An analysis of a radionuclide technique used to measure reactive hyperaemia in limbs

A radionuclide technique (PT) for measuring the blood flow to a limb during reactive hyperaemia is described and analysed. Patients are positioned with lower limbs within the field of view of the gamma camera and pneumatic cuffs are placed below the knees to isolate the blood and induce a hyperaemic response. The remaining blood pool is labelled with 99Tcm-human serum albumin. Following release of the occlusion the rate of inflow to the limb of the radionuclide is measured and hyperaemic flow then determined, during the initial phase of the hyperaemia. The results may be analysed using a single compartment to represent the vascular pool in the lower limb. During the initial phase, activity entered the pool at a constant rate from which the blood flow may be calculated. Results were obtained in a group of 20 normal control volunteers and 20 patients with occlusive arterial disease. They indicate that following release of the cuff the blood flow rises rapidly (within 1-2 s) to a constant value which is maintained for at least 10-12 s in normal subjects and a longer period in arteriopaths. The mean flow in the normal group was 14.4 ml/100 ml min-1 and in the arteriopathic group was 4.6 ml/100 ml min-1. The constant flow measured by PT during the initial phase of reactive hyperaemia appears to differ from the results of venous occlusion plethysmography and washout of a freely diffusible tracer and possible reasons for these differences are discussed.