This study was performed to examine the influence of isoflurane anesthesia on the pulsatility index (PI) and the peak systolic velocity (PSV) of the blood flow in the basilar artery of dogs by duplex Doppler ultrasonography. Twelve healthy dogs were used to measure the PI and the PSV under the conscious state and isoflurane anesthesia. The pulsatility index (PI) and the peak systolic velocity (PSV) in the basilar artery were measured five times with random intervals. The blood pressure was measured. The PI and PSV values in dogs under isoflurane anesthesia were 1.37 +/- 0.32 and 72 +/- 19 cm/sec, whereas those in the conscious dogs were 1.37 +/- 0.13 and 81 +/- 16 cm/sec, respectively. The indirect mean arterial systolic and diastolic pressures under isoflurane anesthesia were 107 and 51 mmHg, whereas those in the conscious dogs were 133 and 74 mmHg. Though the isoflurane is generally known to induce hypotension, there were no significant differences in the PI and PSV between the isoflurane-anesthetized and the conscious dogs. In conclusion, the isoflurane anesthesia did not influence the PI and PSV in the basilar artery of dogs.
Anesthetics, Inhalation/*pharmacology ; Animals ; Basilar Artery/drug effects/*ultrasonography ; Blood Flow Velocity/drug effects/veterinary ; Blood Pressure/drug effects ; Cerebrovascular Circulation/drug effects ; Dogs/*physiology ; Female ; Isoflurane/*pharmacology ; Male ; Pulsatile Flow/drug effects ; Ultrasonography, Doppler, Duplex/veterinary

OBJECTIVEA large body of experimental and clinical observations indicates that disturbances in cerebral blood flow (CBF) and impaired cerebrovascular autoregulation are important in the pathogenesis of germinal matrix-intraventricular hemorrhage (GMH-IVH) and periventricular leukomalacia (PVL), the 2 most important forms of brain injury in pretmature infants. Near-infrared spectroscopy (NIRS) has been used recently to estimate CBF in human newborns. The objectives of this study were to evaluate the correlation of NIRS estimations and cerebral blood flow in newborn piglets, which in turn may help provide the ideal NIRS estimation reflecting the changes of cerebral blood flow and cerebrovascular autoregulation.

METHODSTen newborn piglets, aged 1 - 3 days, were randomly assigned to one of the following groups: normal control group (n = 6) and hypotension group (n = 4). Hypotension was induced by withdrawing blood from an arterial catheter. We NIRS was used to determine quantitative changes in cerebral concentrations of oxygenated hemoglobin (DeltaHbO(2)) and deoxygenated hemoglobin (DeltaHHb), then calculated NIRS estimations DeltatHb (DeltaHbO(2)+DeltaHHb) and DeltaHbD (DeltaHbO(2)-DeltaHHb). Cerebral blood flow (CBF) was determined by colored microspheres, and mean artery blood pressure (MABP) measured by arterial catheter pressure transducer was recorded simultaneously. Linear regression methods were used to analyze the relationships between NIRS estimations, CBF measured by micropheres, and MABP.

RESULTSThe correlation of NIRS estimations and CBF was quantitated by calculating coherence scores. A coherence of 1.0 indicates perfect correlation, a coherence of 0 indicates a complete lack of correlation. In the norm group, the experimental study showed strong correlations beween DeltaHbD, DeltatHb and changes in global CBF (GCBF), cerebral cortex CBF (CBFc), coherence scores r(1a) = 0.409, r(1b) = 0.440, r(2a) = 0.394 and r(2b) = 0.400, respectively, P < 0.05. In the hypotension group, the decrease of CBF was significant when the MABP dropped to 35 mm Hg (P < 0.05). With the decreasing MABP, there was a notable increase of DeltaHHb (P < 0.01), a modest increase (P < 0.05) at the beginning and then a marked fall (P < 0.01) of DeltaHbO(2) and DeltatHb was noted when the MABP dropped to 35 mm Hg. DeltaHbD decreased in parallel with the decline in CBF determined by colored microspheres, DeltaHbD varied with CBF during hypotensive episodes. Notably, there was a very strong correlations between DeltaHbD and changes in CBF (coherence scores GCBF r(3a) = 0.890, CBFc r(3b) = 0.887, P < 0.01); Importantly, decreases in DeltatHb did not correlate significantly with decreases in CBF during hypotension (coherence scores GCBF r(4a) = 0.395, CBFc r(4b) = 0.375, P > 0.05). Concordant changes (correlation coefficient > 0.5) in DeltaHbD, CBF and MABP, consistent with impaired cerebrovascular autoregulation, were observed in newborn piglets when MABP was less than 35 mm Hg. When MABP was more than 35 mm Hg, newborn piglets with intact cerebrovascular autoregulation in which CBF are maintained constant despite alternations in MABP have shown inconsistent changes in DeltaHbD, CBF and MABP (correlation coefficient < 0.5).

