Unpredictable Oscillations Research Articles

Bioavailable heavy metals in estuarine waters as assessed by metal/shell-weight indices in sentinel mussels Mytilus galloprovincialis

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 125:127-136 (1995) - doi:10.3354/meps125127 Bioavailable heavy metals in estuarine waters as assessed by metal/shell-weight indices in sentinel mussels Mytilus galloprovincialis Soto M, Kortabitarte M, Marigómez I Seasonal variations in metal concentrations in soft tissues of marine mussels can be due, to a great extent, to seasonal changes in flesh weight. Consequently, this event results in an unpredictable overestimation of metal bioavailability when the metal concentration in soft tissues is considered as an index of such metal bioavailability. The Abra estuary (Bizkaia, Bay of Biscay, Spain) was used as a natural experimental basin with well-known differences in the levels of metallic pollutants. The level of metal bioavailability was determined at various sites at different times of the year. For this purpose the conventional approach of recording metal concentrations in soft tissues and the approach based on the calculation of metal/shell-weight indices, first proposed by Fischer (1983), were applied. We concluded that seasonal changes in organism condition (Flesh Condition Index) cause unpredictable oscillations in the metal concentration in soft tissues. For this reason the direct use of metal concentration values is not recommended to assess metal bioavailability. The metal/shell-weight indices, however, were not affected by seasonal changes in the flesh weight of sentinel mussels and thus may provide a more realistic indication of metal bioavailability. In the present study, different metal bioavailabilities, assessed by metal/shell-weight indices, were found at different sampling sites, according to the influence of industrial activities. Seasonal trends in metal/shell-weight indices (attributed to different metal inputs at different times) were also recorded. In conclusion, metal/shell-weight indices, characterized by a high sensitivity and a low noise-to-signal ratio, are a simple and reliable tool for assessing metal bioavailability in 'Mussel Watch' monitoring programmes. Metals . Bioavailability . 'Mussel Watch' . Sentinels . Molluscs . Growth . Condition . Seasonality Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 125. Publication date: September 14, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Stability of the head: studies in normal subjects and in patients with labyrinthine disease, head tremor, and dystonia.

The dynamics of postural control of the head were investigated in normal human subjects and patients with neurological disease. The technique adopted was to measure the head movements provoked by passive, unpredictable oscillations of the trunk in the frequency range 0-6-7 Hz when subjects were required (a) to try to stabilise their head "in space" and (b) to try to make their heads move "en bloc" with the trunk. Head movement responses were characterised by the gain and phase with respect to trunk movement (transfer function) and degree of linear relationship between head and trunk (coherence). The normal transfer function approximated a cascade of two second-order, underdamped, systems representing the passive inertial, viscous, and elastic properties of the muscle and joints of the head and neck. Stabilisation of the head "in space" produced about 40% reduction in transmission of body movement, was only evident at frequencies less than 1 Hz and was affected partly by voluntary movements. An alabyrinthine patient could also achieve some spatial stabilisation. The findings indicate a weak role for vestibular-collic reflexes and emphasise that the primary control of head posture during unpredictable movement is through the tonic visco-elastic properties of neck muscles that work to stabilise the head on the shoulders. In patients with dystonia of the neck and essential and cerebellar head tremor, the head showed a tendency to unstable oscillation (resonance). The instability and dystonia could be measured in terms of visco-elastic constants and damping ratios. The head movements of some tremor patients did not linearly follow the trunk movement, showing that the motion stimulus provoked abnormal phasic muscle activity at frequencies other than those of the tremor. The technique quantifies head control in movement disorders and is sensitive to abnormal function.

The Impact of Treatment with Levodopa on Parkinson's Disease

The progress of 178 patients with Parkinson's disease who began treatment with levodopa between November 1969 and December 1972 is reviewed after six years. One hundred and twenty-five patients showed an initial improvement of their individual total disability scores exceeding 25 per cent, but after six years of sustained treatment only 37 patients still obtained similar benefit. By 1978 only five patients had maintained their initial improvement compared to 69 patients after two years therapy; however, 47 patients were still better than before treatment. The overall mortality ratio--the ratio of observed to expected death rate--for all the patients was 1.45:1. In those patients who unable to tolerate levodopa for longer than two years the ratio was 2.38:1; in those who were able to tolerate sustained medication, life expectancy was normal (ratio of 0.91:1 for males and 1.14:1 for females). Involuntary movements were the commonest complication of treatment. Three main types were distinguished. Peak dose dyskinesias, beginning 20 to 90 minutes after an oral dose and most severe midway through the inter-dose period, affected 80 per cent of patients. Early morning and end-of-dose dystonia occurred in 20 per cent of patients and biphasic dyskinesia--two distinct episodes of involuntary movements within each inter-dose period--was the least common pattern affecting 3 per cent of patients. Involuntary movements increased in frequency and severity as treatment continued. End-of-dose deterioration ('wearing-off' effect of individual doses) occurred in 65 per cent of patients: unpredictable oscillations in motor performance (the 'on-off' phenomenon) unrelated to the time and dosage of levodopa, occurred in 10 per cent. Psychiatric side effects included toxic confusional states, visual pseudohallucinations and paranoid psychoses and constituted the most frequent reason for stopping medication. Forty (22 per cent) of the patients had suffered severe depression before the onset of disease and levodopa had no sustained antidepressant effect in this group. After six years of treatment with levodopa, 32 per cent of the patients had unequivocal dementia.