The non-invasive assessment of the ischaemic limb, with particular reference to thermography.

Skin temperature (Tsk) has long been used in assessing limb circulation, and in recent years thermography has been used as an accurate way of measuring Tsk. However, apart from the general proposition that Tsk must be related to that of the blood, the precise relationship between the blood supply to a limb and its Tsk remains poorly understood. Without this knowledge full use cannot be made of thermography in the assessment of the limb with peripheral vascular disease. The purpose of these studies was to provide a scientific basis for the use of thermography on limbs. Previous work had indicated that Tsk was related to skin blood flow in the hand and foot, but not in the forearm or calf. This work has been confirmed and extended by studies on normal subjects at different ambient temperatures, and on subjects with a peripheral A-V fistula. I have shown that Tsk over the forearm and calf is related to the core temperature of the limb, i.e. to the arterial inflow. An attempt was then made to see if these findings could be used to interpret the abnormal thermograms found in a group of patients with intermittent claudication, and in a group with more severe peripheral vascular disease. In claudicants the regression line relating mean calf Tsk to total blood flow was parallel to, but higher than that in normal subjects, i.e. for the same blood flow, claudicants' Tsk was higher than in normal subjects. The reasons for this difference are not apparent. Thermograms in patients with more severe limb ischaemia were often difficult to interpret because of the confusion introduced by other pathologies. Thermography is a useful adjunct in the assessment of the ischaemic limb, but is unlikely to replace more conventional methods of investigation