In the context of Cognitive and Behavioural Therapies, the use of immersion technologies to replace classical exposure could improve the therapeutic process. As it is necessary to validate the efficiency of such a technique, both therapists and VR specialists need tools to monitor the impact of Virtual Reality Exposure on the patients. According to previous observations and experiments, it appears that an automatic evaluation of the Arousal and Valence components of affective reactions can provide significant information. The present study investigates a possible solution of Arousal and Valence computation from physiological measurements. Results show that the dimensional reduction is not statistically meaningful, but the correlations found encourage the investigation of this approach as a complement to cognitive and behavioural study of the patient.