What is the scope of our review on appeal in an usury case?

Contrary to appellants' assertion, our review is limited by the substantial evidence doctrine. " 'In usury cases the trier of fact is vested with the power to resolve many issues attending and including the ultimate question of whether a particular transaction is usurious.' ... [The reviewing court's] task on appeal is merely to view all factual matters in favor of the prevailing party and in support of the judgment, disregarding evidence to the contrary, and decide whether there is any substantial evidence, contradicted or uncontradicted, to support the findings and conclusions of the trier of fact." (Del Mar v. Caspe (1990) 222 Cal.App.3d 1316, 1323, 272 Cal.Rptr. 446.)