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                                                                   EXHIBIT 10.51

                                    AMENDMENT
                                       TO
                                 LOAN AGREEMENT

      THIS AMENDMENT TO LOAN AGREEMENT ("Amendment") dated as of the _25th day
of April, 2001 (the "Effective Date"), is made by and among Bank of America,
N.A., a national banking association, and U.S. BANK NATIONAL ASSOCIATION, a
national banking association, as lenders (individually and collectively
"Lenders"), BANK OF AMERICA, N.A. as agent for Lenders ("Agent"), and SPACELABS
MEDICAL, INC., a California corporation, as borrower ("Borrower").

                                          RECITALS

      A.    Lenders and Borrower are parties to that certain Amended and
Restated Loan Agreement dated as of August 11, 2000, and promissory notes
described therein as amended from time to time by written agreement or other
amendments from time to time executed by Lenders and Borrower (collectively the
"Loan Agreement"). Capitalized terms not otherwise defined herein have the
meaning given in the Loan Agreement.

      B.    Borrower agrees to pay Lenders an additional loan fee and agrees to
reset the interest rates applicable to the Loans on the terms and conditions set
forth in this Amendment.

      C.    Borrower has requested that Lenders amend the Loan Agreement and
modify certain terms and conditions contained in the Loan Agreement and related
Loan Documents. Lenders are willing to modify the Loan Agreement on the terms
herein.

      NOW, THEREFORE, in consideration of the mutually agreed terms and
conditions set forth herein, and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, the parties hereto
agree as follows:

                                         AGREEMENT

      1.    RATIFICATION AND INCORPORATION OF LOAN AGREEMENT. Except as
expressly waived or modified under this Amendment, the parties hereto
acknowledge, confirm and ratify all of the terms and conditions of the Loan
Agreement, the Notes and other Loan Documents.

      2.    AMENDMENTS TO LOAN AGREEMENT.

      2.1   SECTION 2.2(a). Section 2.2(a) of the Loan Agreement is amended to
            provide that the maximum principal amount of the Revolving Loans
            shall not exceed the amount of $32,500,000 at the Effective Date.

      2.2   SECTION 5.15. New Section 5.15 is added to the Loan Agreement to
            read as follows:

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                        SECTION 5.15 REFINANCING EFFORTS. If, on or
                        before July 31, 2001, Borrower shall fail to
                        provide Agent with executed commitment letters
                        upon the terms and conditions listed below,
                        then Borrower shall pay Lenders an additional
                        loan fee, as liquidated damages for loss of a
                        bargain and not as a penalty, equal to
                        one-quarter of one percent (0.25%) of the
                        aggregate of all outstanding commitments of
                        Lenders under (i) the Burdick commitment, (ii)
                        Total Revolving Commitment, and (iii) the
                        outstanding balance of the Term Loan, as of
                        July 31, 2001, which fee shall be due and
                        payable on or before August 6, 2001. The
                        commitment letters shall: (i) provide for
                        aggregate financing to Borrower in amounts
                        sufficient to satisfy and pay in full
                        Borrower's obligations on the Term Note, the
                        Burdick Notes and the Revolving Notes, and all
                        of Borrower's other obligations under the Loan
                        Documents; (ii) be binding commitments by the
                        financing sources subject only to customary
                        closing conditions reasonably satisfactory to
                        Lenders; (iii) provide for a closing date on
                        or before September 1, 2001; (iv) be with
                        reputable financing sources with a recognized
                        capacity to fund the commitments; and (v) be
                        in form and substance satisfactory to Lenders.

      3.    FINANCIAL COVENANT WAIVERS. Borrower's compliance with the
financial covenants set forth in Section 5.11 and 5.12 of the Loan Agreement is
waived for the fiscal quarter ending March 31, 2001 only. Notwithstanding the
foregoing, Borrower agrees that it will be in compliance with Sections 5.11
through 5.14 of the Loan Agreement at the fiscal quarter ending June 30, 2001.
Borrower's failure to comply with any of Sections 5.11 through 5.14 as of June
30, 2001 shall constitute an Event of Default hereunder; provided, however, that
Lenders agree that in such event Lenders shall forbear in exercising remedies
under the Loan Documents on account of such Event of Default until on or after
September 2, 2001, and provided further that no other Event of Default under the
Loan Agreement shall occur and be continuing after any applicable cure period.

      4.    PREPAYMENT OF LOAN OBLIGATIONS. Notwithstanding any conflicting
terms and conditions of the Loan Agreement, Notes or other Loan Documents,
Borrower hereby undertakes and agrees to use good faith efforts to close the
financing referenced in Section 2.2 of this Amendment on or before September 1,
2001. In the event Borrower fails to close on the refinancing set forth in
Section 2.2 of this Amendment by September 1, 2001, the Lenders shall reset the
interest rate. In such case, effective September 2, 2001 (the "Reset Date") and
notwithstanding any other interest rate otherwise applicable under the Loan
Agreement, the Applicable Term Interest Rate, the Applicable Burdick Interest
Rate, and the Applicable Revolving Interest Rate shall each be changed to the
Reset Rate. For purposes hereof, the "Reset Rate" shall equal the Prime Rate
plus two percent (2%) per annum, changing as the Prime Rate changes. Effective
on the Reset Date, Section 2.8(d) of the Loan Agreement shall be of no further
force or effect.

