Display Screen or Portion Thereof with a Graphical User Interface for a Medical Device

The single FIGURE is a front elevation view of a display screen or portion thereof with a graphical user interface for a medical device showing our new design.

The dash-dash broken lines showing the outer border of the display screen or portion thereof and the interior features of the graphical user interface in the drawings forms no part of the claimed design. The dot-dash broken lines and the gray broken lines of the graphical user interface form no part of the claimed design. The subject matter in the drawings indicated with the up-caret and the down-caret forms part of the claimed design.