PROMISSORY NOTE

Exhibit 4.11

PROMISSORY NOTE

References in the shaded area are for Lender’s use only and do not limit the applicability of this document to any particular loan or item. Any item above containing “***” has been omitted due to text length limitations.

PROMISE TO PAY. ALLION HEALTHCARE, INC. (“Borrower”) promises to pay to WEST BANK (“Lender”), or order, in lawful money of the United States of America, the principal amount of One Million Five Hundred Thousand & 00/100 Dollars ($1,500,000.00) or so much as may be outstanding, together with interest on the unpaid outstanding principal balance of each advance. Interest shall be calculated from the date of each advance until repayment of each advance.

PAYMENT. Borrower will pay this loan in one payment of all outstanding principal plus all accrued unpaid interest on September 30, 2005. In addition, Borrower will pay regular quarterly payments of all accrued unpaid interest due as of each payment date, beginning June 30, 2005, with all subsequent interest payments to be due on the same day of each quarter after that. Unless otherwise agreed or required by applicable law, payments will be applied first to any accrued unpaid interest; then to principal; then to any unpaid collection costs; and then to any late charges. Interest on this Note is computed on a 365/365 simple interest basis; that is, by applying the ratio of the annual interest rate over the number of days in a year, multiplied by the outstanding principal balance, multiplied by the actual number of days the principal balance is outstanding. Borrower will pay Lender at Lender’s address shown above or at such other place as Lender may designate in writing.

VARIABLE INTEREST RATE. The interest rate on this Note is subject to change from time to time based on changes in an index which is Lender’s Prime Rate (the “Index”). This is the rate Lender charges, or would charge, on 90-day unsecured loans to the most creditworthy corporate customers. This rate may or may not be the lowest rate available from Lender at any given time. Lender will tell Borrower the current Index rate upon Borrower’s request. The interest rate change will not occur more often than each DAY. Borrower understands that Lender may make loans based on other rates as well. The Index currently is 5.750% per annum. The interest rate to be applied to the unpaid principal balance of this Note will be at a rate of 2.000 percentage points over the Index, resulting in an initial rate of 7.750% per annum. NOTICE: Under no circumstances will the interest rate on this Note be more than the maximum rate allowed by applicable law.

PREPAYMENT; MINIMUM INTEREST CHARGE. In any event, even upon full prepayment of this Note, Borrower understands that Lender is entitled to a minimum interest charge of $7,50. Other than Borrower’s obligation to pay any minimum interest charge, Borrower may pay without penalty all or a portion of the amount owed earlier than it is due. Early payments will not, unless agreed to by Lender in writing, relieve Borrower of Borrower’s obligation to continue to make payments of accrued unpaid interest. Rather, early payments will reduce the principal balance due. Borrower agrees not to send Lender payments marked “paid in full”, “without recourse”, or similar language. If Borrower sends such a payment, Lender may accept it without losing any of Lender’s rights under this Note, and Borrower will remain obligated to pay any further amount owed to Lender. All written communications concerning disputed amounts, including any check or other payment instrument that indicates that the payment constitutes “payment in full” of the amount owed or that is tendered with other conditions or limitations or as full satisfaction of a disputed amount must be mailed or delivered to: WEST BANK, MAIN BANK, 1601 22ND STREET, WEST DES MOINES, IA 50266.

LATE CHARGE. If a payment is 11 days or more late, Borrower will be charged $15.00.

INTEREST AFTER DEFAULT. Upon default, including failure to pay upon final maturity, Lender, at its option, may, if permitted under applicable law, increase the variable interest rate on this Note to 4.000 percentage points over the Index. The interest rate will not exceed the maximum rate permitted by applicable law.

DEFAULT. Each of the following shall constitute an event of default (“Event of Default”) under this Note:

Payment Default. Borrower fails to make any payment when due under this Note.

Other Defaults. Borrower fails to comply with or to perform any other term, obligation, covenant or condition contained in this Note or in any of the related documents or to comply with or to perform any term, obligation, covenant or condition contained in any other agreement between Lender and Borrower.

Default in Favor of Third Parties. Borrower or any Grantor defaults under any loan, extension of credit, security agreement, purchase or sales agreement, or any other agreement, in favor of any other creditor or person that may materially affect any of Borrower’s property or Borrower’s ability to repay this Note or perform Borrower’s obligations under this Note or any of the related documents.

False Statements. Any warranty, representation or statement made or furnished to Lender by Borrower or on Borrower’s behalf under this Note or the related documents is false or misleading in any material respect, either now or at the time made or furnished or becomes false or misleading at any time thereafter.

