To evaluate the safety and effectiveness of the Automatic Expiratory Positive Airway Pressure (Auto-EPAP) feature versus manual expiratory positive airway pressure (EPAP) in the Vivo 45 LS Ventilator.

Inclusion Criteria:

1. Subject has the ability to provide written informed consent.
2. Subject is ≥ 18 years old.
3. Subject has documented respiratory failure (e.g. sleep hypoventilation with historical transcutaneous carbon dioxide (PtCO2) increase ≥ 10mmHg) and/or daytime hypercapnia (>45 mmHg).
4. Subject is currently using non-invasive positive pressure ventilation (NIV) for 1 month.
5. Subject has a previously documented apnea-hypopnea index (AHI) ≥ 5/hr.
6. Subject's expiratory positive airway pressure (EPAP) settings were recently (≤ 12 months) reviewed.

Exclusion Criteria:

1. Subject is not compliant on NIV (e.g., < 4 hr./night).
2. Subject is pregnant.
3. Subject is on oxygen therapy ≥ 5 L/min.
4. Subject has an invasive interface (e.g. tracheostomy).
5. Subject has had an acute exacerbation within the last 3 months that resulted in a hospitalization.
6. Subject is acutely ill, medically complicated, or who are medically unstable.
7. Subject in whom NIV therapy is otherwise medically contraindicated.
8. Subject has had surgery of the upper airway, nose, sinus, or middle ear within the previous 90 days.
9. Subjects with untreated, non-obstructive sleep apnea (OSA) sleep disorders, including but not limited to: insomnia, periodic limb movement syndrome, or restless leg syndrome.
10. Subjects who have the following pre-existing conditions: severe bullous lung disease, recurrent pneumothorax or pneumomediastinum, cerebrospinal fluid leak, or recent cranial surgery or trauma.
11. Subject does not comprehend English.
12. Subject is unable or unwilling to provide written informed consent.
13. Subject is physically and/or mentally unable to comply with the protocol.
14. Subject is not suitable to participate in the trial for any other reason in the opinion of the investigator.

Study subjects will be blinded to the sequence arm that they are randomized to. Investigators and site study staff will be unblinded. The scorer(s) of the polysomnography will be blinded to which therapy is being used for objective determination of the primary endpoint.