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Motors key in design of modern medical ventilator

Motors key in design of modern medical ventilator

There are many experiences in life we would happily do without. An operation under general anaesthetic, with artificial respiration, is definitely one of them. But perfectly tuned drive systems are key to a new generation of ventilation systems that is making the anaesthesia aspect of operations both safer and gentler.

Medical technology has been developing at breath-taking speed in recent few years. A good example of the performance capability of modern medical technology is provided by the Zeus Infinity Empowered (IE) anaesthesia machine from Dräger which makes the entire spectrum – from sophisticated ventilation therapy to the monitoring, integration of infusion technology and automation of sub-functions – possible with a single system.

With a turbine ventilator, the device can also be operated as a closed anaesthesia system with full rebreathing. The precise metering of the anaesthetic gas in the closed system reduces the uptake of the gas and anaesthetic. In addition, the turbine-based ventilation allows the patient to breath freely at all times. Adults, children and even newborns can therefore be adequately ventilated through the entire anaesthesia. 

However, high demands are put on the used components, for example as the turbine and its drive system must be able to withstand the hot steam of autoclave sterilisation. and the choice of material is in no way trivial, as all components installed in the turbine unit come into direct contact with the breathing air of the patient. Furthermore, compact dimensions are required so that the unit can be easily integrated into the anaesthesia machine and is easy to handle when replacing and cleaning. A high power density for the motor used is also necessary.

For a suitable motor for the blower unit, Zeus IE turned to Faulhaber, whose products are available in the UK from EMS. Faulhaber motors are designed for extreme operating conditions and are used anywhere where high reliability, precise function and a long service life are demanded. Other features include very smooth-running operation, low audible noise, high performance and dynamics in a compact size. Nevertheless, the drive that was needed for the blower unit still posed a major challenge to the developers, requiring acceleration and deceleration in milliseconds, as Torsten Theede of Dräger explains: “This is important so that the patient is not forced to breath against the machine. The blower unit and the drive must react extremely quickly and precisely.”

The tailor-made brushless DC motor provided by Faulhaber for the blower unit is housed in a robust stainless steel housing and is only 24mm in diameter and 46mm long. To meet the overall performance requirements, the magnets and materials used had to be optimised. The fact that only biocompatible lubricants and adhesives could be used and that the entire unit had to be autoclavable made the selection of material a challenging task, and Faulhaber worked with external specialists in order to find the optimal material pairing with biocompatible lubricants for extremely high speeds. 

The system is also impressive from a mechanical point of view: the impeller pump, which generates the air current, is mounted directly onto the motor. The electrical connections are embedded into the external casting compound. Furthermore, an EPROM has been integrated into the casting compound, and provides details of the drive history and the number of operating hours performed, in addition to the series number. The signals from the Hall sensors integrated into the motor are processed by the primary system controller which actuates the motor according to the anaesthesia and ventilation requirements.

The entire blower unit has a diameter of 120mm and only is 220mm long. “It has since performed very well in practical use,” says Theede. “Collaboration with Faulhaber has continued with work on the turbine unit for our Perseus A500 anaesthesia workstation. This system also offers sophisticated ventilation strategies which support the spontaneous breathing of the patients at all times and has also been employed successfully in many clinics for several years.”

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