Insolvency. The dissolution or termination of Borrower’s existence as a going business, the insolvency of Borrower, the appointment of a receiver for any part of Borrower’s property, any assignment for the benefit of creditors, any type of creditor workout, or the commencement of any proceeding under any bankruptcy or insolvency laws by or against Borrower.

Creditor or Forfeiture Proceedings. Commencement of foreclosure or forfeiture proceedings, whether by judicial proceeding, self-help, repossession or any other method, by any creditor of Borrower or by any governmental agency against any collateral securing the loan. This includes a garnishment of any of Borrower’s accounts, including deposit accounts, with Lender. However, this Event of Default shall not apply if there is a good faith dispute by Borrower as to the validity or reasonableness of the claim which is the basis of the creditor or forfeiture proceeding and if Borrower gives Lender written notice of the creditor or forfeiture proceeding and deposits with Lender monies or a surety bond for the creditor or forfeiture proceeding, in an amount determined by Lender, in its sole discretion, as being an adequate reserve or bond for the dispute.

Events Affecting Guarantor. Any of the preceding events occurs with respect to any guarantor, endorser, surety, or accommodation party of any of the indebtedness or any guarantor, endorser, surety, or accommodation party dies or becomes incompetent, or revokes or disputes the validity of, or liability under, any guaranty of the indebtedness evidenced by this Note. In the event of a death, Lender, at its option, may, but shall not be required to, permit the guarantor’s estate to assume unconditionally the obligations arising under the guaranty in a manner satisfactory to Lender, and, in doing so, cure any Event of Default.

Change In Ownership. Any change in ownership of twenty-five percent (25%) or more of the common stock of Borrower.

Adverse Change. A material adverse change occurs in Borrower’s financial condition, or Lender believes the prospect of payment or performance of this Note is impaired.

Insecurity. Lender in good faith believes itself insecure.

Cure Provisions. If any default, other than a default in payment is curable and if Borrower has not been given a notice of a breach of the same provision of this Note within the preceding twelve (12) months, it may be cured if Borrower, after receiving written notice from Lender demanding cure of such default: (1) cures the default within twenty (20) days; or (2) if the cure requires more than twenty (20) days, immediately initiates steps which Lender deems in Lender’s sole discretion to be sufficient to cure the default and thereafter continues and completes all reasonable and necessary steps sufficient to produce compliance as soon as reasonably practical.

LENDER’S RIGHTS. Upon default, Lender may declare the entire unpaid principal balance on this Note and all accrued unpaid interest immediately due, and then Borrower will pay that amount.

ATTORNEYS’ FEES; EXPENSES. Lender may hire or pay someone else to help collect this Note if Borrower does not pay. Borrower will pay Lender that amount. This includes, subject to any limits under applicable law, Lender’s attorneys’ fees and Lender’s legal expenses, whether or not there is a lawsuit, including without limitation all attorneys’ fees and legal expenses for bankruptcy proceedings (including efforts to modify or vacate any automatic stay or injunction), and appeals. If not prohibited by applicable law, Borrower also will pay any court costs, in addition to all other sums provided by law.

GOVERNING LAW. This Note will be governed by federal law applicable to Lender and, to the extent not preempted by federal law, the laws of the State of Iowa without regard to its conflicts of law provisions. This Note has been accepted by Lender in the State of Iowa.

CHOICE OF VENUE. If there is a lawsuit, Borrower agrees upon Lender’s request to submit to the jurisdiction of the courts of POLK County, State of Iowa.

RIGHT OF SETOFF. To the extent permitted by applicable law, Lender reserves a right of setoff in all Borrower’s accounts with Lender (whether checking, savings, or some other account). This includes all accounts Borrower holds jointly with someone else and all accounts Borrower may open in

the future. However, this does not include any IRA or Keogh accounts, or any trust accounts for which setoff would be prohibited by law. Borrower authorizes Lender, to the extent permitted by applicable law, to charge or setoff all sums owing on the debt against any and all such accounts, and, at Lender’s option, to administratively freeze all such accounts to allow Lender to protect Lender’s charge and setoff rights provided in this paragraph.

COLLATERAL. Borrower acknowledges this Note is secured by UNLIMITED GUARANTY OF JOHN PAPPAJOHN.

