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                                                                    EXHIBIT 10.5


SECURITY AGREEMENT                                              [CRESTAR LOGO]
        

This Security Agreement ("Agreement") dated February 11, 1997, is made by APACHE
Medical Systems, Inc. (herein, whether one or more, the "Owner") for the use
and benefit of Crestar Bank, its successors and assigns (the "Bank").

SECURITY AGREEMENT.  In order to induce the Bank from time to time to extend or
continue to extend credit to APACHE Medical Systems, Inc., whether one or more
and any combination thereof, (the "Borrower"), the Owner (which may include the
Borrower) hereby grants the Bank a security interest in the collateral and all
proceeds, products, rents and profits thereof and all revenues from the right to
use the collateral described below (the "Collateral") to secure the payment of
all present and future indebtedness of every kind and description, however
evidenced, of the Borrower to the Bank, whether such indebtedness is direct or
indirect, fixed or contingent, liquidated or unliquidated, including any
extensions, modifications or renewals thereof (the "Indebtedness") and to secure
the performance by the Owner of the agreements and warranties contained in this
Agreement.

COLLATERAL.  As used in this Agreement, the term Collateral, whether now
existing or acquired in the future, shall mean:

All accounts ("Accounts"), Inventory ("Inventory"), furniture, fixtures and
equipment ("Equipment"), general intangibles ("General Intangibles"),
instruments, documents and chattel paper, including, without limitation, all
goods represented thereby and all goods that may be reclaimed or repossessed
from or returned by account debtors and all proceeds, products, rents and
profits thereof (as all such terms are defined in the Uniform Commercial Code).

REPRESENTATIONS AND WARRANTIES.  The Owner represents and warrants to the Bank
as follows:

     a)  APACHE Medical Systems, Inc. is/are and will continue to be the
         absolute owner of the Collateral.  There are no other owners or liens
         or security interests affecting the Collateral other than the  
         security interest granted in this Agreement except those previously    
         disclosed to the Bank in writing by the Owner; if the Owner is acting
         in the capacity of trustee, administrator or executor of an estate,
         such fact shall be disclosed and evidence of capacity shall be
         provided to the Bank;

     b)  The Owner will defend the Collateral against the claims and demands of
         all parties.  The Owner will not, without prior written consent of the
         Bank, grant any security interest in the Collateral and will keep it
         free from any lien, encumbrance or security interest;

     c)  If applicable to the Collateral pledged, the Owner represents and
         warrants that the Collateral never has been, and never will be as long
         as this Agreement remains a lien on the Collateral, used for the
         generation, collection, manufacture, storage, treatment, disposal,
         release or threatened release of any hazardous substance, as those
         terms are defined in the Comprehensive Environment Response,
         Compensation and Liability Act of 1980, as amended, 42 U.S.C. Section
         9601, et seq. ("CERCLA"), SuperFund Amendments and Reauthorization Act
         ("SARA"), applicable state laws, or regulations adopted pursuant to
         either of the foregoing.  The Owner agrees to comply with any federal,
         state or local law, statute, ordinance or regulation, court or
         administrative order or decree or private agreement regarding materials
         which require special handling in collection, storage, treatment or
         disposal because of their impact on the environment ("Environmental
         Requirements").  The Owner agrees to indemnify and hold the Bank
         harmless against any and all claims, losses and expenses resulting from
         a breach of this provision of this Agreement and the Owner will pay or
         reimburse the Bank for all costs and expenses for expert opinion or
         investigations required or requested by the Bank which, in the Bank's
         sole reasonable discretion, are necessary to ensure compliance with 
         this provision of this Agreement.  This obligation to indemnify
         shall survive the payment of the indebtedness and the satisfaction of
         the Agreement;                                            CWB
                                                                 --------
                                                                 Initials
                                                                 
     d) The primary use of the Collateral is and will be:  business;

     e)  If applicable to the type of collateral pledged, the Owner warrants and
         represents that all Collateral has been produced in compliance with the
         Fair Labor Standards Act or other applicable wage and employee law,
         rule, regulation or order, and that no existing or future liability
         shall occur as a result. The Owner may contest, in good faith, the
         applicability of any such law, rule, regulation or order, including
         prosecuting any appeals, so long as the Bank's interest in the
         Collateral, in the opinion of the Bank, is not jeopardized thereby;

     f)  The Owner, if an individual, is above the age of majority and has the
         legal capacity to enter into this Agreement;

     g)  The Owner must notify the Bank in writing at least 30 days prior to any
         change of its name, corporate structure or identity;

     h)  The location of the principal place of business (or home address if an
         individual) of APACHE Medical Systems, Inc. in Virginia is the County
         of Fairfax.  There are no other places of business in this state.
         Books of accounts and records are maintained at:  1650 Tysons
         Boulevard, #300, McLean, VA  22102.

     i)  The Collateral will be located at:  1650 Tysons Boulevard, #300,
         McLean, VA  22102 and 224 South Michigan Avenue, Suite 300,
         Chicago, IL 60604-2507. The Owner will maintain the Collateral in
         this/these location(s). The Collateral shall not be moved from the
         above locations without the prior written consent of the Bank;    
                                                                   CWB
                                                                 --------
                                                                 Initials
                                                                 

     j)  All information supplied and statements made to the Bank in any
         financial or credit statements or applications are true, correct,
         complete, valid and genuine in all material respects;

     k) None of the Collateral is being acquired with funds simultaneously
        advanced to the Borrower by the Bank.


