Role of body mass index (BMI) on the oxygen saturation and apneic spells in obstructive sleep apnea (OSA)

Data from the sleep disorder institute showed that subjects with similar apnea hypopnea index (AHI) but different body mass index (BMI) had no difference in oxygen saturation in rapid eye movement (REM) or non-rapid eye movement (NREM) sleep. Only 6 pairs of subjects were evaluated in the study and they were not age-matched. The objective of this study was to evaluate, in age-matched subjects, if there are any differences in oxygen saturation and duration of apenic spells in subjects with similar AHI but different BMI. Ninety eight (98) subjects paired for AHI within one event/hour and BMI difference of 5 and above were grouped in 9 groups. Subjects belonged mainly to normal, mild and moderate AHI group. Diagnostic nocturnal polysomnography inclusion criteria were normal REM sleep and total sleep time of 5 h. Oxygen saturation was continuously assessed throughout the nocturnal polysomnography (NPSG), and was calibrated for each NPSG study, and was visually identified by sleeping physician and artifacts were eliminated from the analyses. For all age groups, differences between matched pairs on BMI were regressed on the following factors: baseline oxygen saturation, lowest oxygen saturation, average oxygen saturation difference between pairs, apnea maximum and mean durations. Mean BMI differences between age- and AHI-matched pairs were 10.2 ± 5.7 (range 5.0 to 29.0). Stepwise regression indicated that BMI differences between pairs best predicted minimum oxygen saturation (p = 0.008, 1-tail). One-way analysis of variance (ANOVA) showed that age differences contributed to the robust finding regarding how BMI differences predicted lowest oxygen saturation. Using a very conservative Bonferroni correction for multiple comparisons, lowest saturation differed only between lower age groups [group 1 < group 2 (p = 0.3) < group 3 (p = 0.001) and < group 4 (p = 0.02)]. Difference in BMI (when AHI is matched), especially between ages 25 and 44 years old, predicts differences in minimum oxygen saturation. Caution is warranted as severe apneics were not evaluated in small sample sizes in subject older than 40.