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.     

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.     

Phenomenology and clinical correlates of delusions in Alzheimer disease.

OBJECTIVES: The objectives of this study were to determine whether anosognosia, depression, and elevated mood are associated with delusions in Alzheimer disease (AD), and to examine the validity of standardized diagnostic criteria for psychosis of dementia. METHOD: The authors assessed a consecutive series of 771 patients with AD attending a dementia clinic with a comprehensive neuropsychologic and psychiatric evaluation that included specific measures of delusions, hallucinations, anosognosia, depression, and elevated mood. RESULTS: Delusions were found in one-third of the patients and hallucinations in 7%. Most patients with hallucinations also had delusions. A principal component analysis of the Psychosis Dementia Scale, which rates the presence and severity of delusions, produced the factors of paranoid misidentification and expansive delusions. Paranoid, but not expansive, delusions increased across the stages of the illness. Anosognosia and depression were significantly and independently associated with the presence of delusions, whereas elevated mood was significantly associated with expansive, but not paranoid, delusions. A multiple logistic regression analysis demonstrated that delusions in AD were significantly associated with depression, anosognosia, overt aggression, and agitation. CONCLUSIONS: Anosognosia, depression, global cognitive deficits, and elevated mood are the main psychiatric correlates of paranoid misidentification and expansive delusions in AD, whereas overt aggression and agitation are the most frequent behavioral concomitants of psychosis in AD.     

Understanding and preventing perinatal, intracerebral, peri- and intraventricular hemorrhage

Antenatal anticipation of problem pregnancies and improvements in resuscitation and care of newborns have led to increasing survival of babies born prematurely. Nevertheless, the potential for neurologic handicaps is significant in this population of children, and the prevention of intracerebral, peri- and intraventricular hemorrhages and associated brain lesions remains a high priority. In this review, we consider the clinical problem of periventricular, intraventricular hemorrhage; means of diagnosis; the EEG and periventricular, intraventricular hemorrhage; sequelae; hypotheses of pathogenesis; experimental approaches to understanding periventricular, intraventricular hemorrhage; agents being tested for use in preventing hemorrhage; and future areas for research toward the prevention of hemorrhage and other neonatal brain lesions.     

Differential effects of BQ-123 against endothelin-1 and endothelin-3 on the rat vas deferens: evidence for an atypical endothelin receptor.

1. Endothelin-1 and endothelin-3 enhanced concentration-dependently the rat vas deferens twitch response to electrical stimulation, endothelin-1 being three times more potent. Sarafotoxin S6c was at least 200 times less active than endothelin-1. 2. The response to endothelin was antagonized in a competitive manner by the supposedly selective ETA receptor antagonist, BQ-123 (pA2:7.0 +/- 0.1). In contrast, the endothelin-1 concentration-response curve was only shifted two fold in the presence of 10 microM BQ-123, while no effect was observed at 1 microM. 3. This evidence suggests the rat vas deferens contains an endothelin receptor not conforming to the ETA/ETB receptor subtype classification so far proposed.     

In vivo 31P NMR studies of paraplegics' muscles activated by functional electrical stimulation

The bioenergetics of paralyzed muscles of spastic paraplegic patients under functional electrical stimulation (FES) was studied in vivo using ³¹P NMR. The protocol included rest, 3 min of induced tetanic isometric contraction through surface electrodes and 40 min of recovery. The continuous stimulation, the force recording and the ³¹P NMR measurements were sampled simultaneously inside the whole body imager. Normal values were found for the phosphorous metabolite ratios at rest. During contraction, prominent changes were detected including: a) accumulation of inorganic phosphate (P) accompanied by an unusually strong signal in the phosphomonoester (PME) region, b) phosphocreatine (PCr) decline, and c) a decrease in the intracellular pH. In the following recovery period the physiological state of the muscle was monitored and quantitated by ³¹P NMR. No metabolic and mechanical irreversible damage was detected in the paraplegics' muscles activated by FES under our experimental conditions.