When a heart-monitoring app on New York-based podcast producer James T Green's Apple Watch told him his heart rate was higher than normal, the 28-year old sought medical advice immediately. A CT scan revealed he had a pulmonary embolism: a blood clot in his lungs.

He was rushed to hospital, where doctors put him on a blood-thinning drip. Green credits the app - HeartWatch - with saving his life. As he told the Daily Telegraph, the clot would have been fatal had he waited any longer.

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“It was the data I needed to prove this wasn’t just a panic attack," he told the newspaper. "It helped me get the ball rolling.”

Green posted his story on Twitter. He appears to have deleted his account since then, but among the replies are similar stories of smartphones and wearable tech alerting their users to potentially life-threatening conditions.

Last year saw the first reported case of wearable tech informing the diagnosis and treatment of a patient. When a 42-year-old man from New Jersey suffered a seizure, emergency doctors discovered he had an irregular heartbeat. They were able to use the heart-rate data from his Fitbit - an activity-tracking device worn around the wrist - to ascertain whether this was a chronic condition, or whether the irregular heartbeat had begun just prior to the seizure.

“Using the patient’s activity tracker, we were able to pinpoint exactly when the patient’s normal heart rate of 70 jumped up to 190,” said Dr. Alfred Sacchetti from the Our Lady of Lourdes Medical Centre New Jersey, in a statement - and treated his patient accordingly.

These are reactive, short-term interventions occasioned by technology - but wearable tech has been improving users' health in a much more sustained way for some time.

Adherents of the quantified self movement - also known as lifelogging - use smartphones, watches, activity trackers and a host of other wearable tech and software to collect and collate data on every aspect of their health and lifestyle, from the calories they consume to the hours of sleep they get and the amount of exercise they take each day. Their aim is to use this data to set goals and drive improvements - to become healthier, longer-living and better functioning humans.

That data could be of use to clinicians, too. We could be on the verge of a healthcare revolution, in which these streams of information are fed to and used by doctors to help catch problems early and to better treat long-term conditions. In the UK, the National Health Service is trialling apps that enable sufferers of chronic conditions such as diabetes and heart disease to transmit data on their blood sugar and blood pressure directly to their doctors.