Visual Field Dependence Is Associated with Reduced Postural Sway, Dizziness and Falls in Older People Attending a Falls Clinic.

Moving visual fields can have strong destabilising effects on balance, particularly when visually perceived motion does not correspond to postural movements. This study investigated relationships between visual field dependence (VFD), as assessed using the roll vection test, and reported dizziness, falls and sway under eyes open, eyes closed and optokinetic conditions. Ninety five falls clinic attendees undertook the roll vection test (i.e. attempted to align a rod to the vertical while exposed to a rotating visual field). Sway was assessed under different visual conditions by centre of pressure movement. Participants also completed questionnaires on space and motion discomfort, fear of falling, depression and anxiety. Thirty four (35.8%) participants exhibited VFD, i.e. had an error > 6.5º in the roll vection test. Compared to participants without VFD, participants with VFD demonstrated less movement of the centre of pressure across all visual conditions, were more likely to report space and motion discomfort and to have suffered more multiple falls in the past year. VFD was independent of fear of falling, anxiety and depression. VFD in a falls clinic population is associated with reduced sway possibly due to a stiffening strategy to maintain stance, dizziness symptoms and an increased risk of falls.

Six minutes of walking leads to reduced lower limb strength and increased postural sway in people with Multiple Sclerosis.

BACKGROUND: Fatigue, lower limb weakness and poor balance can significantly limit safe mobility in people with Multiple Sclerosis (MS). Further research is required to elucidate relationships among these factors. OBJECTIVE: To investigate the effect of walking-induced fatigue on lower limb strength and postural sway in people with moderately disabling MS. METHODS: Thirty-four people (26 female) with moderate MS (mean Expanded Disability Status Scale of 3.7 ± 0.7) underwent assessments of acute fatigue, postural sway and lower limb strength before and after six-minute conditions of seated rest and walking. A matched sample of 10 healthy controls also undertook identical assessments before and after a six-minute walk. RESULTS: Significant time by condition effects for all assessment measures indicated the six-minute walk induced fatigue with associated increases in postural sway and reductions in lower limb strength in people with MS. Increases in sway with eyes closed correlated with increases in acute fatigue and self-reported impact of fatigue on physical and psychological functioning. No changes were observed in healthy controls. CONCLUSION: People with MS show signs of fatigue after 6 minutes of walking, including strength and balance deficits. These findings have implications for both mobility and fall risk in this group.

The effect of haloperidol, spiperone and dantrolene on the concentrations of creatine phosphate, ATP and lactate in brain and skeletal muscle of the rat during halothane anesthesia.

The concentrations of creatine phosphate, ATP and lactate were measured in the brain and skeletal muscle of rats under halothane anesthesia (1 to 2% in oxygen) and in animals either premedicated with haloperidol or spiperone (200 mg kg-1 and 2 mg kg-1) or treated with dantrolene (860 mg kg-1). Haloperidol and spiperone had no effect on ATP or lactate in skeletal muscle, but caused more than a 30% increase in the concentration of creatine phosphate (p less than 0.01). With dantrolene, an 80% increase in creatine phosphate (p less than 0.0001) and a significant decrease in lactate (p less than 0.0001) were found. Haloperidol caused a significant decrease in brain creatine phosphate concentration (p less than 0.05) while at a dosage of 2 mg kg-1, the ATP concentration was higher (p less than 0.05). Spiperone (2 mg kg-1) caused a 19% increase in creatine phosphate (p less than 0.005) as well as a significant decrease in lactate (p less than 0.005). Dantrolene had no significant effect on the concentration of any brain metabolite. Our results indicate that the effect of anesthetics on the concentration of energy metabolites in tissues can be influenced by drug treatment, which may have implications in the choice of an anesthetic regimen to be used in tissue harvesting.

The effect of anaesthetics on the concentration of creatine phosphate, adenosine triphosphate and lactate in brain and skeletal muscle of the rat.

Rats were anaesthetized with ten anaesthetics. Ketamine and enflurane gave the lowest concentration of creatine phosphate and ATP and the highest of lactate in brain, while giving the highest concentration of the high-energy phosphates and the lowest of lactate in skeletal muscle. In general, intraperitoneally-administered anaesthetics gave higher concentrations of creatine phosphate and ATP and lower concentrations of lactate in brain than did the inhalant anaesthetics. The most rapid induction of anaesthesia was achieved with halothane and enflurane, while ketamine gave variable induction times and poor analgesia. Halothane stimulated glycolysis and lowered the concentrations of high-energy phosphates in skeletal muscle.

Action of halothane on rat soleus muscle: temperature dependent induction of contractures and modification of caffeine and potassium contractures.

