Program of the International Research Network on Cerebral Hemodynamic Regulation (CARNet) – #EB2014

The program of the International Research Network on Cerebral Hemodynamic Regulation (CARNet) is now known ! This program is very exciting !! Several world renowned researchers in cerebrovascular physiology will be in San Diego !

Please click on the link below to have a look at the different symposium and titles of posters that will be presented at this meeting.

International Research Network on Cerebral Hemodynamic Regulation Final Program

Will you be in San Diego ??

I won’t have to get rid of my TCD !

Because of its high temporal resolution in monitoring cerebral blood flow velocity changes in cerebral arteries, transcranial Doppler (TCD) represents a very interesting tool to characterize cerebral autoregulation (for basic information in regards to cerebral autoregulation, see post #1 and post #2).

The problem we have with this technology is that we are measuring a velocity, and not blood flow, since the diameter of intracranial arteries cannot be monitored with such a device. We have thus to assume that the diameter of these cerebral arteries remains constant in response to blood pressure changes.

In a recent paper, Liu et al. simultaneously monitored changes in cerebral blood flow velocity in the middle cerebral artery (with TCD) and internal carotid artery as well cerebral blood flow in the internal carotid artery (with color-coded duplex ultrasonography (CCDU) during steady-state changes in arterial pressure using sodium nitroprusside and phenylephrine in a group of healthy volunteers.

The authors tested the hypothesis that cerebral blood flow could be assessed equally well based on the measurements of cerebral blood flow velocity in the middle cerebral artery and volumetric cerebral blood flow in the internal carotid artery.

As stated by the authors, the outcome of this study would provide important information regarding the validity of using TCD (and thus to measure a velocity) to assess cerebral autoregulation during steady-state changes in arterial pressure.

In this study, cerebral autoregulation was characterized by linear regression of percentage changes in cerebral blood flow velocity, cerebral blood flow, cerebrovascular resistance index (estimated as mean arterial pressure/cerebral blood flow velocity), or cerebrovascular reactivity (estimated as mean arterial pressure/cerebral blood flow) in response to percentage changes in mean arterial pressure.

The main results appear in the Figure below:

Diapositive1

*For percent changes in cerebral blood flow/cerebral blood flow velocity: a slope of about 0 = intact autoregulation vs. increased slope = impaired autoregulation; **For percent changes in cerebrovascular resistance index/cerebrovascular resistance: a slope of about 1.0 = intact autoregulation.***This figure represents pooled data and not individual data.

As we can see, changes in cerebral blood flow velocity (A) and cerebrovascular resistance index (D) in response to arterial pressure changes measured in the middle cerebral artery using TCD were rather similar to those monitored in the internal carotid artery using CCDU (B and E). Since the regression slopes of changes in cerebral blood flow velocity to mean arterial pressure were small while those of changes in cerebrovascular resistance index to mean arterial pressure were large, these observations suggest presence of cerebral autoregulation.

Interestingly, when we look at changes in blood flow in the internal carotid artery in response to changes in arterial pressure (C), it remains unchanged notwithstanding large variations in mean arterial pressure. In addition, the regression slope of cerebrovascular resistance to mean arterial pressure (F) was steeper than that of cerebrovascular resistance index to mean arterial pressure. Accordingly, cerebral autoregulation seems underestimated when measuring blood flow velocity with TCD (when using this specific methodology).

Overall, this is great news! I won’t have to get rid of my TCD !!! Further research is however needed to elucidate if the autoregulation curve described by Lassen can be obtained within an individual, since it was not the case in this study.

References

Cerebral autoregulation of blood velocity and volumetric flow during steady-state changes in arterial pressure. Liu J, Zhu YS, Hill C, Armstrong K, Tarumi T, Hodics T, Hynan LS, Zhang R. Hypertension 2013 (Epub ahead of print)

Positions available in cerebral autoregulation

It came to my attention that three post-doctoral research posts are available in the field of cerebral autoregulation: Postdoc positions

You can direct enquiries and apply directly to each of the centres:

  • Southampton: Dr David Simpson (ds@isvr.soton.ac.uk); Dr Tony Birch (tony.birch@uhs.nhs.uk): https://www.jobs.soton.ac.uk/Vacancy.aspx?ref=297913KR
  • Oxford: Dr Stephen Payne (stephen.payne@eng.ox.ac.uk)
  • Leicester: Prof Ronney Panerai (rp9@leicester.ac.uk); Prof Tom Robinson (tgr2@leicester.ac.uk)

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CARnet at EB2014 !

For those who did not know, the 4th meeting of the Cerebral Autoregulation Research Network will be held in San Diego this year, in association with Experimental Biology 2014 !

Make sure to submit your cerebrovascular physiology abstracts before November 8th 2013 !

Topic categories

  1. Cerebral autoregulation in pathological conditions
  2. Cerebral autoregulation: the quandry of quantification
  3. Autonomic and other control of the cerebral circulation
  4. Cerebral blood flow regulation in aging

See you in San Diego !

One important issue regarding the classical model of cerebral autoregulation

I just read a very interesting, and provocative, review on cerebral autoregulation written by Shieak Tzeng and Phil Ainslie. These authors challenged existing paradigms regarding how brain perfusion pressure and brain blood flow are related. I definitely encourage you to read it (open access paper !).

In the first section of the review, they are presenting the original description of cerebral autoregulation from Lassen’s work, that has dominated cerebrovascular physiologists’ thinking on the association between blood pressure and brain perfusion:

CBF* is maintained at a constant level across a wide range of mean arterial blood pressure (60-150 mmHg)

In two previous posts (here and here), I’ve provided some information regarding static and dynamic cerebral autoregulation, skipping one important issue. As highlighted by Tzeng and Ainslie in this review:

Although Lassen’s diagram is widely cited as the “autoregulation curve” describing the pressure-flow relations within an individual, it must be acknowledged that each data point on the curve derives from independent subjects, and therefore represents inter- (not intra-) individual relationships.

Indeed,

In a review paper, Lassen constructed a plot of average pressure and flow from 7 studies involving 11 different patient groups with varying drug and pathology induced blood pressure levels.

So, one need to remember that piece of information from the original review paper when discussing their results related to static cerebral autoregulation !

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* CBF: Cerebral blood flow