HODGKIN'S recent work The possibility of such an interaction between separate, active and resting, units is of interest from several aspects. (i) Normally, local currents set up in the vicinity of an active region do not, and obviously must not, excite adjacent fibres. Some mechanism apparently is present by which, not only the further propagation of the impulse in the active fibre, but also its "isolated conduction" is ensured. (ii) A subthreshold effect of an action potential on an adjacent fibre must be expected, however, since some part of the local current is bound to penetrate the surrounding tissue.The object of the present paper was to investigate the electric interaction between separate axons in a simple case, using a nerve preparation which contains two fibres only, and determining quantitatively (i) any excitability changes which might take place in one fibre during the passage of an impulse in the other, and (ii) any mutual interaction between impulses travelling simultaneously in both fibres.
A method developed for quantifying respiratory sinus arrhythmia (RSA) during voluntary cardiorespiratory synchronization relies on computer-assisted rhythmometric cosinor analysis of instantaneous heart rate data. The RSA was present in all subjects tested, even those at advanced ages. The amplitude of the RSA falls approximately 10 percent per decade. An individual with a transplanted heart and one with severe diabetic neuropathy each had resting RSA values that were normal for their ages. The shape and amplitude of the RSA during voluntary cardiorespiratory synchronization may reflect the suppleness of the heart and its response to rhythmically changing intrathoracic pressure and the subsequent ebb-and-flow of venous return. Our technology allows objective quantitative assessment of the biologic age of the heart and also the effect of any drug, disease, or behavior that affects the RSA.
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