Simultaneous electrical impedance tomography and videofluoroscopy in the assessment of swallowing

Simultaneous videofluoroscopy and electrical impedance tomography (EIT) were performed in 13 patients. Subjects swallowed a low-conductivity and a higher-conductivity bolus of between 5 and 20 ml. EIT images from the two swallows were then subtracted to cancel out movement related changes. The peak in the conductivity change was most closely associated in time with a point at which the pharynx is filled with bolus: this suggests that the subtraction process does produce data and images which are related to the bolus rather than to movement of involved structures. The full width at 50% and 75% of the maximum of the time conductivity plot was correlated with the time taken for the bolus to be cleared from the mouth (r = 0.63 and 0.68 respectively, p < 0.05 for both). Despite the sampling frequency of only 9 frames s-1, compared to 50 frames s-1 for videofluoroscopy, EIT recordings from the neck are able to detect the presence of a conductive bolus in the pharynx and for the first time the relationship between parameters of an EIT time-conductivity plot and a measure of bolus transit using an accepted technique has been established.

Antibody responses and symptoms after DTP and either tetanus or diphtheria Haemophilus influenzae type B conjugate vaccines given for primary immunisation by separate or mixed injection

The safety and immunogenicity of two conjugate Haemophilus influenzae type B (Hib) vaccines administered either mixed with, or in separate limbs to, a whole-cell DTP vaccine, was compared in infants vaccinated at 2, 3 and 4 months of age. Antibody titres to purified polyribosylribitol phosphate, diphtheria, and to pertussis antigens between infants who received the Hib and DPT vaccines in separate limbs or in the same limbs were similar (P > 0.1) while antibody titres to tetanus toxoid were higher in the later group (P < 0.05). This study demonstrated that both Hib vaccines can be mixed with whole-cell DTP vaccine without reducing immunogenicity of either vaccine or increasing the incidence of adverse reactions.

Tissue spectroscopy with electrical impedance tomography: computer simulations

A method is proposed by which bioelectrical spectroscopy could be combined with electrical impedance tomography (EIT) to provide noninvasive characterization of tissue. Multifrequency (2-200 kHz) EIT measurements were simulated with a numerical model for a volume of porcine liver immersed in an electrolytic tank. From the reconstructed EIT images the tissue characterization method was then applied enabling a plot of complex resistivity to be drawn for any selected pixel in the image. Simulations were performed for a small volume of degraded tissue embedded in the normal tissue to examine its effect on the derived spectroscopic parameters. The method could have an application in transplant surgery for screening organs for tissue degradation.

A Cole phantom for EIT

A phantom was designed for testing and comparing multifrequency EIT data collection systems. The phantom simulates a cylinder of homogeneous conductor with 16 drive and 16 receive electrodes interleaved. Combinations of resistors and capacitors were used to simulate the complex impedance, Z*, of a typical tissue in the frequency range 8-2048 kHz obeying the Cole equation Z* = Z infinity + (Z0 - Z infinity)/[1 + (if/fc)(1- alpha )] where Z* is the complex impedance at frequency f, Z0 and Z infinity are the limiting values of impedance at low and high frequencies, fc is the characteristic frequency and alpha is a constant. A practical phantom was then constructed on which four different sets of spectroscopic parameters could be selected: (i) alpha = 0.20, fc = 150 kHz, Z0/Z infinity = 3.31; (ii) alpha = 0, fc = 273 kHz, Z0/Z infinity = 2.64; (iii) alpha = 0, fc = 71.1 kHz, Z0/Z infinity = 1.36; and (iv) Z0/Z infinity = 1.00 with no dispersion.

