A device comprising a light transmission and detection system having transducers (10, 20, 7, 8), control means (5) and output means (7). The transducers are placed at various sites on the body of a patient and the light absorbed and/or reflected at these sites is measured and signals related to vasomotor activity are collected. The output can take the form of a detailed display of the vasomotor signals collected from the transducers (10, 20, 7, 8) to a simple indication of a condition present or absent. For example, the presence of a unilateral DVT can be detected by measuring the dissimilarity between two transducer signals from the soles of a patients feet. The invention can also be used to provide an indication or not of for example, DVT and diabetic peripheral neuropathy.
