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The Nijmegen Questionnaire was introduced over 30 years ago as a screening tool to detect patients with hyperventilation complaints that could benefit from breathing regulation through capnographic feedback 1. It was validated against the Hyperventilation Provocation Test 2, on the assumption at the time that hypocapnia was causally related to complaints. In later studies, the correlation between Nijmegen Questionnaire scores and carbon dioxide tensions appeared highly variable. The diagnosis of hyperventilation syndrome (HVS) was questioned and slowly disappeared. Nevertheless, the Nijmegen Questionnaire has remained in use and we have noticed even a recent increase in studies in clinical medicine as well as requests for permission to use the Nijmegen Questionnaire in new studies. We would like to formally declare here that the Nijmegen Questionnaire is not copyrighted and is free to use. It has been or will be translated, as far as we know, into Greek, Farsi, Finnish, Norwegian, Swedish, Spanish, Filipino and Chinese. However, the validity of the Nijmegen Questionnaire is often a point of discussion and we would like to make a few comments on that issue 3. The Nijmegen Questionnaire is useful to quantify and assess the normality of subjective sensations
Dixhoorn et al. (Fri,) studied this question.