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  l) The corporate Owner is duly organized and existing under the laws of
     Delaware; is duly qualified and in good standing as a foreign corporation
     in every jurisdiction where such qualification is necessary; the execution
     and performance of this Agreement have been duly authorized by action of
     its Board of Directors, no action of its shareholders being necessary; the
     execution and performance of this Agreement will not violate or contravene
     any provisions of law or regulation or its Articles of Incorporation,
     Shareholder Agreement, By-Laws or other agreements to which it is a party 
     or by which it is bound; and that no consent or approval of any 
     governmental agency or authority is required in making or performing the 
     obligations under this Agreement.

SECURITIES, INSTRUMENTS, CERTIFICATES OF DEPOSIT, DOCUMENTS, CHATTEL PAPER AND
GENERAL INTANGIBLES
  a) The Owner also grants the Bank a security interest in all rights to which
     an owner of the Collateral is now or may become entitled by virtue of
     owning such Collateral including, without limitation, interest, cash
     dividends, stock dividends and stock rights, all of which shall, when      
     received, and upon request by the Bank, be delivered to the Bank with
     written authority to sell, transfer or rehypothecate the same.

  b) If the Collateral includes all rights, title and interest in an Estate or
     Trust, the security interest shall not apply to any shares of capital
     stock of Crestar Financial Corporation or any of its affiliates, or to any
     units of participation in the Bank's Common Trust Fund held by the Estate
     or Trust, but shall apply to any proceeds from the sale of such stocks and
     units or cash dividends thereof.
  
  c) The Owner represents and warrants, as may be applicable, that:
     (i)   The Owner has good and marketable title to the Collateral.  The
           Collateral is valid and genuine and represents a bona fide, binding, 
           legal obligation of the maker, issuer, or grantor, and all signatures
           are genuine.
     (ii)  The Collateral is in full force and effect and is not in default and
           no prepayments have been made;
     (iii) The Collateral is not represented by a judgment or any other
           document not provided to the Bank;
     (iv)  The Collateral is not subject to any assignment, claim, lien, right
           of setoff or security interest of any other party;
     (v)   Unless otherwise stated, the face amount on the Collateral is the
           correct amount acutually and unconditionally due or to become due 
           according to the terms of the Collateral, and such amount is not 
           disputed or subject to any setof, credit, deduction or counterclaim;
     (vi)  With respect to any security on the Collateral, the lien or security
           interest represented thereby is not subject to prior claim, lien, or
           security interest of any other party, unless otherwise stated 
           herein, or in the document evidencing such security;
     (vii) With respect to the security on the Collateral, it has been properly
           perfected by the filing or recording of all necessary financing 
           statements, deeds of trust or other documents and the payment of all
           recording, transfer and other taxes and fees made in the appropriate
           public offices.

  d) At any time, and from time to time, whether before or after default, except
     as specified below, without notice, and at the expense of the Owner, the 
     Bank in its name or in the name of its nominee or of the Owner, may, but 
     shall not be obligated to: 
     (i)   After default, notify the obligors on any Collateral to make 
           payment to the Bank of any or all dividends, interest, principal 
           payments and other sums now or hereafter payable upon or on account 
           of the Collateral, may collect the same by legal proceedings or 
           otherwise, and may perform any contract or endorse in the name of 
           the Owner any checks, drafts, notes, instruments or other documents 
           which constitute the Collateral;
     (ii)  Enter into any extension, reorganization, deposit, merger or
           consolidation agreement or any agreement in any way relating to or
           affecting the Collateral and in connection therewith may deposit or
           surrender control of the Collateral, accept other property in
           exchange for the Collateral and do and perform such acts and things
           as it may deem proper, and any money or property received in
           exchange for the Collateral may be either applied to any     
           indebtedness or may be held by the Bank pursuant to the provisions
           of this Agreement; 

     (iii) Make any compromise or settlement it deems desirable or proper with
           reference to the Collateral:
     (iv)  Insure, process and preserve the Collateral;
     (v)   Cause the Collateral to be transferred to its name or the name of
           its nominee;
     (vi)  Exercise as to the Collateral all the rights, powers and remedies
           of an owner.
                                                                       CWB
                                                                  ------------
                                                                    Initials

INVENTORY.
  a) The Owner agrees to maintain books and records pertaining to the Inventory
     in such detail, form and scope as the Bank shall require.  The Owner shall
     promptly advise the Bank of any substantial changes relating to the type,
     quality or quantity of the Inventory or any event which would have a 
     material effect on the value of the Inventory or on the security interest
     granted to the Bank.  Upon reasonable notice by the Bank, the Owner shall
     assemble and make readily available for inspection and examination all of
     the Inventory and all books and records pertaining to the Inventory at any
     time;

  b) If the Inventory remains in the possession or control of any of the
     Owner's agents or processors, the Owner shall notify such agents or
     processors of the Bank's security interest, and upon request, instruct
     them to hold such Inventory for the Bank's account and subject to the
     Bank's instructions;

  c) The Owner will prepare and deliver to the Bank, at the Bank's request, a
     listing of all Inventory and such information regarding the Inventory as 
     the Bank may require.

