New A2/3-xRh2O4 compounds with the CaFe2O4 structure where A is a rare earth or Bi.

New compounds of the type R(2/3-x)Rh(2)O(4) with the CaFe(2)O(4) structure have been prepared, where R is a rare earth. For crystals grown in a Bi/V/O flux, the rare earth was partially replaced by Bi. No evidence of ordering of the A cation vacancies is found, but the A cations are displaced from the ideal A cation site by about 0.24 A. Electrical conductivity measurements on crystals suggest that the materials are degenerate semiconductors with Seebeck measurements showing p-type behavior. This is consistent with our observation that x in R(2/3-x)Rh(2)O(4) ranges up to about 0.09. The compounds were also characterized by magnetic susceptibility and diffuse reflectance measurements.

Osteopenia in systemic mastocytosis: natural history and responses to treatment with inhibitors of bone resorption.

Studies of a 63-year-old woman with osteopenia due to systemic mastocytosis are reported. Delay in making the diagnosis and the occurrence of coincident medical problems meant that radiographs during a 12-year period were available for study. Skeletal symptoms began 20 years after the skin lesions of mastocytosis first appeared, but once established bone loss was rapid, particularly from cortical bone (estimated at 3.75% pa). Biochemical and histological measurements indicated a "high turnover" bone disease and treatment with inhibitors of bone resorption was assessed. Oral, but not intravenous, clodronate was effective in reducing bone turnover as judged by falls in hydroxyproline excretion (p less than 0.01) and serum alkaline phosphatase (p less than 0.01). Mithramycin and chlorambucil were ineffective. Clodronate may be beneficial in arresting bone loss in this disorder.

Estimation of urinary nitrogen losses from urea excretion in patients with intestinal diseases requiring parenteral nutrition, and in those with hepatic decompensation.

A comparison of daily urinary nitrogen excretion measured directly, with values derived from urea excretion, was carried out on 110 occasions in patients with either gastrointestinal disease requiring total parenteral nutrition or with alcoholic liver disease. The values were found to correlate well in both patient groups (r = 0.88 and 0.9 respectively). Values of urinary nitrogen loss calculated from urea excretion may safely be used when performing nitrogen balance studies in such cases.

The proteinuria of diabetic nephropathy.

The results of an investigation into the nature of the proteinuria of diabetic nephropathy are described. Proteinuria increases quantitatively with deteriorating renal function but there is no consistent qualitative change; even with small amounts of proteinuria the selectivity may be poor and the proportion of albumin to the total excretion constant. These and other findings are discussed in relation to the possible pathogenesis of the glomerular dysfunction in diabetic nephropathy.

Plasma uric acid in patients receiving anticonvulsant monotherapy.

In newly diagnosed adult patients with epilepsy followed prospectively on monotherapy, carbamazepine and phenytoin were associated with a fall in plasma uric acid, but sodium valproate and phenobarbitone were associated with a rise in plasma uric acid. The mechanisms and significance of these findings are discussed.

A new prognostic index in surgery and parenteral feeding: the ratio of triiodothyronine to reverse triiodothyronine in serum (T3/rT3 ratio).

Serum concentrations of albumin, triiodothyronine (T3), and reverse triiodothyronine (rT3) were measured in 46 patients on the first day after routine gastrointestinal surgery, and the molar ratio T3/rT3 was calculated. The median value of this ratio, but not of albumin, was significantly lower in 11 who subsequently suffered major septic complications than in the remainder. Measurement of the ratio correctly predicted the outcome of 80% of individuals. The T3/rT3 ratio, midarm muscle circumference (MAMC), triceps skin fold (TSF) and serum concentrations of albumin and transferrin were measured in 23 patients at referral for parenteral feeding. Median values of T3/rT3 ratio, MAMC and transferrin, but not of the other parameters, were significantly lower in nine who died than in survivors. Measurements of the ratio, MAMC and transferrin correctly predicted the outcome of 87%, 78% and 74% of individuals, respectively.

