These are two different (academic) articles from the Psychiatric Times (rapid cycling) and Current Psychiatry (ultra rapid cycling).

Rapid Cycling in Bipolar Disorder: Diagnostic Issues and Treatment Options | Psychiatric Times

Ultra-rapid cycling bipolar disorder: A critical look*:*Current Psychiatry

If the links don't come through, google "bipolar disorder rapid cycling dsm"
and "bipolar disorder ultra rapid cycling dsm"

They're a bit long and can be hard to get through til the end, but I think they're very interesting. But keep in mind that different pdocs (researchers and not) are going to have different opinions when it comes to these diagnoses/issues, so these are not the final words on the subject by any means.

If anyone else has articles on the subjects that would be great, this is a complicated and amongst some pdocs/researchers, controversial issue.