healing powers
A spring-loaded pressure gauge makes an oxygen therapy system available for wider use.
By Gayle Ehrenman, Associate Editor
When it comes to engineering, simple often works
well enough. That was certainly the case with a new portable oxygen treatment
system, called the Numobag.
Created and distributed by Northridge, Calif.-based Numotech Inc., the
Numobag applies topical hyperbaric oxygen therapy, or THOT. It consists
of a plastic bag that resembles a kitchen garbage can liner, hooked up
to a standard pressurized oxygen tank, with a mechanical sensor attached
to the outside of the bag. It's a relatively simple, yet effective approach
that uses pressurized oxygen for treating pressure ulcers, diabetic foot
ulcers, severe burns, and other skin wounds.
According to the Juvenile Diabetes Association, more than one million
Americans per year are afflicted with pressure sores, and it costs approximately
$6.5 billion to treat these problems.
Madalene Heng, a professor at the University of California School of Medicine
and chief of dermatology at the Veterans Administration Center in Sepulveda,
Calif., pioneered the basic concept for the system (sans the sensor).
Heng, who has been using the system for some 20 years, can judge the proper
pressure of the oxygen by touching the bag. But training other people
to have a feel for the pressure was a time-consuming, labor-intensive
process that didn't really make use of the bag practical for more than
a handful of patients.
Before the system could be produced and distributed on a larger scale,
it needed a sensor that could quickly provide feedback as to the pressure
of oxygen in the system. Numotech called on Sandia National Laboratories
in Los Alamos, N.M., to develop the device.
The sensor had to be mechanical—with no electrical parts—because
heat or sparks in the presence of pressurized oxygen can cause fires.
It had to operate without puncturing the bag, because the bag had already
been through the Food and Drug Administration approval process and any
alterations to it would mean going through that process again.
It had to be disposable, inexpensive, and easy to read. That was the challenge
facing Sandia researchers Mark Vaughn and Keith Miller. Oh, and they initially
had to develop the sensor with essentially no budget.
They got together over the weekend in Miller's garage, and forged a mechanical
sensor that would use the surface of the polyethylene bag as a huge sensing
membrane. According to Vaughn, a Sandia technical staff distinguished
member, the first version of the sensor was made up of nothing more than
tongue depressors, springs from a hair barrette, and hot glue. It may
not have been glamorous, but it worked.
Once the pair knew that their basic premise was correct, they kept engineering
until they reached the design for the sensor that's currently in use.
This version, which resembles a board game spinner more than a traditional
medical sensor, operates on the same principle as that primitive model.
The spring-loaded sensor is attached to the top of the bag via special
double-stick tape. (Traditional adhesives won't adhere to the polyethylene.)
As the oxygen pressure inside the bag increases, the tension of the bag
changes. That moves the pointer on the sensor through its three settings:
Low, High, Good.
With that sensor in place, the Numobag system can be easily monitored
and used successfully by medical technicians with much less specific training.
The
Numobag sensor (right) has changed relatively little from the prototype
version (left).
Since the addition of the sensor, the federal government has licensed
the technology for use by the military. The mobile, low-cost technique
is especially interesting to the military because in addition to its utility
for standard wound types, it is also considered an effective treatment
for smallpox and dermal anthrax. And, in a pinch, the oxygen-filled plastic
bags can serve as portable isolation chambers for those suffering from
contagious diseases.
THOT differs from traditional hyperbaric oxygen treatment in the pressure
it uses and its mode of operation. Traditional hyperbaric oxygen treatment
uses 100 percent oxygen at two to three atmospheres—30 to 45 psi,
or about 200 to 300 kilopascals. Topical hyperbaric oxygen treatment also
uses 100 percent oxygen, but at just slightly greater pressure than standard
air, at 1.03 atmospheres.
In traditional, or systemic, hyperbaric oxygen treatment, the patient
enters a sealed room or chamber, and the whole system is exposed to the
pressurized oxygen. With the Numobag, only the patient's body part requiring
treatment is inserted into the bag, and the bag is sealed off with medical
tape. Because this therapy is topical and relatively low pressure, there
is no systemic absorption of oxygen and, therefore, no risk of pulmonary
or central nervous system toxicity that can result from breathing high-pressure
oxygen, Heng said.
The heightened oxygen content of the Numobag helps oxidize disease-causing
organisms on the skin and in wounds, in addition to helping flesh heal.
According to M.R. Beal & Co., a New York investment house providing
backing for this venture, the estimated cost per treatment with a Numobag
is $185, while treatment in a hyperbaric chamber can cost as much as $1,500
per session.
The system is currently in service at hospitals in Florida and California,
and is about to go into use at the University of New Mexico Hospital.
Sandia researchers are working on ways to make the Numobag safer and easier
to use, with the goal of having it available for home use by 2004. According
to Vaughn, some of the areas under development for the next generation
include sensors that use the "aroma" of a wound to detect whether
it's healing, as well as sensors to assess the geometry, color, and depth
of the wounds. These sensors are an important step in making the Numobag
suitable for home use.
In a home healthcare setting, where many of the types
of wounds suitable for such treatment occur, nurses and doctors are not
generally available to monitor a wound's progress—or see if it's
getting worse. Photos don't provide adequate details for the job, either.
The team is also working on regulator switches to control the flow and
pressure of the oxygen, on better sealing technology for the bag, and
on technology to eliminate the need for a pressurized oxygen tank.
Fire safety is another area of concern. Vaughn says that "while nothing
bad has happened yet, one problem is too many." The Sandia team is
assessing the Numobag in as many different environments as possible, trying
to come up with a worst-case scenario in terms of static electricity,
friction, and other hazards. They will then do some real experiments—without
people in the bags, of course—to verify the systems' safety under
a wide range of unfriendly environmental conditions.
In addition to its humanitarian and economic benefits, the project is
of interest to Sandia for other reasons. Sensors developed to detect minute
amounts of effluents expelled by healing wounds during the topical hyperbaric
oxygen treatment are similar to ones used to detect minute amounts of
trace elements from aging nuclear weapons to indicate their state of reliability.