Cortical ischemia: effect upon direct cortical response.

Correlation of cortical blood flow as measured by a thermal diffusion flow probe (CBFp) with the direct cortical response (DCR) was studied in 48 lightly anesthetized cats with global ischemia. Thresholds for attenuation and loss of DCR were 21.3 +/- 4.7 and 8.7 and 3.4 ml/100 g/min respectively. In abrupt ischemia, CBFp of 0-3 ml/100 g/min produced absence of DCR in 6 min or less; however, at CBFp of 5-10 ml/100 g/min, the time to obliteration of DCR varied from 5 to 180 min. DCR was unlikely to recover after 13 min of 0-2 ml/100 g/min and after 35 min of 4-5 ml/100 g/min. At higher flows, DCR could recover over 60 min or more of ischemia. With gradual production of ischemia, flows less than 20 ml/100 g/min for over 60 min had a detrimental effect upon recovery of DCR if DCR was lost for 7.5 min or more. Some evidence that implied adaptability of the cortex to ischemia was found.