ACCOUNTS. 
  a) The Owner warrants that each and every Account, now owned or hereafter
acquired is a bona fide existing obligation, valid and enforceable against the
account debt, for goods sold or leased and delivered or services rendered in
the ordinary course of business; it is subject to no dispute, defense or
offset; the Owner has good title to the Account and has full right and power to
grant the Bank a security interest in the Collateral;


                                    Page 2

<PAGE>   3
     b) The Owner will immediately notify the Bank of any Account to which the 
        above warranties are or become untrue;

     c) The Owner will prepare and deliver to the Bank, at the Bank's request,
        a listing and aging of all Accounts and any further schedules or
        information that the Bank may require.

     d) The Bank shall have the right after default to notify account debtors
        of its security interest in the Accounts and require payments to be
        made directly to the Bank. The Owner appoints the Bank and any
        officer or employee of the Bank, as the Bank may from time to time
        designate, as its attorneys-in-fact for the Owner, to sign and endorse
        in the name of the Owner, to give notice in the name of the Owner, and
        to perform all other actions necessary or desirable at the reasonable
        discretion of the Bank to effect these provisions and carry out
        the intent of this Agreement, all at the cost and expense of the Owner.
        The Owner ratifies and approves all acts of such attorneys-in-fact and
        neither the Bank nor any other such attorneys-in-fact will be liable for
        any acts of commission or omission nor for any error or judgment or
        mistake of fact or law. This power being coupled with an interest is
        irrevocable so long as any Account or General Intangible assigned to
        the Bank remains unpaid and the Borrower has any Indebtedness to the
        Bank. The costs of such collection and enforcement, including
        attorneys' fees and out-of-pocket expenses, shall be borne solely by
        the Owner whether the same are incurred by the Bank or the Owner. 
                                                                          CWB
                                                                        --------
                                                                        Initials

     e) At the option of the Bank, all payments on the Accounts received by the
        Owner shall be remitted to the Bank in their original form on the day
        of receipt; all notes, checks, drafts and other instruments so received
        shall be duly endorsed to the order of the Bank. At the Bank's
        election, the payments shall be deposited into a special deposit
        account ("Special Account") maintained with the Bank. The Bank may
        designate with each such deposit the particular Account upon which
        payment was made. The Special Account shall be held by the Bank as
        security for the Indebtedness. Prior to depositing payments on the
        Accounts into the Special Account, the Owner agrees that it will not
        commingle such payments with any of the Owner's funds or property, but
        will hold them separate and apart and in trust for the Bank. The Bank
        will have the power to withdraw from the Special Account. The Bank may
        at any time and from time to time, in its sole discretion, apply any
        part of the funds in the Special Account to the Indebtedness whether or
        not the same is due. Upon full and final satisfaction of the
        Indebtedness plus termination of any commitment to extend additional
        funds, the Bank will pay to the Owner any excess funds, whether
        received by the Bank as a deposit in the Special Account or as a direct
        payment on any of the Indebtedness.

     f) If any of the Owner's Accounts arise out of contracts with the United
        States or any department, agency, or instrumentality thereof, the Owner
        will immediately notify the Bank in writing and execute any
        instruments and take any steps required by the Bank in order that all
        monies due and to become due under such contracts shall be assigned to
        the Bank and in order that proper notice be given under the Federal
        Assignment of Claims Act;

     g) The Bank shall not be liable and shall suffer no loss on account of
        loss or deprivation of any Account due to acts of omissions of the Bank
        unless the Bank's conduct is willful and malicious, and the Bank shall
        have no duty to take any action to preserve the Collateral or collect
        Accounts.


COVENANTS.

     a) The Owner shall maintain complete and accurate books of account and
        records, and its principal books of account and records, including all
        records concerning Accounts and contract rights, shall be kept and
        maintained at the place(s) specified above. The Owner shall not move
        such books of account and records without giving the Bank at least 30
        days prior written notice and executing and delivering to the Bank
        financing statements satisfactory to the Bank prior to any such move.
        All accounting records and financial reports furnished to the Bank
        shall be maintained and prepared in accordance with generally accepted
        accounting principles consistently applied. It is specifically agreed
        that the Bank shall have and the Owner grants to the Bank a security
        interest in all books of account and records of the Owner and the Bank
        shall have access to them at any time for inspection, verification,
        examination and audit;

     b) The Owner shall furnish to the Bank financial and business information
        and reports in form and content satisfactory to the Bank as and when
        the Bank may from time to time require;

     c) The Owner, if a corporation, shall maintain its corporate existence in 
        good standing and shall not consolidate or merge with or acquire the
        stock of any other corporation without the prior written consent
        of the Bank. If the Owner is a corporation, the Owner shall, at the
        request of the Bank, qualify as a foreign corporation and obtain all
        requisite licenses and permits in each jurisdiction where the Owner
        does business. The Owner shall not discontinue business, liquidate,
        sell, transfer, assign or otherwise dispose of any of its assets,
        except with the prior written permission of the Bank, however, that it
        may sell in the ordinary course of business and for full consideration,
        any product, merchandise or service produced or marketed by it. The
        Bank's security interest shall attach to all proceeds of all sales or
        dispositions of the Collateral;

