Quantitative Correlation of Hyperventilation with Flicker Sensitivity

Abstract

The relationship between hyperventilation and the associated increase in flicker sensitivity is poorly defined but may be relevant to display viewing. This exploratory study investigates the potential for quantifying the relationship between the severity of hypocapnia and critical flicker frequency (CFF). Repeated ascending (fusion) and descending (flicker) measurements were made while breathing normally (normocapnia), and at four levels of progressive, mild to moderate hypocapnia that were induced by voluntary hyperventilation and controlled using continuous respiratory mass spectrometry. The mesopic stimulus was a 2.6 degree-Gaussian blob viewed through a 5.2-mm-diameter artificial pupil. Five discrete respiratory conditions were generated. The influences of intersubject variability and severity of hypocapnia upon mean CFF were examined using two-way analysis of variance, demonstrating a statistically significant effect of target end-tidal partial pressure of carbon dioxide [F(4,40) = 4.63, p = 0.005]. The relationship between decreasing mean end-tidal partial pressure of carbon dioxide and increasing mean CFF was consistent with a linear correlation (Pearson R = -0.949, p = 0.013). The results support a close relationship between the respiratory partial pressure of carbon dioxide and flicker sensitivity. However, the absolute magnitude of the underlying increase in flicker sensitivity with hypocapnia is small and the effect is unlikely to be relevant in aviation.