Written By: Jacob Poliskey

When you see an image of an oil rig floating in the ocean, what do you think of?  The scent of crude oil weighing heavily in the breeze, or maybe the gasoline you pump into your car?  How about inferior vena cava filters?  The oil industry doesn’t seem like the best place to look for an answer to how to make a better filter for thrombotic blood—believe it or not, that’s where the inspiration came from.

Figure 1: An umbrella filter would often become completely thrombosed, stopping blood flow.

A 23-year-old man was in a motorcycle accident. Trauma makes for a terrific environment for blood clots, and soon the man’s blood was clotting in his veins and traveling to his lungs.  The year was 1968, and Dr. Lazar Greenfield was the youthful surgeon who operated on him that day. He successfully removed the clots from his lungs, but the man died from bleeding as a complication of the surgery. Frustrated that he had to treat pulmonary emboli like this, Dr. Greenfield wondered if there was a better way.  Two years later, the first Kim-Ray Greenfield inferior vena cava (IVC) filter was in the making.1

IVC filters had been used before, but they had their share of issues. They were shaped like inverted umbrellas (figure 1). These worked to stop large clots from reaching the lungs, but at the same time the clots would back up and stop blood flow. The umbrella filters would also become so clogged that the built-up pressure would dislodge the filter from the wall of the large vein, letting the clots get through to the lungs.2

Figure 2: A conical filter traps debris from oil and gas, serving as inspiration for the current Greenfield IVC filter.

When Dr. Greenfield set out to make a new filter, he joined up with an unlikely teammate. Garman Kimmel was a prolific inventor of valves and pumps in the oil industry, tinkering with medical devices only on the side. Dr. Greenfield, who had been collaborating with Kimmel on a device to measure pulmonary surfactant, brought the problem up. Kimmel noticed how similar it was to a problem that the oil industry had been dealing with for years: sludge in buried oil pipelines.3 From the minds of Kimmel and Greenfield came the classic IVC filter with six legs in the shape of a cone, not dissimilar to a “witches hat” filter that is still in use today (figure 2). The ingenuity of this invention was that a large clot could form in the center—filling up to 80% of the volume of the cone—without substantially obstructing the blood from flowing around it (figure 3).4 Over time, the clot would slowly dissolve.

Many iterations of the IVC filter have been put forth, with different materials and designs. The Greenfield filter has changed as well. Still, IVC filters would not be so commonly used if these two inventors from completely different fields had not put their heads together and changed medicine forever.

Figure 3: The Greenfield filter compels a clot to gather in the center, redirecting flow around it (red - fastest flow; blue - slowest flow).

Sources

1. Garber K. The Clot Stopper. Invention & Technology Magazine. http://www.inventionandtech.com/content/clot-stopper-0. Published 2006. Accessed July 3, 2020.

2. Greenfield LJ, Zocco J, Wilk J, Schroeder TM, Elkins RC. Clinical Experience with the Kim-Ray Greenfield* Vena Caval Filter. Annals of Surgery. 1977;185(6):692-698. doi:10.1097/00000658-197706000-00012

3. Greenfield LJ. Article Commentary: Historical Reminiscence: Origin of the Greenfield Filter. The American Surgeon. 2010;76(12):1319-1320. doi:10.1177/000313481007601213

4. Greenfield Vena Cava Filters. Boston Scientific. https://www.bostonscientific.com/content/dam/bostonscientific/pi/portfolio-group/vena-cava-filters/greenfield/resources/Greenfield_Sell_Sheet_PI-25210-AA.pdf.

5. McCollum, C. (1987). Vena caval filters: keeping big clots down. BMJ, 294(6587), 1566. https://doi.org/10.1136/bmj.294.6587.1566