Enzyme induction by drugs. Its relevance to clinical biochemistry.

The properties of the hepatic microsomal, drug detoxicating, enzyme system are reviewed with particular reference to its inducibility. Induction is modified by various factors of which the diet is particularly important. A theoretical model system for induction has been proposed and this is discussed. There are a number of methods for assessing microsomal enzyme induction in man, none of which is ideal. Nevertheless, induction is a well recognized phenomenon in man and has a bearing on the metabolism of a number of endogenous substances. The effect of induction on steroid metabolism and the relationship between inducers, vitamin D, and metabolic bone disease is discussed. Bilirubin metabolism is affected by changes in microsomal enzyme activity and inducers have been used therapeutically in some cases of hyperbilirubinaemia. The relationship between drugs and the hepatic porphyrias is reviewed. The hepatic microsomal enzyme system is but one of many inducible enzymes and the role of induction in general in metabolic regulation is emphasised.

Provision of interpretative comments on biochemical report forms.

Providing interpretative comments on reports, particularly those for primary care physicians is an important part of our job. Few clinical biochemists (whether medical or scientific) receive significant training for this. Most work in isolation, and few receive feedback on the utility of their comments. Surveys show an extremely wide divergence of opinion and comment even on apparently straightforward sets of abnormal results. Some comments are regarded as highly inappropriate when assessed by peer review. There is a need for further education and training in this area, concentrating as much on 'how to comment' as on 'what to comment'. There is also a need to establish some form of quality assurance for this important part of the post-analytical phase. A pilot External Quality Assurance Scheme (EQAS) is now being established.

Total parenteral nutrition and the clinical chemistry laboratory.

Parenteral nutrition is a well-established technique for feeding patients with intestinal failure and other conditions which render enteral feeding impossible. Biochemical tests are required in the initial assessment of these patients, for monitoring their response to treatment and for the detection and management of complications. The use of these tests is discussed critically and guidelines are provided for the frequency with which they should be performed. Chemical pathologists and clinical biochemists have an important role in the provision of parenteral nutrition as members of multi-disciplinary nutrition teams.

Log-jam in acid-base education and investigation: why make it so difficult?

Medical students frequently have difficulty in interpreting acid-base data particularly when pH values are used. The difficulty persists when students qualify and has implications for the safe management of patients who require investigation of acid-base status. Simplification of tuition is required together with a change of practice in the reporting of acid-base data by the laboratories. To improve understanding, we recommend that the teaching and reporting of acid-base status should be changed to use [H+] instead of pH, and a greater emphasis placed on the logical interpretation of primary measurements--that is [H+] and PCO2--with less reliance on derived variables.

Leukopenia secondary to silver sulfadiazine: frequency, characteristics and clinical consequences.

Leukopenia associated with silver sulfadiazine (SSD) is a frequent event and may be a risk factor for infectious complications in the burn patient. This study reviews 77 patients with thermal injuries to determine total body surface area (BSA) burned, and white blood cell count (WBC) at time of hospital admission. A subpopulation of 56 patients with serial WBC counts were evaluated to determine lowest WBC count, topical burn therapy, episodes of infection or septic shock and final outcome. There was not a significant incidence of leukopenia on admission. Fifty-six per cent of patients treated with SSD and 12 per cent of silver nitrate-treated patients became leukopenic (P less than .05). The leukopenia was higher among SSD-treated patients who had greater than 15 per cent BSA burns (P less than .05). The onset of leukopenia generally occurred the second day after the burn and the WBC count returned to normal with discontinuance of the drug. The leukopenia was due primarily to a marked decrease in the number of mature neutrophils. There was no difference in the incidence of septic complications or opportunistic infections in the treatment groups. There was no significant difference in final outcome. Silver sulfadiazine-induced leukopenia appears to be a self-limited phenomenon that does not increase the incidence of infectious complications nor affect final outcome.

Diltiazem: dose it affect vasospasm?

