This prospective observational study aims to investigate the association between the autonomic dysfunction and hemodynamic instability during per-oral endoscopic myotomy under general anesthesia in achalasia patients. Per-oral endoscopic myotomy is known as the effective treatment for achalasia patients. During per-oral endoscopic myotomy, capnoperitoneum, capnomediastinum, and systemic CO2 accumulation can potentially impair hemodynamics. Moreover, it has been suggested that achalasia is associated with autonomic dysfunction. We hypothesized that patients with autonomic dysfunstion would esperience more hemodynamic instability during per-oral endoscopic myotomy compared with patients without autonomic dysfunction. In this prospective observational study, the autonomic function test will be performed before surgery, and advanced hemodynamic parameters will be recorded using EV1000 clinical platform (Edwards Lifesciences, USA) during surgery. The association between the autonomic dysfunction and hemodynamic instability during per-oral endoscopic myotomy will be analyzed.