Internet-based ICRP resource for healthcare providers on the risks and benefits of medical imaging that uses ionising radiation.

The purpose of the International Commission on Radiological Protection (ICRP) Committee 3 Working Party was to update the 2001 web-based module 'Radiation and your patient: a guide for medical practitioners' from ICRP. The key elements of this task were: to clearly identify the target audience (such as healthcare providers with an emphasis on primary care); to review other reputable sources of information; and to succinctly publish the contribution made by ICRP to the various topics. A 'question-and-answer' format addressing practical topics was adopted. These topics included benefits and risks of imaging using ionising radiation in common medical situations, as well as pertaining to specific populations such as pregnant, breast-feeding, and paediatric patients. In general, the benefits of medical imaging and related procedures far outweigh the potential risks associated with ionising radiation exposure. However, it is still important to ensure that the examinations are clinically justified, that the procedure is optimised to deliver the lowest dose commensurate with the medical purpose, and that consideration is given to diagnostic reference levels for particular classes of examinations.

The effect of socioeconomic status on bone density testing in a public health-care system.

INTRODUCTION AND HYPOTHESIS: An inverse relationship exists between socio-economic status (SES) and osteoporotic fractures. In publicly funded health-care systems there should be no barriers to accessing bone mineral density (BMD) testing, especially for those at increased fracture risk. Our hypothesis was that there would be a positive association between SES and BMD utilization (i.e. higher utilization rates in higher income women), resulting in disparities that disadvantage lower SES or lower income women. METHODS: A population-based BMD database from the Manitoba Bone Density Program was utilized to assess the association between SES (defined using income quintiles) and BMD utilization rates in women aged 50 years and older (n=107,944) for the 2001-2002 fiscal year. Analyses were stratified by age (50-64 years old and 65 years or older) and by a morbidity index obtained from the Johns Hopkins University Adjusted Clinical Group Case-Mix Adjustment System. RESULTS: Regression models demonstrated significantly higher BMD utilization rates among high SES women in all age and morbidity strata. Rate ratios varied from 1.76 (95% CI: 1.52-2.04) in 50- to 64-year-old women to 2.36 (95% CI: 1.60-3.49) in low morbidity women aged 65 or older. CONCLUSION: Within the context of a publicly funded health-care system significant inverse associations are demonstrated between SES and BMD utilization rates. Further research is needed to better understand the nature of these associations and how they may contribute to health outcomes.

Chemical probes for water-oxidation: synthetic manganese complexes in photoactivation of water splitting complex and as exogenous electron donors to photosystem II.

Photoactivation of the water splitting enzyme was performed with 13 different synthetic manganese complexes and characterized by oxygen evolution yield, thermoluminescence and chlorophyll fluorescence induction kinetics. The efficiency of different compounds in photoactivation correlated with the rate of linear electron transport in the presence of these compounds. The organic ligands, associated with the manganese ions, do not prevent the photoactivation of the water splitting complex (WOC). Photoactivation with different manganese complexes depended on the number of the Mn-ions in the complex, their valence state and the nature of their donor atoms. The most efficient restorations were achieved by using tetrameric complexes having a dimer+dimer structure, complexes containing Mn(II) ions, and having 4-6 oxygen and 0-2 nitrogen atoms as donor atoms. Further, the effectiveness of photoactivation depended largely on the structure of the complexes. Our data support the notion that WOC in intact thylakoids requires the cooperation and well determined arrangement of all four manganese ions, and argue against the hypothesis that two manganese ions are sufficient for water splitting. Photoactivation by some complexes led to anomalous flash-oxygen patterns, which are explained by a modified/perturbed water splitting complex.

Permanent respiratory impairment and upper airway symptoms despite clinical improvement in patients with reactive airways dysfunction syndrome.

