In vitro study of acute elevations of endoneurial pressure in mammalian peripheral nerve sheath

In previous studies of peripheral nerve edema, endoneurial fluid pressure rarely exceeded 7 mm Hg for even the most edematous nerves. In a recent study a time-dependent reduction in elastic modulus was reported. However, because of the chronic nature of the studies, pressure and volume changes were not directly recorded from the same nerves. In the present study mammaliam perineurial compliance was directly studied in vitro. When compliance ( ΔV ΔP) was compared between nerves subjected to slow rates of ΔV (0.7μl/min) and fast rates (7 μl/min), mean values were reduced for all pressure intervals but did not become statistically significant because of considerable variability between nerves. However, in a separate series of experiments, when the same nerve sheath was consecutively subjected to these two rates of Δ V, compliance was consistently and significantly (P < 0.001, paired t test) greater for slow ΔV, confirming directly the importance of a time-dependent change in elastic modulus, i.e., a viscous modulus. A tentative physiologic-morphologic correlation is made. No evidence was found for norepinephrine- or acetylcholine-responsive contractile elements.