Hypogammaglobulinaemia in low grade B cell tumours; significance and therapy

Bacterial infection is an important cause of morbidity and mortality in patients with B-cell tumors; this is related to their secondary hypogammaglobulinaemia. Two studies of intravenous replacement therapy [IVIg] have been performed in such patients: a crossover study over two years and a randomised, multicentre study over one year. Both involved infusions of IVIg [400 mg/Kg] or an equivalent volume of saline every three weeks for one year. In both studies, serious bacterial infections were considerably reduced by IVIg. Viral and fungal infections were uncommon. In the crossover study bacterial infections were more frequent in periods in which patients serum IgG levels were below the normal range [less than 6.4 g/l]. The sites of bacterial infection were similar in these studies to those in previously published reports, namely respiratory tract, skin, urinary tract and blood. There were a few mild adverse reactions which were related to the rate of infusion, but no serious toxic effects. Haematological parameters were not significantly changed by IVIg at this dose and disease progression did not appear to be changed.

Psychotic depression presenting as status epilepticus

A case of status epilepticus was secondary to water intoxication, which in turn was secondary to a depressive psychosis.

Reactive oxygen species modify human DNA, eliciting a more discriminating antigen for the diagnosis of systemic lupus erythematosus

During the development of an ELISA to measure anti-DNA antibodies in systemic lupus erythematosus (SLE) sera, native dsDNA was found not to be the most appropriate antigen to use in ELISA assays for differentiating between SLE patients and those with rheumatoid arthritis (RA), a disease also associated with circulating serum anti-DNA antibodies. By modifying the ELISA technique to incorporate human DNA, denatured by reactive oxygen species, to detect anti-DNA antibodies in SLE sera, results consistently showed an increase in antibody binding when compared with the native antigen; no such trend was observed in the comparable group of RA patients. Using this assay serum anti-dsDNA antibody levels were measured in a group of 20 controls, 20 RA patients (10 seropositive and 10 seronegative) and 30 SLE patients (15 with clinically active disease, 15 with inactive disease). A comparison with the standard radioimmunoassay used to measure anti-DNA antibodies for the diagnosis of SLE showed that the ELISA assay using modified DNA performed better than the standard radioimmunoassay offering an improvement in both clinical specificity and sensitivity. The improved method particularly reduced the problem of false-negative results for SLE patients shown clinically to be either mildly active or inactive.

Thyroid function in choriocarcinoma: demonstration of a thyroid stimulating activity in serum using FRTL-5 and human thyroid cells

Hyperthyroidism is a well recognized complication of gestational trophoblastic tumours (GTT) and may be due to high circulating concentrations of human chorionic gonadotrophin (hCG) or its variants. We have studied 24 clinically euthyroid women with GTT. Eight were biochemically hyperthyroid with low or undetectable serum thyrotrophin (TSH) and had a mean serum hCG of 361.2 x 10(3) IU/l compared to 76.2 x 10(3) IU/l in the other patients (P less than 0.01). Purified hCG stimulated iodide uptake into FRTL-5 cells with 25 x 10(3) IU/l being equivalent in potency to 1 mU/l of thyrotrophin (TSH). Sixteen out of the 24 sera (67%) stimulated iodide uptake when applied to the cells at a 1:10 dilution. Sera from all eight hyperthyroid patients contained thyroid stimulating activity. The mean hCG concentration in the 16 stimulatory sera was 238.2 x 10(3) IU/l compared to 37.1 x 10(3) IU/l in the other eight sera (P less than 0.01). Six men with hCG-secreting testicular tumours were biochemically euthyroid although three of their sera stimulated iodide uptake into FRTL-5 cells. In human thyroid cells the mean cAMP production over 4 h with sera from five healthy controls was 54.2 +/- 1.81 pmol/mg cell protein compared to 67.0 +/- 3.8 pmol/mg protein with sera from five choriocarcinoma patients (P less than 0.02). Serum from patients with gestational trophoblastic tumours contains a thyroid stimulating activity which may be hCG and whose presence correlates with hyperthyroidism.

