A breathing therapy device comprising: a. a blower; b. a processor; c. a motor control component, under control of said processor, for controlling the speed of said blower; and d. a flow sensing element, for sensing total flow of air from said blower, said processor to provide the following functions: i. collecting flow data from said flow sensing element; ii. analyzing said flow data to detect patterns of periodic breathing in a user of said device; iii. rating a severity of said periodic breathing, wherein rating the severity of said periodic breathing comprises configuring said processor to: calculate a power envelope of a normalized amplitude signal representing waxing and waning of cycles of said patient flow data; calculate a signal representing a zero crossing variance of said normalized amplitude signal; and classify the severity of said periodic breathing using said power envelope of said normalized amplitude signal and said signal representing the zero crossing variance; and iv. altering therapy delivered to said user based on said rated severity of said periodic breathing. a. a blower; b. a processor; c. a motor control component, under control of said processor, for controlling the speed of said blower; and d. a flow sensing element, for sensing total flow of air from said blower, said processor to provide the following functions: i. collecting flow data from said flow sensing element; ii. analyzing said flow data to detect patterns of periodic breathing in a user of said device; iii. rating a severity of said periodic breathing, wherein rating the severity of said periodic breathing comprises configuring said processor to: calculate a power envelope of a normalized amplitude signal representing waxing and waning of cycles of said patient flow data; calculate a signal representing a zero crossing variance of said normalized amplitude signal; and classify the severity of said periodic breathing using said power envelope of said normalized amplitude signal and said signal representing the zero crossing variance; and iv. altering therapy delivered to said user based on said rated severity of said periodic breathing. i. collecting flow data from said flow sensing element; ii. analyzing said flow data to detect patterns of periodic breathing in a user of said device; iii. rating a severity of said periodic breathing, wherein rating the severity of said periodic breathing comprises configuring said processor to: calculate a power envelope of a normalized amplitude signal representing waxing and waning of cycles of said patient flow data; calculate a signal representing a zero crossing variance of said normalized amplitude signal; and classify the severity of said periodic breathing using said power envelope of said normalized amplitude signal and said signal representing the zero crossing variance; and calculate a power envelope of a normalized amplitude signal representing waxing and waning of cycles of said patient flow data; calculate a signal representing a zero crossing variance of said normalized amplitude signal; and classify the severity of said periodic breathing using said power envelope of said normalized amplitude signal and said signal representing the zero crossing variance; and iv. altering therapy delivered to said user based on said rated severity of said periodic breathing.