Biomonitoring of aromatic amines and alkylating agents by measuring hemoglobin adducts

Summary Analysis of hemoglobin adducts in blood samples is suitable for the biological monitoring of genotoxic chemicals. The method is specific because the compound to which the individual was exposed is identified. The sensitivity of the method depends on the analytical procedure applied, but is hardly limiting since large amounts of the protein can be obtained. The method provides not only information about the internal exposure to the environmental chemical, but also about the individual's capacity to generate ultimate genotoxic metabolites from it. Since macromolecular damage in blood cells is correlated to that in potential target tissues, this information is relevant to risk assessment, insofar as macromolecular damage produced by a specific chemical can be correlated with the development of tumors.     

A master curve for tensile properties of thermoplastics

Ultimate mechanical properties of polymers can be characterized by a dimensionless Hooke number He ≡ σ_b/(E?_b), where σ_b is the ultimate tensile strength, E the tensile modulus, and ?_b the elongation at break. Hooke numbers are found to be a smooth function of ultimate elongations, independent of the chemical and physical structure of common thermoplastics. This master curve for fracture strengths and elongations can be described by He = [1 + (?_b/?_crit)^ab]^?1/b with empirically found parameters ?_crit = 0,0168, a = 0,918, and b ≈ 4. The decrease of He with increasing ?_b at ?_b > ?_crit reflects the shear flow on deformation. Hooke numbers depend on entanglement densities v_e according to He = 1,285·10³⁶ (v_e/cm^?3)^?1,846 for v_e > 3,65·10¹⁹ cm^?3. A correction for additional segment orientation during tensile testing brings the exponent to ?1,846/0,918 = ?2,01; i. e., a dependence of Hooke numbers on the reciprocal square of entanglement densities.     

A nonlinear model of the arterial vessels within a limb segment

The relationship between the arterial blood pressure and the volume of the arteries within a segment of an extremity is nonlinear. The present paper shows how the flow and volume pulsations of the arteries within a limb segment can be simulated taking this property into account. An electrical model was constructed comprising one resistor and two voltage dependent ‘capacitors’, the latter corresponding to the pressure dependent elasticity, or compliance, of the arteries. Adequate simulations were obtained over a wide pressure range, which is impossible with linear models. The nonlinear, i.e. pressure dependent, relationship between the volume and pressure of arteries, observed under static conditions, must also be taken into consideration when studying pulsatile events with models whether mathematical or physical.     

Crystallization in the nephron

Recent experimental studies on the crystallization of calcium salts at different nephron levels support the theory that the initial formation of calcium concrements starts with an intratubular crystallization of calcium phosphate (CaP) and calcium oxalate (CaOx). CaP seems to be the initial crystallization product in pure CaP and mixed calcium phosphate–calcium oxalate (CaPCaOx) concrements, with the formation of CaP crystals at a nephron level above the collecting duct. Urinary macromolecules and cellular degradation products most probably promote this process. During the passage through the collecting duct, CaP might partly or completely dissolve at the lower pH encountered there. This might result in an increased concentration of calcium and hence an increased supersaturation with CaOx, which in turn can bring about a heterogeneous nucleation of CaOx on or around preformed CaP crystals or crystal aggregates. The final result will be mixed CaOxCaP or pure CaOx concrements. Pure CaOx concrements might also be the result of an initial CaOx crystallization at nephron levels above or in the collecting duct under conditions with a high urinary excretion of oxalate. Whether intratubular crystallization of calcium salts results in the formation of small harmless crystals excreted with urine or calcium stones appears to be determined by a complex process, involving kinetic factors that influence crystal growth and crystal aggregation and crystal retention. Received: 24 December 1998 / Accepted: 11 March 1999     

Crystallization during volume reduction of solutions with a composition corresponding to that in the collecting duct: the influence of hydroxyapatite seed crystals and urinary macromolecules

