Reduction of compartment compliance increases venous flow pulsatility and lowers apparent vascular compliance: Implications for cerebral blood flow hemodynamics

Hu, Xiao; Alwan, Abeer A.; Rubinstein, Eduardo H.; Bergsneider, Marvin

doi:10.1016/j.medengphy.2005.07.006

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Volume 28, Issue 4 , Pages 304-314, May 2006

Reduction of compartment compliance increases venous flow pulsatility and lowers apparent vascular compliance: Implications for cerebral blood flow hemodynamics

Xiao Hu
- Division of Neurosurgery, The David Geffen School of Medicine at UCLA, University of California, 10833 LeConte Ave., 74-134 CHS (Mail-Code 956901), Los Angeles, CA 90095-6901, USA
- Biomedical Engineering Program, The David Geffen School of Medicine at UCLA, University of California, Los Angeles, USA
Abeer A. Alwan
- Biomedical Engineering Program, The David Geffen School of Medicine at UCLA, University of California, Los Angeles, USA
- Department of Electrical Engineering, The David Geffen School of Medicine at UCLA, University of California, Los Angeles, USA
Eduardo H. Rubinstein
- Department of Anesthesiology, The David Geffen School of Medicine at UCLA, University of California, Los Angeles, USA
- Department of Physiology, The David Geffen School of Medicine at UCLA, University of California, Los Angeles, USA
Marvin Bergsneider
- Division of Neurosurgery, The David Geffen School of Medicine at UCLA, University of California, 10833 LeConte Ave., 74-134 CHS (Mail-Code 956901), Los Angeles, CA 90095-6901, USA
- Biomedical Engineering Program, The David Geffen School of Medicine at UCLA, University of California, Los Angeles, USA
- Corresponding author. Tel.: +1 310 206 4100; fax: +1 310 825 7245.

Received 1 November 2004; received in revised form 9 June 2005; accepted 4 July 2005. published online 22 August 2005.

Abstract

The global compliance of a fixed-volume, incompressible compartment may play a significant role in determining the inherent vascular compliance. For the intracranial compartment, we propose that the free-displacement of the cerebral spinal fluid (CSF) directly relates to cerebral vascular compliance. To test this hypothesis, an in vivo surrogate intracranial compartment was made by enclosing a rabbit's kidney within a rigid, fluid-filled container. Opening/closing a port atop the box modulated the free flow of box fluid (open-box state). We observed that the pulsatility of the renal venous outflow increased in response to hampering the free flow of fluid in-and-out of the container (closed-box state). To associate the observed pulsatility changes with the compliance changes, a parametric method was proposed for the computation of the apparent compliance (C_app) of the whole renal vascular system. The calculated C_app for each experiment's closed-box state was favorably compared to a time-domain compliance assessment method at the mean heart rate. In addition, it was revealed that C_app in the open-box state was greater than that in the closed-box state only when the calculations were performed at frequencies lower than the heart rate and closer to the ventilation rate. These experimental results support the concept that the vessel compliance of vascular systems enclosed within a rigid compartment is a function of the global compartment compliance.

Keywords: Intracranial pressure, Windkessel model, Apparent compliance