title: Mechanisms of cerebrovascular O2 sensitivity from hyperoxia to moderate hypoxia in the rat.
abstract: Cerebrovascular dilation over PaO2 ranging from hyperoxia to moderate hypoxia is unexplained. We hypothesize that tissue acidosis is the cause. Local cortical cerebral blood flow (LCBF), tissue hydrogen ion concentration [H+]t, and tissue PO2 (PtO2) were measured with microelectrodes in the parietal cortex of 18 rats during a 30-min steady state on 60 to 10% inspired O2 (PaO2, 300 to 40 torr) during 40% N2O analgesia. Five rats kept on 60% O2/40% N2O served as controls. In 18 rats at a PaO2 of 275 +/- 7 torr (mean +/- SEM) and PaCO2 of 35 +/- 1 torr, cerebral values were: LCBF = 129 +/- 23 (mean +/- SEM) ml.100 g-1.min-1; [H+]t = 62 +/- 6 nM; and PtO2 = 25 +/- 3 torr. As PaO2 was reduced from about 300 to 40 torr, changes in these variables in percentage of control with respect to PaO2, were described by the following equations, all at P less than 0.0001: LCBF = 85.9 + 5,572/Pao2; [H+]t = 97.15 + 1,012/PaO2; and PtO2 = 108.8 - 3,492/PaO2. Simultaneous solution of the LCBF and [H+]t equations at various PaO2 revealed a slope of 8.82%/nM. Direct correlation between LCBF in ml.100 g-1.min-1 and [H+]t in nM revealed a linear relationship defined by the equation Y = -7.472 + 1.6705X (r = 0.6426) for [H+]t between 56 and 160 nM (pH = 7.25 and 6.80) but no correlation at [H+]t values between 56 and 32 nM (pH = 7.25 to 7.50). Cerebrovascular tone is directly correlated with [H+]t during progressive, 30-min steady-state reduction in PaO2 from 350 to 40 torr.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh School of Medicine, Pennsylvania 15261.
authors.forename: T
authors.initials: T
authors.lastname: Shinozuka
authors.forename: E M
authors.initials: EM
authors.lastname: Nemoto
authors.forename: P M
authors.initials: PM
authors.lastname: Winter
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D002560:Cerebrovascular Circulation; D000860:Hypoxia / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D010100:Oxygen