From CpapWiki
Respiratory Disturbance Index
The acronym RDI is commonly used for Respiratory Disturbance Index.
Includes apneas and hypopneas, and may also include other respiratory disturbances such as snoring arousals, hypoventilation episodes, desaturation events, etc. They are often identical, but depending upon what is scored, the RDI may be larger than the AHI.