Short-term changes in carbon-isotope discrimination identify transitions between C3 and C 4 carboxylation during Crassulacean acid metabolism

Short-term measurements of instantaneous carbon-isotope discrimination have been determined from mass-spectrometric analyses of CO2 collected online during gas exchange for the epiphytic bromeliad Tillandsia utriculata L. Using this technique, the isotopic signature of CO2 exchange for each phase of Crassulacean acid metabolism (CAM) has been characterised. During night-time fixation of CO2 (Phase I), discrimination (Δ) ranged from 4.4 to 6.6‰, equivalent to an effective carbon-isotope ratio (δ(13)C) of -12.3 to -14.5‰ versus Pee Dee Belemnite (PDB). These values reflected the gross photosynthetic balance between net CO2 uptake and refixation of respiratory CO2, characteristic of CAM in the Bromeliaceae. When Δ for the relative proportion of external (p a ) and internal (p i) CO2 is taken into account, calculated p i/p a decreased during the later part of the dark period from 0.68 to 0.48. Measurements of Δ during Phase II, early in the light period, showed the transition between C4 and C3 pathways, with carboxylation being increasingly dominated by ribulose bisphosphate carboxylase (Rubisco) as Δ increased from 10.5 to 21.2‰ During decarboxylation in the light period (Phase III), CO2 leaked out of the leaf and the inherent discrimination of Rubisco was expressed. The value of Δ calculated from on-line measurements (64.4‰) showed that the CO2 lost was considerably enriched in (13)C, and this was confirmed by direct analysis of the CO2 diffusing out into a CO2-free atmosphere (δ (13)C = + 51.6‰ versus PDB). Instantaneous discrimination was characteristic of the C3 pathway during Phase IV (late in the light period), but a reduction in Δ showed an increasing contribution from phosphoenolpyruvate carboxylase. The results from this non-invasive technique confirm the observations that "double carboxylation" involving both phosphoenolpyruvate carboxylase and Rubisco occurs during the transient phases of CAM (II and IV) in the light period.

A general surgeon in Vietnam: lessons learned the hard way

As a general surgeon in Vietnam, I learned about readiness, preparation, survival, and support the hard way. Tri-Service cooperation training, logistics, personnel utilization, and evacuation will help to provide the best possible care to our troops.

Thyroid-stimulatory effects of human chorionic gonadotrophin in early pregnancy. In vivo and in vitro studies

Human chorionic gonadotrophin (hCG) shares structural similarity with pituitary thyrotrophin (TSH) and may act as a thyroid stimulator. We have studied serum hCG levels, thyroid function tests and the ability of serum to stimulate cultured thyroid cells in 40 subjects between 6 and 12 weeks of pregnancy. Serum free tri-iodothyronine was increased and serum TSH reduced in pregnancy samples (both p less than 0.05). hCG was detectable in all pregnancy sera with a mean level of 105.6 X 10(3) U/l. Serum from 24 of the 40 (60%) patients stimulated iodide uptake into cultured FRTL-5 thyroid cells. The potency of sera in stimulating cells correlated with the hCG level (r = 0.710, p less than 0.01). The stimulatory activity in some, but not all, sera could be specifically neutralized with antiserum to hCG. Partially purified hCG stimulated iodide uptake and growth of thyroid cells at concentrations of 50 X 10(3) U/l and above. In these experiments, 25 X 10(3) U/l of hCG produced equivalent stimulation to 1 mU/l of TSH. In 8 patients tested before and after termination of pregnancy, the thyroid-cell-stimulatory activity of serum declined rapidly in parallel with serum hCG. hCG may stimulate the thyroid gland at concentrations which prevail in normal pregnancy. Its potential as a physiological regulator of the thyroid gland is not widely appreciated and requires further study.

A dual-frequency electrical impedance tomography system

An electrical impedance tomography (EIT) system has been constructed, operating at two frequencies, 40.96 and 81.92 kHz, for investigating the practicability of the dual-frequency imaging method discussed theoretically in a previous paper. For testing the system, a phantom with a frequency-dependent electrical conductivity was designed. The properties of the phantom can be adjusted to match the frequency dependence observed in a given type of tissue. Dual-frequency images were obtained from a phantom simulating liver and also from 200 g of porcine liver in a saline tank. Prior to image reconstruction, it was necessary to apply a correction to the data to cancel the effects of stray capacitance within the electronics.

