Agreement between ultrasonic Doppler venous outflow and Kety and Schmidt estimates of cerebral blood flow

1, The present study compares the indirect Fick nitrous oxide equilibration method of Kety and Schmidt for cerebral blood dow (CBF) estimation with a direct ultrasonic Doppler index of venous outflow, 2, Cerebral blood how was determined simultaneously by the direct measureme nt of sagittal sinus blood velocity and the indirect Kety and Schmidt metho d in five anaesthetized sheep during high and low steady states of CBF. Hig h- and low-flow states were achieved by altering ventilation to produce hyp ercarbia and hypocarbia, respectively, 3, Four different sets of calculations were used to make the Kety and Schmi dt estimations: arterial-venous nitrous oxide concentration differences dur ing uptake or elution of the indicator and with or without extrapolation of arterial-venous differences to infinity. 4. During 15 min nitrous oxide administration, apparent blood:tissue equili bration of nitrous oxide was rapid in some data sets and slow in others. 5, There were no significant differences in CBF estimates between any of th e four Kety and Schmidt calculations or the direct ultrasonic Doppler venou s outflow method; however CBF estimates based on nitrous oxide uptake corre lated more strongly with the direct method than estimates based on nitrous oxide elution, 6, in the high-how state, CBF estimates based on nitrous oxide uptake, but not those based on elution, distinguished between rapid and slow blood:tiss ue equilibration of nitrous oxide. 7, This provides validation of the Doppler sheep brain venous outflow metho d against the widely used Kety and Schmidt method.