bilateral symmetry. Skin temperature differences from one side of the body compared to the other are not only extremely small, but also very stable, and unaffected by the age of the patient. Data show differences between sides at the forehead to be 0.12°C at the forehead, and 0.25° at the lumbar region of the back. This symmetry forms the foundation for clinical interpretation of the varying surface temperature data.
In general, it is the relative readings between the body surface tem- peratures that are of interest. Hence, the general principle is all detec- tion is by exception. Accordingly, the temperature data from the nor- mal or reference area can then be used to adjust for the circadian varia- tions and for variations in the ambient temperature.
The change in body surface temperature with compromised blood flow is profound. A recent study was undertaken to mimic both partial and complete occlusion of blood flow to an extremity. The results indicate changes in skin surface temperature of an extremity reflect blood flow interruption or alteration in blood flow to that extremity.
A baseline for systolic blood pressure was determined for each subject and the manometer cuff inflated to three levels, 30 mmHg above sys- tolic, 25 mmHg below systolic and 50 mmHg below systolic, with tem- perature readings taken on the inside wrist at 15 second intervals. Even at the lowest cuff pressure, there is a clear indication at the end of three minutes of the surface temperature change due to the lowered tissue perfusion caused by the reduction in arterial blood flow. The data also indicate the time between occlusion or partial occlusion and a measur- able temperature drop is very short, well under one minute.
The surface temperature read- ings of the human body tend to be quite close between the bilaterally symmetric surfaces of region because of perfusion symmetry, but vary by several degrees on different body lo- cations because of perfusion differences. Both the hands and the feet can be substan- tially colder than the rest of the body surface due to vasomo- tor constriction of arterio- venous shunts as a ther- moregulatory response.
Effect of blood flow on body surface
temperature
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