     d) The Owner shall maintain all of the Collateral in good condition and
        repair. The Bank shall have the right to inspect the Collateral at any  
        reasonable time and shall have the right to obtain such appraisals,
        reappraisals, appraisal updates or environment inspections as the Bank,
        in its sole discretion, may deem necessary from time to time;

     e) The Owner shall at all times keep insurable Collateral insured against
        any and all risks, including, without limitation, fire and
        other insurance as may  be required by the Bank from time to time; and
        in amounts as may be satisfactory to the Bank. The Bank shall be named
        as Loss Payee on any such insurance policies. Insurance may be
        purchased from an insurer of the Owner's choice, except as otherwise
        required by law. The Owner shall pay and discharge all taxes,
        assessments and charges of every kind prior to the date when such
        taxes, assessments or charges shall become delinquent and provide proof
        of such payments to the Bank, upon request. However, nothing contained
        in this Agreement shall require the Owner to pay any such taxes,
        assessments and charges so long as it shall contest its validity in
        good faith and shall post any bond or security required by the Bank
        against the payment. Upon the failure of the Owner to pay such required
        amounts, the Bank, at its option, and at the Owner's expense, may
        obtain such insurance or pay such taxes, assessments or charges with
        the costs or premiums.

                                    Page 3

<PAGE>   4
         becoming part of the indebtedness at the option of the Bank, such
         amounts may be payable on demand. Any insurance obtained by the Bank,
         at its option, may be single or dual interest, protecting its rights,
         rights of the Owner or joint rights. Any insurance obtained by the Bank
         may provide, at its option, that such insurance will pay the lesser of
         the unpaid balance of the indebtedness of the repair or replacement
         value of the Collateral. The Owner authorizes the Bank to give effect
         to any of these options without prior notice to Owner or further
         consent from Owner. No matter which insurance coverage or repayment
         options the Bank chooses, the Collateral will secure payment of these
         amounts. The Bank may use the proceeds of any insurance obtained by
         Owner or by the Bank to repair or replace the Collateral or, if the
         Bank elects to do so, to repay part or all of the indebtedness, and the
         Borrowers will still be responsible to repay any remaining unpaid
         balance of the Indebtedness. Owner assigns to the Bank all amounts
         payable under the insurance, include unearned premiums, directing the
         insurer to make payment to the Bank, and Owner appoints us
         attorney-in-fact to endorse any draft;

     f)  The Owner will not pledge or grant any interest in any of the
         Collateral to anyone except the Bank, or permit any lien or encumbrance
         to attach to any of the Collateral, or any levy to be made on the
         Collateral, or any financing statement (except financing statements in
         favor or the Bank) to be on file against the Collateral;

     g)  The Owner agrees that it will not permit any return of merchandise, the
         sale of which gave rise to any of the Accounts, except in the usual and
         regular course of business.

DEFAULT. In addition to any right which the Bank may have to demand payment of
the indebtedness under any other agreement, upon the occurrence of any of the
following events of default, the Bank, at its option, may declare any or all of
the Indebtedness immediately due and payable and may exercise any and all of
the rights and remedies of default of a secured party under the Uniform
Commercial Code and other applicable law and all rights provided herein, all of
which rights and remedies shall, to the full extent permitted by law, be
cumulative.

     a)  If the Borrower fails to pay when due any Indebtedness or shall
         otherwise be in default under any agreement of the Borrower with the
         Bank or with Crestar Financial Corporation, or any subsidiary or
         affiliate of Crestar Financial Corporation, or any subsidiary or
         affiliate of such subsidiary or affiliate (whether now existing or
         hereafter organized or acquired); or

     b)  The failure of the Owner to observe or perform any of the terms or
         provisions of this Agreement, or any such default by the Borrower, any
         endorser, or any guarantor of any Indebtedness of the Borrower to the
         bank (a "Party"); or

     c)  The breach of any of the Owner's representations or warranties in this
         Agreement or any other agreement with the Bank; or

     d)  The death, dissolution, merger, consolidation or termination of
         existence of the Owner or any Party; or

     e)  The insolvency or inability to pay debts as they mature of the Owner or
         any Party, or the application for the appointment of a receiver for any
         of them, or the filing of a petition under any provision of the
         Bankruptcy Code or other insolvency law, statute or proceeding by or
         against any of them, or any assignment for the benefit of creditors by
         or against any of them; or

     f)  The entry of a judgment against the Owner or any Party or the issuance
         or service of any attachment, levy or garnishment against the Owner or
         any Party or the property of any of them or the repossession or seizure
         of property of the Owner or any Party; or

     g)  Any deterioration or impairment of the Collateral or any part of the
         Collateral or any decline or depreciation in the value or market value
         of the Collateral (whether actual or reasonably anticipated), which
         causes the Collateral, in the judgment of the Bank, to become
         unsatisfactory as to character or value; or

     h)  A determination by the Bank that a material adverse change in the
         financial condition of the Owner or any Party has occurred since the
         date of this Agreement; or

     i)  The Owner or any Party commits fraud or makes a material
         misrepresentation at any time in connection with this Agreement.

