Loop gain is Increased and the Arousal Threshold is Decreased in Caucasian Compared to African American Males with Obstructive Sleep Apnea

Abstract

ObjectiveRace and ethnicity may impact the prevalence and treatment of obstructive sleep apnea (OSA). However, only a few studies have made direct comparisons of endotypic characteristics between African Americans and Caucasians. The comparisons completed have focused primarily on differences in anatomical traits (i.e. craniofacial morphology) that may exist between races. The present study was designed to explore if other endotypic traits [(i.e. loop gain (LG) and the arousal threshold (AT)] that influence sleep apnea differ in African American compared to Caucasian males with OSA.Methods26 African Americans [age = 34.9 ± 11.9 years; body mass index = 28.1 ± 4.4 kg/m2; apnea hypopnea index (AHI) = 37.7 ± 21.1 events/hour] and 26 Caucasian male participants (age = 31.2 ± 8.2 years; body mass index = 29.6 ± 3.6 kg/m2; AHI = 41.7 ± 16.5 events/hour) with untreated OSA completed a baseline nocturnal polysomnogram. Thereafter, sleep staging, respiratory events, and arousals were scored according to standard criteria. A MATLAB software program was used to quantify LG and the AT from the ventilatory and sleep measures obtained during non‐rapid eye movement (NREM) sleep throughout the night. LG at the natural frequency (LGn) of obstructive events and at a frequency of 1 cycle/min (LG1, i.e., 60 events/hour) were computed. Data was compared using Student t‐test and is presented as mean ± SD.ResultsAge (p = 0.19), BMI (p = 0.20), and the AHI (p = 0.44) was similar between the two groups. LG was significantly higher in Caucasians compared to African Americans (LGn: 0.44 ± 0.07 vs. 0.40 ± 0.06, p = 0.037; LG1: 0.61 ± 0.12 vs. 0.54 ± 0.12, p = 0.039). In contrast, the AT was significantly lower in Caucasians compared to African Americans (1.22 ± 0.17 vs. 1.38 ± 0.27, p = 0.009). The difference in the AT corresponded to an increased arousal index in Caucasians compared to African Americans (74.99 ± 5.36 vs. 51.13 ± 19.34 arousals/hour, p = 0.029). Furthermore, a subgroup analysis of participants with OSA and co‐existing hypertension also showed that Caucasian males (n = 11) had a higher LG (LGn: 0.45 ± 0.06 vs. 0.39 ± 0.07, p = 0.05; LG1: 0.62 ± 0.12 vs. 0.48 ± 0.09, p = 0.007) and lower AT (1.16 ± 0.12 vs. 1.37 ± 0.27, p = 0.033) than the African American participants (n =10).ConclusionDespite similar anthropometric measures and a similar apnea hypopnea index, loop gain and the arousal threshold were greater in Caucasian compared to African American males with OSA. Our results suggest that these endotypic characteristics may have a more prevalent role in initiating sleep disordered breathing in Caucasians compared to African Americans. Likewise, our findings suggest that Caucasians may be more responsive to therapies that target loop gain and the arousal threshold.