The repeatability and variability of electrical impedance tomography indices of pharyngeal transit time in normal adults

Two electrical impedance tomography (EIT) indices of pharyngeal transit time have been repeatedly measured in 20 normal adults. The time course of change in pharyngeal conductivity whilst swallowing 5, 10 and 20 ml boluses was expressed either as a full width at 20% maximum (FW20) or as a full width at 50% maximum (FW50): the latter could be satisfactorily measured more frequently. Mean coefficients of variation for FW20 and FW50 tended to decrease with increasing bolus volume but this was statistically significant only for FW50 in men. FW20 and FW50 were significantly shorter in men than women and increased with increasing age. FW50 was significantly smaller when larger bolus volumes were swallowed. FW50 was significantly shorter when low-conductivity fluid was used and there was an insignificant trend for it to be longer with electrodes in the highest position. The amplitude of the conductivity change recorded was significantly affected by all factors studied apart from age. If EIT is to be used as a technique for monitoring changes in pharyngeal transit time in patients with neurogenic dysphagia, repeat examinations should be performed under the same conditions and, if possible, large bolus volumes should be used.

Avidity of specific IgG antibodies elicited by immunisation against Haemophilus influenzae type b

AIM

To investigate the avidity of specific IgG polyribosyl ribitol phosphate (PRP) antibodies induced by three Haemophilus influenzae type b (Hib) conjugate vaccines: PRP-meningococcal outer membrane protein complex (PRP-OMP), PRP-non-toxic mutant diphtheria toxin, CRM197 (HbOC) and PRP-tetanus toxoid (PRP-T).

METHODS

One hundred and ten infants were immunised with one of the vaccines at two, three and four months of age. Blood samples were taken after each vaccination and serum stored at -20 degrees C. Serum samples collected after the third course (that is, at five months of age) were submitted to antibody avidity assessment, using a urea enzyme linked immunosorbent assay (ELISA).

RESULTS

All three conjugate vaccines elicited IgG PRP antibodies of high median avidity. The resultant antibody populations were heterogeneous with regard to avidity, which in turn was independent of PRP antibody concentration.

CONCLUSIONS

With the recent findings of a correlation between bactericidal killing and affinity, our data highlight the need for a protective level to be expressed qualitatively as well as quantitatively.

Immunological factors and risk of infection in plateau phase myeloma

AIMS

A series of patients with myeloma were investigated to assess whether immunological risk factors predisposing to serious infection could be identified.

METHODS

Patients (n = 102) with predominantly plateau phase myeloma were monitored prospectively for infections. Immunological parameters including total non-paraprotein immunoglobulins and specific antibody titres were measured in all patients and compared with a control population of healthy individuals of a similar age; response to immunisation with Pneumovax II, tetanus and diphtheria toxoids and IgG subclasses were measured in a subgroup of 41 patients. Other characteristics investigated for any association with infection included age, sex, paraprotein type, disease stage, and chemotherapy.

RESULTS

Specific antibody titres to pneumococcal capsular polysaccharides and tetanus and diphtheria toxoids were significantly reduced compared with the control population. Low antipneumococcal and anti Escherichia coli titres correlated with risk of serious infection and low anti-pneumococcal titres with severity of non-paraprotein immunosuppression. In 41 immunised patients responses to Pneumovax II, tetanus and diphtheria toxoids were poor; IgG subclass levels were significantly reduced and a poor IgG response to Pneumovax II immunisation was associated with an increased risk of septicaemia and low IgG2 levels. The overall serious infection rate was 0.92 infections per patient year and was four times higher during periods of active disease (1.90) compared with plateau phase myeloma (0.49). The predominant site of infection was the respiratory tract. Clinical and laboratory parameters showed only male sex and reduced non-paraprotein IgG and IgA levels to be significantly associated with at least one serious infection.

CONCLUSIONS

A subgroup of patients with myeloma with poor IgG responses to exogenous antigens, who are at increased risk of serious infection, can be identified and may benefit from replacement immunoglobulin therapy to reduce the risk of infection.

