Functional Infrared Thermal Imaging based on the spectral analysis of the skin microvascular blood flow to investigate the role of endothelial, neurogenic and myogenic components in pain sensation as promising biosignals and biomarkers for PAIN assessment: towards a novel and objective instrumental technique for pain measurement; “finanziato dall’Unione europea – Next Generation EU”

Pain is a debilitating condition affecting about 20% of adults in the world. In specific conditions, pain can become chronic so altering feelings and attitudes. It involves complex neuronal processes and it is considered as a personal experience with relevant subjective components. Pain has important physical, psychological and social consequences and it can affect the quality of life. In absence of suitable treatments, the immune system can be compromised and pain sensation can interfere with the ability to eat, concentrate, sleep, or interact with others. Consequently, the prompt pain assessment is essential for expediting therapeutic administration. Today, assessment, management and treatment of chronic pain are still challenging goals for researchers and clinicians. Algologists operate in absence of standardized and objective tools for pain assessment. So it is clear the need to define new and objective assessing instrumental-based techniques. We propose the use of an innovative thermographic technique, named functional Infrared Thermal Imaging (fITI), in order to map the activation of the body area affected by pain so assessing quantitatively pain sensation. Since nociceptive pain may involve activation of the sympathetic nervous system, a neurogenic inflammatory response is typically experienced in the area affected by pain. Our intuition is based on a possible alteration in blood flow dynamics. In detail, microvascular perfusion is, at rest, characterized by periodical oscillations having specific and well-known low-frequency ranges (endothelial, neurogenic, myogenic, respiratory, cardiac). Such oscillatory components of blood flow can be considered like sources of thermal waves propagating from micro–vessels toward the skin surface. In the absence of external thermal sources, we expect skin temperature dynamics to be regulated by the same rhythmical variations as the local microvascular perfusion paying a difference in terms of amplitude and phase in its frequency response according to the thermal conduction law (Fourier's Law). As a result, skin temperature signal detected by infrared thermal imaging can be transformed in the inner blood flow signal. In a preliminary feasibility study, we have observed an alteration in the endothelial, neurogenic and myogenic activities during pain sensation. So, by extracting these blood flow spectral components, it is possible to generate a new image, as a result of the proposed fITI technique, which maps the activation of the areas affected by pain. Preliminary results have shown interesting correlations between pain sensation and changes in the images sequence associated to the blood flow oscillations. So we think that such oscillations can be considered as promising pain biomarkers. The aim of this cutting-edge research is to investigate the pain mechanism and its correlation with endothelial, neurogenic and myogenic components in order to define and develop an objective pain-assessing instrument.