Two rodent models of IH were studied: (1) rats treated with 10 days of IH patterned after blood O2 profiles during OSA; and (2) mice deficient in hemeoxygenase (HO)-2, which experience IH because of high incidence of spontaneous apneas (Peng et al., 2017). This evidence concerns the gene HMOX2 and isolated hemihyperplasia.