Revised views of the refractory period, in relation to drugs reputed to prolong it, and in relation to circus movement / by T. Lewis and A.N. Drury.

  • Thomas Lewis
Date:
[1926]
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Licence: Public Domain Mark

Credit: Revised views of the refractory period, in relation to drugs reputed to prolong it, and in relation to circus movement / by T. Lewis and A.N. Drury. Source: Wellcome Collection.

    7/10 page 99
    block numerals. The measurements support the conclusions already arrived at from our original records that under quinidine the lengthening of the refractory period is more apparent than real, and show in addition, that the real absolute refractory period may be actually shortened by this drug. The shortening of the period is well displayed in Dog ZF, where the refractory period measured by the usual method is conspicuously lengthened. In view of what has been said, it should be apparent that no measure- ments of the absolute refractory period of cardiac muscle which have been obtained by the method of simple response or non-response and which have also shown conspicuous lengthening of the period, can be regarded as reliable. All such have become open to revision. There are many such measurements in past writings, but we shall confine ourselves to our own.? 56 Our previous statements, that quinidine and strophanthin prolong the absolute refractory period of mammalian auricular muscle, are based on evidence which we have now criticised. If these statements are no longer justified by actual evidence, it remains to consider to what extent conclusions based on them still hold. Now these last conclusions apply chiefly to the action of the drugs named upon waves circulating in the auricle ° From this point of view, although our original measurements under quinidine and strophanthin were not of the absolute refractory period in its proper sense, they measured that which it was most desirable for us to obtain, namely, the effective refractory period. Although the end of the absolute refractory period signals the instant at which the muscle will again respond, at least in part, it does not necessarily signal the first instant at which it will again transmit a propagated wave to any distance. | If therefore, the term absolute refractory period, or more briefly refrac- tory period, is read in our previous publications as meaning the effective refractory period, the conceptions expressed as to the action of quinidine and strophanthin upon circus movement, require no revision. Thus, it is our conception that circus movement is brought to an end by quinidine by the action of the drug in prolonging the effective refractory period of the muscle.* One further matter requires comment. In explaining many effects previously recorded, and particularly varieties of intra-auricular block, it has been assumed that the muscle in its recovery passes through what has * Certain incidental conclusions which have been drawn regarding the recovery of excitability and of conduction under quinidine and strophanthin are affected. Thus, because the threshold value of shocks required to drive the auricle rhythmically was raised but little under quinidine, this was thought to be sufficiently explained by a rise in the absolute refractory period, and by the consequent shortening of the period of rest (see a previous article ®, page 60). If there is no material lengthening of the absolute refractory period under quinidine, then the rest period 1s - not materially shortened, and the rise in the threshold value would then be attributable to an actual effect of quinidine on the recovery curve. hie Similar considerations apply to the statements regarding fibre conduction in a previous article’ on strophanthin. . Doubt is also thrown, for the same reason, upon the conclusion drawn by Lewis and Master® that quinidine lengthens the refractory period of the A-V node.
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