Flow Forms

Flowforms


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The pictures and movies above show variants of the Flowform principle, discovered and described by A John Wilkes. Cavities are shaped to accommodate spontaneous cycles of wave propagation over streams that enter continuously, but recirculate asymmetrically and rhythmically. This oscillation may be seen as a liquid counterpart of compression-wave oscillation in wind instruments such as whistles and flutes. John Wilkes' initial discovery was of the dual-cavity type (upper row, left and centre) with symmetrically paired cavities in which flow oscillates from side to side. The single, asymmetric cavity variant, which converts continuous inflow to intermittent outflow (lower row, and upper row, right) was devised by Philip Kilner (writing this), while studying with John Wilkes - a discovery that led on to studies of flow through the heart. The flow sculpture, top right, was made in copper by Philip Kilner and is at Royal Brompton Hospital in London. There may be relationships between the spontaneous, asymmetric flow cycles in cavities of Flowforms, on the one hand, and the cycles of flow through cavities of the heart, on the other. Blood flow cycles, however, are dominated by contraction of heart muscle, initiated by cells of the 'pacemaker' region, whereas cycles in Flowforms arise through cyclic propagation of surface waves, deriving their energy from the inflowing stream. Cyclic redirection the momentum of inflowing blood, with passive displacement of relaxed, compliant cavity walls, must, however, be an aspect of heart rhythm, obscured by the dominance of myocardial contraction. The functional role of this passive interaction, which may prime muscle fibres for subsequent contraction, could be at atrial rather than ventricular level, and more on exercise than at rest. Blood entering from veins takes a finite time to flow in, turn and exit - a period that may be coupled to myocardial compliance and contraction. It is on exertion that dynamics of blood momentum-change, of vascular and myocardial elasticity, and of myocardial contraction are likely come into vigorous, tightly coupled interaction. Asymmetric flow oscillators illustrated above also raise a question about evolutionary origins of the looped, ventrally located heart found in the vertebrates. It seems likely that the ventral heart emerged in a pre-existing circulatory system, through which blood may have been moved by compression or contraction of more widely distributed vessel segments. Could passive or partly passive oscillatory cycles have played a part in establishment of a sinuous vessel region as the favoured location for what evolved to become the looped curvatures of the vertebrate heart? Compare forms of a small water trickle oscillator, flowing downwards and leftwards, with those of (even smaller) chick embryo hearts, which in the drawings below would be flowing up the screen: