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Richard E. Strain, Jr.; William H. Olson, MD
Vanderbilt University School of Medicine Nashville, Tenn

JAMA. 1975;231(8):811.

	Since this article does not have an abstract, we have provided the first 150 words of the full text PDF and any section headings.

To the Editor.—

Dr. Margolis is correct in the special situation where the transmural pressure is directed outward, as in the usual vascular case. However, the P in Laplace's Law^1,2 T=PxR for an infinitely long, infinitely thinwalled cylinder is defined to be the transmural pressure P_tm, which is equal to the internal pressure P_, minus the external pressure P_e, P_tm=P_i—P_e. It is obvious for P_tm greater than 0 that increasing P_e will decrease P_tm and decrease the stress (tension) in the wall of the cylinder. This is the usual vascular case to which he refers. But in the case of a pressure neuropathy, P_tm is less than 0 because the nerve axons are compressed. Thus, increasing P_e causes P_tm to become "more negative" and therefore increases the stress (compression) in the axonal membrane. This stress and . . . [Full Text PDF of this Article]

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