Determination of dose coefficients and urinary excretion function for inhalation of carbon-14-labelled benzene.

Based on existing pharmacokinetic models for benzene, the distribution and retention of activity after inhalation of 14C-labelled benzene in humans were studied. Six different benzene concentrations from 0.1 to 10,000 ppm (corresponding to activity concentrations between 9.6 x 10(6) and 9.6 x 10(11) Bq m(-3)) and five exposure times from 0.1 to 1000 min were considered. The cumulated activities in the different organs and tissues and the urinary excretion rates were observed to depend non-linearly on the activity intake. The fraction of activity removed via urine varies between 52 and 10% of the intake. Nevertheless, for times that are long compared to the exposure duration the urinary excretion rate is determined by the activity clearance from adipose tissue and thus decreases at a constant rate. This decrease is common for all exposure conditions examined and thus allowed determining a mean urinary excretion rate and corresponding dose coefficients for committed equivalent doses as well as for the effective dose. The uncertainty of the dose coefficients is estimated to be about 50% for the exposure range covered. A 14-day interval for the incorporation monitoring by urine activity counting seems to be reasonable.

Determination of the calibration factor of polysulphone film UV dosemeters for terrestrial solar radiation.

Polysulphone film is used as a personal UV dosemeter in dermatological or epidemiological studies. The relative efficiency of this detector does not exactly match the action spectrum as proposed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and to which the UV dose and exposure limits refer. Therefore, the calibration of the dosemeter depends on the spetrum. In the present paper the variation of the calibration factor for terrestrial solar UV spectra is analysed on the basis of a two year observation period at a site near Munich. Germany. A detailed error estimation is included. It is shown that the variation of the calibration factor within this class of spectra is the main contribution to the total uncertainty of the dose determination, which can be up to 40%. The shape of the spectrum of terrestrial solar UV radiation is mainly determined by the total ozone column and the solar elevation angle. It is shown how the calibration depends on these two parameters and how this additional information can help to reduce the measurement error to a residual uncertainty of 17%. Exposure studies of terrestrial solar UV radiation using polysulphone film as a dosemeter would gain in accuracy if total ozone column values at the study's site could be measured or taken from satellite or weather service data. The interpretation of the magnitude of the dose uncertainty depends on the further use of these data.

Cerebral autoregulation in subjects adapted and not adapted to high altitude.

BACKGROUND AND PURPOSE: Impaired cerebral autoregulation (CA) from high-altitude hypoxia may cause high-altitude cerebral edema in newcomers to a higher altitude. Furthermore, it is assumed that high-altitude natives have preserved CA. However, cerebral autoregulation has not been studied at altitude. METHODS: We studied CA in 10 subjects at sea level and in 9 Sherpas and 10 newcomers at an altitude of 4243 m by evaluating the effect of an increase of mean arterial blood pressure (MABP) with phenylephrine infusion on the blood flow velocity in the middle cerebral artery (Vmca), using transcranial Doppler. Theoretically, no change of Vmca in response to an increase in MABP would imply perfect autoregulation. Complete loss of autoregulation is present if Vmca changes proportionally with changes of MABP. RESULTS: In the sea-level group, at a relative MABP increase of 23+/-4% during phenylephrine infusion, relative Vmca did not change essentially from baseline Vmca (2+/-7%, P=0.36), which indicated intact autoregulation. In the Sherpa group, at a relative MABP increase of 29+/-7%, there was a uniform and significant increase of Vmca of 24+/-9% (P<0.0001) from baseline Vmca, which indicated loss of autoregulation. The newcomers showed large variations of Vmca in response to a relative MABP increase of 21+/-6%. Five subjects showed increases of Vmca of 22% to 35%, and 2 subjects showed decreases of Vmca of 21% and 23%. CONCLUSIONS: All Sherpas and the majority of the newcomers showed impaired CA. It indicates that an intact autoregulatory response to changes in blood pressure is probably not a hallmark of the normal human cerebral vasculature at altitude and that impaired CA does not play a major role in the occurrence of cerebral edema in newcomers to the altitude.