To examine the effect of hydroxyapatite (HAP) seed crystals and urinary macromolecules on the crystallization under conditions similar to those in the collecting duct, we evaporated 100 ml samples of salt solutions with an ion composition assumed to correspond to that in the collecting duct without and with HAP seed crystals. The crystallization in seeded solutions was assessed both with and without dialysed urine (dU). After evaporation the number and volume of crystals were recorded in a Coulter Multisizer and the crystal morphology examined with scanning electron microscopy (SEM) and X-ray crystallography. Addition of HAP crystals was apparently followed by an approximately 15–20% increase in heterogeneous nucleation of calcium oxalate (CaOx). In these experiments SEM and X-ray crystallography showed a high percentage of CaOx in the precipitate. In samples reduced to 40–69 ml, addition of dU to the collecting duct solution containing HAP seed resulted in a greater mean (SD) number of crystals; 3895 (1841) in samples with dU and 1785 (583) in samples without. This was mainly explained by an increased mean (SD) number of small crystals. The mean crystal volume was 17.8 (1.1) and 34.3 (9.1) in samples reduced to 40–69 ml with and without dU, respectively. This might reflect the inhibitory effect of dU on the growth and/or aggregation of the CaOx-CaP precipitate or a promoted nucleation resulting in a large number of small crystals. It is concluded that calcium phosphate formed above the collecting duct might induce heterogeneous nucleation of CaOx at lower levels of the renal collecting system, and that urinary macromolecules are powerful modifiers of these processes. Received: 8 July 1998 / Accepted: 12 March 1999     

A logistic regression model for analyzing the relation between dentists' attitudes,behavior, and knowledge in oral radiology

The aim was to study the relation between risk attitude and knowledge in technical, patient-oriented, and organizationally related behavior within oral radiology. A questionnaire was mailed to 2000 randomly selected dentists listed in the register of the Swedish Dental Society, with a response rate of 69.3%. Regression analysis was used for analyzing the effects of the independent variables knowledge, risk attitude, continuing education in oral radiology, counties with specialists in oral radiology, type of practice, work experience, and sex on three categories of dependent variables: 1) technical behaviors: type of film, type of collimator, dose level, frequency of change of chemicals; 2) patient-oriented behaviors: use of patient protection barriers, strict indications for performing full-mouth X-ray examinations and bitewing radiography on new patients and recall patients; and 3) organizationally related behaviors: delegation of X-ray examinations to dental auxiliaries, influence on choice of collimator, influence on choice of film. Knowledge and education had strong direct effects for most of the dependent variables. The technical behaviors were mainly influenced by knowledge, education, and risk attitude, while organizationally related behaviors were influenced by type of practice and sex. The patient-oriented behaviors were influenced by a number of independent variables, such as education, type of practice, work experience, and sex. The present results indicate that both knowledge and the organizational context of dentists influence work.     

The impact of different spectral Doppler criteria on the proportion of high-grade internal carotid artery stenosis in patients undergoing duplex scanning

AIM: To investigate the impact of different spectral Doppler criteria on the proportion of high-grade ICA stenosis in patients undergoing carotid artery duplex scanning. MATERIAL AND METHODS: Duplex scans of 4,548 internal carotid arteries (ICA) in 2,349 patients were retrospectively analyzed. The following different criteria were applied for each scan for definition of ICA stenosis > or = 70%: Criteria I=ICA peak systolic velocity (PSV) > 130 cm/sec and ICA end-diastolic (EDV) > 100 cm/sec, Criteria II=PSV ICA/common carotid artery (CCA) ratio > 4, Criteria III=ICA PSV > or = 230 cm/sec, Criteria IV=ICA PSV > 230 cm/sec and/or ICA EDV > or = 100 cm/sec and/or PSV ICA/CCA ratio > or = 3.2. RESULTS: The frequency of detecting a > or = 70% ICA stenosis with criteria I, II, III, and IV were 5.5%, 6.8%, 8.4%, and 9.6%, respectively (p < 0.05). CONCLUSION: The use of various duplex criteria significantly affected the number of scans receiving a diagnosis of ICA stenosis of > or = 70%.