LINE OF CREDIT. This Note evidences a revolving line of credit. Advances under this Note, as well as directions for payment from Borrower’s accounts, may be requested orally or in writing by Borrower or by an authorized person, Lender may, but need not, require that all oral requests be confirmed in writing. Borrower agrees to be liable for all sums either: (A) advanced in accordance with the instructions of an authorized person or (B) credited to any of Borrower’s accounts with Lender. The unpaid principal balance owing on this Note at any time may be evidenced by endorsements on this Note or by Lender’s internal records, including daily computer print-outs. Lender will have no obligation to advance funds under this Note if: (A) Borrower or any guarantor is in default under the terms of this Note or any agreement that Borrower or any guarantor has with Lender, including any agreement made in connection with the signing of this Note; (B) Borrower or any guarantor ceases doing business or is insolvent; (C) any guarantor seeks, claims or otherwise attempts to limit, modify or revoke such guarantor’s guarantee of this Note or any other loan with Lender; (D) Borrower has applied funds provided pursuant to this Note for purposes other than those authorized by Lender; or (E) Lender in good faith believes itself insecure.

PURPOSE OF LOAN. The specific purpose of this loan is: WORKING CAPITAL.

SUCCESSOR INTERESTS. The terms of this Note shall be binding upon Borrower, and upon Borrower’s heirs, personal representatives, successors and assigns, and shall inure to the benefit of Lender and its successors and assigns.

GENERAL PROVISIONS. Lender may delay or forgo enforcing any of its rights or remedies under this Note without losing them. Borrower and any other person who signs, guarantees or endorses this Note, to the extent allowed by law, waive presentment, demand for payment, and notice of dishonor. Upon any change in the terms of this Note, and unless otherwise expressly stated in writing, no party who signs this Note, whether as maker, guarantor, accommodation maker or endorser, shall be released from liability. All such parties agree that Lender may renew or extend (repeatedly and for any length of time) this loan or release any party or guarantor or collateral; or impair, fail to realize upon or perfect Lender’s security interest in the collateral; and take any other action deemed necessary by Lender without the consent of or notice to anyone. All such parties also agree that Lender may modify this loan without the consent of or notice to anyone other than the party with whom the modification is made. The obligations under this Note are joint and several.

PRIOR TO SIGNING THIS NOTE, BORROWER READ AND UNDERSTOOD ALL THE PROVISIONS OF THIS NOTE, INCLUDING THE VARIABLE INTEREST RATE PROVISIONS. BORROWER AGREES TO THE TERMS OF THE NOTE.

BORROWER ACKNOWLEDGES RECEIPT OF A COMPLETED COPY OF THIS PROMISSORY NOTE AND ALL OTHER DOCUMENTS RELATING TO THIS DEBT.

DISBURSEMENT REQUEST AND AUTHORIZATION

References in the shaded area are for Lender’s use only and do not limit the applicability of this document to any particular loan or item. Any item above containing “***” has been omitted due to text length limitations.

LOAN TYPE. This is a Variable Rate Nondisclosable Revolving Line of Credit Loan to a Corporation for $1,500,000.00 due on September 30, 2005. The reference rate (is the Lender’s base or reference rate, which the Lender may increase or decrease at any time in its discretion, The rate is publicly available and may not necessarily reflect the rate that the Lender charges to its other customers. The rate is, currently 5.750%) is added to the margin of 2.000%, resulting in an initial rate of 7.750. This is an unsecured renewal loan.

PRIMARY PURPOSE OF LOAN. The primary purpose of this loan is for:

SPECIFIC PURPOSE. The specific purpose of this loan is: WORKING CAPITAL.

DISBURSEMENT INSTRUCTIONS. Borrower understands that no loan proceeds will be disbursed until all of Lender’s conditions for making the loan have been satisfied. Please disburse the loan proceeds of $1,500,000.00 as follows:

CHARGES PAID IN CASH. Borrower has paid or will pay in cash as agreed the following charges:

BORROWER ACKNOWLEDGES RECEIPT OF A COMPLETED COPY OF THIS DISBURSEMENT REQUEST AND AUTHORIZATION AND ALL OTHER DOCUMENTS RELATING TO THIS DEBT.

FINANCIAL CONDITION. BY SIGNING THIS AUTHORIZATION, BORROWER REPRESENTS AND WARRANTS TO LENDER THAT THE INFORMATION PROVIDED ABOVE IS TRUE AND CORRECT AND THAT THERE HAS BEEN NO MATERIAL ADVERSE CHANGE IN BORROWER’S FINANCIAL CONDITION AS DISCLOSED IN BORROWER’S MOST RECENT FINANCIAL STATEMENT TO LENDER. THIS AUTHORIZATION IS DATED MARCH 31, 2005.