Laboratory facilities and recommendations for the characterization of biological ultraviolet dosimeters.

A laboratory facility for characterizing biological dosimeters for the measurement of UV radiation has been built and tested. The facility is based on a solar simulator, stabilized by photofeedback, and monitored by a spectroradiometer, with a versatile filter arrangement. This enables the following characteristics of the dosimeters to be ascertained: spectral response, linearity, and reciprocity; angular acceptance and response; calibration in simulated sunlight. The system has been tested on a variety of dosimeters and has the potential to be used with other radiometers, subject currently to the size of their active surface.

[Measurement and evaluation of natural and artificial UV radiation]. / Messung und Bewertung natürlicher und künstlicher UV-Strahlung.

Natural and artificial UV radiation are environmental factors with both beneficial and harmful biological effects. This article will explain the physical measurement quantities and their relation to the biologically effective dose and will summarize the present technical state of the art of personal UV monitoring. In practical use are dosimeters based on polysulphone, a polymer which undergoes changes in its optical properties upon irradiation with UV. Other systems determine the UV dose by quantifying damage induced in Bacillus subtilis spores upon UV exposure. An electronic UV sensor represents a new and interesting development. Personal UV dosimeters will become an useful tool in both clinical and scientific areas within dermatology.

Cerebral vasomotor reactivity at high altitude in humans.

The purpose of this study was twofold: 1) to determine whether at high altitude cerebral blood flow (CBF) as assessed during CO2 inhalation and during hyperventilation in subjects with acute mountain sickness (AMS) was different from that in subjects without AMS and 2) to compare the CBF as assessed under similar conditions in Sherpas at high altitude and in subjects at sea level. Resting control values of blood flow velocity in the middle cerebral artery (VMCA), pulse oxygen saturation (SaO2), and transcutaneous PCO2 were measured at 4,243 m in 43 subjects without AMS, 17 subjects with AMS, 20 Sherpas, and 13 subjects at sea level. Responses of CO2 inhalation and hyperventilation on VMCA, SaO2, and transcutaneous PCO2 were measured, and the cerebral vasomotor reactivity (VMR = DeltaVMCA/PCO2) was calculated as the fractional change of VMCA per Torr change of PCO2, yielding a hypercapnic VMR and a hypocapnic VMR. AMS subjects showed a significantly higher resting control VMCA than did no-AMS subjects (74 +/- 22 and 56 +/- 14 cm/s, respectively; P < 0.001), and SaO2 was significantly lower (80 +/- 8 and 88 +/- 3%, respectively; P < 0.001). Resting control VMCA values in the sea-level group (60 +/- 15 cm/s), in the no-AMS group, and in Sherpas (59 +/- 13 cm/s) were not different. Hypercapnic VMR values in AMS subjects were 4.0 +/- 4.4, in no-AMS subjects were 5.5 +/- 4. 3, in Sherpas were 5.6 +/- 4.1, and in sea-level subjects were 5.6 +/- 2.5 (not significant). Hypocapnic VMR values were significantly higher in AMS subjects (5.9 +/- 1.5) compared with no-AMS subjects (4.8 +/- 1.4; P < 0.005) but were not significantly different between Sherpas (3.8 +/- 1.1) and the sea-level group (2.8 +/- 0.7). We conclude that AMS subjects have greater cerebral hemodynamic responses to hyperventilation, higher VMCA resting control values, and lower SaO2 compared with no-AMS subjects. Sherpas showed a cerebral hemodynamic pattern similar to that of normal subjects at sea level.

Triplets or sequential siblings? A case report of three children born after one episode of in vitro fertilization.

To our knowledge, this is the first case report of three pregnancies resulting from the one batch of embryos. As the survival rate for cryopreserved embryos increases, there will be more families that will be able to be completed after just one cycle of hyperstimulation and oocyte collection, thereby making IVF-ET more cost-effective.

Primary peritoneal pregnancy in association with intrauterine contraceptive devices: two case reports.

Two patients with a primary pelvic peritoneal ectopic pregnancy are reported. Both had been fitted with an intrauterine contraceptive device.