The Bank may require the Owner to assemble the Collateral and make available to
the Bank at a place to be designated by the Bank which is reasonably convenient
to the Bank and the Owner. The Bank may take possession of the Collateral
without a court order. The Owner shall pay to the Bank on demand all legal
expenses and reasonable attorneys' fees, as permitted by applicable law, if the
Bank refers this Agreement to an attorney who is not a salaried employee of the
Bank; appraisal fees and all expenses incurred or paid by the Bank in
protecting and enforcing the rights of the Bank under this Agreement, including 
the Bank's right to take possession of the Collateral and its proceeds, and to
hold, prepare for sale, sell and dispose of the Collateral. Any required notice
by the Bank of sale or other disposition on default, when placed in the mail
and addressed to or left at the premises of the Owner, at the address specified
next to the Owner's signature below or such other address of the Owner as may
from time to time be shown on the Bank's records, at least ten days prior to
such action shall constitute reasonable notice to the Owner.

TERM. This Agreement shall be a continuing agreement and shall remain in full
force and effect irrespective of any interruptions in the business relations
of the Borrower with the Bank and shall apply to any ultimate balance which
shall remain due by the Borrower to the Bank: provided, however, that the Owner
may by written notice terminate this Agreement with respect to all Indebtedness
of the Borrower incurred or contracted by the Borrower or acquired by the Bank
after the date on which the notice is personally delivered to or mailed by
registered mail and accepted by the Borrower's lending officer.

EXECUTION BY MORE THAN ONE PARTY. The term "Owner" as used in this Agreement
shall, if this instrument is signed by more than one Party, mean the "Owner and
each of them" and each shall be jointly and severally obligated and liable. If
any Party shall be a partnership, the agreements and obligations on the part of
the Owner shall remain in force and applicable regardless of any changes in the
individuals composing the partnership and the term "Owner" shall include any
altered or successive partnerships and the predecessor partnership and their
partners shall not be released from any obligation or liability.

                                    Page 4
<PAGE>   5

WAIVERS BY THE OWNER. The Owner hereby waives (a) notice of acceptance of this
Agreement and of any extensions, modifications or renewals of credit by the Bank
to the Borrower; (b) presentment and demand for payment of the Indebtedness; (c)
protest and notice of dishonor or default to the Owner or to any other Party
with respect to the Indebtedness; (c) all other notices to which the Owner
might otherwise be entitled; and (d) if for business  purposes, the benefit of
the Homestead Exemption. The Owner further waives any right to require that any
action be brought against the Borrower or any other Party, to require that
resort be had to any security or to any balance of any deposit account or
credit on the books of the Bank in favor of the Borrower or any other Party.
The Owner further agrees that it shall not be subrogated and will not enforce on
its part or behalf any right of action which the Bank may have against the
Borrower until every Indebtedness secured under this Agreement is paid in full.

NO OBLIGATION TO EXTEND CREDIT. This Agreement shall not be construed to
impose any obligation on the Bank to extend or continue to extend any credit at
any time.

INDEMNIFICATION. The Owner agrees to indemnify and hold harmless the Bank and
its subsidiaries, affiliates, successors, parents, and assigns and their
respective agents, directors, employees, and officers from and against any and
all complaints, claims, defense, demands, actions, bills, causes of action
(including, without limitations, costs and attorneys' fees), and losses of every
nature and kind whatsoever, which may be raised or sustained by any directors,
officers, employees, shareholders, creditors, regulators, successors in
interest, or receivers of the Borrower or any third party as a result of or
arising out of, directly or indirectly, the Bank extending credit as evidenced
by the Indebtedness to the Borrower, and taking the Collateral as security for
the indebtedness, and the Owner further agrees to be liable for any and all
judgments which may be recovered in any such action, claim, proceeding, suit,
or bill, including any compromise or settlement, and defray any and all
expenses, including, without limitation, costs and attorneys' fees, that may be
incurred in or by reason of any actions, claims, proceedings, suits, or bills.

FINANCING STATEMENTS. The Owner will deliver any instruments of further
assignment or assurance that the Bank may from time to time request to carry
out the intent of this Agreement, and will join with the Bank in executing
financing statements and other documents in form satisfactory to the Bank and
pay the cost of filing the same, including all recordation, transfer and other
taxes and fees, continuation statements and any other documents in any public
office deemed advisable by the Bank. The Owner agrees that a carbon,
photographic or other reproduction of a financing statement or this Agreement
shall be sufficient as a financing statement.

SUCCESSOR IN INTEREST. This Agreement shall be binding upon the Owner, its
successors and assigns, and the benefits hereof shall inure to the Bank, its
successors and assigns.

WAIVER BY THE BANK. The Bank may waive any default or remedy any default
without waiving the default remedied or any other prior or subsequent default.
The Bank's failure to exercise any right or take any action under this
Agreement shall not constitute a waiver of that or any other right or action.

WAIVER OF JURY TRIAL. To the extent legally permissible, the Owner waives all
right to trial by jury in any litigation relating to transactions under this
Agreement, whether sounding in contract, tort or otherwise.

GOVERNING LAW. The laws of the Commonwealth of Virginia shall govern the
construction of this Agreement and the rights and duties of the Owner and
Parties.

