July 31, 2020 by Emmanuel Ikimi
Electronics engineers working in industries that design equipment for the healthcare industry are responsible for ensuring their safety and reliability in line with standards of the medical industry. This article will explore the most critical considerations in designing electronics for medical use.
Medical electronics engineering (aka biomedical engineering) is a speciality of electrical engineering that involves the design and maintenance of electronic devices and equipment for the healthcare industry. Electronic applications in the medical field help to assist healthcare professionals in performing their duties, modifying medical treatments, and improving both clinical outcomes and the overall quality of life of patients.
As treatments become more advanced, electronics have become more efficient, too. Thanks to rapid miniaturisation, electronic equipment has become smaller and more component-dense. As covered below, medical electronics broadly cover life support instrumentation, hearing aids, pacemakers, and patient monitoring equipment.
Life support machines help to sustain a patient’s critical body functions until biological systems can regain control. A good example is a medical ventilator that aids respiration in patients with breathing problems. The device comprises gas sensors (for detecting oxygen and carbon dioxide levels), power converters (for converting AC input to DC and DC to DC), an electric pump for ventilation, and a control panel (which serves as a human-machine interface, or HMI.
A top-down view of left and right-ear hearing aids, including their microphone and speaker sections. Image Credit: Pixabay.
Hearing aids fall into the category of implantable medical devices. They are portable, battery-powered devices that aid the hard of hearing by amplifying the sound that reaches the user’s ear. Hearing aids contain a microphone that intercepts sound waves from the environment and converts them into digital signals. An amplifier then increases the strength of the input signal and passes it to a speaker inside the device placed in the ear.
A pacemaker is a life-critical, battery-powered device that sends an electronic signal to the heart to help it beat more regularly. The main components of these devices are the leads and the pulse generator. The former are small wires that pass through a patient’s veins and into the heart muscles. They transmit electrical impulses from the pulse generator, which is a small battery-powered device located on the patient's chest.
Patient monitoring systems are electronic devices and equipment that measure the health status of patients, such as their insulin levels, heart rate, and oxygen saturation. A standard biomedical signal acquisition system comprises sensors, amplifiers, filters, and analogue-to-digital converters.
A doctor shows her patient his readings on a patient monitoring system. Image Credit: Pxfuel.
In the medical industry, errors often prove fatal. Therefore, electronic devices and equipment must operate at a high degree of precision. To facilitate the sound decision making of healthcare professionals, the data obtained from electronic sensors and signal processing systems must have a low margin of error over a large number of samples.
Reliability is also critical. Some electronic equipment utilised in hospitals, clinics, and long-term care facilities (such as insulin pumps, pacemakers, and defibrillators) perform life-critical functions. Moreover, many treatment processes that require the use of electronic medical equipment must carry on continuously, with predictable downtime for scheduled maintenance.
Biocompatibility measures the level of compatibility that an electronic medical device has with the biological systems of the host or patient. Meeting the healthcare industry’s biocompatibility requirements is one of the most challenging aspects for engineers designing implantable medical electronic devices.
Biocompatibility testing determines the impact of electronic medical devices on the human body, particularly by identifying potentially harmful physiological effects. The ISO 10993-1:2018 is a recognised standard within the healthcare industry that allows manufacturers and design engineers to gain a better understanding of how the nature of device parts, manufacturing processes, sterilisation, and so on, all affect the biocompatibility of medical electronics.
Even in the most efficient devices, failures are inevitable and recognised as such. Nevertheless, due to the sensitive and life-critical nature of medical applications, failures must be highly predictable. The partial or total failures of medical devices may stem from manufacturing defects or failures (whether they’re latent or catastrophic) in electronic components, e.g. fuses, relays, contactors, and metal oxide semiconductor field-effect transistors (aka MOSFETs).
Electromagnetic interference can also affect the operation of both implantable devices and fixed electronic equipment. Disturbances from radio-frequency sources, such as local area networks, metal detectors, and Bluetooth devices, can cause medical devices to malfunction and compromise the health of patients.
Mean time to failure (MTTF), mean time between failures (MTBF), and mean time to repair (or recover) (MTTR) are some essential metrics for determining the uptime of electronic medical equipment. Let’s take a closer look at these metrics below:
MTTF is the time taken between the initial deployment of a medical device up to its end of life. It is one of the best ways to assess the reliability of non-repairable medical devices. Determining the MTTF allows for a timely replacement of sensitive devices to minimise the impact of failures on the health of patients.
MTBF assesses the time that passes between an electronic device’s previous failure and its next failure under normal operating conditions. Engineers usually calculate the MTBF to schedule routine inspections for replacements. After they establish that an asset will run for a certain number of hours before the next failure, they can carry out preventive actions, such as recalibration (i.e. the revision of the relevant industrial measurements and specifications), to minimise failure and extend its uptime.
MTTR assesses the mean time taken to restore a piece of electronic medical equipment to optimal functionality following a failure. Consider, for example, the importance of measuring the time it takes to recalibrate an electrocardiogram (aka ECG).
A patient’s first-person view as he applies a portable blood glucose meter to his middle fingertip. Image Credit: Pixabay.
Ultimately, electronic medical devices play an integral role in modern healthcare, enabling healthcare professionals to perform their duties more efficiently and reliably. Like the military, the healthcare industry has standards that promote the safe manufacture and operation of medical-grade devices to protect the safety and health of patients.
After all, reliability, accuracy, and biocompatibility are the most critical considerations for designing electronics for medical use.
