RESUMO
Humans and animals learn the internal model of bodies and environments from their experience and stabilize posture against disturbances based on the predicted future states according to the internal model. We evaluated the mechanism of predictive control during standing, by using rats to construct a novel experimental system and comparing their behaviors with a mathematical model. In the experiments, rats (n = 6) that were standing upright using their hindlimbs were given a sensory input of light, after a certain period, the floor under them tilted backward. Initially, this disturbance induced a large postural response, including backward rotation of the center-of-mass angle and hindlimb segments. However, the rats gradually adjusted to the disturbance after experiencing 70 sequential trials, and a reduction in the amplitude of postural response was noted. We simulated the postural control of the rats under disturbance using an inverted pendulum model and model predictive control (MPC). MPC is a control method for predicting the future state using an internal model of the control target. It provides control inputs that optimize the predicted future states. Identification of the predictive and physiological parameters so that the simulation corresponds to the experiment, resulted in a value of predictive horizon (0.96 s) close to the interval time in the experiment (0.9-1.15 s). These results suggest that the rats predict posture dynamics under disturbance based on the timing of the sensory input and that the central nervous system provides plasticity mechanisms to acquire the internal model for MPC.
RESUMO
Inflammatory bowel disease (IBD) is a group of chronic inflammatory disorders of the gastrointestinal tract including ulcerative colitis (UC) and Crohn's disease. Pain management can be challenging in patients with IBD because there are limitations on the use of analgesics. Use of nonsteroidal anti-inflammatory drugs is not recommended in patients with IBD because there is risk of relapse of IBD and an overall increase in disease activity. Opioids, although frequently used for treating severe acute pain, can have additional risks and complications in patients with IBD such as ileus, toxic megacolon, and narcotic bowel syndrome. Furthermore, little information is available in the literature on pain management in these patients undergoing noncolorectal surgery. This report describes 2 patients with UC in whom postoperative pain following oral and maxillofacial surgery was managed by intravenous patient-controlled analgesia with pentazocine. Apart from the development of acute dystonia in 1 case that was likely due to the use of droperidol for prevention of postoperative nausea and vomiting, postoperative pain was well controlled by pentazocine in both patients without any complications or UC exacerbations.