The undersigned has/have executed or caused this Agreement to be executed under
seal as of the above date.

APACHE Medical Systems, Inc.           APACHE Medical Systems, Inc.
1650 Tysons Boulevard, #300
McLean, VA  22102                  By:  /s/ Brion D. Umidi (Seal)
                                       ----------------------------------------
                                       Brion D.  Umidi, Chief Financial Officer



                                    Page 5
<PAGE>   6
                                                                 [CRESTAR LOGO]

COMMERCIAL NOTE

BORROWER:           APACHE Medical Systems, Inc.
LOAN AMOUNT:        Two Million Dollars and no cents ($2,000,000.00)
BORROWER'S ADDRESS: 1650 Tysons Boulevard, #300
                    McLean, VA  22102

OFFICER:            Christopher W. Bergstrom   CWB     DATE: February 11, 1997
                    (initials)                 ---
ACCOUNT NO:         04300022875599   NOTE NO: 0001     NOTE TYPE: Original Loan
-------------------------------------------------------------------------------

For Value Received, the undersigned (whether one or more) jointly and severally
promise to pay to the order of Crestar Bank (the "Bank") at any of its
offices, or at such place as the Bank may designate in writing, without offset
and in immediately available funds, the Loan Amount shown above, including or
plus interest, and any other amounts due, upon the terms specified below.

LOAN TYPE AND REPAYMENT TERMS
LOAN TYPE:          Revolving Master Borrowing Line

                    This is an open end revolving line of credit. You may borrow
                    an aggregate principal amount up to the Loan Amount shown
                    above outstanding at any one time.

REPAYMENT TERMS:    Principal on demand, plus interest, but the undersigned
                    shall be liable for only so much of the Loan Amount as shall
                    be equal to the total advanced to or for the undersigned,
                    or any of them, by the Bank from time to time, less all
                    payments made by or for the undersigned and applied by the
                    Bank to principal, plus interest on each such advance, and
                    any other amounts due all as shown on the Bank's books and
                    records, which shall be prima facie evidence of the amount
                    owed.  THIS NOTE MAY BE PREPAID AT ANY TIME WITHOUT PENALTY.

                    This Master Borrowing arrangement will terminate upon
                    written notice from the Bank to the undersigned, or if such
                    notice is not sooner given, 36 months from the date of this
                    Note, unless an alternate termination date is indicated in
                    the "Agreement", as defined below.                CWB
                                                                    ------
                                                                    Initials

                    THE BANK SHALL HAVE THE RIGHT TO DEMAND PAYMENT AT ANY TIME
                    EVEN IF AN EVENT OF DEFAULT (AS IDENTIFIED IN THIS NOTE) HAS
                    NOT OCCURRED.

ADDITIONAL TERMS AND CONDITIONS:

This Note is governed by additional terms and conditions contained in a
Commitment Letter between the undersigned and the Bank dated January 6, 1997,
and any modifications, renewals, extensions or replacements thereof (the
"Agreement"), which is incorporated in this Note by reference. In the event of a
conflict between any term or condition contained in this Note and in the
Agreement, such term or condition of the Agreement shall control.

INTEREST

Accrued interest will be payable on the first day of each month beginning on
March 1, 1997.

Interest will accrue daily on a actual 360 basis (that is, on the actual 
number of days elapsed over a year of 360 days).

Each scheduled payment made on this Note will be applied to accrued interest
before it is applied to principal. Interest will accrue from the date of this
Note on the unpaid balance and will continue to accrue after maturity, whether
by acceleration or otherwise, until this Note is paid in full. If this is a
variable rate transaction, the interest rate is prospectively subject to
increase or decrease without prior notice, and if this is a Term-Variable
Payment loan, adjustments in the payment schedule will be made as necessary. If
this is a variable transaction which uses a Crestar Prime Rate as the Index,
the Index is subject to increase or decrease at the sole option of the Bank.

Subject to the above, interest per annum payable on this Note (the "Rate") will
be the "Index" (as defined in this Note) plus a margin of 0.250%. The "Index"
shall be Crestar's Prime Rate, which is the rate established from time to time
by the Bank and recorded in its


--------------------------------------------------------------------------------
                                IMPORTANT NOTICE

THIS INSTRUMENT CONTAINS A CONFESSION OF JUDGMENT PROVISION WHICH CONSTITUTES A
WAIVER OF IMPORTANT RIGHTS YOU MAY HAVE AS A DEBTOR AND ALLOWS THE CREDITOR TO
OBTAIN A JUDGMENT AGAINST YOU WITHOUT ANY FURTHER NOTICE.
--------------------------------------------------------------------------------


                                     Page 1


<PAGE>   7
Central Credit Administration Division as a reference for fixing the lending
rate on commercial loans. The Index is a reference rate only and does not
necessarily represent the lowest rate of interest charged for such
borrowings. Adjustments to the Rate shall be effective as of the date the Index
changes.

COLLATERAL

Any collateral pledged to the Bank to secure any of the undersigned's existing
or future liabilities to the Bank shall secure this Note. To the extent
permitted by law, each of the undersigned grants to the Bank a security
interest in and a lien upon all deposits or investments maintained by the
undesigned with, and all indebtedness owed to the undesigned by, the Bank or any
of its affiliates.

