Apple Machine Learning white paper (via MyHealthyApple):

Respiratory rate (RR) is a clinical metric used to assess overall health and physical fitness. An individual’s RR can change due to normal activities like physical exertion during exercise or due to chronic and acute illnesses. Remote estimation of RR offers a cost-effective method to track disease progression and cardio-respiratory fitness over time.

In a nutshell, the research worked out a process for using AirPods to estimate respiratory rate (RR), with the goal of tracking RR over time, getting a sense of things like fitness, disease progression, chronic breathlessness.

This sort of work makes me hopeful for a future with more sophisticated health care available remotely.