Neurally adjusted ventilatory assist (NAVA) is a new concept of mechanical ventilation. NAVA delivers assistance to spontaneous breathing based on the detection of the electrical activity of the diaphragm. The investigators will study the effects of non-invasive NAVA in respiratory muscle unloading in healthy volunteers.

Inclusion Criteria:

• Subject has given written informed consent.
• Male or female, aged 18 - 80 years (extremes included).

Exclusion Criteria:

• Pregnant or breast-feeding female. A pregnancy test will be performed in all female volunteers less than 60 yrs of age.
• Known intolerance or allergy against local anesthetic drugs such as procain, lidoocaine, xylocain.
• Any contraindication to the insertion of a nasogastric tube, including (but not limited to): severe oropharyngeal malformation or bleeding; esophageal varices, tumor, infection, stenosis, or rupture, bleeding disorder with evidence of active bleeding.
• Presence or suspicion of diaphragm injury.
• Prior medical history that might contribute to a disturbance of the neural system, including, but not limited to: diabetes, prior critical illness, carcinoma, uremia, vitamin B12 deficiency, chronic liver disease, alcohol abuse, malabsorption (sprue), HIV, Lyme disease, Lymphoma, multiple myeloma, hypothyroidism, systemic vasculitis, abnormalities on physical examination of peripheral nervous system (pallesthesia, impaired muscle strength according to the MRC Scale for Muscle Examination in 12 Muscle groups).