In situ transverse elasticity and blood perfusion change of sciatic nerves in normal and diabetic rats.

BACKGROUND: Diabetic neuropathy is the most pervasive complication of diabetes mellitus and its etiopathology is not completely elucidated. The existing literature focuses on the histological and structural changes as well as the longitudinal mechanical properties of nerves. The main objective of this study is to investigate the in situ transverse biomechanical properties and changes of microcirculation of sciatic nerves in diabetic and normal control rats. METHODS: Quasi-static circular compression experiments were conducted on sciatic nerves of six normal and six diabetic Wistar rats. Local blood perfusion during the compression was also measured by laser Doppler flowmetry. The compressive stress and strain were estimated, in order to calculate the apparent Young's modulus. The impact of diabetes on peripheral nerves was examined by analyzing the transverse elasticity and microcirculation changes. FINDINGS: The mean transverse apparent Young's modulus of the sciatic nerves in diabetic rats was 210.7 kPa, which was nearly two times greater than that of normal controls (116.3 kPa). The pressure threshold that blood perfusion started to decrease in diabetic rats (24.1 mm Hg) was smaller than in the normal controls (47.1 mm Hg). INTERPRETATION: These results suggest that the sciatic nerve was stiffer in the diabetic rats. The structural changes in microvessels might lead to earlier decrease of blood perfusion in diabetic nerves under radial compression. These results provide information about the biomechanical and microcirculation changes of peripheral nerves inflicted by diabetes and may also serve as a reference for clinical nerve repair and regeneration for patients with diabetic neuropathy.

In situ biomechanical properties of normal and diabetic nerves: an efficient quasi-linear viscoelastic approach.

Biomechanical properties of nerves were investigated using the quasi-linear viscoelastic model. An improved parameter estimation technique based on fast convolution was developed and tested in sciatic nerves of normal and diabetic rats. In situ dynamic compression response of sciatic nerves was obtained by a modified custom-designed compression system. Six normal and five diabetic neuropathic Wistar rats were used. The model derived from the high strain rate (0.1 s(-1)) data could predict the responses of lower strain rates (0.05 and 0.01 s(-1)) satisfactorily. The computation time was cut down 49.0% by using the newly developed technique without increasing the root-mean-square error. The percentage of stress relaxation of the diabetic and normal rats, calculated directly from the experimental data, was not significantly different (51.03+/-1.96% vs. 55.97+/-5.89%, respectively; p=0.247). After model fitting, compared with the QLV parameters of normal nerves, the smaller parameter C for diabetic nerves (0.27+/-0.06 vs. 0.20+/-0.02, p < 0.05) indicated that diabetic nerves had a smaller amplitude of viscous response (stress relaxation). The larger parameter tau(2) of diabetic nerves (199+/-153 s vs. 519+/-337 s, p<0.05) implied that diabetic nerves needed a longer relaxation period to reach equilibrium.

Transverse elasticity and blood perfusion of sciatic nerves under in situ circular compression.

Biomechanical properties and microcirculation of peripheral nerves under circular compression are vital factors for nerve repair and for developing neural prostheses. Quasi-static circular compression experiments on six rabbit sciatic nerves were performed. The mean estimated Young's modulus of the sciatic nerves in the transverse direction was 66.9+/-8.0 kPa. The blood perfusion of the nerve started to decrease at a mean pressure of 30.5 mmHg and reached a stable lower level of 30% of pre-compression value at 102.8 mmHg. The findings may make a contribution to safer design of cuff electrodes to be used in neural prostheses.