Expose AutoCAD 3D polyline z-value

I'm trying to import some AutoCAD contour lines and write them to a shapefile.  I need the z-value to be included in the shapefile as an attribute.  I've got the reader and an attributeExposer set up.  I cannot seem to find which AutoCAD attribute is the z-value of the lines.  I've tried writing all attributes that have a Z in the name, but each time the shape file has an empty elevation attribute.  Any ideas?