研究のタイプ: 医学／生物学の研究 (experimental study)

[拘束状態で905 MHzばく露を受けたマウスの体温調節閾値および調節破綻閾値] med./bio.

Response, thermal regulatory threshold and thermal breakdown threshold of restrained RF-exposed mice at 905 MHz

著者: Ebert S, Eom SJ, Schuderer J, Apostel U, Tillmann T, Dasenbrock C, Kuster N
掲載誌: Phys Med Biol 2005; 50 (21): 5203-5215
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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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研究目的（著者による）

Determination of the thermal regulatory and the thermal breakdown thresholds for in-tube restrained mice exposed to radiofrequency electromagnetic fields at 905 MHz.

詳細情報

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.

影響評価項目

ばく露

ばく露 パラメータ
ばく露1: 905 MHz
ばく露時間: continuous for 2 h
  • SAR: 20 W/kg average over mass (whole body) (2, 5, 7.2, 10, 12.6, 20 W/kg)

ばく露1

主たる特性
周波数 905 MHz
タイプ
  • electromagnetic field
特性
  • guided field
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.
Modulation
Modulation type unspecified
ばく露装置
ばく露の発生源／構造
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.
パラメータ
測定量 値 種別 Method Mass 備考
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
測定および計算の詳細

Forward and reflected powers as well as the electric field inside the cavity were measured for exposure control. Power measurements were made using a dual directional coupler and a dual head power meter. The incident E-field inside the wheel was measured by two monopole sensors connected to diode detectors. A detailed numerical and experimental dosimetry and a comprehensive uncertainty assessment of the mini wheel setup were performed. The numerical dosimetry was based on FDTD simulations with high resolution mouse models for different animal sizes (20 g, 25 g, 30 g, 35 g). The numerical results were verified by experimental dosimetry subjecting mouse dummies (conical bottles filled with tissue simulating liquid) to precise E-field (using a near-field scanner DASY4) and temperature measurements. In addition to the whole-body SAR, detailed organ/tissue specific SAR values were determined and shown in a table. The uncertainty budget was assessed according to Taylor and Kuyatt [1994], taking all the occurring variabilities and variations into account. An uncertainty assessment for the whole-body and organ averaged SAR was performed according to Kuster et al [2006, publication 13770].

Reference articles

  • Balzano Q et al. (2000): [900 MHzでの動物実験で正確に全身平均SARを決定するための効率的なRFばく露装置]

ばく露を受けた生物:

方法 影響評価項目／測定パラメータ／方法

研究対象とした生物試料:
調査の時期:
  • ばく露前
  • ばく露中
  • ばく露後

研究の主なアウトカム（著者による）

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.

研究の種別:

研究助成

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