We previously reported clinical findings for 19 patients who developed symptomatic airways hyperactivity following an acute exposure to an inhaled irritant and who were given the diagnosis of reactive airways dysfunction syndrome (RADS). We now report on nine of these patients who have been followed for a mean of 9 years, allowing assessment of function, symptoms, and comorbidity beyond the early phase of acute airway injury and inflammation. None of the patients have resolved their airway hyper-responsiveness and symptoms completely, although only in one subject, who had a premorbid history of asthma, has the condition progressed. A common feature has been sinusitis and other upper-airway symptoms. We conclude that in this group of patients, RADS presented in a consistent pattern regardless of the cause of airway injury, resolved only partially, even in subjects without a premorbid history of respiratory disease, and was associated with significant secondary morbidity, especially affecting the upper airway. This pattern was evident regardless of smoking status or age at time of exposure. We conclude that for these subjects, RADS was a distinct entity with a consistent natural history that conferred permanent impairment, but did generally improve somewhat over time.

Non-penetrating glaucoma surgery using AquaFlow(TM)collagen implants.

AquaFlow TM is an absorbable collagen implant for use in non-penetrating surgery for primary open angle glaucoma. Its purpose is to facilitate drainage of fluid from the eye, thereby reducing intraocular pressure. AquaFlow TM is approved for use in Canada in medically refractory cases of primary open angle glaucoma. Non-penetrating glaucoma surgery with the AquaFlow TM implant appears to be a relatively safe procedure. However, there is a steep learning curve for the surgeon and it is initially associated with a high rate of conversion to conventional surgery during the operation. Limited evidence from small non-randomized trials suggests that the AquaFlow TM implant may offer benefits over conventional surgical approaches in terms of reduced complication rates, reduced medication use, an earlier return of improved vision and sustained control of intraocular pressure. However, the efficacy and cost-effectiveness of this approach have not been established. January, 2001 for use in patients with uncontrolled

Short- and long-term redox regulation of photosynthetic light energy distribution and photosystem stoichiometry by acetate metabolism in the green alga, Chlamydobotrys stellata.

The effect of acetate metabolism on the light energy distribution between the two photosystems, on the PS II/PS I stoichiometry and on the expression of psbA and psbB and psaA genes was investigated in the green alga, Chlamydobotrys stellata during autotrophic (CO(2)), mixotrophic (CO(2) plus acetate) and photoheterotrophic (only acetate) cultivation. It was observed that acetate assimilation in the glyoxylate cycle resulted in a large drop in the ATP content and a concomitant increase in the NADPH content of the cells. The combined effect of high NADPH concentration and linear electron transport brought about an over-reduction of the inter-photosystem electron transport components. The reduced state of the inter-photosystem components initiated a state 1/state 2 transition of LHC II and a decrease in the PS II/PS I ratio. The PS II/ PS I ratio was reduced because the synthesis of PS II reaction centers was repressed and that of the PS I reaction centers was slightly enhanced by acetate cultivation. The amount of PsbA and PsbB proteins of PS II and the abundance of psbA mRNA decreased. The abundance of PS I PsaA protein and psaAmRNA were only slightly increased. All of the acetate-induced effects were reversible when the cells were transferred back to an acetate-free medium. Our observations demonstrate that the expression of the PS II psbA and psbB and PS I psaA genes is regulated by the redox state of the inter-photosystem components at the transcriptional level. Experiments carried out in the presence of DBMIB which facilitates the reduction of plastoquinone pool indicate that the expression of genes encoding the components of PS II and PS I are controlled by the redox state of a component (cytochrome b/f complex) located behind the plastoquinone pool.

Disability evaluation.

A physician may be called upon to evaluate disability in the roles of impartial judge of impairment, expert witness in a legal case, or treating physician. Critical to these processes are discernment between disability and impairment, an understanding of legal responsibilities, and knowledge of the elements of examinations and reports.

Involvement of the donor tyrosine-D1 (Y d) in Photosystem II electron transport in the green alga, Chlamydobotrys stellata.

