In order to simulate physiological insulin secretion, continuous insulin subcutaneous infusion methods were attempted as early as the 1960s, and mechanical insulin infusion devices, i.e., prototype insulin pumps, began to be used in the late 1970s, but they were difficult to be popularized in the clinic due to their large size and complicated operation. In the 1990s, the advancement of manufacturing technology made insulin pumps smaller in size, easy to carry, easy to operate, easy to learn and use, and more accurate and stable dose adjustment, and thus more and more widely used in the clinic, and the current insulin pump technology has become more perfect, which can more accurately simulate physiological insulin secretion pattern. In short, insulin pumps simulate basal insulin secretion with adjustable pulsatile subcutaneous infusion through artificial intelligence control; at the same time, during meal time, the preprandial insulin and infusion pattern is set according to the type and total amount of food in order to control postprandial blood glucose.
The insulin pump consists of four parts: an artificial intelligence control system containing a microelectronic chip, a battery-powered
mechanical pump system, a drug reservoir, an infusion tube connected to it, and a subcutaneous infusion device. The front end of the infusion tube can be buried under the patient's skin. In the working state, the pump mechanical system receives the command from the control system, drives the piston in the reservoir, and finally inputs the insulin into the subcutaneous through the infusion tube.
Principle of operation
Insulin pump subsystem
1). Pump and testing protocols
Insulin is measured in "units", with each cc (or mL) divided into 100 units, assuming a standardized concentration of U-100. In this measurement, one unit is equivalent to 10 μL. With an injection rate of 1 unit/hour, and with each injection taking between 3 and 10 minutes, the dose of one tablet is a few units. The dose is a few units, and the syringe typically holds 200 to 300 units of insulin.
Taking into account the very slow flow rate, the motor moves the piston of the syringe very slowly in steps with a gear-driven pump. Only a rough measurement of the angle of the motor is usually needed. Most insulin pump manufacturers use optical encoders and DC motors, but stepper motors can also be used. To reduce the size of the system, there is also the option of using a MEMS pump or a pressure pump, which eliminates the need for motor control.
Pressure sensors are utilized to detect the sealing condition of the system and ensure proper operation. Based on silicon stress gauges, the output signal amplitude of these sensors is in the millivolt order of magnitude, while the output signal range of bound-wire stress gauges is in the microvolt order of magnitude. Stress gauges use a typical bridge structure to produce a differential signal based on a ***mode voltage, which is typically half the supply voltage.
The design can use an analog/digital converter (ADC) with a differential input programmable gain amplifier (PGA), or a microcontroller with a built-in ADC and an external differential amplifier or instrumentation amplifier (for signal conditioning). Pressure measurements do not need to be very accurate because the pressure readings are only used to indicate proper operation and are not used for injection drug dosage metering.
2). Supply Electronics System
Insulin pumps typically employ a boost regulator that boosts the low-voltage (1.5V, nominal) input from a single alkaline battery to 2V or more. To make the most of the battery's energy, the boost converter should be able to operate at the lowest possible input voltage, and Maxim and other power supply vendors offer boost converters capable of operating at voltages as low as 0.6V, with startup voltages as low as 0.7V, which can effectively increase the battery's lifespan.
Boost-type DC-DC converter for such applications is ideal, the input voltage range of 0.7V to 3.6V. 2MHz switching frequency and current control mode greatly reduces the size of the external components, can obtain more than 94% conversion efficiency and has a faster response time. The device integrates all switching conversion circuits (power switch, synchronous rectifier, reverse current isolator), further reducing the solution size. TrueShutdown circuitry completely disconnects the battery from the load in the shutdown state, helping to further extend battery life.
If a device requires a tightly stabilized supply voltage, the design may require further voltage regulation of the boosted supply. In such low-voltage applications, linear regulators can provide higher efficiency due to the absence of switching losses, which are inherent in switching power supplies.
In addition, low dropout linear regulators (LDOs) allow for smaller solution sizes, which is especially important for insulin pumps, where the efficiency of the LDO is very close to the VOUT/VIN ratio, and higher efficiencies can be achieved when the difference between the VIN and the output voltage is slightly higher than the LDO dropout.
If the motor needs to be powered by a regulated source, a switch-mode converter is an option. In order to reduce the size and weight, you can choose the converter with the highest possible switching frequency. For a multi-supply power supply system, a power management IC (PMIC) can be selected.
3). Battery management
Insulin pump manufacturers have made great progress in reducing power consumption and extending battery life. Insulin pumps currently in use on the market can operate for 3 to 10 weeks per battery change or charge, and most insulin pumps use AA or AAA alkaline batteries, or lithium batteries. The use of primary (non-rechargeable) batteries is very popular, but the use of rechargeable batteries helps save money in the long run. Because of the relatively low capacity of rechargeable batteries, they are recharged relatively frequently.
