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. 2014:812:43-49.
doi: 10.1007/978-1-4939-0620-8_6.

Role of microvascular shunts in the loss of cerebral blood flow autoregulation

Edwin M Nemoto  1 , Denis E Bragin  2   3 , Gloria Statom  2 , Mark Krasberg  2 , Suguna Pappu  2 , Bobby Sena  2 , Tracey Berlin  2 , Kim Olin  2 , Howard Yonas  2
Affiliations

Role of microvascular shunts in the loss of cerebral blood flow autoregulation

Edwin M Nemoto et al. Adv Exp Med Biol. 2014.

Abstract

Historically, determination of the critical cerebral perfusion pressure (CPP) was done in animals by a progressive lowering of arterial pressure yielding a nominal critical CPP of 60 mmHg. Subsequently, it was shown that if the CPP was decreased by increasing intracranial pressure (ICP), critical CPP fell to 30 mmHg. This discrepancy was unexplained. We recently provided evidence that the decrease in critical CPP was due to microvascular shunting resulting in maintained cerebral blood flow (CBF) at a lower CPP. We demonstrated by a progressive increase in ICP in rats using two-photon laser scanning microscopy (2PLSM) that the transition from capillary to microvascular shunt flow is a pathological process. We surmise that the loss of CBF autoregulation revealed by decreasing arterial pressure occurs by dilation of normal cerebral blood vessels whereas that which occurs by increasing ICP is due to microvascular shunting. Our observations indicate that the loss of CBF autoregulation we observed in brain injured patients that changes on an hourly or daily basis reflects an important pathophysiological process impacting on outcome that remains to be determined.

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Figures

Fig. 6.1
Fig. 6.1
Effect of altering cerebral perfusion pressure (CPP) by decreasing arterial pressure (thick line) and by increasing intracranial pressure (thin line) in dogs with intact autoregulation on cerebral blood flow (CBF). Significance between changes assessed by paired t-test [11]. *P < 0.05 [11]. Reproduced with permission of the Editor of Elsevier Press
Fig. 6.2
Fig. 6.2
(a) normal CPP (70 mmHg) and by (b) decreased CPP to 30 mmHg by increasing ICP. (c) Decreased MAP to reduce the CPP to 30 mmHg [10]. Reproduced with the permission of the Editor of J Neurotrauma
Fig. 6.3
Fig. 6.3
Ratio of capillary (CAP) and thoroughfare channel (TFC) shunt flow with increasing intracranial pressure (ICP) and different cerebral perfusion pressure (CPP) in rats. Increasing ICP increases TFC flow [11]. Reprinted with the permission of the Editor of Stroke Journal
Fig. 6.4
Fig. 6.4
Correlation coefficient plot of mean arterial pressure (MAP) and thermal diffusion cerebral blood flow (CBF) showing daily variations in correlation coefficients reflecting loss and return of CBF autoregulation
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