The light-induced oxidation of the accessory donor tyrosine-D (YD) has been studied by measurements of the EPR Signal IIslow at room temperature in the autotrophically and photoheterotrophically cultivated alga Chlamydobotrys stellata. After illumination and dark adaptation, YD Signal IIslow was observed only in autotrophic algae, i.e. under conditions of a linear photosynthetic electron transfer from water to NADP(+). The addition of artificial electron acceptors phenyl-p-benzoquinone (PPQ) or dichloro-p-benzoquinone (DCQ) to the autotrophic cells caused an almost negligible increase of this signal. When photosynthetic electron flow and oxygen evolution were diminished by removal of the carbon source CO2 and addition of acetate (photoheterotrophy), a pronounced YD Signal IIslow was seen only in presence of DCQ or PPQ. Several possibilities are discussed to explain the absence of YD Signal IIslow in photoheterotrophic Chl. stellata such as the existence of a cyclic PS II electron flow very effectively reducing P680 and thereby preventing the possibility of YD oxidation. Artificial electron acceptors withdraw electrons from this cycle thus keeping the primary quinone acceptor, QA, oxidized and thereby diminishing the reduction of P680 (+) by cyclic PSII. This leads to the appearance of the YD Signal IIslow also in the photoheterotrophically grown algae.

Noncardiac pulmonary edema, newer environmental aspects. An update.

Accidental spread of potentially toxic gases, fumes, and particulate chemicals has been reported recently in various cities throughout the country and appears to be on the increase throughout the world in the past few years. Moreover, cerebral trauma, septic shock (ARDS), and environmental pulmonary edema from drug intoxication have been commonly encountered. Newer modalities of treatment include selective [corrected] fiber optic bronchoscopy, constant positive airway pressure mask, administration of surfactant, pentoxifylline, and use of newer experimental agents such as nitrous oxide, antitumor necrosis factor (ATNF), and extracorporeal carbon dioxide with low-frequency positive pressure (ECCO2R-LFPPV). The future holds promise for probable reductions in both morbidity and mortality rates of this ubiquitous occupational and environmental health problem, which is of global importance.

Comparative EPR and thermoluminescence study of anoxic photoinhibition in Photosystem II particles.

Photosystem II particles were exposed to 800 W m(-2) white light at 20 °C under anoxic conditions. The Fo level of fluorescence was considerably enhanced indicating formation of stable-reduced forms of the primary quinone electron acceptor, QA. The Fm level of fluorescence declined only a little. The g=1.9 and g=1.82 EPR forms characteristic of the bicarbonate-bound and bicarbonate-depleted semiquinone-iron complex, QA (-)Fe(2+), respectively, exhibited differential sensitivity against photoinhibition. The large g=1.9 signal was rapidly diminished but the small g=1.82 signal decreased more slowly. The S2-state multiline signal, the oxygen evolution and photooxidation of the high potential form of cytochrome b-559 were inhibited approximately with the same kinetics as the g=1.9 signal. The low potential form of oxidized cytochrome b-559 and Signal IIslow arising from TyrD (+) decreased considerably slower than the g=1.9 semiquinone-iron signal. The high potential form of oxidized cytochrome b-559 was diminished faster than the low potential form. Photoinhibition of the g=1.9 and g=1.82 forms of QA was accompanied with the appearance and gradual saturation of the spin-polarized triplet signal of P 680. The amplitude of the radical signal from photoreducible pheophytin remained constant during the 3 hour illumination period. In the thermoluminescence glow curves of particles the Q band (S2QA (-) charge recombination) was almost completely abolished. To the contrary, the C band (TyrD (+)QA (-) charge recombination) increased a little upon illumination. The EPR and thermoluminescence observations suggest that the Photosystem II reaction centers can be classified into two groups with different susceptibility against photoinhibition.

Time is of the essence: a conjecture that hemispheric specialization arises from interhemispheric conduction delay.

