Spinal cord blood flow measured by a hydrogen clearance technique

Spinal cord blood flow (SCBF) has been measured in segments of the thoracolumbar cord of dogs using the hydrogen clearance technique. Clearances were recorded and flows calculated from electrodes placed in grey and white matter. The position of the recording electrodes was marked by diathermy and confirmed in each experiment. The SCBF in the white matter for 82 clearances was 13.7+/-4.5 ml/100 g/min using pentobarbitone anaesthesia. In the grey matter both monoexponential and biexponential clearances were recorded from electrodes placed in grey matter. There was no difference in flows calculated from the monoexponentail and slow components. SCBF from the slow components or monoexponentials was 12.0+/-4.5 ml/100g/min. The flow from the fast component was 69+/-11 ml/100 g/min. with pentobarbitone anaesthesia and 97.5+/-32.9 ml/100g/min with alpha-chloralopse anaesthesia. The flow calculated from the fast component did not correlate to changes of PaCO2. The slow component of any biexponential clearances was used to calculate flows from electrodes placed in the grey matter. There was no significant difference between flows from the grey matter (calculated from the slow component) and the white matter. Simultaneously recorded cortical and sub-cortical -lows were higher than in spinal grey and white matter. There was considerable variation in flow from animal to animal. The area of spinal grey matter is small and surrounded by white matter and the flow recorded from electrodes placed in grey matter is probably the average SCBF representing a mixture of grey and white flow. This will arise because of the rapid diffusibility of hydrogen gas between the tissues. It is therefore difficult to ascribe the flow from a centrally placed cord electrode to a definite anatomical compartment.