Calcium antagonists are being investigated for their role in preventing or ameliorating the vasospasm associated with subarachnoid hemorrhage. We have done a phase I and phase II type trial of diltiazem. No effect on spasm was documented. A tendency to increase the bleeding time was noted, but no detrimental clinical effect occurred. The rebleed rate was not changed. It appears that further study of diltiazem through a proper randomized study would not be cost- or time-effective.

Laser reflections from relatively flat specular surfaces.

A major element in laser range control procedures has been the control of stray reflections from glass reflectors which may be near the laser target. These hazardous reflections have been thought to extend as far as the direct beam for near grazing angles of incidence. Modern military laser rangefinders and designators can be hazardous to the unaided eye to distances of 10 km or even greater. For this reason, many square kilometers of laser range area have been necessary to conduct laser tests when flat specular reflectors may be present on targets. Fortunately, sophisticated pointing systems have been developed with these laser systems to ensure that the direct beam is confined to the immediate target area. In most cases, flat specular reflectors also have been eliminated from the immediate target area. In some instances, however, specular reflectors still exist near or on laser targets. For these special cases, a more definitive mathematical treatment of hazardous laser reflections is desired. The divergence of a laser beam which has been reflected from a flat specular surface is dependent on the size of the reflector, the divergence of the laser creating the reflection, and the curvature of the reflecting surface. It can be shown mathematically that the curvature of even an optical flat, a reference surface used to compare the flatness of other surfaces, will produce a significant additional beam spread, thereby reducing the hazards of reflected beams. The natural curvature of plate glass or window glass is much greater, reducing the hazards even further. The extent of the hazards for reflections of various types of lasers and reflecting surfaces is discussed.

Comparative hazard evaluation of near-infrared diode lasers.

Hazard evaluation methods from various laser protection standards differ when applied to extended-source, near-infrared lasers. By way of example, various hazard analyses are applied to laser training systems, which incorporate diode lasers, specifically those that assist in training military or law enforcement personnel in the proper use of weapons by simulating actual firing by the substitution of a beam of near-infrared energy for bullets. A correct hazard evaluation of these lasers is necessary since simulators are designed to be directed toward personnel during normal use. The differences among laser standards are most apparent when determining the hazard class of a laser. Hazard classification is based on a comparison of the potential exposures with the maximum permissible exposures in the 1986 and 1993 versions of the American National Standard for the Safe Use of Lasers, Z136.1, and the accessible emission limits of the federal laser product performance standard. Necessary safety design features of a particular system depend on the hazard class. The ANSI Z136.1-1993 standard provides a simpler and more accurate hazard assessment of low-power, near-infrared, diode laser systems than the 1986 ANSI standard. Although a specific system is evaluated, the techniques described can be readily applied to other near-infrared lasers or laser training systems.

Field laser hazard calculations.

The authors develop formulae for laser hazard evaluation. Beam diameter, transmitted power through an optical system, nominal ocular hazard distance, and optical density required for eye protection may be calculated. A calculator program is provided which uses experimentally determined laser parameters to return the necessary safety information.

Nonlinear properties of optical filters--implications for laser safety.

Laser safety filter materials must be evaluated at various levels up to the maximum irradiances likely to be encountered, since the absorber may exhibit nonlinear properties. Extreme care is necessary around short-duration lasers due to extremely high peak irradiances in the beam. This is especially true for visible and near-infrared lasers due to the high susceptibility to retinal injury for an observer.

Laser hazard evaluation method for middle infrared laser systems.

Hazard evaluation methods for lasers, with wavelengths greater than 1.4 microns (mostly in the middle infrared), have changed significantly in the current version of the American National Standard for the Safe Use of Lasers, ANSI Z136.1-1993. A correct evaluation involves comparing the hazard potential based on two evaluation models; one based on individual pulses and the other based on an equivalent continuous-wave exposure. An example of the hazard evaluation method within this spectral region is provided.