THE TIME RELATIONS OF THE ELECTRICAL AND MECHANICAL RESPONSE OF HEART MUSCLE

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Abstract
An instrumentation for registering the mechanical and electrical responses of contracting muscle is described. Its advantages are: (a) in sensitivity it compares favorably with and is perhaps superior to Einthoyen''s Saitenmyo-graphion, particularly in the greater delicacy of its moving system; (b) the moving element is conveniently removable, so that interchangeable elements may be used for different experimental applications; (c) it can be largely put together of standard parts; (d) it is comparatively inexpensive. Its chief disadvantage is its susceptibility to adventitious mechanical vibration, necessitating careful mechanical shielding. De Jongh''s study on the temporal relation of the electro- and mechano-gram of the frog''s ventricle was repeated, showing that this apparatus can register all types of curves obtained with the Saitenmyograph. Of 710 curves from the excised terrapin sinus, there was no clear case of simultaneity, the Eg definitely preceding Mg in practically every instance. Implications of the records are that deJongh''s conclusion as to the simultaneity of mechano-and electrogram is not entirely convincing, due to (1) comparative infrequency of simultaneous curves; (2) lack of outside criteria of the reliability of "optimum pressure," and (3) his disposition of the galvanometer leads.

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