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 PaCO(2) and PaO(2) on blood oxygenation level-dependent (BOLD) signal intensity determined by use of susceptibility-weighted magnetic resonance imaging in brains of isoflurane-anesthetized dogs.


METHODS
6 healthy dogs.


METHODS
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 PaCO(2) (20, 40, or 80 mm Hg) and PaO(2) (100 or 500 mm Hg) were combined to establish 6 experimental conditions, including a control condition (PaCO(2), 40 mm Hg; PaO(2), 100 mm Hg). Dogs were randomly assigned to different sequences of conditions. Each condition was established for a period of >or= 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
Compared with control condition findings, BOLD signal intensity did not differ significantly in any region of interest. However, signal intensities in the thalamus and diencephalic gray matter decreased significantly during both hypocapnic conditions, compared with all other conditions except for the control condition.


CONCLUSIONS
In isoflurane-anesthetized dogs, certain regions of gray matter appeared to have greater cerebrovascular responses to changes in PaCO(2) and PaO(2) than did others. Both PaO(2) and PaCO(2) should be controlled during magnetic resonance imaging procedures that involve BOLD signaling and taken into account when interpreting findings.
Rioja
Eva
E
Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada. evrioja@uoguelph.ca
Kerr
Carolyn L
CL
McDonell
Wayne N
WN
Dobson
Howard
H
Konyer
Norman B
NB
Poma
Roberto
R
Noseworthy
Michael D
MD
D018685:Anesthetics, Inhalation / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000502:physiology; D004285:Dogs; D006935:Hypercapnia / Q000097:blood*; D018496:Hyperoxia / Q000097:blood*; D016857:Hypocapnia / Q000097:blood*; D007530:Isoflurane / Q000494:pharmacology; D008279:Magnetic Resonance Imaging / Q000662:veterinary*; D008297:Male; D008991:Monitoring, Physiologic / Q000662:veterinary; D010100:Oxygen / Q000097:blood
D018685:Anesthetics, Inhalation; D007530:Isoflurane; D010100:Oxygen