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                                                                   EXHIBIT 10.18

SILICON VALLEY BANK

                              ASSUMPTION AGREEMENT

         THIS ASSUMPTION AGREEMENT dated as of January 9, 2003 is entered into
between SILICON VALLEY BANK ("Silicon"), on the one side, and QUINTON CARDIOLOGY
SYSTEMS, INC., QUINTON INC. AND BURDICK, INC. ("BURDICK," hereinafter referred
to as the "New Borrower"), on the other side. Capitalized terms used but not
defined in this Agreement shall have the meanings set forth in the Loan and
Security Agreement between Silicon, on the one side, and Quinton Cardiology
Systems, Inc. and Quinton Inc. (jointly and severally, the "Existing Borrower"),
on the other side, dated December 30, 2002 (as amended from time to time, the
"Loan Agreement").

         The parties agree as follows:

         1.       ASSUMPTION. New Borrower hereby assumes and agrees to pay and
perform when due all present and future indebtedness, liabilities and
obligations of Existing Borrower under, based upon, or arising out of the Loan
Agreement and any and all documents, instruments and agreements relating
thereto, including without limitation all of the "Obligations" as defined in the
Loan Agreement. Existing Borrower shall remain as an obligor with respect to all
of the Obligations, and Existing Borrower and New Borrower shall be jointly and
severally liable for all of the Obligations. All references in the Loan
Agreement, and in all related documents, to "Borrower" shall be deemed to refer,
jointly and severally, to Existing Borrower and New Borrower.

         2.       GRANT OF SECURITY INTEREST. Without limiting the generality of
the provisions of Section 1 above, as security for all Obligations, New Borrower
hereby grants Silicon a continuing security interest in all of New Borrower's
interest in the "Collateral" (as defined in the Loan Agreement) including,
without limitation, the types of property described below, whether now owned or
hereafter acquired and wherever located: (a) All accounts, contract rights,
chattel paper, letters of credit, documents, securities, money, and instruments,
and all other obligations now or in the future owing to New Borrower; (b) All
inventory, goods, merchandise, materials, raw materials, work in process,
finished goods, farm products, advertising, packaging and shipping materials,
supplies, and all other tangible personal property which is held for sale or
lease or furnished under contracts of service or consumed in the New Borrower's
business, and all warehouse receipts and other documents; and (c) All equipment,
including without limitation all machinery, fixtures, trade fixtures, vehicles,
furnishings, furniture, materials, tools, machine tools, office equipment,
computers and peripheral devices, appliances, apparatus, parts, dies, and jigs;
(d) All general intangibles including, but not limited to, deposit accounts,
goodwill, names, trade

                                      -1-

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         SILICON VALLEY BANK                                ASSUMPTION AGREEMENT

names, trademarks and the goodwill of the business symbolized thereby, trade
secrets, drawings, blueprints, customer lists, patents, patent applications,
copyrights, security deposits, loan commitment fees, federal, state and local
tax refunds and claims, all rights in all litigation presently or hereafter
pending for any cause or claim (whether in contract, tort or otherwise), and all
judgments now or hereafter arising therefrom, all claims of New Borrower against
Silicon, all rights to purchase or sell real or personal property, all rights as
a licensor or licensee of any kind, all royalties, licenses, processes,
telephone numbers, proprietary information, purchase orders, and all insurance
policies and claims (including without limitation credit, liability, property
and other insurance), and all other rights, privileges and franchises of every
kind; (e) All books and records, whether stored on computers or otherwise
maintained; and (f) All substitutions, additions and accessions to any of the
foregoing, and all products, proceeds and insurance proceeds of the foregoing,
and all guaranties of and security for the foregoing; and all books and records
relating to any of the foregoing. By the execution hereof, New Borrower hereby
authorizes Silicon to prepare and file UCC-1 Financing Statements listing New
Borrower as the debtor therein and in such form as Silicon shall specify.

         3.       LOANS. Borrower hereby understands, acknowledges and agrees
that Loans, if any, will be made to each Borrower based on the Eligible
Receivables and Eligible Inventory of each Borrower, subject to the Maximum
Credit Limit set forth in the Loan Agreement for all Loans to all Borrowers
combined.

         4.       CONDITIONS PRECEDENT TO LOANS. Notwithstanding anything herein
to the contrary, Borrower hereby understands and acknowledges that prior to any
Loans, if any, being made to New Borrower, the following shall have occurred:
(i) that certain Stock Purchase Agreement dated December 23, 2002 by and among
Spacelabs Medical, Inc., Spacelabs Burdick, Inc., Datex-Ohmeda, Inc. and Quinton
Cardiology Systems, Inc. (the "Burdick Acquisition") shall have become
effective, (ii) Silicon shall have received evidence satisfactory to Silicon in
its sole discretion of the effectiveness of the Burdick Acquisition and (iii)
Silicon shall have received evidence, satisfactory to Silicon in its sole
discretion, of Silicon's first-priority perfected security interest in the New
Borrower's interest in the Collateral subject to Permitted Liens, if any.

         5.       NEW BORROWER ADDED TO GUARANTY. Reference is made to that
certain Continuing Guaranty dated December 30, 2002, executed by each of the
undersigned Guarantors in favor of Silicon (the "Guaranty"). Each of the
undersigned Guarantors hereby acknowledges and agrees that the New Borrower is
hereby added as a named "Borrower" under the Guaranty and that each of the
Guarantors hereby unconditionally guarantees and promises to pay on demand to
Silicon in lawful money of the United States, and to perform for the benefit of
Silicon, all of the Borrower's (including without limitation with respect to the
New Borrower) present and future Indebtedness (as defined in the Guaranty) to
Silicon, subject in all respects to the terms, conditions, waivers and all other
provisions of the Guaranty.

