A microcomputer system for monitoring and analysing oxyhemoglobin saturation during sleep

A computerized data acquisition and analysis routine was developed to quantitate respiratory disturbances [1,2] in sleeping patients. Polysomnographic recordings of patients consisted of electroencephalograms, electro-occulograms, submental electromyograms, air flow at the nose and mouth, esophogeal pressure, and oxyhemoglobin' saturation (SaO₂). SaO₂, a physiological effect of ventilatory airflow, was sampled every two seconds and stored on disk' during the night's study for subsequent analysis. Wild points in the data file can be marked so that they will be skipped during analysis. Patient polysomnographs were scored manually for sleep stage by a sleep technician. A file was then created containing the scored sleep information with time marks corresponding to each change in sleep stage during the study. An analysis routine used this file to develop indices of sleep apnea, severity for combinations or specific stages of sleep. These indices were:

• 1.

  (A) number of oxyhemoglobin desaturation episodes per hour;

• 2.

  (B) average maximum desaturation per episode; and

• 3.

  (C) desaturation index, the product of (A) and (B). A graph was plotted showing cumulative sleep time at given SaO₂ values [4]. The degree of sleep apnea can be determined using these indices.