In WO 00/38591 there is disclosed tubing, especially blood flow tubing, which induces helical flow in such fashion as to eliminate or substantially reduce turbulence and dead flow regions in the tubing, with the aim of eliminating or substantially reducing tendency to thrombus and plaque formation. There is also disclosed helical formation in stents, with the same end in view. It is natural to suppose that, the vascular system being the primary source of clots and plaques, it is sufficient to protect it, or at least whatever part of it is being replaced, by conditioning flow through it by means of formations within the system itself.

It now appears, however, that further measures will lead to further improvements, and the invention provides such further measures.

The invention comprises a pulsatile pump having an internal configuration and/or action such as to induce helical flow in the fluid being pumped.

The use of a pulsatile pump as a prosthetic heart, or a heart assist device, assumes surgery at the site of the heart. Surgery inevitably involves anastomosis of blood vessels, which involves modification, almost certainly not for the better, to the pattern of blood flow and increased risk of plaque and thrombus formation at or near that site. Using the teachings of WO 00/38591 aforementioned, helical flow is not induced until the blood enters the vascular system from the heart pump, and almost certainly not straight away. There is now seen to be considerable advantage in having the blood already flowing with a helical component as it enters the vascular system, and the

provision of an internal configuration to the pump according to the invention can ensure that the blood already has a helical flow component on leaving the pump.

The pump may have an internal helical configuration.

Such configuration may be a static such configuration, the helical flow being induced by the fluid's passing along it.

The helical configuration may be of a core with an external helix. A distendable chamber may surround the core and be alternately expanded to fill with fluid and contracted to expel fluid.

The internal helical configuration may, however, be of a chamber with an internal helix. A distendable body may expand and contract within the said chamber alternately to expel fluid from the chamber and fill the chamber.

However, the internal helical formation may be distendable and comprise a variable volume chamber, expansion and contraction of which expels the fluid therefrom and draws fluid thereinto.

Expansion and contraction, in any event, may be effected by means of a driving fluid, itself pumped by a mechanical pump. Contraction may be effected by elastic recovery from an expanded condition.

The pump may have valving determining the direction of flow through the pump.

The pump may have an electrically driven prime mover, which (or any other prime mover) may drive a piston-in-cylinder or like arrangement to expand and contract a pumping volume.

Embodiments of pumps according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic lengthwise section of a first embodiment; Figure 2 is a section like Figure 1 of a second embodiment; and Figure 3 is a section like Figure 1 of a third embodiment.

The drawings illustrate pulsatile pumps 11 having an internal configuration and/or action such as to induce helical flow in the fluid being pumped. In each case, the pump 11 has an internal helical configuration 12.

In the embodiments of Figures 1 and 2, the internal helical configuration 12 is static, and the helical flow is induced by the fluid's passing along it.

In Figure 1, the internal helical configuration 12 is of a core 13 with an external helix 14. A distendable chamber 15 surrounds the core and is alternately expanded (solid line) to fill with the fluid being pumped and contracted (broken line) to expel the fluid.

In Figure 2, the internal helical configuration is of a chamber 21 with an internal helix 22. A distendable body 23 expands (solid line) and contracts (broken line) within the chamber 21 alternately to expel fluid from the chamber 21 and fill the chamber 21.

Figure 3 illustrates an embodiment in which the internal helical formation 12 is itself distendable and comprises a variable volume chamber 31 which has a lengthwise corrugated shape and which is twisted. Expansion (solid line) draws the fluid into the chamber 31 and contraction (broken line) expels it, the helical formation 12 imparting a helical component to the flow.

In each embodiment, expansion and contraction is effected by means of a driving fluid 16, itself pumped by an electrically driven mechanical pump 17, contraction being effected by elastic recovery of the distendable component from an expanded condition. The distendable component is in each case contained within a rigid vessel 18 into which the driving fluid 16 is pumped. The mechanical pump 17 is shown as a piston-in-cylinder arrangement.

Valving 19 at the inlet and outlet of the pump 11 determines direction of fluid flow through the pump. The valving 19 could itself have an internal helical formation to augment the rotational component of flow induced by the pumping action.

For use as prosthetic hearts, the pumps 11 will be fashioned in biocompatible materials. The action of the embodiments described with reference to the drawings is such as not to apply shear forces and undue compression through a small space such as might damage blood components, but other arrangements could be designed based on different pumping principles with those aims in view. The pumps can be made small enough to be accommodated within the chest cavity in place of or alongside a natural heart to substitute for or assist same. The pumps may be driven otherwise, of course, than electrically, and, particularly in the case of a heart-assist pump, may be driven by muscular contraction, surgically arranged.

Pumps according to the invention may find numerous other uses, both within and outwith the clinical field. Such pumps might well find application in dialysis,

for example, being kinder to blood than some rotary pumps. The inducement of a helical flow within the pump may well improve flow at pump-pipeline interfaces in pumping oil and other industrial products, especially where flow is required to be, or will benefit from being, pulsatile, or where piston-in-cylinder pumps are used in any event.

Rotary pumps will usually impart rotation to a flow, but this may be simply regarded as an artefact of the pumping method rather than as something deliberately introduced, and the rotation may be totally unsuitable to the circumstances, it being generally desirable, according to WO 00/38591, to reduce turbulence and eliminate dead regions in the flow. It may be that rotary pumps could benefit from modification to the helical flow they necessarily induce, as by having a flow modifying section after an impeller.