Bone density estimation using tissue heat capacity.

Osteoporosis onset is relatively asymptomatic, the condition often being identified only once a significant fracture occurs, leading to a potentially serious prognosis. Currently, early identification of osteoporosis is complicated by the difficulty in measuring bone density without using x-ray absorptiometry or quantitative ultrasound, so a simpler method for estimating bone density is needed. Given that bone is reported to have a lower specific heat than other tissues, we investigated the possibility of estimating bone density using this difference in tissue thermal properties. The tibia medial surface (shin) and medial malleolus (ankle) of 68 healthy volunteers were cooled using an ice bag, and skin surface temperatures and heat flow were recorded. These measurements were then used to calculate the heat energy transferred per unit temperature. Bone density was estimated by quantitative ultrasound using the T score OSISD, which is the participant's osteo sono-assessment index (OSI) compared to the average OSI of young adults. The heat energy transfer per unit temperature at the shin, but not the ankle, showed a significant negative correlation with T score OSISD (r = -0.413, p = 0.001). Multiple regression analysis showed that heat energy transfer per unit temperature at the shin was a significant predictor of T score OSISD, along with age and height. These results show that tissue thermal property measurements are useful for estimating bone density.

Quantitative Assessment of the Heat Transfer Capacity of Ice Bags and their Cooling Effects on the Skin Surface and Core Temperature.

Ice bags are frequently used in medical care settings for pain relief, comfort, and in some cases, whole-body cooling. This study quantifies heat energy transfer capacity of ice bags and evaluates their cooling effects on body temperature. Forty-eight healthy adults in their 20s were recruited. An ice bag wrapped in two layers of dry towel was applied to the forehead, neck, or palm of each participant for 10 min. The skin surface temperature, heat flow, and core temperature were recorded during the cooling and non-cooling periods, with energy transfer calculated by integrating heat flow over time. Over the non-cooling period, 31.4-53.6 kJ·m-2 of energy was dissipated over 10 min, whereas during the cooling period, the range increased to 180.0-218.7 kJ·m-2 over 10 min. Skin surface temperature decreased by 3.2-5.7°C, whereas core temperature was unchanged. Ice bag use augmented energy transfer by about 150-180 kJ·m-2 over 10 min, but this was insufficient for rapid whole body cooling due to the small skin-surface area in contact with the ice bag. The measured energy transfer indicated that topical ice bag application absorbs insufficient energy to affect core temperature. Quantitative assessment of energy transfer was shown to inform the safe and appropriate use of thermotherapy.