Masimo look as though they may have a case regarding the method Apple use, but if you look at the latest Masimo watch then I'd be very surprised if that doesn't infringe Apple patents somewhere.
This is one occasion where perhaps Masimo and Apple would be better off reaching out of court settlement and perhaps even an agreement on incorporating future health related improvements, as Masimo's direction is 100% health related, a growing market, where it may be mutually beneficial to have agreement, and no doubt Apple will also implement more and more health related improvements to other devices.