Opioids and Esophageal Function

Inclusion Criteria: * 18 -40 year old healthy volunteers from both sexes. * have signed and dated Informed Consent. * willing and able to comply with the protocol for the duration of the trial. Exclusion Criteria: * anamnesis of pharyngoesophageal dysfunction. * known or history of cardiac, pulmonary or neurological disease. * ongoing medication. * allergies to or history of reaction to methylnaltrexone, remifentanil or fentanyl analogues. * pregnancy or breast feeding. * participation in another clinical medicinal trial during the last 30 days or where follow-up is not completed.