Extracirculatory effects of noise of various frequency spectra in humans--effect of pink and blue noise on gastric myoelectrical activity and gastrointestinal passage of nutrients.

Recent investigations in humans point out to a disturbing effect of auditory stimuli on the functional integrity of the brain-gut axis. The study was devoted to a systematic comparative evaluation of the effect of noises of different frequency spectra on the postprandial electrical and transport functions of the digestive tract in humans. Twenty six healthy subjects attended a cross-over study, which aimed at comparison of the effect of pink contrasted to blue noise within a given category (band or tonal) and a meal stimulus type (semi-liquid or solid test meal). A panel of noninvasive measurement methods was applied: heart rate variability (HRV) analysis, surface electrogastrography, (13)CO(2) breath tests for gastric emptying (GE), lactulose hydrogen breath test for orocecal transit time (OCTT). The blue tonal noise was rated the most annoying one, whereas solely the pink noises exerted discernible cardiovascular effects. No one of the four noises was capable of overriding the meal-induced preponderance of the sympathetic tone. The postprandial gastric myoelectrical activity and the GE of either the semiliquid or the solid test meal appeared to be ;resistant' to the noise exposure, irrespective of the noise type. Similar was the finding in the case of the OCTT, with the exception of a statistically significant retardation of the OCTT with the blue band noise. Ingestion of mixed caloric meals seems to elicit a protective influence against noise-elicited derangements of the functional integrity of the digestive tract proven formerly to occur during the fasting period.