Experimental measurements of particle retention efficiency of filters used to prevent contamination in respiratory devices.

OBJECTIVE: Various types of filters have been designed to prevent cross contamination of ventilation and respiratory devices. The aim of this study was to experimentally measure the retention efficiency of four simple filters (antibacterial and antiviral and seven combined filters (antibacterial and antiviral plus heat and water exchangers). SETTING: The respiratory function testing (EFR) central department of a university teaching hospital. MEASUREMENTS AND RESULTS: The same aerosol test with a wide range of particle sizes (0.15 to 15 micrometers) was used to compare the retention efficiency of each filter used in various conditions. The particle sizes and the concentration of the aerosol were measured by a laser velocimeter. For all the filters studied, the retention efficiency was found to be higher than 99%. However some of them let large particles let through. CONCLUSION: These data, performed in vitro, should be assessed also by further clinical studies.

Use of unstable chromosome aberrations for biological dosimetry after the first postirradiation mitosis.

The loss of unstable chromosome aberrations after the first postirradiation mitosis makes their use difficult in radiation dosimetry. We describe here a method which, in a cell population observed at this stage, allows retrospective estimation of the frequencies of the unstable aberrations induced at the time of irradiation, and their use as a dosimeter. The laws controlling the behavior of unstable aberrations during mitosis were defined from a large-scale experiment on irradiated human lymphocytes. For cells undergoing the first, second, or third mitosis after irradiation, relationships were determined between the frequency, at irradiation time, of acentric fragments not arising from formation of dicentrics or rings, and the ratio of dicentrics and centric rings appearing without acentric fragments to the total number of dicentrics plus rings. On the basis of this ratio, the method described here provides an assessment of the postirradiation mitotic activity in a cell population. This assessment permitted estimation of the cell distribution and frequency of dicentrics plus centric rings, and of the frequency of acentric fragments at the time of irradiation. The use of this method for retrospective dosimetry after whole-body irradiation under various conditions of exposure is illustrated.

Chromosomal aberrations and DNA repair ability of in vitro irradiated white blood cells of monkeys previously exposed to total body irradiation.

Six monkeys (Macaca fascicularis) were total-body-irradiated with 60Co (fractionated irradiation of 8 or 10 Gy). Blood samples were collected at different times post total-body irradiation, then in vitro irradiated in order to test whether a prior in vivo irradiation could affect the radiosensitivity of their leukocytes. We suggested in a preliminary report that the enhanced chromosomal radiosensitivity of in vivo irradiated monkeys could be correlated with a DNA repair deficiency (Guedeney et al., 1986). Chromosomal aberrations, the rate of initial strand breaks and their rejoining estimated using a fluorescent assay for DNA unwinding were chosen as the endpoints in this more extensive study. We observed that the yield of dicentrics induced by a subsequent in vitro irradiation was lower than that scored in unirradiated monkeys in few cases (6/22) whereas the number of acentrics was found to be modified in 16 of the 22 samples. An altered DNA repair ability was observed in most but not all blood samples tested. Thus, in view of such intra-individual variability, the results of this more extensive study lead us to conclude that a previous total-body irradiation does not alter the gamma-induced chromosome aberrations and DNA repair ability in a reproducible manner.

Chromosomal aberrations in cynomolgus peripheral lymphocytes during and after fractionated whole-body gamma-irradiation.

Cynomolgus monkeys (Macaca fascicularis) were exposed to fractionated whole-body gamma-irradiation at high and low dose rates for 4 or 5 weeks. The time-dependence of chromosomal aberrations was studied in relation to the number of lymphocytes during irradiation and after exposure for periods of up to about 600 days for chromosomal aberrations and 200 days for lymphocyte counts. Additivity of the daily effects on the number of chromosomal aberrations was observed during the exposures. Immediately after the end of the exposures the number of chromosomal aberrations decreased to reach low values. The disappearance of chromosomal aberrations seemed to be related to recovery of the lymphocyte counts. The data presented here emphasize the different kinetic patterns of chromosomal aberrations after fractionated and acute irradiation.

Time dependence of chromosomal aberrations induced in human and monkey lymphocytes by acute and fractionated exposure to 60Co.

Changes in the numbers of peripheral lymphocytes with chromosome aberrations were observed in cynomolgus monkeys after fractionated or acute 60Co irradiation at the same total doses. Immediately after irradiation, the yield of dicentrics decreased when the dose was fractionated but remained constant for 20 to 80 days, depending on the dose, when irradiation was acute. Lymphopenia was greater than expected when the dose was fractionated. The kinetics of the loss of chromosome aberrations and the changes in peripheral lymphocyte count occurring in monkeys after acute irradiation were compared to those observed in accidentally irradiated men.

[Change in rabbit blood lymphocyte count after repeated extracorporeal irradiation with cesium 137. Comparison of heparin and acenocoumarol effects]. / Modification du taux des lymphocytes sanguins chez le lapin aprés irradiation extra-corporelle répétée (IECSR) au césium 137. Action comparée de l'héparine et de l'acénocoumarol

During repetitive extracorporeal irradiation, heparin treatment is responsible for a very high lymphocytic peak which does not last more than two days. This peak is not observed after using acenocoumarol as anticoagulant. That is why the degree of lymphocyte depletion after RECIB is to be interpreted in function of the anticoagulant used. This peak is temporary. No matter the anticoagulant used, lymphopenia is obtained after 15 days. The level of lymphocytic depletion is independent of the initial lymphocytosis.

[Repeated extracorporeal irradiation of rabbit blood (RECIB). Effect on lymphocytes]. / Irradiations extracorporelles sanguines répétées (IECSR) chez le lapin. Conséquence sur les lymphocytes du sang

Haemotological data are described after repetitive extracorporeal irradiation of blood (RECIB) is rabbits for two hours a day, five days a week. Cesium 137 can deliver 125000 rads/hour, i.e. a cummulative dose equivallent to 1.25 X 10(6) rads/week. The blood lymphocytes were investigated in detail, lymphopenia was obtained after 15 days and remain stable after the third week.