The assessment of nocturnal oxygen saturation.

1. Existing methods of assessing nocturnal episodic hypoxaemia are either insensitive or ignore the majority of the available data. 2. We describe a method of analysis using offline digital processing. A distribution of oxygen saturation ( S ao 2 ) with time is produced from all the available data, and subjected to moment analysis to produce a simple index which describes an entire night9s S ao 2 . 3. Our results suggest that the mean and the coefficient of skew fully described a night9s S ao 2 . However, in subjects with chronic air-flow obstruction, the third moment about 100% oxygen saturation (M 3 100), a single figure, has the same descriptive power as mean and skew. 4. In 17 subjects with chronic air-flow obstruction a significant correlation was found between both daytime S ao 2 and P aco 2 when plotted against either the M 3 100 or the skew. 5. Measurements made on two occasions in seven subjects showed good reproducibility for the skew and M 3 100 indices.