Cold Stress Dynamic Thermography for Evaluation of Vascular Disorders in Hand‐Arm Vibration Syndrome

Exposure to hand-transmitted vibration can cause a variety of disorders collectively known as the Hand-Arm Vibration Syndrome (HAVS). Its neurovascular component is Vibration-induced White Finger (VWF), a type of secondary Raynaud’s phenomenon (RP), which manifests itself as episodic blanching of the fingers in response to cold. Due to the episodic nature of this condition, an occupational health physician rarely observes the blanching; thus, VWF has often been diagnosed based only on patient’s history together with a history of occupational exposure to vibration and the exclusion of other known causes of RP . For the assessment of VWF, measurements of finger skin temperature (FST) and finger systolic pressure (FSP) in response to cold stress are most widely used . The FST-based assessment relies on the principle that the pattern of FST following cooling reflects the degree of cold-induced vasoconstriction in the digital blood vessels. The rise in FST during recovery reflects the increase in blood flow in the investigated skin area. Abnormal rewarming times indicate different patterns of vascular dilatation following vasomotor responses to cooling. A lower FST is expected to reflect a persistent abnormality of blood flow in patients with HAVS 2, . Merla et al. described a technique that used infrared imaging to record the thermal recovery and produced images which visualized the τ times of individual pixels, assuming an exponential rewarming process ( τ being the time needed for rewarming to 63% of the total temperature change). The damaged areas exhibited a slower recovery and longer τ time. This was a novel approach in that it used dynamic parameter (Tau) imaging, but the parameter was derived as a cutoff-value, not from all the available rewarming data. Using a non-imaging infrared-based device, Foerster et al. also reported that a rewarming pattern could be described using the τ value. According to Darton and Black , thermographic images of the hands and rewarming curves after cold provocation show characteristic differences among patients with primary and secondary RP, and normal subjects. We propose a novel method of dynamic infrared thermography for assessing the dynamic response of the microcirculation during rewarming.