Predicted and Measured Muscle Forces after Recoveries of Differing Durations Following Fatigue in Functional Electrical Stimulation

Abstract: Using ³¹P nuclear magnetic resonance (NMR) spectroscopy, the bioenergetics of paralyzed muscles activated by functional electrical stimulation (FES) were studied in vivo during fatigue and recovery on paraplegic subjects. During the activation phase of the muscle, the muscle force was also monitored. The phosphorus metabolites were found to vary systematically during fatigue and to recover slowly to their rest state values after cessation of FES. During fatigue, a good correlation was found between the decaying force and each of the profiles of phos-phocreatine, inorganic phosphorus, and intracellular pH. A musculotendon 5 element model was proposed for the activated muscle to predict its force generation capacity. A fatigue recovery function, based on the metabolic profiles, was introduced into the model. This model allowed us to predict the force expected to be developed as a function of the time after recovery of given time durations. Validation experimental measurements of force were carried out and included recurrent fatigue tests, both in the initially un-fatigued state and at various times in the postfatigue stage of the muscle. Comparison of the predicted and measured forces indicated satisfactory agreement of the results. The developed model of muscle dynamics should help to design a strategy for reducing muscle fatigue under FES.     

Nodular regenerative hyperplasia: a controversial indication for orthotopic liver transplantation

Nodular regenerative hyperplasia of the liver is an uncommon cause of portal hypertension. Patients with nodular regenerative hyperplasia have signs and symptoms of portal hypertension, without evidence of hepatocellular failure or encephalopathy. We report the case of a 44-year-old woman with recurrent esophageal bleeding and refractory ascites who had a history of hemosiderosis, hepatitis C, and chronic renal allograft rejection. Our preoperative diagnosis was cirrhotic end-stage liver disease and end-stage renal disease for which the patient underwent combined hepatic and renal transplantation. Her portal hypertension symptoms resolved, and her renal function has been normal for 18 months of follow-up. Histologic examination of the liver revealed nodular regenerative hyperplasia, and a review of the literature regarding the surgical management of patients with nodular regenerative hyperplasia revealed that various shunting procedures are generally recommended. After the failure of medical management in patients with nodular regenerative hyperplasia, portosystemic shunting may be indicated before proceeding to hepatic transplantation.     

125I]His-neurokinin A binds selectively to NK2 receptors of the B-type in rat small intestine smooth muscle membranes.

The high-affinity, reversible binding of [125I]His-neurokinin A (NKA) to rat small intestine smooth muscle membranes was investigated. Endogenous neurokinin agonists, selective neurokinin analogues, both agonist and antagonist, were used to define the selectivity of the binding. Both the endogenous and selective neurokinin analogue agonists displayed orders of potency indicating that [125I]His-NKA was binding to NK2 receptors. The use of recently developed NK2-selective antagonists indicated that the NK2 receptors present in this preparation were similar to those described in hamster trachea preparations (NK2B), and not endothelium-denuded rabbit pulmonary artery (NK2A). The absence of NK2A receptors and the predominance of NK2B was confirmed by blocking experiments using MEN10376 and L659877. Low-affinity binding of NKA was also observed with this preparation, which was not sensitive to the NK2-selective agonist, [beta-Ala8]NKA4-10. This was shown not to be due to the presence of NK1 or NK3 receptors by using selective agonists for NK1 and NK3 to block any such receptors. (No evidence for the presence of these receptors was obtained during these blocking experiments.) Guanylylimidodiphosphate appears to discriminate between the high- and low-affinity binding sites for NKA. It was thus concluded that high-affinity binding of [125I]His-NKA to rat small intestine smooth muscle membranes was selective for NK2B receptors. No evidence was found for the binding of [125I]His-NKA to NK1, NK3 or NK2A receptors.     

Is balance impaired by recurrent sprained ankle?

OBJECTIVE: To evaluate uninjured and recurrent sprained ankles during single leg standing, both with and without visual input, and the contribution of related proprioceptive feedback in this event. METHODS: A force measuring system was used for monitoring reaction forces in the anteroposterior and mediolateral directions during single leg standing. Differences between selected variables obtained in the uninjured and sprained ankles were analysed using two way analysis of variance. RESULTS: Foot-ground reaction forces in both anteroposterior and mediolateral directions were the same in normal and sprained ankles of each subject while standing with either open or closed eyes. However, standing with closed eyes, irrespective of the ankle status, always produced significantly higher reaction forces than those obtained with open eyes (P < 0.05). CONCLUSIONS: The amount of postural sway during single leg standing is similar in the chronically sprained and the uninjured ankle joint.