Method of fabricating a heater coil for a catheter used to monitor cardiac output

• US 5,676,784 A
• Filed: 03/15/1995
• Issued: 10/14/1997
• Est. Priority Date: 03/15/1995
• Status: Expired due to Term

• Current Assignee: Hospira Incorporated (Pfizer Inc.)
• Original Assignee: Abbott Laboratories Incorporated
• Inventors: McGaffigan, Thomas Haynes
• Primary Examiner(s): ECHOLS, PERCY W
• Application Number:
  US08/404,893
• Time in Patent Office: 944 Days
• Field of Search: 29/611, 29/447, 128/713, 128/691, 607/115, 607/122, 604/113, 604/114, 174/47, 156/86, 156/187, 156/194, 156/195, 156/172, 156/274.2, 156/309.6
• US Class Current: 156/172
• CPC Class Codes: A61B 5/028 by thermo-dilution
• CPC Class Codes: A61M 25/0012 with embedded structures, e.g. coils, braids, meshes, strands or radiopaque coils
• CPC Class Codes: Y10T 29/49083 Heater type
• CPC Class Codes: Y10T 29/49865 by temperature differential [e.g., shrink fit]

Abstract

A heater (12) for a catheter (10) used in monitoring constant cardiac output is fabricated using a bifilar wire (21) coated with polyvinyl chloride (PVC) like the material used for the catheter. The bifilar wire is coated with the PVC using a conventional extrusion technique, producing a coated lead (24, 32). This coated lead is wrapped around the exterior surface of the catheter, forming a helical coil. Heat is applied to the coated lead to melt the PVC coating, causing it to bond the lead to the catheter. The melted PVC also flows into gaps (23) or notches between adjacent coils of the lead, producing a relatively smooth outer surface for the heater coil when the PVC coating cools. The bifilar wire can alternatively be wrapped in-line with PVC tape (29) or film and the PVC material heated to flow around the wire, bonding it to the catheter'"'"'s outer surface.

Claims

1. A method for making a heater for a catheter that is employed to monitor cardiac output, comprising the steps of:

(a) providing a catheter having at least one lumen adapted to accept a heater lead;

(b) coating a wire with a thermoplastic material to form a coated lead;

(c) winding the coated lead around the catheter to form a heater coil, said heater coil having gaps between adjacent coils of the coated lead; and

(d) elevating the temperature of the heater coil above a melting temperature of the thermoplastic material, causing said material to flow into and fill the gaps between adjacent coils of the coated lead and bonding the heater coil to the catheter.

2. The method of claim 1, wherein the adjacent coils of the coated lead do not contact each other when the heater coil is wound, and wherein when the thermoplastic material melts, said material flows into and fills the gaps to form a generally smooth outer surface on the heater coil.

3. The method of claim 1, wherein the adjacent coils of coated lead contact each other when the heater coil is wound, said gaps comprising notches disposed adjacent the surface of the catheter and outwardly of points where the coils of the coated lead contact each other, and wherein when the thermoplastic material melts, said material flows into the notches to form a generally smooth outer surface on the heater coil.

4. The method of claim 1, wherein the coated lead has a generally circular cross-sectional shape.

5. The method of claim 1, wherein the coated lead has a generally quadrilateral cross-sectional shape.

6. The method of claim 1, wherein the wire that is coated comprises a bifilar wire.

7. The method of claim 1, wherein the step of elevating the temperature comprises the steps of.

(a) positioning a heat-shrink tube over the heater coil;

(b) applying heat to the heat-shrink tube to elevate the temperature of the heater coil above the melting temperature of the thermoplastic material via conduction of the heat through heat-shrink tubing and to shrink the heat-shrink tubing to form the thermoplastic material as said material melts; and

(c) removing the heat-shrink tubing from the heater coil after the thermoplastic material cools.

8. A method for attaching a heater to a catheter comprising the steps of:

(a) winding an insulated heater wire around an exterior surface of the catheter;

(b) applying a plastic material over the insulated heater wire;

(c) subjecting the plastic material to an elevated temperature so that the plastic material experiences a change in state and secures the insulated heater wire to the exterior surface of the catheter; and

(d) cooling the plastic material to an ambient temperature.

9. The method of claim 8, wherein the step of winding the insulated heater wire comprises the step of forming a plurality of helical windings of the insulated heater wire around the exterior surface of the catheter, adjacent helical windings having a notch between them.

