I recently completed a technical feasibility project (as part of my work at the Centre for Creativity) part-funded by Innovate UK showing that it is possible to track and improve attention and relaxation levels in real-time using biofeedback of heart rate variability (HRV) measures. The software solution I developed, together with Dimitrios Zampelis, runs on an iPhone and communicates wirelessly in real-time with ‘Bluetooth smart’ heart rate monitors such as the Mio Alpha 2 and Mio Fuse watches.
You can see more details on the results of the study on the Centre for Creativity website.