Effects of changes in carbon dioxide tension in abnormally prolonged contingent negative variation (CNV).

The effects of changes in pCO2 in the development and resolution of normal (return to base line within 2 sec after S2) and abnormal (return to base line in more than 2 sec after S2) CNVs were studied. Decreased pCO2 produced by hyperventilation induced a significant reduction in the duration of the post-imperative negative variation (PINV) without significantly affecting the amplitude of the CNV. Increased pCO2, by inhalation of 5% CO2, on the contrary, produced prolongation of the PINV in two subjects. Control subjects with normal CNVs did not show significant changes in the amplitude or in the duration of the CNV wave when pCO2 was altered. The results are discussed in terms of the possible independence and higher sensitivity to metabolic changes of the PINV brain generators compared with the generators of the CNV wave per se.