Influence of Arterial Blood Pressure Variability on Cerebral Hemodynamics of TBI patients

Turalska,MS, Denton, TX; Dariusz Latka,PhD, Opole, Poland; Bruce J. West,PhD, Research Triangle, NC;

Marek Czosnyka,PhD, Cambridge, United Kingdom;

Abstract:

Introduction:

Aggressive cerebral perfusion pressure (CPP) oriented therapy has been associated with increased

extracranial complications of cardiovascular and respiratory origins. Surprisingly, CPP elevation does not lead

to a significant reduction of ischemic brain volume in most brain injury patients. To elucidate this paradox we

investigate the physiological significance of variability of cerebral blood flow.

Methods:

We employ wavelet variability V(f) to quantify dynamics of arterial blood pressure (ABP) and blood flow

velocity in the middle cerebral artery (MCA) in the very low-frequency band (VLF, 0.02-0.07 Hz). We

retrospectively analyzed the hemodynamic data of of 38 brain injury patients with low intracranial pressure

(ICP).

Results:

In the patients the ABP variability 0.36±0.28 mmHg was significantly smaller than that of the control group of

healthy volunteers 0.70±0.25 mmHg (p=7×10-5). Interestingly enough, the corresponding variabilities of MCA

flow for both cohorts are comparable, 0.90±0.50 cm/s of the brain injury patients is not statistically different

from that of the volunteers 1.06±0.41 cm/s (p=0.11).

Conclusions:

In the patients the VLF oscillations must have been spontaneously generated in the intracranial volume to

compensate for the reduced ABP variability. Vasomotion is indentified as a plausible physiological mechanism

underling spontaneous generation of blood flow oscillations. The variability of CBF induced by vasomotion

may be beneficial for brain tissue oxygenation, especially during critically low perfusion. We also discuss the

possibility of using pharmacological intervention or variable ventilation to increase the ABP fluctuations. These

oscillations may in turn enhance brain tissue oxygenation.

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