According to the U.S. Food and Drug
Administration (FDA), home healthcare
is the fastest-growing segment of
the medical device industry. Longer life
spans, an increasing number of patients
with chronic medical conditions, and
rising health costs are the main forces
behind the trend of immersing the consumer
home market with “smarter” and “friendlier” medical
devices (Fig. 1).
What kinds of medical care products are turning up in
the home? Blood glucose meters, digital blood-pressure
meters, blood gas meters, digital pulse and heart-rate monitors,
digital thermometers, pregnancy testers, iontophoresis
transdermal drug-delivery systems, dialysis systems, and
oxygen concentrators. Many can be interconnected via the
Internet, often wirelessly, to the offices of healthcare providers
for constant on-the-spot monitoring of vital signs
and diagnostics.
As technological medical product developments become more
complicated, so do the requirements for their design—many
of which can be conflicting—to ensure that they can be used
safely and effectively by everyone, including healthcare providers
and patients, and most importantly, the home user. For the
design engineering community, all of this has meant doing more
on the chip or circuit board in a given
amount of space while dissipating the
least amount of power.
“The biggest problem for a
designer of ICs for home healthcare
products is knowing how to
properly balance issues like small
size, lower power, costs, reliability,
lifetime, processing power, and safety,”
explains Steve Kennelly, senior
manger of the Medical Products
Group of Microchip Technology.
“The amount of processing power
needed is influenced by who the
user of the medical device is.”
Many medical devices aren’t produced
in very large quantities, making
it difficult to automate their
manufacture and achieve low market
costs. One positive note on this front
is that prices for individual electronic components within these
products (sensors, MCUs, displays, memory, etc.) are sliding.
Yet another roadblock is achieving hermetic levels well beyond
those required for non-medical applications. Across-the-board
miniaturization makes hermeticity even harder to attain.
Get To Know Your Device
Operating medical equipment is more
intuitive for doctors and clinicians since
they’re trained to use such tools. For a home
patient, however, operational simplicity
is much more important. Fortunately, the
latest highly integrated ICs, sophisticated
DSPs and microcontrollers, high-density
flash memories, and advanced microelectromechanical
systems (MEMS) sensors
help to achieve that goal.
“We welcome conflicting requirements
since they represent an opportunity for us
to innovate,” explains Todd Schneider, vice
president in the Medical Business Unit
of AMI Semiconductor, which largely
uses application-specific standard products
(ASSPs) and application-specific ICs
(ASICs) in its medical designs. “We’ve
been in the medical device business for
over 20 years and understand the technical
challenges posed.”
Every healthcare medical product
requires a different set of performance priorities,
depending on the application. For
example, low cost is one of the top parameters
for something like portable glucose
meters, which often use disposable chemical
strips. A portable home dialysis system,
on the other hand, must have reliability and
long life as top-of-the-list requirements in
a design, with cost being a secondary factor.
Implantable devices like automated
pacemakers primarily
must be highly reliable
and small with a long
life and as little power
dissipation as possible.
Cost isn’t a factor in this
case.
Size Does Matter
As a result of the large
number of performance
requirements
for medical products,
engineers face various
design tradeoffs. This
means they must carefully
balance what kind
of sensor, analog-to-digital conversion,
amplification and filtering, control and
data-processing, power supply, display,
and wireless transceiver circuits to use.
Size often is a major design constraint,
particularly for medical implants, where
minimal invasiveness is an absolute must.
Such implants typically contain a sensor,
some signal-processing circuitry, and possibly
a transmitter, all designed to fit into
a tiny catheter or probe that’s inserted into
the human body. Small size also makes it
easier for the physician or healthcare provider
to place the implant in the body.
For example, some smart pills contain
sensors, cameras, and RF transmitters that
provide a clear and non-invasive view of
internal organs. Similarly, DexCon Inc. uses
an ultra-low-power ASIC system-on-achip
(SoC) from AMI Semiconductor in its
implantable glucose monitor, which continuously
monitors diabetics using RF transmissions
in the 402- to 405-MHz range.
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