Antibody responses to Haemophilus influenzae type b and Streptococcus pneumoniae vaccines in children with human immunodeficiency virus infection

Antibody responses to Haemophilus influenzae type b (Hib) conjugate (ActHIB; Pasteur Merieux) and pneumococcal (Pneumovax II; Morson) vaccines were measured in 56 infected children (VI) and 44 uninfected children (U) older than 18 months of age, born to human immunodeficiency virus-positive mothers. Preimmunization, 21% U and 20% VI had protective concentrations of anti-Hib polysaccharide antibodies. Postimmunization, 100% U and 86% VI achieved protective titers (P = 0.008). The geometric mean increase in anti-Hib polysaccharide antibody was 7.6 (95% confidence interval, 3.5 to 16.3; P = 0.0001) times higher in U than in VI children after adjusting for age and ethnicity. Sixty-one percent U compared to 54% VI showed a 2-fold increase in antibody levels to at least one of the four pneumococcal vaccine serotypes (3, 6, 19, 23) measured (P = 0.4). For both vaccines there was a significant trend toward poorer responses in children with acquired immunodeficiency syndrome but no correlation with age adjusted CD4 counts. These data suggest that human immunodeficiency virus-infected children should be immunized with these polysaccharide vaccines early in the course of their disease.

Haematological and acute-phase responses associated with delayed-onset muscle soreness in humans

Delayed-onset muscle soreness following unaccustomed or eccentric exercise is associated with inflammation, tissue necrosis and the release of muscle enzymes (Newham et al. 1983). We have investigated the time course of changes in circulating leucocytes and serum levels of some acute phase reactants, serum creatine kinase activity (CK) and muscle pain after a 40-min bout of bench-stepping exercise in eight healthy untrained subjects. Leg muscle soreness was greatest 2 days after the exercise bout. Peak serum CK values [mean (SD) 540 (502) IU.1-1] occurred 1-7 days post-exercise. Serum C-reactive protein (CRP) was unchanged from pre-exercise levels [7.8 (3.4) mg.1-1] immediately post-exercise [7.9 (2.3) mg.1-1] but rose to a peak of 17.0 (3.9) mg.1-1 1 day post-exercise, thereafter declining to basal levels. Serum levels of iron and zinc fell below pre-exercise levels for 1-3 days post-exercise. Serum albumin, IgG and IgM fell below pre-exercise levels from 1 day post-exercise, reaching minimal values (about 80% of basal levels) at 7 days post-exercise. The exercise did not appear to significantly affect serum levels of alpha-1-antitrypsin and alpha-1-acid glycoprotein. Two and three days after the exercise bout the circulating numbers of total leucocytes, neutrophils, monocytes and basophils fell 15-20% below pre-exercise levels, whereas lymphocytes, eosinophils and platelets were unchanged. The results indicate that a rapid acute phase inflammatory response is initiated within 1 day of a bout of exercise that induces delayed-onset muscle soreness, and that any later tissue necrosis that may occur is not accompanied by further marked changes in acute-phase reactants such as CRP.

A dosing scheme for carboplatin in adult cancer patients based upon pre-infusion renal function and platelet count

The most important risk factors for the development of carboplatin-induced thrombocytopenia are total dose, glomerular filtration rate (GFR) and pre-infusion platelet count (P0). Pharmacokinetic and toxicity data from 23 patients with ovarian or testicular cancer were combined with published values from four other centers and the relationships between plasma clearance of ultrafilterable platinum and GFR, and between percentage reduction in platelet count and area under the plasma platinum curve were determined. The scatter in the data was estimated and used in a Monte-Carlo computer simulation to derive the following five-level dosing scheme. [table: see text] The scheme is based on 5% of patients incurring grade IV thrombocytopenia. Using this scheme, the majority of patients with ovarian or testicular cancer receiving carboplatin will be given an initial dose of 900 mg.

Carbon-Isotope Composition of Biochemical Fractions and the Regulation of Carbon Balance in Leaves of the C3-Crassulacean Acid Metabolism Intermediate Clusia minor L. Growing in Trinidad

