Effect of radiofrequency exposure on body temperature: Real-time monitoring in normal rats

Abstract

Effect of radiofrequency exposure on body temperature: Real-time monitoring in normal rats Kim HS, Kim Y, Jeon SB, Choi HD, Lee AK, Lee HJ, Pack JK, Kim N, Ahn YH. Effect of radiofrequency exposure on body temperature: Real-time monitoring in normal rats. J Therm Biol. 2022 Dec;110:103350. doi: 10.1016/j.jtherbio.2022.103350. Abstract Radiofrequency radiation (RFR) can generate heat in living organisms. In this study, we monitored the body temperature of healthy animals during RFR exposure in real time using an implantable iButton data logger. A reverberation chamber system for small animals was used for this radiofrequency (RF) exposure in vivo study. Healthy male Sprague-Dawley rats were divided into two groups: with versus without iButton implantation (n = 20 per group). Each group was further divided into a sham-exposed and RF-exposed group (n = 10 per subgroup). Rats were exposed to a 1,760-MHz long-term evolution (LTE) signal in the reverberation chamber system at a whole-body average specific absorption rate of 0 W/kg (sham-exposed) or 4 W/kg (RF-exposed) for 6 h. The body temperature of iButton-implanted rats was recorded using an intraperitoneally implanted iButton every minute over 6 h of RF exposure, whereas that of non-implanted rats was measured directly using a rectal thermometer immediately before and after the 6-h RF exposure period. The temperature values measured by the two types of thermometers were significantly positively correlated (r = 0.63, P < 0.01, linear regression), and changes in body temperatures recorded in iButton-implanted and non-implanted rats measured using two thermometers after 6 h of RF exposure were maintained within <1°C (P = 0.87, general linear model, followed by univariate model). Similar results were obtained for rectal thermometer measurements (P = 0.12, paired t-test). These results suggest that RF exposure at a whole-body average specific absorption rate of 4 W/kg does not induce significant changes in body temperature in healthy rats over a 6-h RF exposure period. pubmed.ncbi.nlm.nih.gov Highlights • RF exposure of 4 W/kg wbSAR is known to alter rat behavior, but it is unclear whether it raises body temperature. • The iButton, an implantable intraperitoneal thermometer, can be used to monitor body temperature in real time. • Body temperatures measured by both the iButton and the rectal thermometer and the temperature change patterns were similar. • The body temperature of healthy rats was not altered by RF exposure of 4 W/kg wbSAR. Reverberation chamber for RF exposure The methods used in this study were adapted from those of a previous study (Jin et al., 2021). Briefly, a reverberation chamber (IRETEC, Anyang, Korea) was used as the RF exposure system. The external dimensions (L × W × H) of the reverberation chamber were 2,295 × 2,293 × 1,470 mm. An LTE RF source with a center frequency of 1,706 MHz, a bandwidth of 20 MHz, and quadrature phase-shift keying modulation was used in this study. The input signal was amplified using a high-power amplifier (PCS60WHPA_CW; Kortcom Co., Anyang, Korea). The output power level (maximum: 60 W) was controlled using an 11-bit digital PIN diode attenuator (model 349; General Microwave, Farmingdale, NY, USA). Commercial transmitting antennae (patch type, KCAN1900PA; Korea Telecommunication Components, Anyang, Korea) were used. Exposure level and time were set using a computer. The input power was monitored in real time using a power meter (N1912A, Keysight, Santa Rosa, CA, USA) through a 20-dB directional coupler (778D, Keysight). The field uniformity of the reverberation chamber was measured at 24 points within the working volume. An isotropic field probe (HI-6005; ETS-Lindgren) was used for electric field measurements. Uniformity averaged over a period of 1 min was evaluated. The field distribution in the working volume remained within ±2 dB. The chambers were installed at the Korea Institute of Radiological & Medical Sciences in Seoul, Korea. The reverberation chamber was housed at an animal facility, and its ventilation, temperature, and humidity were controlled. The SAR distribution was calculated for each caged rat using a rat phantom (Electronics and Telecommunications Research Institute, Daejon, Korea); the simulation featured 40 tissues and a voxel size of 1 mm. The power output was adjusted to 45.5 W to achieve a wbSAR of 4 W/kg.

AI evidence extraction

Main findings

Rats exposed to a 1,760-MHz LTE signal at whole-body average SAR 4 W/kg for 6 h showed no significant change in body temperature compared with sham exposure. Body temperature measurements from intraperitoneal iButton loggers and rectal thermometers were significantly positively correlated (r = 0.63, P < 0.01), and temperature changes after 6 h of exposure were within <1°C (P = 0.87).

Outcomes measured

• Body temperature (real-time intraperitoneal iButton)
• Body temperature (rectal thermometer pre/post exposure)
• Correlation between iButton and rectal thermometer measurements

Limitations

• Only healthy male Sprague-Dawley rats were studied
• Exposure duration limited to 6 h
• Body temperature in non-implanted rats was measured only immediately before and after exposure (not continuously)

Suggested hubs

• animal-studies (0.9)
  In vivo RF exposure experiment in rats assessing thermoregulatory outcome (body temperature).

{
    "study_type": "animal",
    "exposure": {
        "band": "RF",
        "source": "LTE signal (reverberation chamber exposure system)",
        "frequency_mhz": 1760,
        "sar_wkg": 4,
        "duration": "6 h"
    },
    "population": "Healthy male Sprague-Dawley rats",
    "sample_size": 40,
    "outcomes": [
        "Body temperature (real-time intraperitoneal iButton)",
        "Body temperature (rectal thermometer pre/post exposure)",
        "Correlation between iButton and rectal thermometer measurements"
    ],
    "main_findings": "Rats exposed to a 1,760-MHz LTE signal at whole-body average SAR 4 W/kg for 6 h showed no significant change in body temperature compared with sham exposure. Body temperature measurements from intraperitoneal iButton loggers and rectal thermometers were significantly positively correlated (r = 0.63, P < 0.01), and temperature changes after 6 h of exposure were within <1°C (P = 0.87).",
    "effect_direction": "no_effect",
    "limitations": [
        "Only healthy male Sprague-Dawley rats were studied",
        "Exposure duration limited to 6 h",
        "Body temperature in non-implanted rats was measured only immediately before and after exposure (not continuously)"
    ],
    "evidence_strength": "low",
    "confidence": 0.7800000000000000266453525910037569701671600341796875,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "radiofrequency radiation",
        "LTE",
        "reverberation chamber",
        "whole-body average SAR",
        "body temperature",
        "iButton",
        "Sprague-Dawley rat",
        "thermoregulation"
    ],
    "suggested_hubs": [
        {
            "slug": "animal-studies",
            "weight": 0.90000000000000002220446049250313080847263336181640625,
            "reason": "In vivo RF exposure experiment in rats assessing thermoregulatory outcome (body temperature)."
        }
    ]
}

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