Amiodarone and the thyroid

An antiarrhythmic drug, amiodarone, contains 37% iodine by weight and is structurally similar to the thyroid hormones. The drug inhibits hepatic 5'-deiodinase, resulting in increases in serum thyroxin and "reverse" triiodothyronine, whereas the concentration of triiodothyronine in serum is decreased. There is a significant incidence of either hypothyroidism or hyperthyroidism in patients who are being treated with the drug. This is largely the effect of iodine released from the drug during chronic therapy, but in susceptible individuals amiodarone may unmask autoimmune thyroid disease. Some effects of the drug suggest that it may interfere with the action of thyroid hormones at the cellular level, inducing a state of localized hypothyroidism.

Amiodarone and the thyroid

An antiarrhythmic drug, amiodarone, contains 37% iodine by weight and is structurally similar to the thyroid hormones. The drug inhibits hepatic 5'-deiodinase, resulting in increases in serum thyroxin and "reverse" triiodothyronine, whereas the concentration of triiodothyronine in serum is decreased. There is a significant incidence of either hypothyroidism or hyperthyroidism in patients who are being treated with the drug. This is largely the effect of iodine released from the drug during chronic therapy, but in susceptible individuals amiodarone may unmask autoimmune thyroid disease. Some effects of the drug suggest that it may interfere with the action of thyroid hormones at the cellular level, inducing a state of localized hypothyroidism.

Recycling of respiratory CO2 during Crassulacean acid metabolism: alleviation of photoinhibition in Pyrrosia piloselloides

The regulation of Crassulacean acid metabolism (CAM) in the fern Pyrrosia piloselloides (L.) Price was investigated in Singapore on two epiphytic populations acclimated to sun and shade conditions. The shade fronds were less succulent and had a higher chlorophyll content although the chlorophyll a:b ratio was lower and light compensation points and dark-respiration rates were reduced. Dawn-dusk variations in titratable acidity and carbohydrate pools were two to three times greater in fronds acclimated to high photosynthetically active radiation (PAR), although water deficits were also higher than in shade fronds. External and internal CO2 supply to attached fronds of the fern was varied so as to regulate the magnitude of CAM activity. A significant proportion of titratable acidity was derived from the refixation of respiratory CO2 (27% and 35% recycling for sun and shade populations, respectively), as measured directly under CO2-free conditions. Starch was shown to be the storage carbodydrate for CAM in Pyrrosia, with a stoichiometric reduction of "C3-skeleton" units in proportion to malic-acid accumulation. Measurements of photosynthetic O2 evolution under saturating CO2 were used to compare the light responses of sun and shade fronds for each CO2 supply regime, and also following the imposition of a photoinhibitory PAR treatment (1600 μmol·m(-2)·s(-1) for 3 h). Apparent quantum yield declined following the high-PAR treatment for sun- and shade-adapted plants, although for sun fronds CAM activity derived from respiratory CO2 prevented any further reduction in photosynthetic efficiency. Recycling of respiratory CO2 by shade plants could only partly prevent photoinhibitory damage. These observations provide experimental evidence that respiratory CO2 recycling, ubiquitous in CAM plants, may have developed so as to alleviate photoinhibition.

Crossover study of immunoglobulin replacement therapy in patients with low-grade B-cell tumors

A randomized crossover study of prophylactic immunoglobulin (IgG) therapy was performed in patients with chronic lymphocytic leukaemia (CLL) or non-Hodgkin's lymphoma (NHL). Twelve patients with hypogammaglobulinemia or a history of recurrent infections received infusions of IgG or placebo intravenously (IV) every 3 weeks for 1 year. They were then switched to the alternative preparation for another year. The number of serious bacterial infections was significantly less (P = .001; Mainland's cross-over method) in the months in which patients received IgG. Serious bacterial infections showed a trend to be associated with an IgG level less than 6.4 g/L (P = .046; Fisher's exact test).

