Response of spinal cord oxygen tension to aortic occlusion

In order to study the factors influencing spinal cord injury resulting from occlusion of the descending aorta, the local surface PO2 (sPO2) was measured in the lumbar region (L4-5) of the exposed spinal cord after laminectomy in the pig. This is the area supplied by the arteria radicularis magna anterior (ARMA). The following aspects were considered: duration of occlusion, blood supply by the ARMA, distribution and width of spinal cord collaterals. The animals were divided into two groups. In group I (n = 7) the descending aorta was occluded immediately below the left subclavian artery; in group II (n = 7) the abdominal aorta was occluded immediately superior to the ARMA. Occlusion induced a rapid sPO2 decrease in all animals, from 29 to 3 mm Hg in group I (-14 mm Hg/min) and from 28 to 8 mm Hg in group II (-12 mm Hg/min). After 45 minutes of occlusion the blood flow through the aorta was released giving a pronounced sPO2 overshoot (36 mm Hg) about 10 minutes later. After 20 minutes there had been a return to initial sPO2 values. The results of this study confirm the hypothesis that spinal cord injury during occlusion of the descending aorta is primarily due to ischemic hypoxia/anoxia.