Prediction of propagation block on the basis of impulse shape in single unit recordings from human nerves.

The occurrence of impulse block was studied in single unit recordings and related to impulse shape when peripheral nerves were impaled with tungsten needle electrodes. Exposed nerves were exploited in frog and cat and non-exposed nerves in man. Three different impulse shapes were seen: 1. Negative spikes of very short durations which nearly all propagated. 2. Positive double peaked spikes which all propagated. 3. Positive single peaked spikes which were of two different natures: one which propagated and one which did not. The findings suggest that urinary impulses recorded witha needle electrode impaling the myelin are positive and single peaked when the injury is minimal. Gradually a propagation delay might develop at the site of impalement giving rise to a double peak. Later the propagation may be blocked which is seen as a drop out of the second peak. The collected sample of observations indicates that it was possible to predict in practically all cases whether the propagation was blocked or not from the shapes of the single unit impulses and their alterations as seen by the tungsten needle electrode.