Elektrolüfter von Expositionskammern: Prof. Kuster antwortet (Allgemein)

H. Lamarr @, München, Samstag, 07.07.2012, 23:56 (vor 2689 Tagen) @ H. Lamarr

Mich würde interessieren, ob der Hersteller (ITIS) diese Fragen (bzw solche eventuellen Confounder) berücksichtigt hat.

Ich habe eine Anfrage an ITIS rausgelassen, sollte Antwort eintreffen, stelle ich's natürlich hier ein.

Es hat ein bisschen gedauert, aber heute traf Antwort aus der Schweiz ein.

ITIS-Chef Niels Kuster schreibt:

anbei unsere antwort zu den elektrolueftern. wir haben diese ueberlegungen im design einfliessen lassen um alle moeglichen cofounders zu minimieren. falls doch vorhanden, waere der effekt bei scham/exposure identisch.

Response to "Elektrosmog‐Forum des IZgMF" of May 8th, 2012, 21:27

The systems sXc-1800/1950 for in-vitro exposure of cells as used in the reflex project have been designed in such a way as to minimise the non-Radio Frequency (RF) differences in exposure. For example the system consists of two identical waveguide exposure chambers which are randomly assigned under computer control to expose and sham (no exposure) so that the experiment and the control can be simultaneously executed and what is more the two exposure chambers are placed within the same incubator so that the differences in environment (temperature, humidity and CO2) are minimized. The shielding effectiveness of the waveguide exposure chambers is excellent, the air flow is via a grid of small holes which provides a large attenuation of the electromagnetic field inside the chamber, this is for two reasons, firstly to ensure good isolation between sham and exposure cells cultures and secondly to protect other systems from potential interference.

Considering that the most important confounders in biological experiments where the expected effects are small are, changes in temperature or temperature differences and differences in cell cycle then the ability to run the sham and expose groups at the same time and have the same air circulating in both chambers are of paramount importance.

To ensure that the temperature is the same in both chambers air is drawn through the chambers from a common air input port. The air is circulated using DC fans placed at the air outlet, such that any heating of the fan does not impact the circulated air temperature. These fans run continuously during the time that the exposure system is switched on, in both, the exposed and sham chamber. Furthermore, each system is characterized and the maximum SAR is limited such that the maximum temperature increase in the cell culture media will be < 0.1°C, this equates to the maximum difference in temperature between the cells in each chamber. Without suitable fans to maintain air flow the environment in the chambers would be less well defined. Throughout the experiments the voltages and currents of the two fans are monitored along with the temperature using temperature sensors.

The two exposure chambers are mounted together and positioned near the centre of the incubator using 4 rigid POM supports. Therefore any vibration will be tightly coupled from one chamber to the other. Some vibration is generated by the fans, but this will be essentially the same in both exposure chamber cell cultures. The fans in the system operate from a common 12V DC source and have 5 fan blades, the fans do not necessarily rotate at exactly the same speed for both chambers, due to manufacturing tolerances.

The magnetic fields from the fans are related to both the commutation and the angular velocity. The main components have fundamental frequencies of approximately 440 Hz and 220 Hz respectively, the 220 Hz signal is essentially sinusoidal whereas the 440 Hz has narrow spikes, both fields are more pronounced on the side of the fan away from the exposure cell and decay rapidly. The fan is mounted on a spacer and then onto the thick aluminium wall of the waveguide, the peak field inside the waveguide is < 0.5 μT with the high frequencies significantly attenuated by the aluminium. The field is then attenuated much more by the time it reaches the closest petri dishes. Any stray exposure would be the same in both the sham and exposure chambers and hence would not act differentially on the cell samples, the majority of the petri dishes would be completely unaffected.

Though the inclusion of the fans might give unintended exposure to low frequency magnetic fields and vibration, this exposure will be essentially the same for both the sham and exposure groups, but the advantage of minimising the known confounder of temperature and environmental differences cannot be overstated.

Nicht die Masten sind das Problem, sondern die Handys!

In-Vitro, Expositionskammer, Niels Kuster, Lüfter

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