Due to size constraints, most insulin pumps are powered by alkaline batteries to eliminate the need for a charger. Due to the lack of a power meter, the battery indicator meter mainly uses simple voltage measurement, sometimes combined with temperature measurement. The system feeds voltage and temperature signals to an ADC for quantization, and a microcontroller processes this data and uses a look-up table to determine the remaining battery charge. The power value is then sent to the display (usually a battery icon, which is divided into compartments on the icon to show the remaining power), and when the power drops to the last compartment, the insulin pump generates a low battery voltage alarm.
4). Programming and control unit
As mentioned above, the patient needs to adjust the dosage of the medicine according to the specific needs, and this adjustment requires a fairly simple interface through which, for example, the user can control only a few buttons. The user can also set several prompts to help manage the dose of insulin injected.
Most insulin pumps use a monochrome, custom-characterized liquid crystal display (LCD), and a few insulin pumps have a color display. The display provides information about insulin dose, injection rate, remaining battery power, time, date, alert messages, and system alarm conditions (e.g., lockout or low insulin reservoir), etc. The FDA requires the display to perform a self-test at power-up, and the design needs to have built-in and tested functionality. In addition, users need to provide audiovisual response to touchscreen input.
The new generation of insulin pumps includes continuous monitoring displays.These systems utilize a continuous monitor with a transmitter.Measurements are transmitted via a wireless transmitter that reports the glucose value detected by the sensor to activate the pump for injection at the appropriate time. The insulin pump also provides an analytical graph based on historical measurement data that guides the calculation of insulin injections.
5). Self-Test Functions
In accordance with FDA regulations, all insulin pumps must first run a self-test (POST) program when powered up to test critical processor, circuitry, indicators, and alarm functions. Some POST operations require user observation, and additional self-test circuitry helps reduce the risk of potential failure.
For example, some modules use a safety processor to monitor the operation of the main processor and signal an alarm as soon as an unforeseen condition is detected; some self-test systems may simply monitor the current, indicated by the on and off indication of a light-emitting diode (LED). Once the current falls below the set threshold, a fault indication can be generated. The more common self-test circuits use a watchdog timer (WDT), and microprocessor supervisory circuits with a WDT function monitor the operation of the program. Medical devices typically do not allow the monitoring circuitry to be integrated within the microprocessor IC itself, as the monitoring circuitry can fail at the same time as the processor in this architecture.
The supervisory circuitry is critical to ensure that the insulin pump functions properly during patient use, and the microcontroller must be in a reset state before all circuitry reaches a tolerance range and remains stable. The voltage monitoring circuitry monitors the power supply for over- and under-voltage conditions, and is also required to detect motor operation and shutdown conditions; motor failure is a serious system fault and has the highest priority for sounding an alarm.The ADC, which can be built into the microprocessor internally, or an external microprocessor, is used to quantify readings from the sensors (temperature, motor, loading, insulin pump pressure, and battery voltage).
6). Alarm and I/O functions
The insulin pump requires audio-visual alarms to alert the user when a malfunction is detected, a specified time is reached, or certain warning conditions are triggered. LEDs can be used as visual indicators for remote glucose monitoring and insulin pumps, with a blinking green LED usually indicating normal operation and a red LED signal used to indicate an alarm or warning condition.
The buzzer must be equipped with a self-test circuit that indirectly monitors the speaker's impedance to see if it is in the normal range, or it can be mounted close to the speaker with a microphone that directly generates an audio output to check if the level is in the normal range. Various operational amplifiers, comparators, audio amplifiers, microphone amplifiers, and other components are typically used in the design of building alarm and self-test functions. An audio digital/analog converter (DAC) can generate a unique alarm output signal.
Eccentric rotating block (ERM) motors are also used in newer insulin pumps to generate vibration alarms.The ERM motor drive is not stringent, but requires the use of an amplifier or voltage regulator. Installing a battery is what produces a brief ERM self-test.
All insulin pumps must meet IEC61000-4-2 electrostatic discharge (ESD) protection requirements, which can be implemented with devices that have built-in protection or by adding ESD line protection externally.Maxim offers a wide range of interface devices with higher ESD protection, as well as a matrix of ESD protection diodes.
Considering the stringent requirements for the safety of insulin injections, the system needs to log events and time stamp changes to the logged data and processes. This function requires the support of a real-time clock (RTC), and of course, the clock can also provide an alarm function.
Most insulin pumps provide a data port that allows data to be sent to a computer or downloaded to upgrade firmware. Using this feature, historical data can be entered into an application that transmits it to a monitoring center for support regarding diabetes treatment.USB ports are the most common data ports, and data ports for memory cards should have ESD protection, current limiting, and logic level shifting.
In addition, the RF interface provides an additional link for the insulin pump to support the glucose continuous monitor, which predicts the trend of blood glucose based on the data delivered; it can also send the data to the host computer, which downloads the recorded data of the pump operation, the history of the blood glucose, and even sends upload commands to the insulin pump if necessary. The wireless interface can be Bluetooth or ISM band transceiver.