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LACTULOSE-INDUCED REDUCTION IN PARASYMPATHETIC AUTONOMIC NEURAL ACTIVITY: A MECHANISM FOR GASTRO-ESOPHAGEAL REFLUX (GER)?
N Chauhan, M Kamath, D Armstrong
Division of Gastroenterology & Intestinal Diseases Research Program, McMaster University, Hamilton, Ontario
BACKGROUND: Gastroesophageal reflux disease (GERD) and obesity are common and both are increasing in prevalence. It is proposed that obesity predisposes to GERD but the mechanisms are unknown. However, GERD and obesity are associated with abnormal function of the autonomic nervous system (ANS), including decreased vagal activity and dietary factors, including non-absorbed carbohydrates, fermented in the colon, can cause GER.
AIM: To test the hypothesis that administration of lactulose, a non-absorbed, fermentable sugar will reduce vagal activity.
METHODS: A pilot study was conducted in 5 healthy subjects, fasted overnight, who received lactulose, 20 g orally. ANS function was monitored by continuous ECG recording over a 3 hour observation period; after digitization of the ECG signal, spectral analysis of heart rate variability (HRV) identified the sympathetic (high frequency: HF) and parasympathetic (low frequency: LF) components of cardiotropic ANS activity. The effect of lactulose was determined by comparing heart rate (HR), LF areas (%), the HF areas (%) and the LF:HF area ratios for the baseline (–20 to 0 mins) and final (120-180 mins) periods (t-test for dependent samples).
RESULTS: Six non-obese subjects (3 male; age 25-27 yrs) were studied; 1 female subject was excluded due to sinus arrhythmia. HR (mean+SD) increased between the baseline (59±11) and final (64±12, p<0.01) periods. HF area decreased (from 50±6 to 43±4, p<0.05) and LF area increased (from 49±6 to 57±4, p<0.05) resulting in a significant increase in the LF:HF area ratio (from 1.0±0.3 to 1.3±0.2, p<0.05).
SUMMARY: Oral lactulose increases HR and increases the LF:HF area ratio, consistent with a reduction in the ratio of parasympathetic to sympathetic activity in healthy subjects.
CONCLUSIONS: The effect of lactulose on ANS activity is temporally consistent with its known effects of increasing breath hydrogen production and increasing GER. Further study is needed to determine whether colonic fermentation of other non-absorbed macronutrients will induce changes in sympathovagal balance and, hence, GER in obese and non-obese individuals.