The stiffer and denser the material the greater the absorption coefficient. Bone and teeth have high absorption coefficients. Collagen deposition in tissue increases the absorption coefficient. The absorption coefficient of bone is 30 times greater than that of soft tissue and the rate of heat deposition in bone can be as high as 50 faster than in soft tissue. Gas also responds to acoustic energy with the greatest change in temperature.
Tissues containing gas absorb more sound energy, i.e. adult lung.
Diurnal variation of 0.3 to 1.0 degree C. Sleep cycles, exercise cycles related to diurnal pattern. Most adults have experienced a 4 degree Celsius increase on one or more occasions with no obvious harm. Variance of 9 degrees Celsius compatible with life. Hypothermia is more benign and even useful in medical surgeries. Vasodilation and increased blood flow with erythema help maintain internal termperature.