Carbon-isotope ratios ([delta]13Cs) were measured for various bio-chemical fractions quantitatively extracted from naturally exposed and shaded leaves of the C3-Crassulacean acid metabolism (CAM) intermediate Clusia minor, sampled at dawn and dusk on days during the wet and dry seasons in Trinidad. As the activity of CAM increased in response to decreased availability of water and higher photon flux density, organic acids and soluble sugars were enriched in 13C by approximately 3.5 to 4%[per mille (thousand) sign] compared to plants sampled during the wet season. The induction of CAM was accompanied by a doubling in size of the reserve carbohydrate pools. Moreover, stoichiometric measurements indicated that degradation of both chloroplastic reserves and soluble sugars were necessary to supply phosphoenolpyruvate for the synthesis of organic acids at night. Results also suggest that two pools of soluble sugars exist in leaves of C. minor that perform CAM, one a vacuolar pool enriched in 13C and the second a transport pool depleted in 13C. Estimates of carbon-isotope discrimination expressed during CAM, derived from the trafficking among inorganic carbon, organic acids, and carbohydrate pools overnight, ranged from 0.9 to 3.1%[per mille (thousand) sign]. The [delta]13C of structural material did not change significantly between wet and dry seasons, indicating that most of the carbon used in growth was derived from C3 carboxylation.

Binding of anti-DNA antibodies to oxidatively damaged DNA in spouses and relatives of patients with systemic lupus erythematosus

The prevalence of serum anti-DNA antibodies was evaluated by ELISA using oxidatively damaged DNA as antigen in 21 patients with systemic lupus erythematosus (SLE), in 9 spouses and in 15 first-degree relatives. These were compared with 12 healthy controls. There was no significant difference in the levels of serum antibodies detected between the group of spouses and normal controls with all results within the normal range of the assay. Binding of serum antibodies to the oxidatively damaged DNA was detectable in 12 (80%) of the relatives studied, and the range of values obtained overlapped significantly with the SLE patient group. The relevance of these antibodies to the immunopathology of SLE is unclear since they appear to be present in the absence of any clinical symptoms. However, they may be useful predictively as a marker for those individuals who are more likely to develop SLE.

An analysis of studies comparing electrical impedance tomography with x-ray videofluoroscopy in the assessment of swallowing

Electrical impedance tomography can be used to record the conductivity change occurring in the neck during a swallow. X-ray videofluoroscopy provides excellent anatomical detail of the structures involved in swallowing and of the position of the swallowed bolus. The two techniques have been performed simultaneously on seven patients with swallowing problems to establish what produces the peak change in conductivity when a solution of low conductivity is swallowed. The results suggest that the exclusion of air from the larynx and pharynx is the major factor influencing the change in conductivity when a solution of low conductivity is swallowed.

Bioelectrical spectroscopy from multi-frequency EIT

A method is described by which bioelectrical spectroscopy could be combined with multi-frequency electrical impedance tomography (EIT) enabling a Cole-Cole plot to be drawn for any selected pixel in the image for tissue characterization. To demonstrate the principles of the method, multi-frequency EIT measurements were simulated with a numerical model. As an example, porcine myocardium, immersed in an electrolytic tank, was simulated for a frequency range of 20 kHz to 2 MHz. The method could have an important application in transplant surgery for screening organs for viability prior to transplant.

The incidence of deep-vein thrombosis after upper tibial osteotomy. A venographic study

We performed postoperative venography on 84 consecutive patients who had undergone upper tibial osteotomy for medial compartment osteoarthritis of the knee. Deep-vein thrombosis was demonstrated in 41%. Only 15% of the cases were diagnosed clinically, all in the calf veins. Cases of proximal thromboses (3) and mixed-vein thromboses (12) were only revealed by venography.

Haemophilus influenzae type b carriage and immunity four years after receiving the Haemophilus influenzae oligosaccharide-CRM197 (HbOC) conjugate vaccine

Late in 1991, before the implementation of a national immunization program against Haemophilus influenzae type b (Hib) in the United Kingdom, we performed a 4-year follow-up of 120 children who in 1987 had been enrolled in an immunogenicity trial in which 60 of them (vaccinees) received an Hib conjugate vaccine (HbOC) at the same time as diphtheria-tetanus toxoid-pertussis vaccine at the ages of 3, 5 and 9 months. Sixty others (controls) received only diphtheria-tetanus toxoid-pertussis vaccine at the same ages and were not subsequently immunized against Hib. We investigated Hib pharyngeal colonization using the antiserum agar method and the concentrations of serum IgG antibody to the type b capsule by enzyme-linked immunosorbent assay. At 4 years of age the Hib colonization rates in vaccinees and controls were 8% (5 of 60) and 5% (3 of 60), respectively. The children colonized with Hib had greater serum anti-capsular IgG concentrations than did noncolonized children (P < 0.001), and colonized vaccinees tended to have higher concentrations than colonized controls (P = 0.053). Regardless of Hib colonization status vaccinees had greater antibody concentrations than controls (P < 0.001). Forty-nine percent of vaccinees had an antibody concentration > 1 microgram/ml. There was an inverse relationship between the Hib colony count on culture and the serum IgG concentration. These data indicate that the increase in serum antibody concentration after immunization with an Hib conjugate vaccine is sustained and that immunization primes for a booster response on exposure to Hib. There may be a relationship between previous Hib conjugate immunization and the density of Hib colonization in children.

