Finapres Medical Systems has set a standard with its technology for non-invasive continuous blood pressure monitoring, the Finapres NOVA. This blood pressure monitor was fitted up with various (optional) hardware modules and software applications. Due to its success there was a demand for a ‘stripped’ OEM module based on the Finapres technology. The core of the Finapres NOVA (controls and separate monitoring module) was to be compressed into a single module that could be attached to the patient’s wrist. This OEM module, the Finapres Nano Core, can be connected to the Finapres NOVA or to a system of a different manufacturer. Just as they did for the development of the Finapres NOVA, Finapres Medical Systems and DEMCON developers worked closely together to develop the Nano Core.
Miniaturisation was the biggest mechatronic challenge: to accommodate the full functionality in a small form factor, with limited mass and heat emission (in part to ensure wearing comfort). The software challenge was to develop a new architecture that would make the Nano Core suitable for diverging OEM applications. The NOVA is primarily used in research and to a limited extent in the clinical domain, however, the Nano Core makes it much easier to enter the clinical market. Specific requirements had to be met for this application: stricter certification criteria as a medical product, sufficient accuracy and reliability with a view to standardisation and the ability to issue alerts, and the need to be defibrillator-proof. Naturally, DEMCON also considered factors such as cost price and producibility (availability of components) during the design phase.
The Finapres technology operates on the basis of an inflatable finger cuff that contains an inflatable bladder and a sensor system. The sensor system uses an optical signal to record the changes in diameter of the artery in the finger as a result of blood pressure. The changes are countered by quickly – in milliseconds – increasing or decreasing the pressure in the inflatable bladder around the set point. The blood pressure is then calculated from the pressure measured in the inflatable bladder. The challenge for this sensor system was to integrate the regulation, electronics and the tiny pump for the supply pressure into a compact module.
DEMCON managed to consolidate the electronics onto a single rigid-flex circuit board ‘folded’ around the tiny pump’s plunger. By focusing on digitalisation – the entire complex pressure generation control loop has been optimised and is digitally implemented – the design resulted in a gain in space and flexibility. The Nano Core is equipped with two manifolds, sensors and valves (in part for switching the measurement between two fingers to make long-term measurement possible). Due to the limited space, the manifolds are complex and therefore manufactured using 3D printing.
DEMCON produced a prototype, supported the medical certification process, looked after the industrialisation and built a baseline series. Together with Finapres Medical Systems, DEMCON provided for a finetuned stable control system that enables the Finapres Nano Core to serve a broad population of patients.