この研究は、円筒管内に拘束された状態で905 MHzの無線周電磁界ばく露を受けたB6C3F1およびNMRIマウスにおいて、体温調節閾値および調節の破綻閾値を決定する実験を行った。「フェリスホイール」と称するばく露用セットアップ（温度22±2 ℃、湿度30 – 70 %）内のマウスに、さまざまな全身平均比吸収率（SAR = 0、2、5、7.2、10、12.6、および20 W / kg）で2時間のばく露を与えた。ばく露の前、中、後に、直腸温度を測定した。B6C3F1マウスの場合は、オスおよびメスのそれぞれでの３つの体重グループ（20 g、24 g、29 g）および妊娠マウスにおいて熱応答を調べた。さらに、系統間比較のために、体重36 gのNMRIマウスの熱応答も調べた。その結果、管内拘束マウスの体温調節閾値は、2 W / kgと5 W / kgの間のSARレベルであると見られた；調節破綻が生じる閾値は、B6C3F1マウスでは10.1±4.0 W/ kg、NMRIマウスでは7.7±1.6 W / kgと決定された；単純化した熱平衡方程式に基づけば、閾値は代謝率と体重に明確に依存した；NMRIマウスは、熱ストレスに対してより敏感であり、体温調節および調節破綻のどちらもより低いSARが閾値となった、と報告している。
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Determination of the thermal regulatory and the thermal breakdown thresholds for in-tube restrained mice exposed to radiofrequency electromagnetic fields at 905 MHz.
Three regions of thermal response are distinguished: 1) a non-thermal regulatory region, where no measurable temperature response occurs, 2) a thermal regulatory region, where the regulatory system is able to compensate the absorbed energy (to achieve a stable body temperature), and 3) a thermal breakdown region, where the organism is not able to compensate the temperature increase.
For B6C3F1 mice, the thermal response was investigated for three different weight groups (20 g, 24 g, 29 g), both genders and for pregnant mice. In addition, NMRI mice with a weight of 36 g were examined for an interstrain comparison.
ばく露時間: continuous for 2 h
|ばく露時間||continuous for 2 h|
|Additional information||Taylor B N and Kuyatt C E ,1994, Guidelines for evaluating and expressing the uncertainty of NIST measurement results, Nat. Inst. Stand. & Technol. (Washington, DC), p 26.|
|Distance between exposed object and exposure source||111.5 mm|
|チャンバの詳細||The mice were exposed inside a 'Mini Wheel Setup', the concept of which was derived from the 'Ferris Wheel Setup' [Balzano et al., 2000]. The mini wheel setup was designed as a mono-mode cavity resonant waveguide structure of two parallel, circularly shaped metallic plates (diameter 332 mm, separation 120 mm) shorted with metallic bars along the outer edge and with an isotropic antenna at the centre. The system was matched for resonance (return loss ≤ -18 dB) using a triple stub tuner.|
|ばく露装置の詳細||The mice were circularly positioned in restrainer tubes at a radial distance of 111.5 mm from the antenna with their body axis oriented parallel to the E-field.|
|Sham exposure||A sham exposure was conducted.|
|Additional information||Groups of eight mice were exposed to a series of increasing SAR levels on consecutive days (one exposure per mouse group per day). Four additional animals of the same breed, gender and weight group were always sham exposed in a second setup.|
|SAR||20 W/kg||average over mass||測定値および計算値||whole body||2, 5, 7.2, 10, 12.6, 20 W/kg|
The thermal regulatory threshold of in-tube restrained mice was revealed at SAR levels between 2 W/kg and 5 W/kg, whereas the breakdown of regulation was determined at 10.1 +/- 4.0 W/kg for B6C3F1 mice and 7.7 +/- 1.6 W/kg for NMRI mice. The thresholds show a clear dependence upon the metabolic rate and weight. NMRI mice were more sensitive to thermal stress and responded at lower SAR values with regulation and breakdown.
The data suggest that the thermal breakdown for restrained mice, exposed to radiofrequency fields, may occur at SAR levels of 6 W/kg at laboratory conditions.