Large Negative Stress Phase Angle (SPA) Attenuates Nitric Oxide Production in Bovine Aortic Endothelial Cells

[+] Author and Article Information
Michael B. Dancu

Biomolecular Transport Dynamics Laboratory, Department of Bioengineering, The Pennsylvania State University, University Park, PA 16802email: mbd131@psu.edu

John M. Tarbell

Department of Biomedical Engineering, The City University of New York, NY 10031email: tarbell@ccny.cuny.edu

J Biomech Eng 128(3), 329-334 (May 15, 2006) (6 pages) doi:10.1115/1.1824120 History: Received December 08, 2003; Revised May 12, 2004; Online May 15, 2006
Copyright © 2006 by ASME
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Representation of the stress phase angle (SPA). Blood flow (Q) in the axial direction induces tangential frictional force of wall shear stress (WSS) on the endothelial cell (EC) lined vascular wall. Blood pressure (P) imposes a normal (radial) stress on the wall from the lumen. Changes in pressure distend (strain) the wall and EC monolayer resulting in uniform circumferential strain (CS) due to the axisymmetric tubular geometry. EC experience pulsatile WSS and CS simultaneously; however, their magnitude and temporal phase may vary throughout the vasculature and in disease conditions. The stress phase angle (SPA) is used to characterize the dynamic mechanical stimuli experienced by the EC monolayer.
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Schematic of the hemodynamic simulator test section. Arrows indicate fluid path. Fluid flow enters upstream. Flow and pressure are recorded simultaneously in real-time, upstream, and downstream, respectively, along with diameter variation at the middle of the test section. Waveforms are generated via control of upstream, downstream, and external pressures. Fluid contacts only biocompatible materials (no metals). The test section can accommodate many specimens such as artificial arteries, ex vivo vascular segments, and parallel flow chambers.
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Various hemodynamic conditions in a silicone elastic tube with physiologic significance. (A), (B) The waveform ranges are: WSS 10±10 dyne/cm2 , P=70±20 mmHg, CS=4±4%, Q=700±500 ml/min, all at 1 Hz. Relevant features: tube of 8 mm diameter (unpressurized)×15 cm length (L) with 500 μm wall thickness, optically clear noncytotoxic silicone; media viscosity was increased with dextran to 6.4 centipoise (cP); unsteadiness parameter α=4.3; total media volume=175 ml; peak Reynolds number, Repeak=460; pH=7.2±0.05, at 37°C. (A) and (B) Corrected Q waveform magnitudes are shown that achieve the same WSS at different SPA in elastic tubes when P and D waveforms remain unchanged [see Eq. (4)].
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Production of NO (nitric oxide) from BAECs exposed to hemodynamic conditions in media at 5 h. Pairwise significant differences indicated by * for 0 deg and −180 deg, # for 0 deg and SS, and * * for dynamic and static controls with p values<0.05 (n=5). SC, static control; PC, pressurized control; SS, steady state; 0 deg and 180 deg, SPA.




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