Effect of heating rate on evaporative heat loss in the microwave-exposed mouse.

Abstract

Male CBA/J mice were administered heat loads of 0-28 J X g-1 at specific absorption rates (SARs) of either 47 or 93 W X kg-1 by exposure to 2,450-MHz microwave radiation at an ambient temperature of 30 degrees C while evaporative heat loss (EHL) was continuously monitored with dew-point hygrometry. At an SAR of 47 W X kg-1 a threshold heat load of 10.5 J X g-1 had to be exceeded before EHL increased. An approximate doubling of SAR to 93 W X kg-1 reduced the threshold to 5.2 J X g-1. Above threshold the slopes of the regression lines were 1.15 and 0.929 for the low- and high-SAR groups, respectively. Thus the difference in threshold and not slope attributes to the significant increase in EHL when mice are exposed at a high SAR (P less than 0.02). In separate experiments a SAR of 47 W X kg-1 raised the deep body temperature of anesthetized mice at a rate of 0.026 degrees C X s-1, whereas 93 W X kg-1 raised temperature at 0.049 degrees C X s-1. Hence the sensitivity of the EHL mode of heat dissipation is directly proportional to the rate of heat absorption and to the rate of rise in body temperature. These data contradict the notion that mammals have control over whole-body heat exchange only (i.e., thermoregulation) but instead indicate that the EHL system is highly responsive to the rate of heat absorption (i.e., temperature regulation).

AI evidence extraction

Main findings

Male CBA/J mice exposed to 2,450-MHz microwaves at ambient 30C received heat loads of 08 Jd7g^-1 at SARs of 47 or 93 Wd7kg^-1 while EHL was monitored. The threshold heat load for increased EHL was 10.5 Jd7g^-1 at 47 Wd7kg^-1 and 5.2 Jd7g^-1 at 93 Wd7kg^-1; above threshold, regression slopes were 1.15 (low SAR) and 0.929 (high SAR). In separate experiments, deep body temperature rose at 0.026 b0Cd7s^-1 (47 Wd7kg^-1) and 0.049 b0Cd7s^-1 (93 Wd7kg^-1), suggesting EHL sensitivity is proportional to heat absorption/heating rate.

Outcomes measured

• Evaporative heat loss (EHL)
• Threshold heat load for increased EHL
• Deep body temperature rise rate

Limitations

• Sample size not reported in abstract
• Exposure duration not reported in abstract
• Primarily physiological/thermoregulatory endpoints in mice; generalizability to humans not addressed in abstract

{
    "study_type": "animal",
    "exposure": {
        "band": "microwave",
        "source": null,
        "frequency_mhz": 2450,
        "sar_wkg": null,
        "duration": null
    },
    "population": "Male CBA/J mice",
    "sample_size": null,
    "outcomes": [
        "Evaporative heat loss (EHL)",
        "Threshold heat load for increased EHL",
        "Deep body temperature rise rate"
    ],
    "main_findings": "Male CBA/J mice exposed to 2,450-MHz microwaves at ambient 30\u0000C received heat loads of 0\u0013\u00028 J\u0000d7g^-1 at SARs of 47 or 93 W\u0000d7kg^-1 while EHL was monitored. The threshold heat load for increased EHL was 10.5 J\u0000d7g^-1 at 47 W\u0000d7kg^-1 and 5.2 J\u0000d7g^-1 at 93 W\u0000d7kg^-1; above threshold, regression slopes were 1.15 (low SAR) and 0.929 (high SAR). In separate experiments, deep body temperature rose at 0.026 \u0000b0C\u0000d7s^-1 (47 W\u0000d7kg^-1) and 0.049 \u0000b0C\u0000d7s^-1 (93 W\u0000d7kg^-1), suggesting EHL sensitivity is proportional to heat absorption/heating rate.",
    "effect_direction": "unclear",
    "limitations": [
        "Sample size not reported in abstract",
        "Exposure duration not reported in abstract",
        "Primarily physiological/thermoregulatory endpoints in mice; generalizability to humans not addressed in abstract"
    ],
    "evidence_strength": "low",
    "confidence": 0.7800000000000000266453525910037569701671600341796875,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "mouse",
        "microwave",
        "2450 MHz",
        "specific absorption rate",
        "SAR",
        "evaporative heat loss",
        "thermoregulation",
        "heating rate",
        "deep body temperature"
    ],
    "suggested_hubs": []
}

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