FIG. 1 is a top perspective view of a chamber for use in implantable devices in accordance with the present design; FIG. 2 is a bottom perspective view thereof; FIG. 3 is a top view thereof; FIG. 4 is a bottom view thereof; FIG. 5 is a left side view thereof; FIG. 6 is a right side view thereof; FIG. 7 is a upper side view thereof; and, FIG. 8 is a lower side view thereof.