10. The method of claim 9, wherein a predetermined distance between the adjacent helical windings is selected so that a cross-sectional area of a gap formed between adjacent windings of the insulated heater wire is less than a cross-sectional area of a portion of the plastic material disposed radially beyond the insulated heater wire in the helical winding, said portion of the plastic material flowing into and substantially filling the gap between the adjacent helical windings when heated.

11. The method of claim 9, wherein the plastic material is applied to the insulated heater wire by wrapping the plastic material to form a layer over an outer diameter of the helical windings.

12. The method of claim 8, wherein the plastic material comprises polyvinyl chloride (PVC), and wherein a characteristic melting temperature of the PVC is less than or equal to a melting temperature of a material comprising the catheter.

13. The method of claim 8, wherein the insulated heater wire comprises a pair of conductors, said conductors comprising the pair extending substantially parallel to each other, each conductor being covered with an insulating sheath, said insulating sheath of each conductor being bonded together along a line extending longitudinally along the insulating sheath.

14. The method of claim 8, wherein the step of subjecting the plastic material to the elevated temperature comprises the steps of electrically coupling the insulated heater wire to a source of an electrical current;

and, causing the electrical current to flow through the insulated heater wire, said electrical current heating the insulated heater wire above a characteristic melting temperature of the plastic material to cause the change in state.

15. The method of claim 8, wherein the step of subjecting the plastic material to the elevated temperature comprises the step of applying an external source of heat to the plastic material, said external source of heat transferring heat to the plastic material so that the temperature of the plastic material effects the change in state.

16. The method of claim 9, further comprising the step of enclosing the catheter with the insulated heater wire wound around the catheter in a mold prior to subjecting the plastic material to the elevated temperature, said mold forcing the plastic material to flow into the gap between the adjacent helical windings.

17. A method for producing a coiled conductor having a substantially smooth surface, on an exterior of a catheter, said method comprising the steps of:

(a) extruded a thermoplastic coating on a wire, said thermoplastic coating being selected in part for its characteristic melting temperature, said wire having an electrically insulating layer that is substantially covered by the thermoplastic coating;

(b) coiling the wire covered by the thermoplastic coating around the catheter, forming a plurality of adjacent coils; and

(c) heating the thermoplastic coating on the wire that is coiled above its characteristic melting temperature, causing the thermoplastic coating to melt and flow, forming a substantially smooth outer surface over the adjacent coils and adhering the wire to the catheter.

18. The method of claim 17, wherein the wire is bifilar, comprising a pair of side-by-side conductors, separately covered with the insulation.

19. The method of claim 17, wherein the step of heating the wire, comprises the step of enclosing the catheter with the wire coiled around it in a mold, and wherein heat is applied externally to the mold.

20. The method of claim 17, wherein the step of heating comprises the steps of attaching a source of electrical current to the wire, and enabling sufficient electrical current to flow through the wire to increase its temperature above the characteristic melting point of the thermoplastic coating.

21. The method of claim 17, wherein the step of heating comprises the steps of:

(a) positioning a heat-shrink tube around the adjacent coils of the wire;

(b) heating the heat-shrink tube, causing it to shrink around the coils of the wire, heat being transferred through the heat-shrink tubing to the thermoplastic coating to raise said coating above its melting temperature, and said heat-shrink tube shrinking around the thermoplastic coating to form it around the coils of the wire; and

(c) removing the heat-shrink tube after the thermoplastic coating has cooled.

22. A method for securing a heater on an exterior of a catheter, said method comprising the steps of:

(a) coiling an insulated wire around an outer surface of the catheter, forming a plurality of adjacent coils;

(b) covering the coils of the insulated wire with a plastic material; and

(c) heating the plastic material to an elevated temperature so as to cause the plastic material to change state and form around the outer surface of the coils, said plastic material thereby securing the insulated wire to the outer surface of the catheter.

23. The method of claim 22, wherein the plastic material comprises a heat-shrink material that shrinks when heated to the elevated material, shrinkage of the heat-shrink material comprising the change of state.

24. The method of claim 23, wherein the heat-shrink material comprises a tube that is slipped over the coils of the insulated wire, and which is shrunk tightly around the wire when heated to the elevated temperature.

25. The method of claim 23, wherein the heat-shrink material is heated to the elevated temperature with hot air.

26. The method of claim 22, wherein the plastic material comprises a tape that is wrapped around the coils of the insulated wire, said tape being melted when heated to the elevated temperature and flowing around the coils and bonding to the outer surface of the catheter.