A longitudinal study of thyroid function in pregnancy

We undertook a prospective longitudinal study of thyroid function in 36 pregnant women. There were significant increases in thyroxin-binding globulin, thyrotropin, and triiodothyronine. Albumin, free thyroxin (measured by an analog and a nonanalog method), and the free thyroxin index were significantly decreased. Results for the free thyroxin methods were correlated with each other in each trimester. We could find no evidence for artifacts related to albumin or thyroxin-binding globulin with either method for free thyroxin.

Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela: IV. Tillandsia flexuosa Sw. and Schomburgkia humboldtiana Reichb., epiphytic CAM plants

A comparison of the performance of two epiphytes with crassulacean acid metabolism (CAM) was made during the rainy season and dry season at the Ciénega el Ostional, Chichiriviche in northern Venezuela. The epiphytic bromeliad, Tillandsia flexuosa has water-retaining tanks and leaf trichomes, and propagates mainly vegetatively to produce large populations in the shrubby island vegetation. The epiphytic orchid, Schomburgkia humboldtiana formed smaller populations, and had large succulent leaves with uniform chlorenchyma and no distinct water-storage parenchyma, unlike T. flexuosa. Both epiphytes were myrmecophilous. Leaf succulence (kg m^-2 ) declined by ∼ 10% in the dry season for both plants. Both epiphytes showed reduced CO₂ uptake during Phase I (dark period) and (dawn-dusk) titratable acidity (ΔH⁺ ) in the dry season. Water-use efficiency (WUE) was higher for S. humboldtiana (16.0 × 10^-3 mol CO² per mol H² O compared with 5.0 × 10 ^-3 for T. flexuosa) although WUE remained constant during rainy and dry season for each species. Sixty to seventy per cent of the dawn dusk titratable acidity was derived internally from respiratory CO₂ (recycling) for both species, and in absolute terms, recycling decreased in the dry season, in contrast to the expected progression under drought stress. Recycling is an important facet of carbon balance for both species in both rainy and dry seasons. Leaf Na⁺ concentration was higher than values quoted for terrestrial salt stressed CAM plants. Fructose and glucose declined in leaf bases of T. flexuosa during the dark period, but not in the more distal regions of the leaf. S. humboldtiana showed a decrease in sucrose at night, and mannitol was also an important constituent of the leaves. Xylem sap tension maxima increased from 0.38 ± 0.09 MPa (rainy season) to only 0.55 ± 0.06 MPa (dry season) for T. flexuosa, these values being much lower than those found for terrestrial shrubs and herbs at the same site, the two epiphytes use CAM in conjunction with differing morphological adaptations to maintain growth throughout the year at the Ciénega el Ostional, but it would seem that T. flexuosa has better physiological characteristics for maintenance of carbon acquisition during the dry season.

Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela: V. The Batis maritime-Sesuvium portulacastrum vegetation unit

The perennial halophytes, Batis maritima L., Sesuvium portulacastrum L., and Portulaca rubricaulis H.B.K. which inhabit the extreme environment on parts of the salt plain and at the edges of the vegetation islands of Ciénega el Ostional were examined to determine their strategies for growth and survival in the rainy and dry seasons. All of the three species are leaf-succulents. High leaf-sap osmotic pressures, xylem tensions and Na⁺ and Cl^- levels indicated that S. portulacastrum and B. maritima are salt-accumulating halophytes. Succulence, leaf-sap osmolalities and Na⁺ and Cl^- levels increased in the dry season in B. maritima by a factor of 1.5-2.0 and in S. Portulacastrum by a factor of 1.9-2.7. B. maritima also accumulated sulphate with a two-fold increase of concentrations in the dry season. In S. portulacastrum Na⁺ accumulation much exceeded Cl^- accumulation and oxalate synthesis was found to serve charge balance. In this species the compatible solutes, proline and pinitol, were clearly detectable in both seasons; their levels increased by a factor of about 6 in the dry season. Exchange of water vapour and CO₂ was measured with a portable steady-state porometer. Photosynthesis in B. maritima showed little response to the transition from the rainy to the dry season while S. portulacastrum was severely impaired in the dry season, showing pronounced midday depressions of gas exchange and about 40% inhibition of light-saturated rates of CO₂ uptake. P. rubricaulis shed its leaves in the dry season. According to carbon isotope ratios (δ¹³ C), B. maritima (δ¹³ C =-26.4‰) and S. portulacastrum (δ¹³ C =-25.8 ‰) are C₃ plants while P. rubricaulis (δ¹³ C =-12.3‰) performed C⁴ photosynthesis.

