Automated assessment of intranasal trigeminal function

Background:The intranasal trigeminal system is a key player in the perception of intranasal airflow. Why it has not been studied very well may be due to the lack of techniques that allow for fast, reliable and inexpensive routine investigation of the system. The basis of the current study is the notion that - within limits - the intranasal trigeminal system detects the overall mass of a stimulus and not just its concentration. Thus, changing the duration of the stimulus at a given concentration has a similar effect as changing its concentration. Methodology: Ninety-nine normosmic subjects participated [48 women and 51 men; mean (range) age = 45 years (20-88 years)]. In addition, 50 patients with olfactory loss were investigated once (28 women, 22 men; mean age 58 years, SD = 14 years; age range 24-88 years; causes of olfactory loss: viral infections n = 22, head trauma n = 8, chronic sinunasal disease n = 3, idiopathic n = 17). CO2-stimuli with various durations (multiples of 50 ms) were presented through a standard bilateral nasal cannula at an interval of 10 s; stimulus duration was increased by 50 ms from one stimulus presentation to the next, until the subject pushed a button indicating a painful sensation. This was the basis for automated assessment of CO2-pain responsiveness. Results:This current study had four main findings: (1) Using the new, automated device CO2 pain responsiveness can be measured reliably, (2) CO2 pain responsiveness correlates with olfactory function, (3) as with olfaction, women are more sensitive to CO2, and CO2-pain responsiveness also correlates with aging, (4) CO2-pain responsiveness is lower in patients with olfactory loss compared to normosmic, healthy controls, even when controlling for age. Conclusion: We have demonstrated that the current approach is a reliable and valid measure of intranasal trigeminal function.