We investigated metabolic changes in prefrontal and parietal cortices and EEG changes during a long-term breath holding (BH) in professional divers. He/she performed BH for 2 to 7 minutes following a preparatory period of approximately 5 minutes. Such BH procedures were repeated 3 times in this study. We measured metabolic changes in cerebral cortex using near-infrared spectroscopy (NIRS) and made spectral analysis of EEG before, during and after BH. Concentration of deoxygenated hemoglobin (deoxyHb) showed a gradual increase during BH in both prefrontal and parietal cortices. There is a linear relationship between the maximal level of deoxyHb and the duration of BH. In contrast, concentration of oxygenated hemoglobin (oxyHb) of BH decreased along with prolonged duration of BH. Voluntary abdominal breathing (VAB) was performed during the preparatory period before BH. Spectral analysis of EEG was focused on the high-frequency alpha (HF-alpha) band (10-13Hz) in this study. The higher power of HF-alpha band was observed before and immediately after the onset of BH, and thereafter the HF-alpha power exhibited a gradual decrease until the end of BH. Since previous study showed that VAB produced increase in HF-alpha power and urinary 5-HT level (fumoto et al, 2004), we suggest that the higher HF-alpha power evoked before BH may contribute to the tolerance to cerebral hypoxia during BH. [J Physiol Sci. 2006;56 Suppl:S75]