CONCLUSIONDeltaHbD signal is more sensitive to changes in CBF than DeltatHb signal, in terms of cerebral hemodynamic changes both in normal and hypotensive conditions, while DeltatHb in normal condition. The lower limit of CBF autoregulation in newborn piglets aged 1 - 3 days was 35 mm Hg, and correlation between NIRS estimation (DeltaHbD) and MABP could be used to identify cerebrovascular autoregulation in newborn piglets.

Animals ; Animals, Newborn ; Blood Flow Velocity ; drug effects ; Cerebrovascular Circulation ; physiology ; Homeostasis ; Hypotension ; physiopathology ; Oxygen ; metabolism ; Spectroscopy, Near-Infrared ; methods ; Swine

In the present study, we tested whether maintenance of adequate cerebral perfusion pressure (CPP) by pharmacologically preventing systemic hypotension with dopamine infusion would prevent cerebral ischemia and attenuate energy depletion and neuronal injury even though intracranial pressure remains elevated in a newborn piglet meningitis model. Cerebral blood flow, measured at the end of the experiment using fluorescent microspheres, was significantly increased by dopamine infusion. The decreased cerebral cortical cell membrane Na+, K+-ATPase activity and increased lipid peroxidation products, indicative of meningitis-induced brain damage, were significantly attenuated by dopamine infusion. Dopamine also significantly attenuated the meningitis-induced reduction in both brain ATP and phosphocreatine levels and the increase in brain lactate level. In summary, maintenance of adequate CPP with dopamine prevented cerebral ischemia, reduced cerebral energy depletion, and attenuated brain injury in neonatal bacterial meningitis.
Animals ; Animals, Newborn ; Brain/cytology/drug effects/*physiology ; Cell Membrane/*metabolism ; Cerebrovascular Circulation/*drug effects ; Dopamine/metabolism/*pharmacology ; Fluorescent Dyes/metabolism ; Hemodynamic Processes ; Meningitis, Escherichia coli/*metabolism ; Microspheres ; Random Allocation ; Regional Blood Flow ; Support, Non-U.S. Gov't ; Swine

The aim of this study was to develop a nonlinear mixed-effects model for the increase in cerebral oximetry (rSO2) during the rapid introduction of desflurane, and to determine the effect of hypocapnia and N2O on the model. Twelve American Society of Anesthesiologist physical status class 1 and 2 subjects were allocated randomly into an Air and N2O group. After inducing anesthesia, desflurane was then increased abruptly from 4.0 to 12.0%. The PET(CO2), PET(DESF) and rSO2 were recorded at 12 predetermined periods for the following 10 min. The maximum increase in rSO2 reached +24-25% during normocapnia. The increase in rSO2 could be fitted to a four parameter logistic equation as a function of the logarithm of PET(DESF). Hypocapnia reduced the maximum response of rSO2, shifted the EC50 to the right, and increased the slope in the Air group. N2O shifted the EC50 to the right, and reduced the slope leaving the maximum rSO2 unchanged. The N2O-effects disappeared during hypocapnia. The cerebrovascular reactivity of rSO2 to CO2 is still preserved during the rapid introduction of desflurane. N2O slows the response of rSO2. Hypocapnia overwhelms all the effects of N2O.
Adult ; Anesthetics, Inhalation/*pharmacology ; *Cerebral Cortex/blood supply/drug effects/physiology ; Cerebrovascular Circulation/*drug effects/physiology ; Female ; Hemodynamics ; Humans ; Hypocapnia/*metabolism ; Isoflurane/*analogs & derivatives/pharmacology ; Male ; Middle Aged ; Models, Theoretical ; Nitrous Oxide/*metabolism ; *Oximetry ; Random Allocation ; Regional Blood Flow/drug effects