A longitudinal study of thyroid function in pregnancy

We undertook a prospective longitudinal study of thyroid function in 36 pregnant women. There were significant increases in thyroxin-binding globulin, thyrotropin, and triiodothyronine. Albumin, free thyroxin (measured by an analog and a nonanalog method), and the free thyroxin index were significantly decreased. Results for the free thyroxin methods were correlated with each other in each trimester. We could find no evidence for artifacts related to albumin or thyroxin-binding globulin with either method for free thyroxin.

Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela: VI. Water relations and gas exchange of mangroves

Seasonal effects on leaf gas exchange and water relations were compared for Avicennia germinans, a true mangrove, and Conocarpus erectus, a mangrove associate, at coastal sites in northern Venezuela. On the Ciénega el Ostional at Chichiriviche, A. germinans was most abundant around lagoons on the seaward side of the vegetation-free alluvial sand plain. C. erectus was the dominant shrub in inland communities, but the two species co-occurred on vegetation islands at the landward edge of the alluvial plain. On the vegetation islands of the Ciénega el Ostional, gas exchange in A. germinans (a species with foliar salt glands) was less severely curtailed in the dry season compared with the rainy season than was gas exchange in C. erectus (a species lacking salt glands). Average rates of photosynthesis at near-saturating light intensities and total diurnal CO₂ uptake were reduced in the dry season to 69 and 61%, respectively, of their values in the rainy for A. germinans, but to 48 and 30%, respectively, of their rainy-season values for C. erectus. Similarly, stomatal conductance and transpirational water loss were more reduced in the dry season for C. erectus than for A. germinans, with the result that C. erectus showed a 3.4-fold increase in water-use efficiency in the dry season compared with the rainy season. The importance of the soil environment in determining plant gas-exchange Patterns was evidenced by large seasonal shifts in dawn xylem tension for the two species (which increased from 1.34 MPa in the rainy season to 5.50 MPa in the dry season for A. germinans, and from 0.40 to 5.78 MPa for C. erectus). These values reflected changes in the soil environment caused by inundation of the upper soil layers by fresh water in the rainy season and a progressive increase in salt concentrations (to almost twice those in sea water) by evaporation from the soil in the dry season. Large changes in xylem tension were observed for both species during individual day-night cycles, reaching a maximum of 2.36 MPa for A. germinans. For C. erectus, the magnitude of these day-night changes was greatly reduced in the dry season, consistent with its very low transpiration rates at this time of year. Leaf-cell osmotic pressures also tended to be higher in A. germinans than C. erectus (attaining a maximum of 8.3 MPa for A. germinans in the dry season), and were related to the more seaward distribution of the true mangrove on the alluvial plain. Whereas leaves of A. germinans did not show any changes in succulence, leaf succulence in C. erectus increased with leafage and was slightly higher in the dry season than the rainy season. The more succulent leaves also had higher cell-sap osmotic pressures and NaCl concentrations. The most succulent leaves of C. erectus were observed for exposed shrubs growing on the shoreline. During the dry season, these shoreline plants showed high rates of gas exchange and low values for dawn xylem tension (0.89 MPa), indicating that they had access to relatively non-saline water from the shallow water table. On individual plants, exposed shoots had more succulent leaves and higher osmotic pressure and NaCl concentrations than sheltered leaves, demonstrating the importance of foliar absorption of salt borne in sea spray for the ionic relations of C. erectus. Thus, although the distribution of C. erectus is centred on brackish-water zones, this species can apparently extend from habitats with permanent access to a shallow water table through to areas where it is seasonally exposed to low soil water potentials and high salt concentrations in the substratum.

