Input impedance, wave travel, and reflections in the human pulmonary arterial tree: studies using an electrical analog.
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Electronics, Medical↗
Biomedical subjects
G H Pollack
Publications and source records attributed to G H Pollack.
Is stepwise sarcomere shortening an artefact? A response.
Like any other signals, optical signals from muscle fibres inevitably contain noise. The noise here is of predictable character. Because the structure of muscle is periodic, or almost so, translational movement of an illuminated fibre will inevitably give rise to a periodic noise fluctuation as striations pass across the optical field. The frequency of this fluctuation should be linearly related to the speed at which the fibre translates. By mistaking this noise component for the signal, Altringham and colleagues have amply succeeded in confirming this expected relationship, but they have left unanswered the question of the source and nature of stepwise shortening. I show here that: (1) by having obtained records in conditions in which the noise dominated, Altringham et al. have inadvertently confused the steps with the translation-induced fluctuation; and (2) when records are obtained using a method designed specifically to circumvent the effects of translation, the steps still remain in evidence.
Animals↗
[The mechanism of muscle contraction: along the path carved by Academician G.M Frank].
On the issue of the mechanism of muscle contraction, the views of the late G.M. Frank, to whom this symposium is dedicated, differed fundamentally from those of the then-current orthodoxy. Frank could not accept the idea of filament sliding brought about by swinging cross-bridges. He seemed particularly moved by two observations from his laboratory: the first, that the A-band shortened during active contraction; and the second, that sarcomere shortening occurred in stepwise fashion. From these findings principally, Frank came to the view that contraction involved a stepwise shortening of thick filaments. Although this view is broadly held to be incorrect, I will present evidence that it may constitute at least a partial answer. I will consider the evidence that both of Frank's principal findings-stepwise shortening and thick filament shortening-may be valid attributes of the contractile mechanism. I will then go on to show how these two attributes fit into an overall mechanism-not dissimilar to the one put forth by Frank.
Actins↗