A quick look at the medical experts, via Mark Gurman at 9to5Mac:
Roy J.E.M. Raymann, an expert in sleep research. His LinkedIn bio doesn't list him as an Apple employee, but it does say this: "Main topic of research is states of performance and how to optimize rest and activity. Why are some people able to perform at peak level for weeks in a row? What is the difference to be able to perform and willing to perform. What is the role of sleep, motivation, physiology. How can we optimize sleep?"
Ueyn Block, who came from C8 MediSensors. It seems like C8 Medisensors shut down. It was developing a continuous, non-invasive glucose measuring system. C8 was working on a product that you wore and it gave a read out every 8-10 minutes. Block was an engineer at the company.
Todd Whitehurst, hardware director at Senseonics. Senseonics is also working on a wearable glucose monitoring system. It works with a smartphone to provide data for a user.
Dr. Michael O'Reilly, formerly chief medical officer at a company called Masimo. Masimo developed hardware that worked with the iPhone to measure your pulse. The company says of itself, "[Masimo] develops and manufactures innovative noninvasive patient monitoring technologies, including medical devices and a wide array of sensors."
Nancy Dougherty, of Sano Intelligence. Gurman says of Dougherty, her past work "included a health metric-reading wearable patch and ingestible, Bluetooth-connected smart pills for monitoring dosages and scheduling." At Sano, Gurman says she was developing a wearable sensor system.
Ravi Narasimhan, formerly in R&D for Vital Connect. Vital Connect makes monitors you stick on your skin to track your health. Gurman says Narasimhan focused on "measuring respiration and activity levels and wearable medical devices."
Marcelo Lamego, formerly CTO of Ceracor. According to NetworkWorld, Lamego has 70 patents, developed a hemoglobin monitor for Ceracor