Actions of extracellular chloride ion substitution on contractility of isolated ventricular myocardium

OBJECTIVE

Replacement of extracellular chloride ions by some other anions exerts a positive inotropic effect on isolated cardiac muscle preparations. The aim of this study was to determine whether the increase of force was mediated by an intracellular alkalosis.

METHODS

Isometric tension development was measured using guinea pig papillary muscles during replacement of superfusate Cl- with isethionate ions. Intracellular pH and L-type Ca2+ currents were measured in isolated myocytes using epifluorescence microscopy and a switch-clamp technique respectively.

RESULTS

Reduction of extracellular Cl- increased tension, a phenomenon which was partially inhibited with the anion exchange blocker SITS. Force was also increased by reducing superfusate PCO2. Reduction of superfusate [Cl-] and PCO2 both produced concentration dependent intracellular alkalosis. The relationship between the changes to tension and intracellular pH was different when either the superfusate [Cl-] or PCO2 was reduced, less pronounced when the [Cl-] was reduced. An increase of the L-type Ca2+ current was produced in low [Cl-] solutions which could be attributed to the accompanying intracellular alkalosis.

CONCLUSIONS

The positive inotropic effect of superfusate Cl- removal can only partially be explained by intracellular alkalosis. Other, as yet unknown, changes must determine the remainder of the inotropic response.

Morphologic changes in the human patellar tendon after bone-tendon-bone anterior cruciate ligament reconstruction

Magnetic resonance imaging (MRI) was performed on 15 patients, an average of 2.5 years after arthroscopically assisted bone-tendon-bone (BTB) anterior cruciate ligament (ACL) reconstruction, to evaluate the patellar tendon donor site. Five patients who had arthroscopically assisted ACL reconstruction using the semitendinosus tendon as a graft also were scanned bilaterally and evaluated. The mean difference between the involved and uninvolved patellar tendon length was -0.2 mm for the BTB patients and -2.6 mm for the semitendinosus patients. The mean difference between patellar tendon width for the BTB patients was 1.1 mm and 1.9 mm for the semitendinosus patients. The mean difference between patellar tendon thickness was 0.4 mm for the BTB surgery group and 0.02 mm for the semitendinosus surgery group. None of the differences were statistically significant. Results indicate that harvesting the central one third of the patellar tendon does not significantly affect the length, width, or thickness of the tendon at least 22 months after arthroscopically assisted BTB-ACL.

Effect of beta propiolactone on specific antibody measurements by ELISA

Serum samples from 30 HIV seronegative patients were treated with beta propiolactone (BPL) to determine whether BPL interfaces with ELISA for specific antibodies against protein and carbohydrate antigens. BPL had no discernible effect on specific antibody measurements by ELISA. With the measuring need for specific antibody measurements in the management of HIV seropositive patients, it is reassuring that this laboratory safety measure does not impair the reliability of results.

