Cerebral blood flow and tissue oxygen saturation in immediate and progressive ischemia in rat brain

Abstract

The aim of the present study was to investigate whether immediate ischemia is more harmful to the brain than progressive ischemia. To do so, we examined the correlation between the degree and the process of ischemia using hypobaric hypotension technique, which was used to reduce systemic blood pressure acutely or progressively below the lower threshold of CBF regulation, in rat brain. In Wistar rats (n = 21), global ischemia using bilateral carotid arteries occlusion coupled with hypobaric hypotension was induced by lowering mean arterial blood pressure (MABP) progressively to 55, 45 and 35 mmHg or immediately to 35 mmHg. Local cerebral blood flow (lCBF) by laser Doppler (LD) flowmetry and tissue hemoglobin oxygen saturation (HbSO₂) by a microspectrophotometric method were measured at 25 corresponding locations using a 'scanning' technique which employs a computer-controlled micromanipulator. Regional CBF (rCBF) and rHbSO₂ were determined by calculation of the median value from the 25 ICBF and lHbSO₂ data. In the 'progressive' group, rCBF and rHbSO₂ decreased gradually and reached 12.2 ± 15.8 LD-units and 44.9% ± 13.4% at 35 mmHg of MABP, respectively. In the 'immediate' group, both parameters dropped suddenly to 7.86 ± 10.6 LD-units (p < 0.01 vs. CBF of the progressive group) and 22.5% ± 15.5% (p < 0.001 vs. tissue HbSO₂ of the progressive group) from the control at 35 mmHg. These data suggested that cerebral ischemia is better tolerated if it is induced gradually. CBF recorded by LD-scanning technique and HbSO value by microspectrophotometric method correlated well in the ischemic condition, indicating that HbSO₂ can be preserved if CBF is decreased gradually. [Neurol Res 2001; 23: 875-880]