Abstract
This paper describes an instrument to measure, in situ, the longitudinal stresses and strains that are developed in a blood vessel segment subjected to a small sinusoidal longitudinal deformation. The instrument generates length changes of arbitrary amplitude and frequency and measures electrically both the magnitude of these length changes and the corresponding longitudinal force in the segment. Even though the overall tissue response is nonlinear, the axial stress due to the small pulsatile changes in force is linearly related to the ensuing strain and, because of the viscous components of the tissue, the strain lags the stress. Experiments on ten canine aortic segments indicate that for frequencies between 0.5 and 5 Hz this phase angle is small (less than 10°) and increases slightly with frequency.
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