An investigation into the role of reactive oxygen species in the mechanism of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity using neuronal cell lines

The study of oxygen radical generation and effects during 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) metabolism was undertaken in an in vitro test system. Three neurochemically discrete neuronal cell lines, B50 (cholinergic) and B65 rat cell lines and SKNSH human neuroblastoma (both catecholaminergic), were exposed to MPTP (0-200 microM). Parallel experiments were performed using reagent H2O2, an intermediate which may be generated during MPTP metabolism, to determine whether MPTP and H2O2 had any selectivity of toxicity and whether the mechanisms of cell death were similar. MPTP toxicity was shown to be reduced by monoamine oxidase B inhibitors, pargyline (P < 0.01) and selegiline (P < 0.05), indicating that toxicity was due to metabolism of MPTP rather than the parent compound. Cytotoxicity was also decreased in the presence of antioxidants, most notably in the presence of superoxide dismutase and catalase together (P < 0.01), suggesting that reactive oxygen species (ROS) play a role in MPTP-induced cell death. Attempts to determine the intracellular target for oxidative attack did not identify significant levels of lipid peroxidation products, but did demonstrate nucleoid expansion, possibly the result of double stranded DNA breaks induced by ROS.

Dentine hypersensitivity: the measurement in vitro of streaming potentials with fluid flow across dentine and hydroxyapatite

Stimulus transmission across dentine, in conditions such as dentine hypersensitivity, is considered to occur via a hydrodynamic mechanism. This fluid flow in dentine may then induce a mechanoreceptor response in pulpal nerves. However, when fluid flows through a porous structure electrical potentials are also generated. The aim of this study was to develop a reproducible model system to measure streaming potential across dentine and hydroxyapatite and determine the influence of pressure. Using an acrylic cell, with silver electrodes, streaming potentials were recorded across dimensionally standardized dentine and hydroxyapatite specimens, over a pressure range of 1-6 atmospheres. Streaming potentials were found to be directly proportional to pressure and dependent on the electrical conductivity of the saline used in the cell. The results confirm the limited existing data on streaming potentials across dentine and indicate that at these low pressures excitation of pulpal nerves would not occur. However, if, as may be the case, stimuli applied to dentine create very high pressures, the resultant potentials generated could indeed evoke a neural response. The model system is worthy of further use to study this phenomenon and the factors which may influence it.

Imaging the complex impedance of the thorax

Respiration-related changes in the complex impedance were obtained on the thorax in three volunteers. The real part of the image clearly showed the lungs as regions of increased conductivity on expiration. The imaginary part of the image, reflecting changes in the ratio of permittivity to conductivity, showed a central negative region surrounded by a positive region extending to the periphery of the lungs. These features may be due to movement of the diaphragm and liver within the sensitive volume during respiration.

Measurement of pharyngeal transit time by electrical impedance tomography

The feasibility of using electrical impedance tomography (EIT) for measuring pharyngeal transit time has been investigated. Imaging sequences were obtained on the neck in a group of eight healthy subjects when swallowing solutions of different electrical conductivities. The solutions used were aqueous Dioralyte (1.5 S m-1) and tap water (0.04 S m-1). The effects of movement upon the images were large compared with the changes due to the solutions, but these were cancelled by a subtraction technique. The mean value of the EIT pharyngeal transit time parameter was 370 +/- 120 ms. EIT has the advantage that repeated measurements could be performed without fear of hazard in contrast to the established technique of video fluoroscopy which involves ionising

On the ecophysiology of the Clusiaceae in Trinidad: expression of CAM in Clusia minor L. during the transition from wet to dry season and characterization of three endemic species

A study was made of photosynthesis and expression of crassulacean acid metabolism (CAM) in naturally exposed and shaded populations of Clusia minor L. during the transition from wet to dry season in Trinidad (mid-February to mid-April, 1990). At the start of the dry season, plants from exposed and shaded habitats showed a capacity for CAM either through the fixation of external or internal (respiratory) CO₂ . Exposed plants showed continuous uptake of CO₂ over 24 h although dark fixation accounted for only a small proportion of CO₂ fixed over the day. The expression of CAM was considerably enhanced as the dry season progressed with substantial increases in the overnight accumulation of titratable acidity, particularly in leaves of exposed plants. This was accompanied by a reduction in day-time photosynthesis and an increase in dark fixation, with shaded plants showing only night-time fixation of CO₂ . The magnitude of CAM in C. minor was substantial with a maximum ΔH⁺ of 1410 mol m^-3 measured in leaves from exposed branches. Both malic and citric acids were accumulated overnight. The highest citric:malic acid ratios were found in young leaves from exposed plants with 250 mol m^-3 malic and 125 mol m^-3 citric acid accumulated near the time of maximum CAM activity. Photosynthetic efficiency, measured as light responses of O₂ evolution, also varied on a daily basis dependent on the incident photosynthetic photon flux density (PPFD). Apparent quantum yield and photosynthetic capacity showed marked reductions depending on the degree of exposure, suggesting that photoinhibitory responses are important under natural conditions. An analysis of three members of the Clusiaceae endemic to Trinidad showed that each had the capacity to induce CAM activity, despite being found in a narrow range of habitats which have higher rainfall than those of C. minor. However, despite the variable expression of CAM activity, carbon isotope composition suggested that when integrated throughout the year, carbon accumulation is predominantly mediated via the C₃ pathway in all the species studied.

