Rumination syndrome is a condition in which people repeatedly and unintentionally regurgitate undigested or partially digested food from the stomach, rechew it, and then either re-swallow it or spit it out. The mechanism of the disease is not well understood. The investigators believe that discomfort in the stomach during and immediately after meals may be an important factor for this disease. The reason for such discomfort can be due to an alteration of nervous regulation of the stomach. The investigators can study the nervous regulation that affects the stomach and other parts of the body by analysing in detail an electrocardiogram that is performed continuously for several hours. From this analysis, The investigators can study a parameter called cardiac vagal tone (CVT).

Diaphragmatic breathing (DiaB) is a respiratory exercise, in which people mainly move their abdomen to breath. DiaB is a common treatment for rumination syndrome. Patients doing DiaB can reduce the number of rumination episodes. The mechanism by which DiaB improves rumination is unknown. There is another type of breathing called slow deep breathing (SlowDB), in which people mainly breathe with their chest. SlowDB is used as a therapy for increased pain in the food pipe (oesophagus) and it might also be effective on rumination syndrome. The investigators believe that both DiaB and SlowDB can improve rumination, by modifying the nervous control of the stomach (that the investigators can monitor by measuring continuously cardiac vagal tone (CVT)). The aims of the study are to investigate the association between gastric discomfort during a meal, CVT variations (measured with the electrocardiogram during the meal) and the severity of rumination episodes. The investigators will also study how DiaB and SlowDB can modify this variable during the test. In a second step, The investigators will assess the clinical effect of respiratory exercises (DiaB and SlowDB) on the severity and frequency of regurgitations in patients diagnosed with rumination syndrome.

Method This research consists of two separate studies.

1. Study1 (to investigate the mechanism of rumination syndrome) 10 healthy volunteers and 10 rumination patients will join Study1 on 3 separate days. On each visit, the investigators will place electrocardiogram sensors and a belt that can measure the thorax or abdominal movement. All subjects will get instructions to perform SlowDB or DiaB, answer some questionnaires, eat the test meal, perform normal breathing/DiaB/SlowDB for 15 minutes, and stay quietly on the chair for 3 hours.
2. Study 2 (to assess the effect of DiaB and SlowDB on rumination syndrome) 10 patients with rumination syndrome will join Study 2. On the first visit, subjects will have the test meal, answer the symptom questionnaire 1 hour after the meal, and learn how to perform either DiaB or SlowDB. After the first visit, subjects perform DiaB or SlowDB during 15 minutes after every meal for 4 weeks. On the second visit, subjects will have the test meal, answer the symptom questionnaire 1 hour after the meal, and learn how to perform the other respiratory exercise. After a 2-week break, subjects will perform the other respiratory exercise for the next 4 weeks. On the last visit, subjects will have the test meal and answer the symptom questionnaire 1 hour after the meal.

Inclusion Criteria:

1. Healthy volunteers (HVs)

   • 18-65 years old
   • No history of any gastrointestinal (GI) symptoms in the 3 months prior to the study.
   • No medications 3 months prior to the study

2. Rumination patients

   • 18-65 years old
   • Fulfilling ROME IV clinical criteria for rumination
   • Confirmed rumination syndrome by High Resolution Impedance Monometry within 12 months prior to the study
   • No history of performing DiaB as a therapy for rumination syndrome.
   • No medications which may affect vagal tone, the number of rumination episodes and GI motility 3 months prior to the study. (i.e. opioids, Baclofen , anticholinergics drugs, prokinetics, beta-blockers)

Exclusion Criteria:

• Pregnant or lactating women
• History of GI surgeries apart from appendectomy
• Alcohol or substance abuse, mental health illness
• Inability to obtain informed consent
• Non-fluent English speakers
• Participants with food intolerances or allergies that would not be able to take in the test meal (McDonalds Big Mac meal)
• Major comorbidities such as significant cardiac/pulmonary disease, cancer, life-threatening conditions or other life-limiting conditions
• Evidence of relevant organic diseases. (in endoscopy, CT.)
• Evidence of major esophageal motility disorders (Chicago classification ver3.0) (21)
• Known allergy to ECG electrodes or latex
• History of diabetes

The investigators will not share the data with other researchers outside of our team.

When the investigators analyze the data, the investigator will be blinded to the conditions of the participants and the types of breathing exercises.