The prototype implantable device used by the resaerchers [Credit: IOP Publishing/Journal of Neural Engineering]

Implantable device to tackle high blood pressure

An implantable device that reduces blood pressure by sending electrical signals to the brain has been invented by researchers in Germany.

The device has successfully reduced the blood pressure in rats by 40 per cent without any major side effects, and could offer hope for a significant proportion of patients worldwide who do not respond to existing medical treatment for the condition.

In their study, the researchers from the University of Freiburg tested a 2cm-long prototype device consisting of 24 individual electrodes integrated into a micro-machined cuff designed to wrap around the vagal nerve, which extends from the brainstem to the thorax and helps control blood pressure.

Lead author of the research, Dr Dennis Plachta, said: “Our proof-of-concept interface has shown that it is possible to use the left vagal nerve to reduce blood pressure without any adverse side effects, which is important for a wide variety of potential treatments that could utilise nerve stimulation without actually penetrating the nerve.”

The device works by picking up signals from a specific group of baroreceptors – a type of sensory neuron that are activated when blood vessels stretch – concentrated in areas of the aortic arch that function to control short-term fluctuations in blood pressure.

This particular group of neurons report their information to the brainstem via fibres in the vagal nerve and the device has been designed to identify only those nerve fibres that influence blood pressure and avoid those responsible for heart rate, the power of heart beat, ventilation and other vital functions.

In their study published today in the Journal of Neural Engineering, the researchers tested their prototype, capable of delivering 40 pulses per second to the fibres of the baroreceptors in the vagal nerve, on five male rats.

The researchers experimented on various areas of the vagal nerve, exploring different stimulation sites around the nerve with different frequencies, amplitudes and durations of stimulation. Using the appropriate parameters, the researchers showed that the blood pressure could be easily reduced to 60 per cent of its original value in a wide range of stimulation frequencies and pulse widths.

No major side effects, such as a significant decrease in heart rate or breathing rate, occurred when the electrode sites closest to the baroreceptor fibres were chosen for stimulation.

“As the device will require surgery, it is not intended to be the first port of call for treatment and will come into play when patients, for whatever reasons, are resistant to medication,” said Plachta.

“Nevertheless, the long-term goal is to provide ‘treatment-on-demand’ for the patient, whereby the implantable device uses an intelligent circuit to record the activity of the patient, for instance when they are doing exercise, and adjust the blood pressure accordingly.

“We will now look to develop the implantable device further and investigate whether it interferes with existing medication, and ultimately test it on larger animals such as pigs and sheep.”

The paper 'Blood pressure control with selective vagal nerve stimulation and minimal side effects' is available for download here.

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