Halothane induced calcium-dependent contractures in rat soleus muscle at temperatures between 4 degrees C and 13 degrees C, but not at higher temperatures. The peak tension of the contractures increased as temperature was decreased below 13 degrees C. The magnitudes of the contractures were reduced by the addition of cobalt or lanthanum ions to the medium in the water bath. The anaesthetic also potentiated caffeine-induced contractures in muscle at 22 degrees C and 37 degrees C in a calcium-dependent manner. The contractures at 37 degrees C were more sensitive to the concentration of this ion than were contractures at 22 degrees C. Halothane increased peak tension and prolonged the time course of potassium-induced contractures, but did not alter their threshold values at either 22 degrees C or 37 degrees C. It was concluded that, in rat muscle, halothane may act at a site on the plasmalemma, retard the onset of inactivation and move the inactivation curve further from the resting membrane potential.

The effects of external potassium, multivalent cations and temperature on caffeine contractures in rat skeletal muscle.

The effects of multivalent cations, membrane potential and temperature on caffeine contractures of rat soleus and extensor digitorus longus (e.d.l.) muscles were investigated. The amplitude of the caffeine contracture was depressed by the removal of calcium and by the addition of a high concentration (1 mM) of lanthanum. Low concentrations of lanthanum (0.1-0.5 mM) augmented the caffeine contracture. Low levels of depolarization by potassium (10-40 mM) augmented the amplitude of the caffeine contracture, while higher concentrations of potassium depressed the contracture. Maximum augmentation of the caffeine contracture occurred with a higher concentration of potassium (20 mM vs 10 mM) in the e.d.l. than in the soleus muscle. The amplitude of contractures was directly related to temperature between 22 and 37 degrees C and inversely related to temperature below 22 degrees C. The effects of caffeine in rat skeletal muscle are suggested to be exerted on the sarcolemma and the mechanisms of action are by modification of the processes of activation and inactivation.

Potassium contractures and mechanical activation in rat skeletal muscle: effects of multivalent cations, temperature and tetracaine.

The effects of cations, temperature and tetracaine on potassium-induced contractures of rat soleus and extensor digitorus longus (e.d.l.) muscles were investigated. In the soleus, the threshold for the potassium contracture was lower (10-20 vs 20-40 mM), the peak amplitude was up to fourteen times larger, and the time course was about one half that in the e.d.l. muscle. The extent of inactivation of a test potassium contracture was directly related to the concentration of potassium in the conditioning solution and the period of exposure. Removal of calcium reduced the amplitude and time course of potassium contractures in both preparations. Addition of cobalt (10 mM) reduced the amplitude but prolonged the time course of contractures. Exposure of muscles to tetracaine (10(-5)-10(-6) M for 30 min) increased, but higher concentrations reduced, the amplitude of potassium contractures. When present for one minute, tetracaine (1 mM) moved the potassium activation curve to higher, and the potassium inactivation curve to lower, potassium concentrations.

Metabolism of monoamines in malignant hyperthermia-susceptible pigs.

A comparison of monoamine oxidase activities in the hypothalamus and striatum between malignant hyperthermia-susceptible (Pietrain) and malignant hyperthermia-resistant (Landrace/Large White) pigs showed no significant difference between the two breeds. The concentrations of noradrenaline, dopamine and their non-O-methylated metabolites did not reflect the low activities of monoamine oxidase type A differentially. The malignant hyperthermia-susceptible pigs had significantly greater concentrations of 3,4-dihydroxyphenyl glycol in the striatum, and of 3,4-dihydroxymandelic acid in the hypothalamus. Consequently, in the brain, low monoamine oxidase type A activity does not appear to be involved in susceptibility to malignant hyperthermia. In addition, monoamine oxidase activities in the heart, liver, kidney and intestinal mucosa and catechol-O-methyl transferase activities in the kidney were the same in the susceptible and resistant pigs.

Inhibition of actomyosin ATPase by high concentrations of 5-hydroxytryptamine. Possible basis of lesion in 5HT-induced experimental myopathy.

The effect of 5-hydroxytryptamine (5HT) on the ATPase activity and sulphydryl group reactivity of mammalian skeletal muscle actomyosin has been studied. 5HT inhibited the Mg2+-activated but not the Ca2+-activated ATPase activity of actomyosin. It slightly activated myosin ATPase. The sulphydryl groups of actomyosin reacting with 5,5'-dithiobis-(2-nitrobenzoic acid) were blocked by concentrations of 5HT which inhibited the Mg2+-activated ATPase. The significance of the results are discussed in relation to the muscle lesions in the experimental myopathy induced by 5HT and imipramine.