Effects of hypercapnia, hypocapnia, and hyperoxemia on blood oxygenation level-dependent signal intensity determined by use of susceptibility-weighted magnetic resonance imaging in isoflurane-anesthetized dogs.

Objective—To assess the effects of alterations in PaCO2 and PaO2 on blood oxygenation level–dependent (BOLD) signal intensity determined by use of susceptibility-weighted magnetic resonance imaging in brains of isoflurane-anesthetized dogs. Animals—6 healthy dogs. Procedures—In each dog, anesthesia was induced with propofol (6 to 8 mg/kg, IV) and maintained with isoflurane (1.7%) and atracurium (0.2 mg/kg, IV, q 30 min). During 1 magnetic resonance imaging session in each dog, targeted values of PaCO2 (20, 40, or 80 mm Hg) and PaO2 (100 or 500 mm Hg) were combined to establish 6 experimental conditions, including a control condition (PaCO2, 40 mm Hg; PaO2, 100 mm Hg). Dogs were randomly assigned to different sequences of conditions. Each condition was established for a period of ≥ 5 minutes before susceptibility-weighted imaging was performed. Signal intensity was measured in 6 regions of interest in the brain, and data were analyzed by use of an ANCOVA and post hoc Tukey-Kramer adjustments. Results—Compa...