**2.1 Duodenal hypersensitivity to acid in patients with FD**

Lee *et al.* (2004) reported that acid infusion into the duodenal bulb induced dyspepsia in healthy volunteers, and the symptoms of dyspepsia are more readily observed in patients with FD than in healthy subjects (Samsom *et al.*, 1999). Increased duodenal acid exposure plays a role in the onset of dyspeptic symptoms in patients with FD having prominent nausea (Lee *et al.*, 2004). A recent study indicated that acid infusion into the stomach predominantly induced dysmotility-like dyspeptic symptoms in healthy Japanese control subjects (Miwa *et al.*, 2007). PPIs and H2-receptor antagonists have been proposed as effective therapies for treating FD (Delaney *et al.*, 2005; Veldhuyzen van Zanten *et al.*, 2005; Kinoshita *et al.*, 2005; Seno *et al.* 2005). Guidelines for the management of dyspepsia suggest that PPI therapy is more effective than a placebo or H2-receptor antagonists in relieving the symptoms of patients with uninvestigated dyspepsia (Talley *et al.*, 2005).
