The purpose of the study is to test whether noninvasive positive pressure ventilation (NIPPV) without expiratory positive airway pressure (EPAP) (inspiratory positive airway pressure (IPAP)-only) will result in an increase in patient usage of NIPPV compared with standard, Bi-level NIPPV. Secondarily, the investigators will assess measures of dyspnea, quality of life, patient satisfaction, and side effects.

Subjects will be randomized on a 1:1 basis to one of two groups differing in the sequence of NIPPV settings ((a) standard, Bi-level NIPPV followed by IPAP-only NIPPV or (b) IPAP-only NIPPV followed by standard, Bi-level, NIPPV). Subjects will then spend 6 weeks using the first NIPPV set-up before crossing over to the other NIPPV treatment for 6 weeks. At the beginning of the study, subjects will undergo approximately two hours of training and education by a respiratory therapist regarding proper use of the Viasys® Healthcare, Pulmonetic Systems, lap-top ventilators (LTV machine). They will be fitted with the appropriate NIPPV set-up. The patients will use the same mask interface with the study NIPPV machine that they were using with their NIPPV (bi-level positive airway pressure (BiPAP)) machine prior to study entry.

The patients will have two additional study visits after the consent/training session: one at the end of 6 weeks, after the first NIPPV treatment period (prior to crossing over to the second NIPPV treatment), and the second at the end of 12 weeks, after the second NIPPV treatment period.

NIPPV usage will be recorded as hours of use as measured objectively by the NIPPV machine hour meter. When the patient returns for his/her first study visit at the end of week six, the NIPPV machine hour meter will be recorded by the study investigator. By subtracting the hours recorded at the beginning of week two from the hours recorded at the end of week six, the NIPPV hours of usage for weeks two, three, four, five and six will be obtained. This same procedure will be repeated to record NIPPV hours of usage for the beginning of week eight and the end of week twelve to measure the hours of usage with the second NIPPV set-up for weeks eight, nine, ten, eleven and twelve. This allows study subjects one week to adjust to the new pressure settings of each treatment arm.

Dyspnea as measured by the transition dyspnea index (TDI), and quality of life as measured by the EuroQol Visual analogue scale(VAS) will be re-administered at both 6 and 12 week study visits by study personnel. Lastly, patient preference of NIPPV treatment will be subjectively assessed at the 12 week study visit on a Likert scale (definitely first treatment, probably first treatment, no preference, probably second treatment, definitely second treatment).

Inclusion Criteria:

1. Age greater than 18 years
2. Definite or probable ALS by El Escorial criteria
3. Maximal inspiratory force < 60 cm/H2O or FVC <50% predicted (American College of Chest Physicians' criteria for initiating NIPPV)
4. Patients must have used NIPPV (typically administered as BiPAP) for at least 2 months
5. Currently using NIPPV ≥5 days a week with an EPAP = 4 cm H2O.

Exclusion Criteria:

1. Any medical condition that will interfere with participation
2. Inability to consent for him/herself
3. Known obstructive sleep apnea or obstructive pulmonary disease.