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[LOGO]                                                              EXHIBIT 28.7

               [DEPARTMENT OF HEALTH & HUMAN SERVICES LETTERHEAD]



Mr. Louie Goryoka
Chad Therapeutics, Inc.
21622 Plummer Street
Chatsworth, CA 91311


Re:  K971889
     Chad TOTAL 0[subscript]2 Delivery System 
     Regulatory Class: II (two) 
     Product Code: 73 CAW
     Dated: August 19, 1997
     Received: August 20, 1997

Dear Mr. Goryoka:

This letter corrects our substantially equivalent letter of November 17, 1997,
regarding the error in the name of the contact person.

We have reviewed your Section 510(k) notification of intent to market the device
referenced above and we have determined the device is substantially equivalent
(for the indications for use stated in the enclosure) to devices marketed in
interstate commerce prior to May 28, 1976, the enactment date of the Medical
Device Amendments or to devices that have been reclassified in accordance with
the provisions of the Federal Food, Drug, and Cosmetic Act (Act). You may,
therefore, market the device, subject to the general controls provisions of the
Act. The general controls provisions of the Act include requirements for annual
registration, listing of devices, good manufacturing practice, labeling, and
prohibitions against misbranding and adulteration.

If your device is classified (see above) into either class II (Special Controls)
or class III (Premarket Approval) it may be subject to such additional controls.
Existing major regulations affecting your device can be found in the Code of
Federal Regulations, Title 21, Parts 800 to 895. A substantially equivalent
determination assumes compliance with the Good Manufacturing Practice for
Medical Devices: General (GMP) regulation (21 CFR Part 820) and that, through
periodic GMP inspections, FDA will verify such assumptions. Failure to comply
with the GMP regulation may result in regulatory action. In addition, the Food
and Drug Administration (FDA) may publish further announcements



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concerning your device in the Federal Register. Please note: this response to
your premarket notification submission does not affect any obligation you might
have under sections 531 through 542 of the Act for devices under the Electronic
Product Radiation Control provisions, or other Federal laws or regulations.

This letter will allow you to begin marketing your device as described in your
510(k) premarket notification. The FDA finding of substantial equivalence of
your device to a legally marketed predicate device results in a classification
for your device and thus, permits your device to proceed to the market.

If you desire specific advice for your device on our labeling regulation (21
CFR Part 801 and additionally 809.10 for in vitro diagnostic devices), please
contact the Office of Compliance at (301) 594-4648. Additionally, for questions
on the promotion and advertising of your device, please contact the Office of
Compliance at (301) 594-4639. Also, please note that the regulation entitled,
"Misbranding by reference to premarket notification" (21 CFR 807.97). Other
general information on your responsibilities under the Act may be obtained from
the Division of Small Manufacturers Assistance at their toll free number (800)
638-2041 or at (301) 443-6597 or at its internet address
"http://www.fda.gov/cdrh/dsmamain.html".

                                        Sincerely yours,



                                        /s/ Thomas J. Callahan
                                        Thomas J. Callahan, Ph.D.
                                        Director
                                        Division of Cardiovascular, Respiratory,
                                          and Neurological Devices 
                                        Office of Device Evaluation 
                                        Center for Devices and
                                          Radiological Health