Neuro-fuzzy systems in internet of medical things: a systematic review on applications, taxonomy, challenges and open issues.

Functional dyspepsia (FD) is a common disorder of the gut–brain interaction (, ). Under Rome IV criteria, FD is defined by chronic or recurrent postprandial fullness, early satiation, epigastric pain, or epigastric burning without a structural, systemic, or metabolic explanation (, ). Because many FD symptoms are meal-related, the fasting-to-postprandial transition is a clinically relevant window during which gastric accommodation, antral motor activity, slow-wave rhythm, and sensory feedback must be coordinated (). Surface electrogastrography (EGG) records gastric myoelectrical rhythm from the body surface. Normal gastric slow-wave activity occurs at approximately three cycles per minute and supports the timing of gastric contractions, although surface EGG is not a direct measure of gastric emptying or contractile force (, ). FD has been associated with reduced normogastria and increased bradygastria or tachygastria, but many previous studies have focused on patients who already meet FD criteria (). Psychological symptoms and poor sleep are frequent in FD and may interact with gastric physiology through brain–gut and autonomic pathways (, , ). RMSSD and high-frequency (HF) HRV are commonly used as vagal-related indices, whereas LF/HF should be treated as a relative spectral ratio rather than a direct measure of sympathovagal balance (). Sleep disturbance may further affect autonomic tone, arousal, pain processing, inflammatory signaling, and interoceptive regulation.