An implantable device includes an outer tubular member defining a longitudinal axis and a lumen. The outer tubular member includes: an outer wall portion having a plurality of first strands defining a plurality of first openings therebetween, the outer wall portion having a first porosity; and an inner baffle portion disposed within the lumen, the inner baffle portion including a plurality of second strands defining a plurality of second openings therebetween, the inner baffle portion having a second porosity that is lower than the first porosity of the outer wall portion.