Chronic hypertension alters the relationship between collateral blood flow cortical cerebral blood flow, and brain tissue oxygenation

Abstract

This study measured the relationship between pial collateral (leptomeningeal anastomoses, LMA) flow, intraparenchymal cortical cerebral blood flow (cCBF) and brain tissue oxygenation (btO2) during acute ischemic stroke to investigate how pial flow translates to downstream cCBF and btO2 and examined how this relationship is altered in hypertension. Proximal transient middle cerebral artery occlusion (tMCAO) was performed in male Wistar (n = 8/group) and Spontaneously Hypertensive Rats (SHR, n = 8/group). A combination laser Doppler-oxygen probe was placed within the expected cortical peri-infarct in addition to a surface laser doppler probe which measured LMA flow. Phenylephrine (PE) was infused 30 minutes into tMCAO to increase blood pressure (BP) by 30% for 10 minutes and assessed CBF autoregulation. During the initial 30-minute period of tMCAO, btO2 and cCBF were lower in SHR compared to Wistar rats (btO2: 11.5 ± 10.5 vs 17.5 ± 10.8 mmHg and cCBF: −29.7 ± 23.3% vs −17.8 ± 41.9%); however, LMA flow was similar between groups. The relationship between LMA flow, cCBF and btO2 were interdependent in Wistar rats. However, this relationship was disrupted in SHR rats and partially restored by induced hypertension. This study provides evidence that cCBF and btO2 were diminished during tMCAO in chronic hypertension, and that induced hypertension was beneficial regardless of hypertensive status.