This Note is also secured by the following collateral and proceeds thereof:

All accounts, inventory, furniture, fixtures and equipment, general
intangibles, instruments, documents and chattel paper now existing or
hereafter acquired and all proceeds and products thereof owned by, and as more
particularly described in a Security Agreement by, APACHE Medical Systems, Inc.
dated this date.

All of this security is referred to collectively as the "Collateral." The
Collateral is security for the payment of this Note and any other liability
(including overdrafts and future advances) of the undersigned to the Bank,
however evidenced, now existing or hereafter incurred, matured or unmatured,
direct or indirect, absolute or contingent, several, joint, or joint and
several, including any extensions, modifications or renewals. The proceeds of
any Collateral may be applied against the liabilities of the undersigned to the
Bank in any order at the option of the Bank.                   CWB
                                                              -------
                                                              Initials

LOAN PURPOSE AND UPDATED FINANCIAL INFORMATION REQUIRED

The undersigned warrant and represent that the loan evidenced by this Note is
being made solely for the purpose of acquiring or carrying on a business,
professional or commercial activity or acquiring real or personal property as an
investment (other than a personal investment) or for carrying on an investment
activity (other than a personal investment activity). The undersigned agree to
provide to the Bank updated financial information, including, but not limited
to, tax returns, current financial statements in form satisfactory to the Bank,
as well as additional information, reports or schedules (financial or
otherwise), all as the Bank may from time to time request.

DEFAULT, ACCELERATION AND SETOFF

Any one of the following will constitute an event of default under the terms of
this Note: (1) the failure to make when due any instalment or other payment,
whether of principal, interest, late charges or other authorized charges due
under this Note, or the failure to pay the amount demanded by the Bank if this
Note is payable on demand; (2) the death, dissolution, merger, acquisition,
consolidation or termination of existence of the undersigned, any guarantor of
the indebtedness of any of the undersigned to the Bank, any endorser, or any
other party to this Note (collectively called a "Party"); (3) the insolvency or
inability to pay debts as they mature of any Party, or the application for the
appointment of a receiver for any Party or the filing of a petition under any
provision of the Bankruptcy Code or other insolvency law, statute or proceeding
by or against any Party or any assignment for the benefit of creditors by or
against any Party; (4) the entry of a judgment greater than $50,000.00 against
any Party or the issuance or service of any attachment, levy or garnishment
greater than $50,000.00 against any Party or the property of any Party, or the
repossession or seizure of property of any Party; (5) a good faith determination
by the Bank that it deems itself insecure or that a material adverse change in
the financial condition of any Party or decline or depreciation in the value or
market value of any Collateral has occurred since the date of this Note or is
reasonably anticipated; (6) the failure of any Party to perform any other
obligation to the Bank under this Note or under any other agreement with the
Bank; (7) the occurrence of an event of default with respect to any existing or
future indebtedness of any Party to the Bank or any other creditor of the Party;
(8) a material change in the ownership, control or management of any Party that
is an entity, unless such change is approved by the Bank in its sole
discretion; (9) if any Party gives notice to the Bank purporting to terminate
its obligations under or with respect to this Note; (10) the sale or transfer by
a Party of all or substantially all of its assets other than in the ordinary
course of business; or (11) any Party commits fraud or makes a material
misrepresentation at any time in connection with this Note. If an event of
default occurs, or in the event of non-payment of this Note in full at maturity,
the entire unpaid balance of this Note will, at the option of the Bank, become
immediately due and payable, without notice or demand. Upon the occurrence of an
event of default, the Bank will be entitled to interest on the unpaid balance at
the stated Rate plus 2.00% (the "Default Rate"), unless otherwise required by
law, until paid in full. To the extent permitted by law, upon default, the Bank
will have the right, in addition to all other remedies permitted by law, to set
off the amount due under this Note or due under any other obligation to the Bank
against any and all accounts, whether checking or savings or otherwise, credits,
money, stocks, bonds or other security or property of any nature on deposit
with, held by, owed by, or in the possession of, the Bank or any of its
affiliates to the credit of or for the account of any Party, without notice to
or consent by any Party. The remedies provided in this Note and any other
agreement between the Bank and any Party are cumulative and not exclusive of any
remedies provided by law.                                         CWB
                                                                -------- 
                                                                Initials

CAPITAL ADEQUACY

Should the Bank, after the date of this Note, determine that the adoption of any
law or regulation regarding capital adequacy, or any change in its
interpretation or administration, has or would have the effect of reducing the
Bank's rate of return under this Note to a level below that which the Bank could
have achieved but for the adoption or change, by an amount which the Bank
considers to be material, then, from time to time, 30 days after written demand
by the Bank, the undersigned shall pay to the Bank such additional amounts as
will compensate the Bank for the reduction. Each demand by the Bank will be made
in good faith and accompanied by a certificate claiming compensation under this
paragraph and stating the amounts to be paid to it and the basis for the
payment.


