Blood pressure implant

People who suffer from high blood pressure can now be monitored without discomfort with an implanted pressure sensor being developed by researchers at the Fraunhofer Institute in Germany.

The device, 1mm in diameter, is implanted into the femoral artery in the patient's groin and measures the blood pressure 30 times a second. The sensor is connected via a flexible micro-cable to a transponder unit that is also implanted in the groin under the skin. This unit digitises and encodes the data from the sensor and transmits information to an external reading device that patients can wear on their belt like a mobile phone. Then the readings can be sent to a monitoring station to be analysed by a doctor.

'There are certain types of patients suffering from hypertension where it's difficult to regulate their blood pressure,' said Hoc Khiem Trieu, head of Fraunhofer's microelectronic circuits and systems, the department leading the study. 'For this type of patient you need to constantly monitor their blood pressure in order to adjust the dose of their drugs.'

Trieu said these patients now monitor their blood pressure every 30 minutes with meters that require an inflatable sleeve to be strapped around the arm. 'The cuff must be pumped up and deflated even at night when a patient wants to sleep,' he said. 'This procedure can be extremely uncomfortable for the patient.'

The implanted system requires little energy and is powered by inductive coupling. One coil is implanted beneath the skin and another is located inside the external reading device. 'The two coils work like a transformer,' said Trieu. 'The external coil generates a magnetic field and this will induce voltage in the second coil. That is then used for powering the device.'

The Fraunhofer researchers are developing the device with medical technology company Dr Osypka and other partners in a German government-funded project called Hyper-IMS (intravascular monitoring system for hypertension patients).

The main risk that such an implantable device poses for a patient is blood clotting. However, Trieu said the project partners have mitigated this danger by developing a special biocompatible surface for the device.

The researchers are now testing the device on animals.

Siobhan Wagner