Table 4.

Extent to which traits explain differences in apnea–hypopnea index with obesity and demographics in Multi-Ethnic Study of Atherosclerosis

		Percentage Mediated by Endotypic Traits [95% CI]
Factor	Association with AHI (β ± SEM)	Collapsibility	Loop Gain	Collapsibility + Compensation	Collapsibility + Loop Gain	All Traits
BMI (2 SD)	19.1 ± 1.1	17 [12, 22] *	17 [13, 22] *	17 [12, 22] *	26 [20, 32] *	26 [20, 32] *
Age (20 yr)	8.3 ± 1.3	39 [26, 53] †	21 [12, 32] *	38 [24, 52] †	48 [34, 63] †	47 [33, 62] †
Male vs. Female	13.4 ± 1.0	52 [45, 60] †	11 [7, 16]	57 [50, 66] †	54 [46, 61] †	59 [51, 67] †
Black vs. White	−5.0 ± 1.0	41 [24, 64] †	<0	52 [34, 77] †	21 [−3, 40]*	32 [10, 52] †
Chinese vs. White	5.4 ± 1.5	87 [57, 100] ‡	16 [−1, 36]*	94 [63, 100] ‡	88 [59, 100] ‡	95 [65, 100] ‡

Definition of abbreviations: AHI = apnea–hypopnea index; BMI = body mass index; CI = confidence interval; SEM = standard error of the mean.

Data describe the percentage reduction in association strength (β) with the addition of individual endotypic traits to the primary model between AHI and obesity/demographics (95% confidence intervals were calculated using bootstrapping with 5,000 iterations). Bold denotes a significant mediation effect. Exposures with an observed association with AHI (per Table 2) were examined. For example, the association between Chinese (vs. White) and AHI (5.4 events/h) was diminished by 87% after collapsibility was included; greater collapsibility was therefore considered a potential explanation for increased AHI in Chinese versus White participants. Note that AHI data were square root transformed for analysis; results were back transformed for interpretability.

^*Denotes 15–30% mediation (“modest”).

^† Denotes 30–60% mediation (“substantial”).

^‡ Denotes >60% mediation (“strong”).