Lumbar erector spinae oxygenation during prolonged contractions: implications for prolonged work

Owing to the recent interest in torso stabilization exercises together with many questions regarding the duration of prolonged isometric holds in occupational settings, the authors attempted to assess the level of back muscle oxygenation during prolonged isometric contractions. Specifically, this study recorded relative oxygen saturation of haemoglobin/myoglobin using Near Infrared Spectroscopy (NIRS) in the L3 erector mass during prolonged isometric contractions at intensities from 2 to 30% of maximum voluntary contraction (MVC). It was hypothesized that available oxygen to these muscles is severely compromised even at moderate levels of activation observed in occupational work. Eight volunteers without a history of lower back pain or injury participated in this study. The exercise task involved isometric contraction of the lower erector spinae at five different levels of each subject's maximal voluntary contraction: 2, 5, 10, 20 and 30% MVC, presented in random order. Subjects were placed in a sitting position, with a curved plastic plate secured horizontally to the pelvis to minimize movement at the hip joint. During extensor exertions, they were restrained with a harness that was attached at chest level to a load cell. Each isometric contraction was performed for 30 s followed by 1 min of rest. All levels of contraction demonstrated reduction in oxygen. Given the concern for motion artefact on the NIRS signal, sham trials were conducted where the subjects went through the procedure of attaching the pulling cable but no active pull was performed. These trials showed no change in the NIRS signal. At this time NIRS appears to be the only non-invasive instrumentation available to indicate total available muscle oxygen during low level, prolonged work. Although the specific tissue volume sampled by NIRS cannot be positively identified, it appears that tissue oxygenation in the lumbar extensor musculature is reduced as a function of contraction intensity, even at levels as low as 2% of MVC. These data have implications for prolonged work where postures requiring isometric contractions are sometimes held for hours, and where musculoskeletal illness has been linked to prolonged contraction levels above 2%MVC--these data suggest a possible biological pathway.     

Quantification of haemodynamic response to auditory stimulus in intensive care

Measuring effects of sensory stimuli on haemodynamics could provide information about the interplay between central and autonomous nervous system (ANS). However, ANS response to sensory stimulus has received little attention. In this paper we present a signal processing scheme to extract the responses of heart rate and systemic arterial pressure on auditory stimulus in intensive care patients (N=5). In short, the effect of mechanical ventilation is rejected by optimal linear modelling. Other disturbances are attenuated by filtering and efficient rejection of outlying sweeps of data. The results show identifiable responses on three out of five cases. The response characteristics may be explained by synchronisation of spontaneous variability in systemic arterial pressure to auditory stimulus.     

A longitudinal study of lifestyle factors as predictors of injuries and crashes among young adults

This study was part of the Dunedin Multidisciplinary Health and Development Study. This is a longitudinal study of the health, development and behaviour of a cohort of 1037 young people born in Dunedin, New Zealand between 1 April 1972 and 31 March 1973. Explanatory measures covering background, behavioural and personality factors were obtained at ages 15 and 18 and were used as potential predictors of outcomes reported at age 21. Four outcomes were considered: any crash, injury crash, non-injury crash, and serious injury (not motor vehicle related). Overall, very few lifestyle factors were important predictors of any of these outcomes. Factors that were shown to predict injury crashes differed from those that predicted non-injury crashes. Also, those that predicted a traffic crash differed from those that predicted a serious non-traffic injury. These results suggest that focusing injury prevention efforts on changing the lifestyles of young adults is unlikely to reduce overall crash risk, and would have little impact on the risk of serious injury.     

Impact forces following the unexpected removal of a chair while sitting

This report documents the impact forces measured during trials of dropping an anthropometric dummy (80.3 kg) (Hybrid III, First Technologies Corporation) in three different positions onto it's pelvis (gluteal region) from a seated height, which was meant to simulate a chair being pulled out from an individual in the process of sitting. Peak forces on the pelvis were measured by a force plate covered with industrial carpet. These impact forces were translated to the compressive and shear forces on the lumbar spine. The peak impact forces during the different body postures were 20000-29900 N (torso upright); 13000-22200 N (torso-legs 45 degrees to floor); 6000-15200 N (layout position). The impact forces generated from falling onto the pelvis from a seated height, appear to be sufficient to cause injury as the forces well exceed documented injury tolerance levels.     

Quantitative in Situ Measurement of Ion Transport in Polypyrrole/Poly(styrenesulfonate) Films Using Rotating Ring-Disk Voltammetry

An approach based on rotating ring-disk electrode (RRDE) voltammetry is described for the quantitative, in situ measurement of ion transport between solution and conducting polymer films. The specific composite film studied in this report is polypyrrole/poly(styrenesulfonate) (pPy(+)/pSS(-)). Cation flux in and out of the polymer was obtained from the mass-transport-limited reduction current for the dopant cation(s) measured at the ring during redox cycling of the polymer. Crucial to this method is the use of a supporting electrolyte that is sterically inhibited from passing into the film and the use of dopant ions that adhere to specific electrochemical constraints. With this method it was possible to quantitatively account for all changes in charge compensation in the film by the specific cation(s) involved. Three different cations were explored alone and in paired combinations. Solutions containing mixtures of dopant cations were studied to determine whether the pPy(+)/pSS(-) films exhibit preferential doping. Kinetic factors, likely due to steric differences in the dopant cations, were found to lead to significant preferential doping of the polymer.     