Tomasch (1954) and Aboitiz et al. (1992) found the majority of the fibers of the human corpus callosum are under 1 micron in diameter. Electron microscopic studies of Swadlow et al. (1980) and the detailed study of LaMantia and Rakic (1990a) on macaques show the average size of the myelinated callosal axons also to be less than 1 micron. In man, the average-sized myelinated fiber interconnecting the temporal lobes would have a one-way, interhemispheric delay of over 25 msec. Thus, finely detailed, time-critical neuronal computations (i.e., tasks that strain the capacity of the callosum and hence could not be handled by just the larger fibers) would be performed more quickly via shorter and faster intrahemispheric circuits. While one transit across the commissural system might yield tolerable delays, multiple passes as in a system involving "setting" would seem prohibitively slow. We suggest that these temporal limits will be avoided if the neural apparatus necessary to perform each high-resolution, time-critical task is gathered in one hemisphere. If the, presumably overlapping, neural assemblies needed to handle overlapping tasks are clustered together, this would lead to hemispheric specialization. The prediction follows that the large brains of mammals such as elephants and cetaceans will also manifest a high degree of hemispheric specialization.

Participation of the g = 1.9 and g = 1.82 EPR forms of the semiquinone-iron complex, QA-.Fe2+ of photosystem II in the generation of the Q and C thermoluminescence bands, respectively.

Following illumination at 200 K, the charge recombination reactions and the origin of the thermoluminescence (TL) bands appearing at about 0 degree C (Q band) and +50 degrees C (C band) in the glow curve were investigated by comparative TL and EPR measurements in DCMU-treated photosystem II particles. Decay half-time measurements carried out at -25 degrees C and +25 degrees C, respectively, suggest that the S2 state (multi-line signal) undergoes charge recombination with the g = 1.9 form of the semiquinone-iron complex, QA-.Fe2+, resulting in the appearance of the Q band, and that the g = 1.82 form of QA-.Fe2+ back-reacts with the oxidized tyrosine, YD+ (Signal IIs), accounting for the generation of the C band.

Hydrogen Photoevolution Indicates an Increase in the Antenna Size of Photosystem I in Chlamydobotrys stellata during Transition from Autotrophic to Photoheterotrophic Nutrition.

The changes in the light-harvesting antenna size of photosystem I were investigated in the green alga Chlamydobotrys stellata during transition from autotrophic to photoheterotrophic nutrition by measuring the light-saturation behavior of hydrogen evolution following single turnover flashes. It was found that during autotrophic-to-photoheterotrophic transition the antenna size of photosystem I increased from 180 to 250 chlorophyll. The chlorophyll (a + b)/P700 ratio decreased from 800 to 550. The electron transport of photosystem I measured from reduced 2,6-dichloro-phenolindophenol to methylviologen was accelerated 1.4 times. In the 77K fluorescence spectra, the photosystem II fluorescence yield was considerably lowered relative to the photosystem I fluorescence yield. It is suggested that the increased light-harvesting capacity and redistribution of absorbed excitation energy in favor of photosystem I is a response of photoheterotrophic algae to meet the ATP demand for acetate metabolism by efficient photosystem I cyclic electron transport when the noncyclic photophosphorylation is inhibited by CO(2) deficiency.

Thermoluminescence evidence for light-induced oxidation of tyrosine and histidine residues in manganese-depleted photosystem II particles.

In the thermoluminescence (TL) glow curve of photosystem II, particles depleted of manganese, a tyrosine modifier, 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD) abolishes the TL band appearing around -55 degrees C (TL-55). Addition of a histidine modifier, diethylpyrocarbonate results in the disappearance of the band peaking around -30 degrees C (TL-30). NBD treatment also abolishes the EPR signal IIfast of oxidized tyrosine donor, Yz, and inhibits the electron transport from diphenylcarbazide to 2,6-dichlorophenol-indophenol. It is concluded that the TL-55 and TL-30 bands can be assigned to oxidized tyrosine (Yz+) and histidine (His+) residues, respectively, which participate in electron transfer from manganese to the reaction center of chlorophyll, P680+.