STUDIES IN THE BEHAVIOUR OF LIMB MUSCLES AND NERVES DURING EXPERIMENTAL ISCHÆMIA
Authors: Reid Charles 
Published: December 2014

Skeletal muscle shortens slightly in the early part of an ischæmic period, but tends to lengthen in the later part. The readmission of blood is followed by an immediate shortening of the muscle. The length of the muscle varies irregularly during the fibrillary phase, which occurs between the 2nd and 7th minute in the human limb.The extent of the voluntary contraction, as tested by infrequent single contractile efforts, is hardly affected by ischæmic of 15 minutes' duration. After this time a rapid decline sets in, with the result that the power of voluntary movement disappears almost completely in the course of 25 to 30 minutes, while (diminished) contractile response can be still got from nerve‐trunk and from direct muscle‐stimulation by single induced shocks, faradic and galvanic currents. The earlier failure of the voluntary effort is not accounted for by the raised threshold referred to below.During ischæmic there is decreased excitability (raised threshold) to single induced shocks and faradic currents, the stimuli being applied to nerve‐trunk, motor point, or muscle direct; after ischæmic has lasted for some minutes, there is evidence of increased excitability to galvanic currents. After the re‐establishment of the circulation, the full extent of the voluntary contraction is recovered in about 10 to 15 minutes. Decreased excitability to single induced shocks and faradic currents is well‐marked, especially with minimal and submaximal stimuli; at the same time the muscle is relatively more excitable to galvanic stimuli. But the characteristic reactions of degeneration are not fully reproduced.During the phase of fibrillary twitchings the response to voluntary and all forms of peripheral stimulation (minimal and submaximal) is depressed, faradic stimulation being least affected; in the later part of this phase there is prolongation of the muscle curve.In the rabbit, ischæmic of a portion of a nerve‐trunk of nearly two hours' duration did not abolish conduction or excitability. Likewise the direct excitability of muscle was not lost during ischsemia of over two hours' duration. A muscle, however, will not respond to nerve‐trunk stimulation after nearly one hour of ischwemia. This indicates a selective effect of ischaomia on the field of conjunction between nerve and muscle.In animal experiments the results obtained as regards muscular response to electrical stimulation are in substantial agreement with those for man, although the fibrillary phase and lengthening of the muscle#x2010;curve were not seen.The staircase phenomenon, in contractions excited voluntarily or artificially during a period of ischemia, is well#x2010;marked in the early stages; but is absent or of a descending order in the later stages. It is well#x2010;marked in the early post#x2010;ischlumic recovery stage; indefinite during the early part of the fibrillary phase, but present in the subsequent depressive post#x2010;ischwmic period with strong stimuli.While ischamia of under 15 minutes' duration has little effect on the strength of response to a single voluntary effort, it reduces greatly the total amount of work (prior to fatigue) of which a voluntary muscle is capable during a series of active contractions, as compared with the muscle with continuous circulation. The total work differs little when begun at different periods of time in the first 15 minutes of ischæmic. Thereafter the decline in the sum of voluntary work proceeds much more rapidly in the course of the succeeding 10 minutes.Faster rates of voluntary contraction produce more work (up to the fatigue point) than slower rates in experiments carried out shortly after the induction of ischæmic‐this is due possibly to the augmenting influence of a rapid series of contractions.I am indebted to Professor
MacWilliam for much help and suggestion in the above studies, the expense of which has been assisted by a grant from the Carnegie Trust for the Universities of Scotland.