Another article from EE Times, August 12, copyright CMP Publications.
Of interest to people who design hardware, are diabetic, or deal with
the FDA.
Medical design's a bloody long haul
By Terry Costlow
LINCOLNSHIRE, Ill. -- Companies seeking a slice of the huge
medical-electronics market might do well to heed the cautionary tale
of Aksys Ltd. The startup has been laboring for six years to bring to
market the first home system for blood dialysis for U.S. kidney
patients. But because of a welter of technical and regulatory issues,
breaking new ground is not easy. Even with the technology basically in
place, the company's goal is still at least a year away.
Aksys' challenge brings many of the issues facing designers in the
medical portion of the embedded-systems world into high relief:
There's huge potential, but the technology is especially difficult
when lives are at stake. On top of that is the daunting task of
dealing with the Food and Drug Administration, an agency many
criticize as slow-moving even by the lumbering standards of a
government bureaucracy.
The brass ring is a U.S. market that approaches $1 trillion a year.
"In what we classify as electro-medical gear, the 1995 market figures
reached $9.5 billion, which is a lot of gear," said a spokesman for
the Electronic Industries Association (Arlington, Va.). "The market
virtually doubled in size from 1986 to 1995."
In its corner of that burgeoning marketplace, Aksys hopes to move
hemodialysis--the purification of blood--from the clinic or hospital
to the home. The company's Personal Hemodialysis System uses a
real-time operating system (RTOS), multiple processors and a host of
sensors to pull blood from a patient with kidney failure, purify it
and return it to the body. A patented hot-water cleaning system makes
it feasible to set the system up at home, since microprocessors
monitor all facets of this sterilization task as well as the actual
dialysis process itself.
One non-medical hurdle Aksys has encountered lies in
telecommunications. Once seen as a feature that could be put off for a
while, remote access is now considered a must-have for the first
iteration of the device.
"My focus the last year or so has been on the remote interface," said
Frank Naber, manager of PC-based software products at Aksys, here.
"Everything has to be verifiable. How you get data out of the
instrument to show that the treatment is doing what it's supposed to
do is a major concern. We're doing that with TCP/IP going to PC
software.'' The Personal Hemodialysis System is now able to transfer
data over phone lines, "and clinicians can use Windows 95 to export
information to any clinical software they want."
Sending data is complicated by the fact that major kidney-treatment
clinics might have 30 or so incoming phone lines, and doctors must
monitor data in real-time during dialysis. They monitor the patient
before treatment starts, and often want to check vital signs
afterwards. Aksys is also considering an e-mail feature so patients
and clinicians can share other types of data.
The firm was preparing to take its system to the FDA for testing late
this summer, but it recently moved that timetable back nine months.
Unlike many programs, there wasn't any one key reason.
"The delay wasn't for technical issues, or anything in our initial
production," said Dennis Cavender, vice president at Aksys. "It was
simply an understanding of the magnitude of work required to prove all
modes of operation, to write the software and do the documentation.
There are over 150,000 lines of code to be written and looked at."
Even after the system goes to the FDA, revenues will be a while off.
Simply submitting the hardware for testing is only the first step.
"By the middle of next year, we should be ready to submit an
Investigational Device Exemption request to the FDA so we can do
limited medical trials with living humans," Cavender said. "Then we
will collect data and submit it in early 1999. The next step is to
submit a 510k approval request, which the FDA generally turns around
in 90 days. We've allowed for some questions on that, to be
conservative. We feel that we'll get clearance to market the system in
the middle of the third quarter of 1999."
Like many medical-system firms, Aksys will be running a parallel
approval process in Europe. That process is simpler, so it's likely
that the system will get its CE mark late in 1998 or early in 1999,
Cavender said, about six months ahead of American approval. The
anticipated early European okay will help shorten the time the company
has to live off funds from its initial public offering, made in May
1996.
The intricately designed Personal Hemodialysis System is an exercise
in redundancy. Like many embedded systems, it must operate flawlessly
under sometimes unusual conditions.
"Our system has two 386SX Ampro Little boards," Naber said. "One is
for normal operation, such as running the modes of operation and
handling the user interface. The other board is dedicated to the
safety of the patient, providing redundancy for the monitoring systems
and redundant feedback from all transducers."
Safety is an obvious concern for a product that is working with a
patient's blood. Home hemodialysis systems that were offered years ago
occasionally sent cleaning fluids into the tubes while they were
connected to the patient, creating trauma and even fatalities. Aksys
does not want to repeat that situation, which for a time put the
kibosh on the concept of home hemodialysis.
"If the safety processor decides that things are not in the proper
range, it will clamp down immediately, shutting off the valves and
putting the system in a safe mode," Naber said.
Sensors make the link between the real world of analog signals and the
digital world of the controller boards. There is no shortage of them
in the machine.
"There are 40 or 50 sensors in our system, mostly transducers and
thermistors," Naber said. "They're checking temperature, pressure and
conductivity, which tells you how pure the chemicals are."
These sensors are used in three primary operations: preparing the
dialysate (the dialysis liquid), performing the dialysis task itself
and cleaning the system for its next use. All three operations are
quite demanding. A few grams' difference in preparing the dialysate,
pumping blood out of the patient too fast or cleaning the system a few
degrees below necessary levels could cause severe medical problems or
even death. The system relies heavily on processors and sensors to
make these medical/mechanical functions safe.
"The first stage is to produce ultrapure water, which we determine
with conductivity sensors. The purer the water is, the less conductive
it is," Naber said. "Once the water is pure, we drop in dry chemical.
This is done in phases, and we tell when it's ready by monitoring
conductivity. The dialysate has to be kept at the right temperature
during this whole process."
Once this dialysate is prepared, the patient connects to the machine
and the actual dialysis begins. The need for precise monitoring while
chemicals are prepared pales in comparison to what's needed when the
patient's blood is being purified.
"During this process, there are multitudes of things to watch," Naber
said. "We've got to continue to assure that the dialysate is delivered
at the proper temperature and pressure. We've got to be very careful
in the way we pull blood out and put it back. All these parameters are
programmed by the physician, so the system has to be programmable."
The third stage is to clean the system and prepare it for the next
usage, and here is where Aksys has developed a key technology. The
firm came up with a way to disinfect the system with hot water, which
is much safer than using chemical disinfectants, even traces of which
can cause major problems if they get into the patient's bloodstream.
-- Lloyd Rasmussen
Senior Staff Engineer, Engineering Section
National Library Service for the Blind and Physically Handicapped
Library of Congress 202-707-0535
(work) lras@loc.gov www.loc.gov/nls/
(home) lras@sprynet.com
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