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A ventilator, when used for intensive care, is used to improve the rate and depth of breathing during respiratory failure by generating and regulating the flow of gas into the lungs. Often it is necessary to first treat a patient with mandatory ventilation and then slowly wean them into spontaneous or assisted mode. A ventilator operating in mandatory mode must control all aspects of breathing such as tidal volume, respiration rate, inspiratory flow pattern, and oxygen concentration of the breath. Once in spontaneous mode, the ventilator must allow the patient to initiate a breath and control the breathe rate, flow rate, and the tidal volume. Whether for short-term treatment of acute respiratory problems or for long-term therapy to treat patients with chronic respiratory disorders, many of the same design concepts and components apply.
Pressure sensors play an important role for respiration equipment by converting physical values such as airway pressure and flow into a differential signal. The accurate processing of these signals is life critical. The air and oxygen flow sensors generate signals to help the microprocessor control the valves to deliver the desired inspiratory air and oxygen flows. The airway pressure sensor generates the feedback signal necessary for maintaining the desired positive end expiratory pressure (PEEP). Often, the sensors are very cost-effective with large offset and offset drift causing the signals to be over or under scaled, temperature variant and non-linear. Amplifiers with low offset voltage and drift over time and temperature as well as low-noise and a high common-mode rejection ratio are ideal for signal conditioning.
A number of control design strategies may be appropriate for the control of the air and oxygen flow delivery valves. The microprocessor performs multiple operations including sampling the pressure signals, computing a desired airway pressure and total inspiratory flow level and actuating the air and oxygen valves for each individual inspiratory cycle. To achieve these operations efficiently and in real-time, a high-speed, low-power, highly-integrated microprocessor is needed. DSPs can be used for such demanding control applications. A DSP can also provide fast interrupt response and processing and simultaneous conversions.
Some systems are equipped with compressed-gas tanks and backup batteries to provide ventilation in case of power failure or defective gas supplies. It is important that the battery management components accurately assess the energy levels to ensure safety and reliability. Ideal parts include Impedance Track™ technology that measures and maintains a more accurate record of available charge in the battery using its high-performance analog peripherals.
If functional safety certification is required, Hercules™ Safety MCUs are built to ease the development and certification of safety critical systems to the IEC61508 safety standard, for example. Based on the ARM® Cortex™-R4F core Hercules MCUs provide floating point, SIMD and DSP capability. Hercules MCUs include up to 3MB of flash, 12-bit ADCs, flexible HET Co-Processor and communication peripherals such as USB, Ethernet and CAN that enable the MCU to act as a safe networked controller that can perform safe control as well.
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