Biofeedback of alveolar carbon dioxide tension and levels of arousal

This is a preliminary study designed to investigate the potential usefulness of alveolar (lung) CO₂ feedback training in promoting sleep onset in primary insomniacs. The present study was undertaken to determine if normal subjects could, without obvious manipulation of breathing, bring alveolar (lung) CO₂ tension under voluntary control using biofeedback techniques and, if so, whether this control would be accompanied by shifts in level of wakefulness. Subjects participated in five baseline and five training sessions in which EEG, alveolar CO₂ tension, and thoracic/abdominal respiratory movement were monitored. The feedback consisted of a pitch-modulated tone plus visual scores. We found that CO₂ tension in awake portions of up trials was significantly higher than for awake portions of down trials (p<.01), indicating that learning had occurred. In the initial trials, when subjects raised CO₂ tension they became drowsy and often fell asleep, and when they lowered CO₂ tension they aroused themselves. However, when subjects were awakened immediately upon falling asleep, there developed a decoupling of EEG and CO₂ changes. The presence of such a decoupling phenomenon makes it unclear whether CO₂ feedback will be useful in promoting sleep onset in primary insomniacs.This study was supported by National Institute of Mental Health Research Fellowship MH05151, Research Grant MH29369, Research Scientist Development Award MH38897, and by a Biomedical Research Support Grant to Langley Porter Institute, 507RR05755.