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Thermal Imaging Reveals Temperature Retention in Hindlimbs of Mice up to 4 Hours after Targeted Intermittent Limb Heating
Author(s) -
Racine Holly L,
Ion Gabriela,
Kerby Jenna C,
Gray Miles X,
Meadows Chad A,
Serrat Maria A
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1032.2
Subject(s) - medicine , weanling , lower limb , zoology , regimen , surgery , thermography , biomedical engineering , nuclear medicine , infrared , biology , physics , optics
Our lab has previously demonstrated that daily unilateral limb heating permanently increases bone length in growing mice. We hypothesize that limb temperature remains elevated on the treated side due to a heat‐induced increase in vascular supply that accelerates bone lengthening. In order to test the temperature retention hypothesis, we conducted an extensive pilot study to determine the period of time in which limb temperature remains elevated on the heat‐treated side after each daily regimen. By collecting hourly and daily temperatures at scheduled time points throughout the trial, our goal was to determine optimal conditions for recording temperature data in our subsequent studies, as well as to identify potential technical problems that could interfere with outcomes of the heat‐treatment. Weanling female mice (N=6) were treated daily at 7am for 2‐weeks with 40C unilateral heat for 40 minutes per day following our published methods. Infrared thermal images were captured at 320 X 240 resolution using a FLIR E8 infrared camera (sensitivity <0.06C in temperature range of −20 to 250C). Surface temperatures of the heat‐treated (right) and non‐treated (left) hindlimbs were obtained from calibrated images using FLIR tools software. Statistical comparisons were made using ANOVA and paired t‐tests in SPSS. Data from multiple days were pooled at each time point since there were no significant differences among days analyzed. Common trends in temperature differences between heat‐treated and non‐treated limbs were seen throughout the day. At 6am baseline prior to treatment, the heat‐treated side was over 1% warmer than the non‐treated side (t=1.84, p=0.06). After the treatment at 8am, limb temperatures were nearly equivalent (t=1.13, ns), suggesting a systemic post‐anesthesia thermoregulatory response. By 11am, 4 hours after the treatment start, the heat‐treated side was over 2% warmer than the non‐treated side (t=8.06, p<0.001), indicating sustained heat retention. By 3pm, limb temperatures were again similar (t=0.13, ns), reflecting increased activity as mice approached the dark cycle. Excessive imaging (up to once per hour) negatively impacted daily gain in body mass, but this effect was mitigated by increasing intervals between imaging. These pilot results support our hypothesis that limb temperature remains elevated on the heated side up to 4 hours after treatment. This study is an important step toward understanding the mechanisms by which heat enhances limb elongation. Support or Funding Information Supported by ASBMR Grants in Aid Program and the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (1R15AR067451‐01).