A phantom for electrical impedance tomography

A method has been developed for constructing phantoms for electrical impedance tomography (EIT). A mesh of resistors is soldered to pins in a matrix board and forms a physical realisation of a finite element numerical model. To simulate different body tissues, changes in the apparent electrical conductivity and permittivity can be introduced at a particular location within the phantom by shunting the resistors in the mesh with additional resistors and capacitors. The phantom was used to test an EIT system employing phase-sensitive detection to separate the real and imaginary parts of the peripheral electric potentials. From the measurements images of conductivity and permittivity were reconstructed using an algorithm developed recently. The phantom has good mechanical strength and is electrically stable. The design could easily be reproduced and distributed to other centres developing similar EIT systems to enable testing on a common basis.

Effect of glucose loading on concentrations of chromium in plasma and urine of healthy adults

We report here a small study designed to identify the effect of a 75-g oral glucose load on concentrations of chromium in plasma and urine of apparently healthy volunteers. We detected a consistent and significant (P less than 0.01) decline in plasma chromium after glucose administration, the nadir of the chromium response coinciding with the zenith of the glucose concentration.

Effect of glucose loading on concentrations of chromium in plasma and urine of healthy adults

We report here a small study designed to identify the effect of a 75-g oral glucose load on concentrations of chromium in plasma and urine of apparently healthy volunteers. We detected a consistent and significant (P less than 0.01) decline in plasma chromium after glucose administration, the nadir of the chromium response coinciding with the zenith of the glucose concentration.

Applied potential tomography for non-invasive temperature mapping in hyperthermia

In the field of hyperthermia for cancer treatment, much effort is being put into the development of non-invasive temperature monitoring so that the trauma of implanting thermocouple or thermistor probes in the patient can be avoided. Preliminary studies investigating the use of applied potential tomography (APT) for this purpose have been reported. APT has the advantages over other tomographic methods that the instrumentation is inexpensive, transportable, and could easily be accommodated in a hyperthermia treatment environment. Moreover, the temperature coefficient of electrical conductivity is large (2% degrees C-1) compared, for example, with the corresponding quantity in CT, the x-ray attenuation coefficient, which changes by only 0.04% degrees C-1. In our experimental system, 16 electrodes were fixed around a cylindrical block of agar simulating a human thigh. The system was driven with 5 mA at 50 kHz. The agar was heated using the 13.56 MHz capacitive system currently in clinical use in this hospital. By relating data sets recorded at different times during heating to a set recorded before heating, images of the temperature change in the agar with time were computed and are presented. The experiment was then repeated in vivo on the thigh of a volunteer.

The importance of phase measurement in electrical impedance tomography

A method is described for reconstructing images of electrical conductivity and relative permittivity in electrical impedance tomography (applied potential tomography). The method relies on measurement of both the amplitude and the phase of the surface electric potential profile. The principle is demonstrated using a computer model to simulate measurements. The reconstructed images, referenced to homogeneous saline, agree qualitatively with the values of conductivity and permittivity used in the computer model. In addition, by displaying the imaginary part of the logarithm of the complex electrical conductivity, certain tissues, e.g. liver and kidney, are emphasised on the image. When the same parameter is displayed for simulated dual-frequency measurements, in which 150 kHz values are referenced against 100 kHz, liver and pancreas are emphasised. These results suggest the possibility of distinguishing between different types of soft tissue more effectively than if only signal amplitudes are measured. The phase changes in the simulated signals, on which the formation of such images depends, have a mean value of 13.3 degrees for the saline-referenced simulation but only 1.6 degrees for the dual-frequency simulation requiring accurate measurement in practice.

Immunogenic and antigenic epitopes of immunoglobulin--XX. Denaturation of human IgG3 by free radicals

It has previously been demonstrated that exposure of polyclonal IgG to free radicals results in denaturation evidenced by aggregation, auto-fluorescence and destruction of cysteine, proline and aromatic amino acids. In the present study we have used a panel of monoclonal antibodies (McAb) to epitopes expressed on the IgG3 heavy chain to detect changes in antigenicity. When IgG3 was exposed to u.v. irradiation, as a source of free radicals, subclass specific epitopes were rapidly lost whilst other epitopes were unaffected. Prolonged exposure resulted in further denaturation and a progressive loss of expression of further epitopes. The IgG3 subclass specific McAb are specific to epitopes localized to the hinge region of IgG3. Thus, this exposed cysteine and proline rich region is shown to be particularly vulnerable to free radical attack; however, prolonged exposure results in structural alterations throughout the heavy chain.

