The word mudra covers three bodies of material that get printed together and are neither the same age nor the same kind of thing. The iconographic layer is a hand position that identifies a figure in sculpture and painting, readable from the early centuries CE onward. The textual layer is the mudras named in the hatha and tantric corpus, where a mudra is a whole bodily technique rather than a hand shape. The third is a twentieth century therapeutic literature of finger positions matched to elements and ailments, which borrows the vocabulary of the other two and is continuous with neither.
Apana Mudra belongs to the third layer. It is one of a set of finger positions, each formed by joining the thumb to one or more of the other fingers and each matched to an element or a planet, that circulates through modern yoga teaching and through a large popular literature on mudra therapy published from the middle of the twentieth century onward. The set has a genuine root in the older material: the hatha compendia do name five dharana mudras after the elements. But those are concentration practices on the elements, not the finger positions taught under these names now, and the modern set is not found in that form in the classical texts.
This matters for how the claims should be read. The therapeutic effects attached to Apana Mudra in the popular literature, on digestion, on circulation, on particular complaints, are claims made by that literature and by the teachers within it. They are not claims of the classical tradition, they are not supported by clinical evidence, and the atlas records who makes them rather than making them. Describing the practice accurately and endorsing its stated effects are different jobs, and only the first belongs here.