The effect of formulation on radioiodide thyroid uptake in the hyperthyroid cat

This investigation was designed to compare in vitro dissolution profiles from sodium iodide capsules with radioiodide thyroid uptake in hyperthyroid cats using sodium iodide capsules prepared with a formulation exhibiting a complete release of radioiodide (I-123) in vitro and a formulation with an incomplete release of radioiodide. In vitro dissolution profiles for I-123 sodium iodide capsules with two different formulations were determined using the USP XXIII dissolution test. The two formulations studied in vitro were sodium phosphate dibasic powder with 1% magnesium stearate and calcium phosphate dibasic powder with 3% magnesium stearate. By 20 min after initiation of the dissolution test, over 95% of the I-123 was released from capsules of sodium phosphate dibasic powder. The capsules of calcium phosphate dibasic powder reached 75% at 65 min, with no further release occurring thereafter. There was a statistically significant difference in the dissolution profiles of the two formulations. The thyroid uptake of I-123 from capsules exhibiting complete release and incomplete release of radioiodide was determined in hyperthyroid cats. At 4 hr, the mean percentage thyroid uptake value for sodium phosphate dibasic powder with 1% magnesium stearate (complete release formulation) was 12.0% compared to 9.4% for calcium phosphate dibasic powder with 3% magnesium stearate (incomplete release formulation); at 24 hr, the values were 34.4% compared to 23.7%. The data suggest that the incomplete dissolution profile observed in vitro may correlate with a reduction in the bioavailability of the radioiodide in vivo. However, using the Wilcoxon signed rank test, statistically significant differences did not occur between the complete release formulation and incomplete release formulation at either 4 hr or 24 hr (p > .05). The results of the in vivo study with five hyperthyroid cats were not conclusive due to the variability in response between individual cats.     

Determination of nonlinear electromechanical energy conversion and the field-dependent elastic modulus of Pb(Mg(1/3)Nb(2/3 ))O(3)-based electrostrictors

Energy conversion efficiency is a critical parameter for all electromechanical materials. Although excellent techniques are available for linear materials, nonlinearities complicate the determination of conversion efficiency in electrostrictive Pb(Mg(1/3)Nb(2/3 ))O(3) (PMN). The field dependence of the elastic modulus presents additional problems. A technique combining pulse-echo ultrasound has been developed to approximate the change in the Young's modulus with applied field. A 30% decrease was observed at 1 MV/m (from ~100 to ~70 GPa). The boundary condition for these measurements was a constant electric field as opposed to constant dielectric displacement. In combination with the results from harmonic analysis, the modulus data may be used to determine the electromechanical conversion efficiency. This has been accomplished using an energy balance criterion for a PMN-based composition (with and without dc bias). The resulting longitudinal coupling values are >0.5 for practical electric fields (<1 MV/m peak).     

Production and characterization of new calcium phosphate bone cements in the CaHPOv4–α-Ca3(PO4)2 system: pH, workability and setting times

The initial setting properties of calcium phosphate cements in the CaHPOv₄–-Ca₃(PO₄)₂ (DCP–-TCP) system have been investigated. Interest was focused on the pH, workability, cohesion time and initial and final setting times. The addition of CaCO₃ modified the structure of the cement reaction product such that it became more similar to the apatite phase in bone mineral. The addition of 10% w/w of CaCO₃ reduced the viscosity of the cement pastes resulting in an increase in initial and final setting times and improved injectability. © 1999 Kluwer Academic Publishers     

A new class of auditory warning signals for complex systems: auditory icons

This simulator-based study examined conventional auditory warnings (tonal, nonverbal sounds) and auditory icons (representational, nonverbal sounds), alone and in combination with a dash-mounted visual display, to present information about impending collision situations to commercial motor vehicle operators. Brake response times were measured for impending front-to-rear collision scenarios under 6 display configurations, 2 vehicle speeds, and 2 levels of headway. Accident occurrence was measured for impending side collision scenarios under 2 vehicle speeds, 2 levels of visual workload, 2 auditory displays, absence/presence of mirrors, and absence/presence of a dash-mounted iconic visual display. For both front-to-rear and side collision scenarios, auditory icons elicited significantly improved driver performance over conventional auditory warnings. Driver performance improved when collision warning information was presented through multiple modalities. Brake response times were significantly faster for impending front-to-rear collision scenarios using the longer headway condition. The presence of mirrors significantly reduced the number of accidents for impending side collision scenarios. Subjective preference data indicated that participants preferred multimodal displays over single-modality displays. Actual or potential applications for this research include auditory displays and warnings, information presentation, and the development of alternative user interfaces.