Table 6.
Maximum likelihood model-based heritability estimates of heart rate response to arousal measures in twinsa.
| Measure | MLE estimates of proportion of variability explained for Genetic (G), Common Environment (C) and Individual (E) factors within best fitting modelb | |||
|---|---|---|---|---|
| Unadjusted | ||||
| Model | h2G (95% CI)c | h2C (95% CI) | h2E (95% CI) | |
| Arousal index | AE | 0.625 (0.482, 0.768) | – | 0.375 (0.232, 0.518) |
| Average arousal duration | AE | 0.457 (0.261, 0.652) | – | 0.543 (0.348, 0.739) |
| Average arousal intensity scale | AE | 0.692 (0.554, 0.830) | – | 0.308 (0.170, 0.446) |
| Slope of ΔHR per arousal intensity | CE | – | 0.513 (0.359, 0.666) | 0.487 (0.334, 0.641) |
| Arousal intensity threshold of ΔHR | ADE | 0.533 (0.349, 0.717) | – | 0.467 (0.283, 0.651) |
| Average ΔHR | AE | 0.723 (0.608, 0.838) | – | 0.277 (0.162, 0.392) |
| ΔHR at arousal intensity scale 4 | CE | – | 0.593 (0.458, 0.728) | 0.407 (0.272, 0.542) |
| ΔHR at arousal intensity scale 5 | CE | – | 0.621 (0.493, 0.749) | 0.379 (0.251, 0.507) |
| ΔHR at arousal intensity scale 8 | CE | – | 0.609 (0.479, 0.740) | 0.391 (0.260, 0.521) |
| Measure | Adjusted† | |||
| Model | h2G (95% CI)c | h2C (95% CI) | h2E (95% CI) | |
| Arousal Index | CE | – | 0.543 (0.396, 0.690) | 0.457 (0.310, 0.604) |
| Average arousal duration | AE | 0.437 (0.236, 0.639) | – | 0.563 (0.361, 0.764) |
| Average arousal intensity scale | AE | 0.641 (0.479, 0.803) | – | 0.359 (0.197, 0.521) |
| Slope of ΔHR per arousal intensity | CE | – | 0.318 (0.131, 0.505) | 0.682 (0.495, 0.869) |
| Arousal intensity threshold of ΔHR | ADE | 0.464 (0.252, 0.677) | – | 0.536 (0.323, 0.748) |
| Average ΔHR | AE | 0.565 (0.390, 0.739) | – | 0.435 (0.261, 0.610) |
| ΔHR at arousal intensity scale 4 | AE | 0.514 (0.336, 0.692) | – | 0.486 (0.308, 0.664) |
| ΔHR at arousal intensity scale 5 | CE | – | 0.445 (0.278, 0.612) | 0.555 (0.399, 0.722) |
| ΔHR at arousal intensity scale 8 | CE | – | 0.412 (0.239, 0.585) | 0.588 (0.415, 0.761) |
Abbreviations: h2G = proportion of phenotypic variability explained by genetic factors; h2C = proportion of phenotypic variability explained by shared environment; h2E = proportion of phenotypic variability explained by individual factors; ΔHR: heart rate response to arousal.
aModel adjusted for race, age, sex, and age × sex interaction.
b“Best Fitting Model” determined through goodness of fit tests, utilizing likelihood ratio tests for nested models (i.e., ACE vs. AE, CE or E and ADE vs. AE or E) and AIC statistics for non-nested models (e.g., CE vs. AE), when both models indicated better fit than the full model. The starting model (ACE or ADE) was chosen based on the estimated common environment effect in the ACE model heritability analyses, such that h2C ≤ 0 implies an ADE model and h2C > 0 implies an ACE model.
c h2G represents to proportion of phenotypic variability explained by genetic factors, based on the best-fitting model. If AE or ACE are chosen as the best fitting model, h2G is equal to the heritability due to additive genetic effects only, whereas h2G is equal to the combination of the additive and dominant genetic effects when ADE is chosen as the best model; Model Descriptions: A = additive genetic effects, C = common environmental effects, D = dominant genetic effects, and E = unique individual effects. Thus, ACE model suggests additive genetic, common environment and individual effects, whereas ADE model suggests additive and dominant genetics and individual effects.