Cortical blood flow autoregulation revisited using laser Doppler perfusion imaging

Abstract

Methods of laser Doppler perfusion monitoring (LDPM) and imaging (LDPI) have been validated and found useful for measurements of brain blood flow in several studies. The present work was undertaken to examine the cortical blood flow autoregulatory phenomenon as it has lately been questioned and claimed to be method-dependent and related to sample volume. Spatial variations in cerebral cortical blood flow (CBF(cortex)) in the pressure range 20-140 mmHg (static cerebral autoregulation; caval block/angiotensin infusion) were studied in six mechanically ventilated (hypocapnic, normocapnic and hypercapnic) pigs anaesthetized with propofol and fentanyl. Although the cortical blood flow values sampled were highly heterogeneously distributed, they were strongly pressure-dependent as well as CO2-dependent (P < 0.001). A cumulative cerebral blood flow (CBF)-pressure (MAP) plot comprising all values obtained indicated a pressure range between 70 and 120 mmHg where CBF remained almost constant. However, at the local level in the cortex (mm2) the same type of 'classic' autoregulatory flow : pressure graphs (FPG) were found in only a few of the cases of the cortical areas examined (n = 96). Alterations in blood P(a)CO2 saturation did not affect the pressure : flow relationship at low perfusion pressures, whereas at normal or above normal values, and as anticipated, hypercapnia considerably increased CBF (P < 0.001). 'Classic' autoregulatory FPGs were found only when all values sampled were clustered together, whereas, as a new finding, data are presented indicating that autoregulatory capacity is lacking at the local level at some cortical surface areas.

Carotid compression: Investigation of cerebral autoregulative reserve in rats

“…The advantage of laser-Doppler in cerebral perfusion studies is its ability to measure continuously for up to several hours (Dirnagl et al, 1989). Compared with classical techniques of cerebral blood-flow measurement, such as tracer or radioactive labelling techniques, the laserDoppler has the necessary high time resolution to measure the dynamic properties of autoregulation (Eyre et al, 1988;Fabricius and Lauritzen, 1996;Kimme et al, 2002). According to recommendations of published protocols, we assured a position of the laser-Doppler probe in the capillary territory.…”

Microcirculatory Dysfunction in the Brain Precedes Changes in Evoked Potentials in Endotoxin-Induced Sepsis Syndrome in Rats

“…Although the technique measures flow velocity rather than flow, it is well accepted that relative signal changes allow accurate measurement of changes in regional cerebral blood flow [13, 22]. Together with appropriate surface electrodes, signals can be obtained nearly from the same cortical area [16, 19].…”

“…The laser Doppler technique has the needed high temporal and spatial resolution to investigate local changes in the dynamic vasoregulative function of the activation flow coupling [13, 22]. Although the technique measures flow velocity rather than flow, it is well accepted that relative signal changes allow accurate measurement of changes in regional cerebral blood flow [13, 22].…”

The predominance of metabolic regulation of cerebral blood flow and the lack of "Classic" autoregulation curves in the viable brain

“…One useful paper is by Kimme et al ., using laser Doppler perfusion imaging in pigs. [12] Varying CPP, they found “’classic autoregulatory flow pressure graphs’ were present only when all values sampled were clustered together.” With a different non-real time technique, positron emission tomography (PET) scanning, Steiner et al . found no relationship between CPP and CBF in normal appearing and abnormal appearing pericontusional brain.…”