Predictors of infection in chronic lymphocytic leukaemia (CLL)

A group of patients with chronic lymphocytic leukaemia (CLL) were studied to determine whether particular clinical and laboratory parameters might help to identify those patients at risk of recurrent infection who would benefit from immunoglobulin replacement therapy. The case notes of 59 patients were reviewed with regard to stage and duration of disease, chemotherapy and frequency of infection over the preceding 2 years. Serum IgG levels and specific antibodies to tetanus, diphtheria and pneumococcal capsular polysaccharide were measured at the end of the 2-year period. A group of 56 healthy age-matched volunteers were used as controls. Eighteen patients had severe or multiple infections during the study period, 11 patients had recurrent infections and the remaining 30 patients had only minimal infections. Overall, serum IgG levels were low in 32 patients but in none of the control group (P = 8.8 x 10(-11). However, less than half of those patients with hypogammaglobulinaemia suffered from severe or multiple infections. Specific antibodies to pneumococcal capsular polysaccharide were low in 23 patients compared with six of the control group (P = 4.9 x 10(-4)). The majority of patients with severe or multiple infections (13/18) had low levels of both total IgG and specific antibodies to pneumococcal capsular polysaccharide. However, in the groups of patients with less frequent infections, a higher proportion had low serum IgG than low pneumococcal antibody levels. Low levels of pneumococcal antibodies were particularly associated with severe or multiple infections (P = less than 0.00001).

Labelling and illness in primary care: comparing factors influencing general practitioners' and psychiatrists' decisions regarding patient referral to mental illness services

GPs and psychiatrists from South Wales were asked to make decisions based on the information included in each of 16 vignettes describing depressed and anxious subjects. This information contained randomly assigned sex, psychiatric label, good and bad psychosocial context and age as well as eight different severity ratings of depression and anxiety symptoms. Our results showed that both GPs and psychiatrists were influenced in their decision making by the severity of the illness, but that GPs alone were also strongly influenced by the presence of male sex and by the presence of a psychiatric label. Good or bad psychosocial context had no influence on the GPs' referral decision, and previous experience in psychiatry or other vocational training had no detectable effect, but this may be because of the sample size.

Comparison of methods for the determination of unbound triiodothyronine in pregnancy

OBJECTIVE

To study the changes in unbound T3 concentration in the first trimester of pregnancy.

DESIGN

We measured serum unbound T3 concentration before and after termination of pregnancy.

PATIENTS

Twenty-six clinically euthyroid women.

MEASUREMENTS

We used one non-analogue assay (Sclavo) and three analogue assays (Amersham, Becton Dickinson and Diagnostic Products Corporation).

RESULTS

Regression analysis did not show any significant agreement between the analogue and non-analogue assays. After termination of pregnancy, unbound T3 concentration as measured by Sclavo and Amersham assays did not change whereas unbound T3 concentration increased and decreased as measured by Becton Dickinson and Diagnostic Products assays respectively. Changes were not directly related to albumin or thyroid binding globulin.

CONCLUSION

We believe unbound T3 concentrations as measured by the analogue assays used in this study are due to a balance of errors and cannot be used to determine true physiological changes in pregnancy.

