Diabetes mellitus is a chronic metabolic disease which can affect multiple systems and lead to devastating complications. DGP is one of its chronic complications of diabetes, which refers to the presence of chronic gastric motor dysfunction and delayed gastric emptying in the absence of mechanical obstruction of the gastrointestinal tract, and its main pathological basis is GMD[14]. There are no overt symptoms in the early stage of DGP. As the condition worsens, some gastrointestinal symptoms such as nausea, vomiting, and epigastric fullness appear alone or together[15]. In many cases, diabetes patients' gastrointestinal symptoms may not always accurately reflect their gastric motility status, necessitating the use of objective measures to assess gastrointestinal function[16]. Gastric emptying scintigraphy (GES), as the "gold standard" for gastric motility testing, is limited used because of its high cost, expensive equipment, and radiation. The myoelectric activity of the stomach controls the contractile activity, and the patients with GMD often have abnormal gastric electric rhythms. EGG, as a non-invasive method of recording gastric electrical signals through the body surface, can indirectly reflect gastric motility changes and has the advantage of being less expensive and easy to operate compared to GES. Besides, it has no stimulation to the gastrointestinal tract and can observe gastric electrical activity for a long time. EGG is considered to be an ideal examination method for the screening of DGP with important clinical application value[17]. EGG is of great significance for the diagnosis, severity evaluation, and treatment guidance of patients. In the present study, we applied EGG to evaluate gastric motility in patients with T2DM, and found that the T2DM patients generally suffered from gastric electrical rhythm disorder and decreased gastric motility. The analysis of influencing factors showed that FBG, HbA1c were significantly higher in the AGER group, and the presence of AGER was associated with the presence of DPN and DCAN.
High FBG reflects immediate hyperglycemia, and high HbA1c reflects the average high blood glucose in the recent 3 months which means chronic hyperglycemia. Acute changes in blood glucose concentration affect gastric emptying in patients with diabetes[18]. Gastric emptying is slower during hyperglycemia and accelerated during hypoglycemia. This response is a physiological defense mechanism to prevent further hyperglycemia and hypoglycemia[19]. Under acute hyperglycemia conditions, gastric emptying can be slowed down through a series of combined actions, including inhibited vagus nerve activity and proximal gastric tension, reduced antral pressure, and stimulated pyloric contraction[20, 21]. This conclusion was also confirmed in healthy people that acute hyperglycemia inhibited gastric antrum movement and induced abnormal gastric rhythm in healthy volunteers[22]. Chronic hyperglycemia can also cause GMD, which was concluded from several physiological studies on diabetic gastrointestinal function[21, 23]. Studies have found that chronic hyperglycemia leads to the formation of advanced glycation end products (AGEs), excessive oxidative stress, inflammatory activation, through a series of pathways, which damage the structure of nerve cells, reduce the number of neurons, and lead to degeneration of the nervous system[24]. In addition, it also reduces the number of interstitial cells of Cajal (ICC) and damages gastric smooth muscle cells, resulting in decreased contractility and ultimately delayed gastric emptying[14, 25].
On the other hand, gastric emptying also has an impact on the level of blood glucose, and delayed gastric emptying affects the absorption of food, which directly affects the blood glucose level after a meal. DGMD can also lead to poor absorption of drugs, which in turn has an adverse effect on blood glucose control. For patients who use insulin, the effect of exogenous insulin on the body does not match the digestion and absorption of food in the gastrointestinal tract caused by DGMD[26]. It is very easy to have large fluctuations of postprandial blood glucose including early postprandial hypoglycemia and late postprandial hyperglycemia[27]. The onset of hypoglycemia will cause irreversible damage to the human body, which must be taken seriously. In clinical practice, the possibility of DGMD should be considered in diabetic patients with poor blood glucose control after repeated adjustment of treatment regimens who encounter repeated hypoglycemia after meals and large fluctuations in postprandial blood glucose.
Diabetic autonomic neuropathy is currently recognized as one of the main pathophysiological foundations of DGMD[14, 15]. The autonomic nervous system includes sympathetic and parasympathetic nerves that innervate multiple organs, including cardiovascular, gastrointestinal, respiratory, urogenital, and pupillary. The sympathetic and parasympathetic nerves of T2DM patients are damaged to varying degrees, resulting in cardiac autonomic neuropathy, gastrointestinal autonomic neuropathy, etc[28]. In the present study, we found that DCAN was independently associated with AGER, and there was a strong association between HRV and AGER. HRV is a good indicator of cardiac autonomic balance. Growing studies supported the use of HRV to assess cardiac autonomic activity. We also found that LF and HF, two HRV indicators, were significantly lower in the AGER group, indicating that AGER patients had both sympathetic and vagus nerve damages, which was in line with prior research findings[29, 30]. In clinical practice, autonomic neuropathy is often underdiagnosed and poorly treated. More attention should be paid to diabetic autonomic neuropathy[31].
For the evaluation of severity of symptoms in DGP patients, GCSI is considered an effective, non- invasive, inexpensive assessment tool for epidemiological screening. There is a large body of studies supporting the reliability of the GCSI scoring scale[32]. In the present study, AGER, detected by EGG, correlated with upper gastrointestinal symptoms. As expected, subjects in AGER group had more severe symptoms compared with NGER group subjects. Patients in AGER group were more likely to experience feeling excessively full after meals, loss of appetite, stomach or belly visibly larger after meals. As an object measure that correlates with symptoms, EGG can be used widely in clinic to evaluate gastric disease progression and the effectiveness of treatment.
Certain oral hypoglycemic drugs may cause gastrointestinal symptoms in patients with diabetes. Studies have shown that metformin treatment was significantly associated with gastrointestinal symptoms in DGP patients[33]. However, we didn’t get the same conclusion in the present study. The average course of diabetes in this study was 7 years, patients who were still using metformin may have adapted to the drug, or they may have switched to other anti-diabetic regimens if they have any severe gastrointestinal symptoms. This may explain our failure to detect a causal link between metformin and gastrointestinal symptoms. Glucagon-like peptides receptor agonists (GLP-1RA) may also cause gastrointestinal symptoms in diabetic patients. However, patients using GLP-1 receptor agonists were excluded from this study. In clinical practice, it is recommended that patients who are ready to use GLP-1RA have their gastrointestinal symptoms be evaluated, using GCSI, EGG and gastric emptying tests, to avoid obvious gastrointestinal side effects.