradient to R>L (becomes a R->L shunt and causes cyanosis for the same reason as in early cyanosis). The reversal of pressure gradients is called Eisenmenger syndrome

 

[Hemichordate]

Ok thanks I think I get that. But if the L->R shunt doesn't become a R -> L shunt, do you still get late cyanosis?

 

[loveoforganic2]

You can have transient episodes of cyanosis (e.g. in ToF), but those are still due to reversal of the shunt (the cause of the reversal is different though - physiologic increases in right sided pressure/resistance rather than pathologic)