Cerebral blood flow and resistances during hypotensive haemorrhage in the rabbit: transcranial Doppler and laser‐Doppler flowmetry

Abstract

Transcranial Doppler (TCD) determined cerebral blood flow velocity and laser Doppler flowmetry (LDF) measured cortical perfusion were simultaneously assessed during hypotensive haemorrhage in 15 anaesthetized rabbits. Systolic (Fsys), diastolic (Fdia) and mean (Fmean) blood flow velocities were recorded into the intracranial internal carotid (ICA) and basilar artery (BA). Resistance (RI = Fsys-Fdia/Fsys) and pulsatility (PI = Fsys-Fdia/Fmean) indices were calculated. Step decreases of 10 mmHg of mean arterial pressure (MAP) from 80 to less than 30 mmHg provoked a fall of LDF signal below 50 mmHg. Blood velocities decreased into BA below 40 mmHg, and below 50 mmHg into ICA indicating regional differences in cerebral autoregulation. Cortical resistances (resLDF = MAP/LDF) fell below 60 mmHg whereas RI and PI increased when MAP decreased into BA below 40 mmHg and ICA below 50 mmHg. A weak correlation was found between Fmean and LDF (BA: r = 0.55, P < 0.01 and ICA = 0.46, P < 0.01). Both RI and PI were poorly correlated to resLDF into BA (RI-resLDF: r = -0.39, P < 0.01; PI-resLDF: r = -0.39, P < 0.01) and ICA (RI-resLDF: r = -0.18, ns; PI-resLDF: r = -0.22, ns). Pulse pressure (systolic-diastolic pressure) correlated with RI (ICA: r = -0.62, P < 0.001; BA: r = -0.61, P < 0.001) and PI (ICA: r = -0.61, P < 0.001; BA: r = -0.62, P < 0.001). In conclusion, during haemorrhagic shock, TCD correlates with LDF and indicates regional differences in autoregulatory settings. However, Doppler indices do not reflect the changes in cerebral resistances because they are influenced by the changes in pulsatile pressure.

The effects of body mass index on cerebral blood flow velocity

“…This analysis was cross-sectional and was focused on long-term relationship between BFV and background variables, rather than dynamics of autoregulation using beat-to-beat BFV-BP variablity or CO 2 reactivity, to assess long-term adaptation of cerebral vasculature at baseline and during orthostasis. Previous studies have shown that BFVs in the MCA correlate with invasive measurements of blood flow with xenon clearance [22], laser Doppler flux [15] and PET [30]. MCA diameter was not different between the groups and remains relatively constant under physiological conditions [27].…”

Comparison of Carotid Arterial Resistive Indices With Intima-Media Thickness as Sonographic Markers of Atherosclerosis

“…This could be explained by the self-regulating intracranial flow. 19 The extensibility of elastic vessels (such as the CCA and ICA), and thus the windkessel function, decreases with age, as does the diastolic flow fraction, and the vascular resistance increases. 20 -22 The correlation we find between RI and IMT of the ICA is much greater than that reported by Ishimura et al 12 for IMT of the CCA and the RI of the renal arteries in diabetics, which clearly indicates that structural vascular wall alterations directly influence the RI.…”

Hypocapnia and Cerebral Hypoperfusion in Orthostatic Intolerance

“…These techniques accurately measure relative changes in a wide range of conditions. MCA flow velocity correlates with cerebral blood flow, measured with xenon clearance techniques 14 or with laser Doppler flux 15 and flow velocity estimates. Flow velocity can increase because of an increased flow through the arterioles distal to the probe or a constriction of the insonated trunk.…”