CRH administration The effect of CRH-administration on esophageal motility will be studied. After positioning of the HRM probe the investigators will first study esophageal motility at baseline conditions. After the baseline procedure, 100µg CRH powder for injection (CRH ferring®, Ferring, Aalst, Belgium) will be dissolved in 1 mL of sodium chloride (NaCl) 0.9%, the solution will be injected intravenously over the course of 1 minute. With this dose, the side-effects are limited to transient facial flushing that lasts from 5 to 45 minutes in 75% of patients. CRH is clinically used as a diagnostic tool in locating the source of hypercortisolism in Cushing's disease. After 20 minutes, esophageal peristalsis will be studied again.