                                     Page 2

<PAGE>   8
LATE CHARGES AND OTHER AUTHORIZED CHARGES

If any portion of a payment is at least ten (10) days past due, the undersigned
agree to pay a late charge of 5.00% of the amount which is past due.  Unless
prohibited by applicable law, the undersigned agree to pay the fee established
by the Bank from time to time for returned checks if a payment is made on this
Note with a check and the check is dishonored for any reason after the second
presentment.  In addition, as permitted by applicable law, the undersigned
agree to pay the following:  (1) all expenses, including, without limitation,
all court or collection costs, and actual attorneys' fees whether suit be
brought or not, incurred in collecting this Note; (2) all costs incurred in
evaluating, preserving or disposing of any Collateral granted as security for
the payment of this Note, including the cost of any audits, appraisals,
appraisal updates, reappraisals or environmental inspections which the Bank from
time to time in its sole discretion may deem necessary; (3) any premiums for
property insurance purchased on behalf of the undersigned or on behalf of the
owner(s) of the Collateral pursuant to any security instrument relating to the
Collateral; (4) any expenses or costs incurred in defending any claim arising
out of the execution of this Note or the obligation which it evidences, or
otherwise involving the employment by the Bank of attorneys with respect to
this Note and the obligations it evidences; and (5) any other charges permitted
by applicable law.  The undersigned agree to pay these authorized charges on
demand or, at the Bank's option, the charges may be added to the unpaid balance
of the Note and will accrue interest at the stated Rate.  Upon the occurrence
of an event of default, interest will accrue at the Default Rate.    CWB
                                                                   -------
                                                                   Initials

WAIVERS

The undersigned and each other Party waive presentment, demand, protest, notice
of protest and notice of dishonor and waive all exemptions, whether homestead
or otherwise, as to the obligations evidenced by this Note.  The undersigned
and each other Party waive any rights to require the Bank to proceed against
any other Party or person or any Collateral before proceeding against the
undersigned or any of them, or any other Party, and agree that without notice
to any Party and without affecting any Party's liability, the Bank, at any time
or times, may grant extensions of the time for payment or other indulgences to
any Party or permit the renewal or modification of this Note, or permit the
substitution, exchange or release of any Collateral for this Note and may add
or release any Party primarily or secondarily liable.  The undersigned and each
other Party agree that the Bank may apply all monies made available to it from
any part of the proceeds of the disposition of any Collateral or by exercise of
the right of setoff either to the obligations under this Note or to any other
obligations of any Party to the Bank, as the Bank may elect from time to time. 
The undersigned also waive any rights afforded to them by Sections 49-25 and
49-26 of the Code of Virginia of 1950 as amended.  TO THE EXTENT LEGALLY
PERMISSIBLE, THE UNDERSIGNED WAIVE ANY RIGHT TO TRIAL BY JURY IN ANY LITIGATION
RELATING TO TRANSACTIONS UNDER THIS NOTE, WHETHER SOUNDING IN CONTRACT, TORT OR
OTHERWISE.
        
JUDGEMENT BY CONFESSION

The undersigned hereby duly constitute and appoint Susan M. Banks or C.B.
Bohannon or Brian C. Middleton as the true and lawful attorney-in-fact for them
in any or all of their names, place and stead, and upon the occurrence of an
event of default, to confess judgment against them, or any of them, in the
Circuit Court for the County of Fairfax, Virginia, upon this Note and all
amounts owed hereunder, including all costs of collection, actual attorneys' 
fees and court costs, hereby ratifying and confirming the acts of said
attorney-in-fact as if done by themselves, expressly waiving benefit of any
homestead or other exemption laws.      ANB
                                     --------
                                     Initials

SEVERABILITY, AMENDMENTS AND NO WAIVER BY BANK

Any provision of this Note which is prohibited or unenforceable will be
ineffective to the extent of the prohibition or unenforceability without
invalidating the remaining provisions of this Note.  No amendment,
modification, termination or waiver of any provision of this Note, nor consent
to any departure by the undersigned from any term of this Note, will in any
event be effective unless it is in writing and signed by an authorized employee
of the Bank, and then the waiver or consent will be effective only in the
specific instance and for the specific purpose for which given.  If the
interest Rate is tied to an external index and the index becomes unavailable
during the term of this loan, the Bank may designate a substitute index with
notice to the Borrower.  No failure or delay on the part of the Bank to
exercise any right, power or remedy under this Note may be construed as a
waiver of the right to exercise the same or any other right at any time.


                                    Page 3
<PAGE>   9
LIABILITY, SUCCESSORS AND ASSIGNS AND CHOICE OF LAW

Each of the undersigned shall be jointly and severally obligated and liable on
this Note. This Note shall apply to and bind each of the undersigned's heirs,
personal representatives, successors and assigns and shall inure to the benefit
of the Bank, its successors and assigns. The undersigned agree that certain
material events and occurrences relating to this Note bear a reasonable
relationship to the Commonwealth of Virginia. The validity, terms, performance
and enforcement of this Note shall be governed by applicable federal law and
the internal laws of the Commonwealth of Virginia which are applicable to
agreements which are negotiated, executed, delivered and performed solely in
the Commonwealth of Virginia.

By signing below, the undersigned agree to the terms of this Note and
acknowledge receipt of a loan in the Loan Amount shown above.

                              APACHE Medical Systems, Inc.

                         By:  /s/ Brion D. Umidi
                              -------------------------------------- (SEAL)
                              Brion D. Umidi, Chief Financial Officer





                                     Page 4