If we suppose that the smooth muscle of the vessel wall develops an additional stress when the vessel wall is stretched, a mathematical analysis shows that in the absence of a natural positive damping of the pulse wave a negative damping constant might result, whereas the propagating speed of the pulse wave will be but slightly altered. This effect occurs only when the additional stress lags behind the elastic deformation. In reality, the positive damping due to visco-elasticity will generally be greater than the negative one due to muscle activity, in such a way that the positive damping will only be reduced by the latter. But some experiments on dogs let us surmise, that the negative damping exceeded the positive one.
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