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         SILICON VALLEY BANK                                ASSUMPTION AGREEMENT

         6.       CONTROL AGREEMENTS. As to any Deposit Accounts and investment
accounts maintained with another institution, New Borrower shall cause such
institution, within 30 days after the date of this Agreement, to enter into a
control agreement in form acceptable to Silicon in its good faith business
judgment in order to perfect Silicon's security interest in said Deposit
Accounts and investment accounts.

         7.       REPRESENTATIONS TRUE. Borrower represents and warrants to
Silicon that all representations and warranties set forth in the Loan Agreement,
as amended hereby, are true and correct.

         8.       CHOICE OF LAW AND VENUE; JURY TRIAL WAIVER. This Agreement and
the other Loan Documents shall be governed by, and construed in accordance with,
the internal laws of the State of California, without regard to principles of
conflicts of law. Each of Borrower and Silicon hereby submits to the exclusive
jurisdiction of the state and Federal courts located in the County of Santa
Clara, State of California. BORROWER AND SILICON EACH HEREBY WAIVE THEIR
RESPECTIVE RIGHTS TO A JURY TRIAL OF ANY CLAIM OR CAUSE OF ACTION BASED UPON OR
ARISING OUT OF ANY OF THE LOAN DOCUMENTS OR ANY OF THE TRANSACTIONS CONTEMPLATED
THEREIN, INCLUDING CONTRACT CLAIMS, TORT CLAIMS, BREACH OF DUTY CLAIMS, AND ALL
OTHER COMMON LAW OR STATUTORY CLAIMS. EACH PARTY RECOGNIZES AND AGREES THAT THE
FOREGOING WAIVER CONSTITUTES A MATERIAL INDUCEMENT FOR IT TO ENTER INTO THIS
AGREEMENT. EACH PARTY REPRESENTS AND WARRANTS THAT IT HAS REVIEWED THIS WAIVER
WITH ITS LEGAL COUNSEL AND THAT IT KNOWINGLY AND VOLUNTARILY WAIVES ITS JURY
TRIAL RIGHTS FOLLOWING CONSULTATION WITH LEGAL COUNSEL.

         9.       INTEGRATION. This will confirm that this Agreement, the Loan
Agreement and the other Loan Documents represent the final agreement between the
parties and may not be contradicted by evidence of prior, contemporaneous, or
subsequent oral agreements of the parties. There are no unwritten oral
agreements between the parties.

         10.      GENERAL PROVISIONS. This Agreement, the Loan Agreement, any
prior written amendments to the Loan Agreement signed by Silicon and the
Borrower, and the other written documents and agreements between Silicon and the
Borrower set forth in full all of the representations and agreements of the
parties with respect to the subject matter hereof and supersede all prior
discussions, representations, agreements and understandings between the parties
with respect to the subject hereof. Except as herein expressly amended, all of
the terms and provisions of the Loan Agreement, and all other documents and
agreements between Silicon and the Borrower shall continue in full force and
effect and the same are hereby ratified and confirmed.

                                      -3-

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         SILICON VALLEY BANK                                ASSUMPTION AGREEMENT

NEW BORROWER:                                  SILICON:

BURDICK, INC.                                  SILICON VALLEY BANK

BY /s/ Michael Matysik                         BY /s/ Silicon Valley Bank
  -------------------------------                -------------------------------
   PRESIDENT OR VICE PRESIDENT                 TITLE____________________________

BY /s/ Tim Way
  -------------------------------
   SECRETARY OR ASS'T SECRETARY

BORROWER:                                      BORROWER:

QUINTON CARDIOLOGY SYSTEMS, INC.               QUINTON INC.

BY /s/ Michael Matysik                         BY /s/ Michael Matysik
  -------------------------------                -------------------------------
   PRESIDENT OR VICE PRESIDENT                    PRESIDENT OR VICE PRESIDENT

BY /s/ Tim Way                                 BY /s/ Tim Way
  -------------------------------                -------------------------------
   SECRETARY OR ASS'T SECRETARY                   SECRETARY OR ASS'T SECRETARY

                                      -4-

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         SILICON VALLEY BANK                                ASSUMPTION AGREEMENT

                                     CONSENT

         The undersigned acknowledges that his consent to the foregoing
Agreement is not required, but the undersigned nevertheless does hereby consent
to the foregoing Agreement and to the documents and agreements referred to
therein and to all future modifications and amendments thereto, and any
termination thereof, and to any and all other present and future documents and
agreements between or among the foregoing parties. Nothing herein shall in any
way limit any of the terms or provisions of the Continuing Guaranty of the
undersigned, all of which are hereby ratified and affirmed.

GUARANTOR:                                     GUARANTOR:

QUINTON CARDIOLOGY SYSTEMS, INC.               QUINTON INC.

BY /s/ Michael Matysik                         BY /s/ Michael Matysik
  -------------------------------                -------------------------------
   PRESIDENT OR VICE PRESIDENT                    PRESIDENT OR VICE PRESIDENT

BY /s/ Tim Way                                 BY /s/ Tim Way
  -------------------------------                -------------------------------
   SECRETARY OR ASS'T SECRETARY                   SECRETARY OR ASS'T SECRETARY

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