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      5.    RELEASE OF LENDERS. Borrower and Guarantor hereby waive, release,
acquit and forever discharge Agent, Lenders, and each of their parents,
subsidiaries, and affiliates, and their officers, directors, agents,
representatives, and employees, and their successors, heirs, and assigns, and
each of them of and from any and all claims, demands, actions, rights, damages,
costs, expenses, and causes of action whatsoever, of every kind and nature,
whether presently known or unknown, contingent or noncontingent, arising or
alleged to have arisen to date in connection with the Loan Agreement, Notes and
other Loan Documents.

      6.    MISCELLANEOUS.

            6.1   ENTIRE AGREEMENT. This Amendment, together with the Loan
Agreement and the other Loan Documents is the entire agreement between Lenders
and Borrower with respect to the subject matter hereof. This Amendment
supersedes all prior and contemporaneous oral and written agreements and
discussions with respect to the subject matter hereof. Except as otherwise
expressly modified, the Loan Documents remain in full force and effect.

            6.2   COUNTERPARTS. This Amendment may be executed in one or more
identical counterparts, each of which shall be an original, but all of which
shall constitute one and the same agreement. Delivery of an executed counterpart
of a signature page to this Amendment by facsimile transmission shall be
effective as delivery of a manually executed counterpart.

            6.3   HEADINGS. Section headings used herein are for convenience of
reference only, are not part of this Amendment, and are not to be taken into
consideration in interpreting this Amendment.

            6.4   RECITALS. The recitals set forth at the beginning of this
Amendment are true and correct, and such recitals are incorporated into and are
made a part of this Amendment.

            6.5   GOVERNING LAW. This Amendment shall be governed by, and
construed and enforced in accordance with, the laws of the State of Washington
applicable to contracts made and performed in such state, without regard to the
principles thereof regarding conflict of laws.

            6.6   CONFLICTING TERMS. In the event of any inconsistency between
the provisions of this Amendment and any provision of the Loan Agreement or any
other Loan Document, the terms of this Amendment shall govern and control.

                            [SIGNATURE PAGE FOLLOWS]


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      IN WITNESS WHEREOF, Borrower has caused this Amendment to Loan Agreement
to be duly executed by its duly authorized signatory as of the date first
written above.

BORROWER:                           SPACELABS MEDICAL, INC., a Delaware
                                    corporation

                                    By
                                      -----------------------------------------
                                    Its
                                       ----------------------------------------

                                    Address:
                                    15220 N.E. 40th Street
                                    P.O. Box 97013
                                    Redmond, Washington  98073-9713
                                    Attn: Mr. James A. Richman
                                          Vice President & Corporate Controller

                                    Telecopy No.:  (425) 885-4877
                                    Telephone No.:  (425) 882-3700


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      IN WITNESS WHEREOF, Lender has caused this Amendment to Loan Agreement to
be duly executed by its duly authorized signatory as of the date first written
above.

LENDER:                                  BANK OF AMERICA, N.A., a national
                                         banking association


                                         By
                                           -------------------------------------
                                         Its:
                                             -----------------------------------

                                         Address:
                                         701 Fifth Avenue, 12th Floor
                                         WA1-102-12-06
                                         Seattle, Washington  98104
                                         Attn: Mr. Hank T. Knottnerus
                                               Senior Vice President

                                         Telecopy No.:  (206) 358-3971
                                         Telephone No.: (206) 358-3369

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      IN WITNESS WHEREOF, Lender has caused this Amendment to Loan Agreement to
be duly executed by its duly authorized signatory as of the date first written
above.

LENDER:                                  U.S. BANK NATIONAL ASSOCIATION, a
                                         national banking association


                                         By
                                            ------------------------------------
                                         Its:
                                             -----------------------------------

                                         Address:
                                         111 S.W. Fifth Avenue, Suite 810
                                         Portland, Oregon  97208-3108
                                         Attn: Ms. Betty J. Kinoshita
                                               Vice President

                                         Telecopy No.:  (503) 275-3220
                                         Telephone No.: (503) 275-5919


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      IN WITNESS WHEREOF, Agent has caused this Amendment to Loan Agreement to
be duly executed by its duly authorized signatory as of the date first written
above.

AGENT:                                   BANK OF AMERICA, N.A., a national
                                         banking association


                                         By
                                            ------------------------------------
                                         Its:
                                             -----------------------------------

                                         Address:
                                         701 Fifth Avenue, 16th Floor
                                         WA1-102-12-20
                                         Seattle, Washington  98104
                                         Attn: Ms. Dora A. Brown
                                               Vice President

                                         Telecopy No.:  (206) 358-0971
                                         Telephone No.: (206) 358-0101


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                            GUARANTOR ACKNOWLEDGMENT

      The undersigned ("Guarantor") hereby affirms that the Amended and Restated
Guaranty Agreement dated August 11, 2000 ("Guaranty"), executed and delivered to
Lenders, is in full force and effect, and the Obligations (as defined in the
Guaranty) shall include, but not be limited to, the payment and performance of
the Borrower's obligations under the Loan Agreement as amended by the forgoing
Amendment, and Guarantor further represents and agrees that the Guaranty is an
unconditional unlimited continuing guaranty of payment enforceable by its terms,
without defense or counterclaim thereto. Guarantor hereby consents to the terms
of this Amendment.

GUARANTOR:                               SPACELABS MEDICAL, INC.


                                         By
                                            ------------------------------------
                                         Name:
                                              ----------------------------------
                                         Title:
                                               ---------------------------------

                                         Address:
                                         15220 N.E. 40th Street
                                         P.O. Box 97013
                                         Redmond, Washington  98073-9713
                                         Attn: Mr. James A. Richman
                                               Vice President & Corporate
                                                  Controller

                                         Telecopy No.:  (425) 885-4877
                                         Telephone No.: (425) 882-3700


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