The Science Journal of the American Association for Respiratory Care
Purpose: To study the degree of variability in upper airway resistance in Obstructive Sleep Apnea (OSA) patients.
Background: The use of automatically adjusting CPAP devices to treat patients diagnosed with OSA presented an opportunity to study the variation of OSA since the pressure usage profiles obtained from these devices are derived from individual patient fluctuations in upper airway resistance. The device is capable of storing over a month worth of data; such as, mean CPAP pressure used (CPAPmean) and 90th percentile CPAP pressure (CPAPmax).
Method: We examined the first full week of CPAP pressure utilization data in 12 OSA patients. Attention was focused on the CPAPmean and CPAPmax as indicators of each nightís pressure need. The standard deviation of these numbers was calculated for each individual patient as well as for the entire group. For each individual patient, the week's highest mean pressure (CPAPmean max), lowest mean pressure (CPAPmean min), and the difference between the two (CPAPmean diff) was noted. The same was done for CPAPmax so as to calculate the greatest difference in the CPAPmax during the course of a week (CPAPmax diff).
Results: The CPAPmean for the 12 patients studied was 6.9 cm H2O. The CPAPmax was 8.5 cm H2O. The standard deviation of CPAPmean was .62. The standard deviation for CPAPmax was .80. CPAPmean diff was 1.8 cm H2O for the entire group and was noted to be > 1 cm H2O in 9/12 (75%) and greater than 2 cm in 3/12 (25%) of OSA patients. CPAPmax diff was 2.2 cm H2O for the entire group and was found to be > 1 cm H2O in 10/12 (83%) and > 2 cm H2O in 6/12 (50%) of the 12 patients studied.
Conclusions: Both the mean and maximal CPAP pressure needs of OSA patients vary on a night to night basis. One centimeter differences in these pressures should be expected. Two centimeter differences in these pressures are surprisingly frequent. This data should raise concern regarding the adequacy of any CPAP pressure data derived from a one night sample period to predict the ongoing pressure needs of an OSA patient over multiple nights.