Baseline physiological state and the fMRI-BOLD signal response to apnea in anesthetized rats

✍ Scribed by Sridhar S. Kannurpatti; Bharat B. Biswal; A. G. Hudetz

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 243 KB
• Volume: 16
• Category: Article
• ISSN: 0952-3480
• DOI: 10.1002/nbm.842

✦ Synopsis

To decipher the biophysical mechanism behind the fMRI-BOLD response to apnea and its dependence on the baseline cerebral blood flow and oxygenation, fMRI and laser Doppler flow (LDF) studies were carried out in anesthetized rats. Baseline cerebral blood flow (CBF) and P a O 2 were modulated by ventilating with different gas mixtures namely, room air (21% O 2 ), 100% O 2 , carbogen (95% O 2 þ 5% CO 2 ), 2% CO 2 in air or 5% CO 2 in air, respectively. A decrease in BOLD signal intensity was observed after the onset of apnea with either room air, 2% CO 2 or 5% CO 2 ventilation. P a O 2 and cerebral tissue PO 2 decreased during apnea under these conditions. However, the apnea-induced BOLD signal intensity was unaffected with carbogen ventilation and increased with 100% O 2 ventilation, during which P a O 2 remained constant and cerebral tissue PO 2 increased. When baseline CBF was high during hypercapnia, a faster decrease occurred in the apneainduced BOLD signal. Apnea induced the largest increase in CBF of 85 AE 25% when ventilated with 2% CO 2 while a 44 AE 8% increase was observed with room air. During the other ventilatory conditions, minimal or no significant change in CBF was observed during apnea. These results show a significant correlation between the BOLD signal change and tissue PO 2 in response to apnea under different physiological conditions. Apnea-induced increase in CBF affects the magnitude of the BOLD signal response when P a O 2 remains constant or changes minimally.