Immunogenicity and safety of PRP-T conjugate vaccine given according to the British accelerated immunisation schedule

The immunogenicity and safety of a new Haemophilus influenzae type b conjugate vaccine, PRP-T, was studied in 107 infants from the Oxford district. The vaccine was given concurrently with diphtheria, pertussis, tetanus, and polio vaccines at 2, 3, and 4 months of age. Symptoms after immunisation were recorded by a parent. Sera were obtained before the first immunisation and at 5 months of age and the antibodies were measured by both radioimmunoassay and enzyme linked immunosorbent assay (ELISA). No serious adverse reactions were observed and there was no increase in the incidence of expected minor side effects. By radioimmunoassay, the geometric mean titre of serum anticapsular antibody increased from 0.09 micrograms/ml before immunisation to 5.01 micrograms/ml after three immunisations. Ninety eight per cent of children had antibody concentrations consistent with protection (greater than or equal to 0.15 micrograms/ml). IgG antibody concentrations measured by ELISA correlated well with total antibody concentrations measured by radioimmunoassay (r = 0.864). These results provide encouragement that routine immunisation against H influenzae type b at 2, 3, and 4 months of age, could prevent most cases of disease in children in the UK.

Immunogenicity of combined diphtheria, tetanus, and pertussis vaccine given at 2, 3, and 4 months versus 3, 5, and 9 months of age

In the UK an accelerated schedule for immunisation against diphtheria, tetanus, and pertussis (injections at 2, 3, and 4 months of age) was introduced in 1990 to replace the more widely spaced schedule of 3, 5, and 9 months. There is concern, however, that the new schedule may be less immunogenic and therefore less protective than the old schedule. We have measured serum concentrations of antibodies against diphtheria, pertussis, and tetanus in infants immunised according to the two regimens. Both schedules resulted in protective concentrations of antibody against tetanus and diphtheria and in satisfactory antibody responses to three pertussis antigens (filamentous haemagglutinin, pertussis toxin, fimbriae). However, immunisation by the old schedule led to significantly higher antibody concentrations against both diphtheria and tetanus than did immunisation by the new schedule (p less than 0.01). In infants immunised with the new schedule, postimmunisation antibody concentrations against tetanus toxoid and against two pertussis antigens (pertussis toxin and fimbriae) were significantly lower in infants in whom preimmunisation (maternally derived) antibody concentrations were high (p less than 0.02). The findings suggest that with an accelerated immunisation schedule maternal antibodies can have an inhibitory effect on the responses to immunisation against tetanus and pertussis.

Human chorionic gonadotropin may not be responsible for thyroid-stimulating activity in normal pregnancy serum

Although hCG can activate thyroid cells in culture there is considerable doubt as to whether it is responsible for the changes in thyroid function which occur during normal pregnancy. Thyroid-stimulating activity (TSA), measured using iodide uptake into FRTL-5 cells, was demonstrated in 32/51 (63%) first and 15/29 (52%) third trimester sera. Free T3 was increased (P less than 0.001) and TSH decreased (P less than 0.01) in first trimester. In the early pregnancy group there was a positive correlation between hCG and TSA (r = 0.594, P less than 0.001) and a negative correlation between hCG and TSH (r = -0.329, P less than 0.02). In third trimester hCG concentration was often below that required to produce TSA in vitro and TSA could not be neutralized by antibodies to hCG. There was no correlation between hCG and TSH or thyroid hormones in the third trimester. In 26 women TSA decreased in parallel with serum hCG concentration after termination of pregnancy (P less than 0.001). Free T3 also decreased (P less than 0.01) and TSH increased (P less than 0.05) after termination. TSA persisted in many patients even after hCG was either very low or undetectable. Purified hCG stimulated iodide uptake in a concentration-dependent manner. Stimulation of iodide uptake by TSH was inhibited by the simultaneous presence of low concentrations of hCG while activity was restored with high concentrations. hCG may contribute to the thyroid changes in early pregnancy. However the poor correlation between TSA and thyroid tests suggests that other factors may be involved. The partial agonist activity of hCG may account for some of the inconsistencies observed but TSA in serum from late pregnancy or after termination of pregnancy is almost certainly due to another hormone or growth factor.