A dual-frequency applied potential tomography technique: computer simulations

Applied potential tomography has been discussed in relation to both static and dynamic imaging. We have investigated the feasibility of obtaining static images by measuring profiles at two frequencies of drive current to exploit the differing gradients of electrical conductivity with frequency for different tissues. This method has the advantages that no profile for the homogeneous medium is then needed, and the electrodes can be coupled directly to the skin. To demonstrate the principle, computer simulations have been carried out using published electrical parameters for mammalian tissues at frequencies of 100 and 150 kHz. The distribution of complex electric potentials was calculated by the successive over-relaxation method in two dimensions for an abdominal cross-section with 16 electrodes equally spaced around the surface. From the computed electrode potentials, images were reconstructed using a back-projection method (neglecting phase information). Liver and kidney appeared most distinctly on the image because of their comparatively large conductivity gradients. The perturbations in the electrode potential differences between the two frequencies had a mean value of 5%, requiring accurate measurement in a practical system, compared with 150% when the 100 kHz values were related to a simulation of homogeneous saline equal in conductivity to muscle. The perturbations could be increased by widening the separation of the frequencies. Static imaging using a dual-frequency technique appears to be feasible, but a more detailed consideration of the electrical properties of tissues is needed to determine the optimum choice of frequencies.

Serum creatine kinase-BB levels and cerebral cortical creatine kinase activity in senile dementia of the Alzheimer type

A rise in serum creatine kinase-BB (CK-BB) levels has been reported previously in cases of dementia. In the present study the levels of serum CK-BB have been measured in patients clinically assessed to have senile dementia of the Alzheimer's type (SDAT) and in cognitively intact individuals, matched for age, by a specific two-site monoclonal immunoradiometric assay. No significant difference was found between the 2 groups. Total creatine kinase activity in temporal cortex (Brodmann area 21 and 22) was also found to be similar in brains from SDAT or control cases, obtained at autopsy. These results suggest no major change in the permeability of the blood-brain barrier to this enzyme in SDAT patients.

A modified pharmacokinetic model for platinum disposition in ovarian cancer patients receiving cisplatin

We have fitted a first-order multicompartment pharmacokinetic model to plasma platinum concentrations measured in nine ovarian cancer patients who received intravenous infusions of cisplatin for 6 h. The time-course of ultrafilterable plasma platinum was similar in all patients studied, and was fitted by a single compartment within the limits of experimental detection. However, the time-course of protein-bound platinum showed marked differences between patients, the differences being explained by distribution to two peripheral compartments. The wide inter-patient variation observed in protein-bound plasma platinum concentrations supports the view that pharmacokinetic modelling should be carried out separately for each patient, since averaging plasma concentrations would have obscured some individual pharmacokinetic characteristics.

Specific absorption rate and tissue temperature in local hyperthermia

Specific absorption rate (SAR) and tissue temperature were measured for a total of 83 treatments in 33 patients who received local hyperthermia treatment for cancer. The patients were grouped into three categories according to tumor size. Hyperthermia was induced by 13.56 MHz electromagnetic energy applied using capacitive coupling. A method is described for evaluating SAR from the tissue temperature traces at any time in the treatment when a step change is made in applied power. The method is possible only if the temperature traces are free from interference and the total power delivered to the patient is monitored. Mean values of SAR ranged from 4.6 to 89 W kg-1 depending on the treatment site. Satisfactory heating was achieved for superficial tumors, with temperatures greater than 42 degrees C being recorded in 69% of treatments. For axillary nodes only 4% of treatments exceeded 42 degrees C. For cervix tumors an idealized tumor model was used to estimate tumor temperature from the temperature and SAR measured in the adjacent normal tissue. From the model it appears necessary either to raise the systemic temperature to 40 degrees C or to increase the SAR by at least a factor of 4 to obtain a temperature of 42 degrees C in a typical tumor. Measurements of SAR and temperature are essential for feedback control of computer models which, in principle, could provide a complete distribution of temperature during a hyperthermia treatment. Furthermore, measured SAR provides a direct comparison of the power deposition from different treatment machines in a clinical environment. The data presented form a basis for comparison with the clinical use of other heating systems.