FEW places on earth are as isolated as Tristan da Cunha. This small huddle of volcanic islands, with a population of just 269, sits in the middle of the South Atlantic, 1,750 miles from South Africa and 2,088 miles from South America, making it the most remote settlement in the world. So it is a bad place to fall ill with an unusual disease, or suffer a serious injury. Because the islands do not have an airstrip, there is no way to evacuate a patient for emergency medical treatment, says Carel Van der Merwe, the settlement's only doctor. “The only physical contact with the outside world is a six to seven day ocean voyage,” he says. “So whatever needs to be done, needs to be done here.”

Nevertheless, the islanders have access to some of the most advanced medical facilities in the world, thanks to Project Tristan, an elaborate experiment in telemedicine. This field, which combines telecommunications and medicine, is changing as technology improves. To start with, it sought to help doctors and medical staff exchange information, for example by sending X-rays in electronic form to a specialist. That sort of thing is becoming increasingly common. “What we are starting to see now is a patient-doctor model,” says Richard Bakalar, chief medical officer at IBM, a computer giant that is one of the companies in Project Tristan.

A satellite-internet connection to a 24-hour emergency medical centre in America enables Dr Van der Merwe to send digitised X-rays, electrocardiograms (ECGs) and lung-function tests to experts. He can consult specialists over a video link when he needs to. The system even enables cardiologists to test and reprogram pacemakers or implanted defibrillators from the other side of the globe. In short, when a patient in Tristan da Cunha enters Dr Van der Merwe's surgery, he may as well be stepping into the University of Pittsburgh medical centre. It is a great comfort to local residents, says Dr Van der Merwe, knowing that specialist consultations are available.

Most of the technology this requires is readily available, and it was surprisingly simple to set up, says Paul Grundy, a health-care expert at IBM. The biggest difficulty, he says, was to install the satellite-internet link. In theory, this sort of long-distance telemedicine could go much further. In 2001 a surgeon in New York performed a gall-bladder removal on a patient in Paris using a robotic-surgery system called Da Vinci. Although that was technologically impressive, it may not be where the field is heading.

Home is where the technology is

For advances in telemedicine are less to do with the tele- than with the medicine. In the long term, it may be less about providing long-distance care to people who are unwell, and more about monitoring people using wearable or implanted sensors in an effort to spot diseases at an early stage. The emphasis will shift from acute to chronic conditions, and from treatment to prevention. Today's stress on making medical treatment available to people in remote settings is just one way telemedicine can be used—and it is merely the tip of a very large iceberg that is floating closer and closer to home.

That is because telemedicine holds great promise within mainstream health care. Countless trials are under way to assess technology that can monitor people who have been diagnosed with heart conditions, or diseases like diabetes, from the comfort of their own homes. Rather than having their devices periodically checked at a clinic, some pacemaker patients can now have their implants inspected via mobile phone. That way, they need only visit the clinic when it is absolutely necessary.

The shift to telehealth reflects the broader shift from diagnosis and treatment to “wellness”.

Similarly, BodyTel, based in Germany, is one of several firms to have developed sensors based on Bluetooth wireless technology that can measure glucose levels, blood pressure and weight, and upload the data to a secure web server. Patients can then manage and monitor their conditions, even as they give updates to their doctors. Honeywell, an American industrial giant, has devised a system that patients can use at home to measure peak flow from their lungs, ECG, oxygen saturation and blood pressure, in order to monitor conditions ranging from lung disease to congestive heart failure. Doctors continually review the data and can act, by changing the patients' medication, for example, if they spot any problems.

This sort of thing appeals to both patients and health-care providers alike. The patients keep their independence and get to stay at home, and it costs less to treat them. And as populations age in developed countries, the prospect of being able to save money by treating people at home looks increasingly attractive.

It is not just people with diagnosed conditions who are starting to receive this kind of equipment. Since 2006, Britain has spent £80m ($160m) on “preventative technology grants” which provide special equipment to enable 160,000 elderly people to stay in their homes.

Most of today's technology, however, calls on the patients to remember to monitor themselves, and also requires them to operate the equipment. For some patients, such as those in the early stages of Alzheimer's disease, that is impractical. So a lot of work is being done to automate the monitoring process and make the equipment easier to use.

William Kaiser and his colleagues at the University of California, Los Angeles, have developed a “smart cane” to help monitor and advise people convalescing at home, for example. “It has force sensors that measure pressure at the tip of the cane and around the handle. It also has motion sensors and accelerometers,” says Dr Kaiser. It uses these to calculate the gait of the patient and work out how they are doing with the cane, giving them feedback about how they could make better use of it to recover from, for example, a hip replacement. “It provides guidance, either as beeps or it can talk to you,” he says.

Another approach is to use sensors embedded in the home. Oliver Goh of Implenia, a Swiss building-management firm, has come up with a system to monitor the well-being of the occupant of a house. Using sensors on doors and mattresses, smart pill boxes that can tell when they are being opened, heart-monitors and a location-sensing wristwatch—the system allows carers to keep tabs on elderly people. Implenia now has six elderly volunteers lined up to test the technology, says Mr Goh. He hopes that if they have a heart attack, cannot get out of bed or need help, their carers will soon know. Ultimately, he says, the aim is to see if this sort of approach can help to extend life expectancy.

Prevention is better than cure

Looking even further ahead, some day it may make sense to give these technologies to healthy people, the “walking well”. If sensors can monitor people without a threat to their privacy or comfort, doctors may able to spot diseases before the patient notices any symptoms. “It's moving from telemedicine to telehealth and teleprevention,” says Dr Grundy of IBM. It could also improve the efficiency of health-care systems, he says.

Illustration by Andy Baker

This kind of approach could save money as well as spotting illnesses early, says Dr Kaiser. “We'll detect them earlier when the cost of treatment and impact on an individual will be less,” he says. The technology for this does not yet exist, admits John Linkous, executive director of the American Telemedicine Association. “There still isn't a device that can give you a complete body check,” he says. “But I'm very optimistic about it in the long run.”

One idea is to use wireless infra-red skin sensors to measure blood-count, heart-rhythm and the level of oxygen in the blood. Another is to implant wireless sensors powered by the wearer's own body heat. Yet another common idea is to use smart toilets that can monitor human waste for the telltale signs of intestinal disease or cancer. The hard part is not so much developing the sensor technology, says Dr Linkous, as sifting through the results. “It would produce a tsunami of data, and the problem is that we aren't set up with health-care systems that can deal with all that,” he says.

The answer will be even more technology, says Dr Bakalar. “There has to be a way of filtering this information so that it doesn't overwhelm the medical services,” he says. The obvious approach is to use “expert systems”—software programmed with expert medical knowledge and that can make clinical judgments.

Like telemedicine, expert systems have been around for some time. Trials in Denmark, to advise doctors how to prescribe, suggest the technology has great scope. Sometimes they can reach better clinical judgments than human experts do. But they are not widely used, partly because doctors are unwilling to be bossed around by a computer in the corner, but also because they have been difficult to integrate into medical practice. They could be ideally suited to telehealth, however, quietly sifting through the data generated by sensors and only raising the alarm and calling in their human colleagues when it becomes necessary to do so.

The shift from telemedicine to telehealth reflects a broader shift from diagnosis and treatment to “wellness”. Taken to its technological conclusion, this would involve using wireless sensors and implants to screen entire populations for early signs of disease as they go about their daily lives. If it can be made to work, the days of making an appointment to see your doctor when you are not feeling well could be over. Instead, it may be your doctor who calls you.