its a good start..
Id say it is a bit bland looking.
I dont know how lungs correctly look so i cant comment on that aspect.
from a pixeling standpoint, id suggest dropping the dithering since it suggests a bit of texture, and as far as i know lungs are smooth and shiney.. perhaps you could add some speculars/shininess to it..
also the aa around the line art makes it seem blurry.
I'd try to make the forms look more volumous, id suggest studying some basic forms like a cylinder for the breathing pipe to get ideas on how to do it.
