Cardiac prosthetics and fully implanted artificial limbs.

Oct 20, 2014

No matter how you cut it, heart failure is one of those conditions that sends a chill down your spine. When the heart muscle grows weak and inefficient, it compromises blood flow through the body and can cause a host of other conditions, some weird, some additionally dangerous. Depending on how severe the condition is there are several ways of treating it. For example, my father in law has an implanted defibrillator that monitors his cardiac activity, though fairly simple lifestyle changes have worked miracles for his physical condition in the past several years. Left ventricular assist devices, implantable pumps that connect directly to the heart to assist in its operation are another way of treating heart failure. Recently, a research team at the Wexner Medical Center of Ohio State University reported remarkable results with a new assistive implant called the C-Pulse. The C-Pulse is a flexible cuff that wraps around the aorta and monitors the electrical activity of the heart; when the heart muscle contracts the C-Pulse contracts a fraction of a second later which helps push blood through the aorta to the rest of the body. A lead passes through the skin of the abdomen and connects to an external power pack to drive the unit. The test group consisted of twenty patients with either class III or class IV heart failure. The patients were assessed six and twelve months after the implantation procedure, and amazingly a full 80% of the patients showed significant improvements, and three of them had no symptoms of heart failure. Average quality of life metrics improved a full thirty points among the test subjects. I'm not sure where they're going next, but I think a full clinical trial is on the horizon for the C-Pulse. One to keep an eye on, to be sure.

A common problem with prosthetics, be it a heart, an arm, or what have you is running important bits through the skin to the outside world. Whenever you poke a hole through the skin you open a door to the wide, fun world of opportunistic infections. Anything and everything that can possibly sneak through that gap in the perimeter and set up shop in the much more hospitable environment of the human body will try. This is one of the major reasons why permanently attaching prosthetic limbs has been so difficult. To date various elaborate mechanisms which temporarily attach prosthetic limbs to the remaining lengths of limbs, including straps, fitted cups, and temporary adhesives have been tried with varying degrees of success. At the Royal National Orthopaedic Hospital in London they've begun clinical trials of ITAP, or Intraosseous Transcutaneous Amputation Prosthesis. In a nutshell, they've figured out how to implant attachment sockets in the remaining bones of limb amputees that can penetrate the skin with minimal risk of infection by emulating how deer antlers pass through and bond with the skin. This means that prosthetic limbs can be locked onto the body and receive just as much physical support (if not slightly more) than organic limbs do. Test subject Mark O'Leary of south London received one of the ITAP implants in 2008 (yep, six years ago and only now is it getting any press) and was amazed at not only how well his new prosthetic limb worked, but how being able to feel the road and ground through his prosthetic and into the organic part of his leg. Discomfort on the end of his organic limb is also minimized because there is no direct hard plastic-on-skin contact causing him pain. Apparently not one to do things by halves, O'Leary put his new prosthetic limb to the test by undertaking a 62 mile walk on the installed limb, and for an encore he climbed Mount Kilimanjaro with it.

Another hurdle toward the goal of fully operational prosthetic limbs has been restoring the sense of touch. Experiments have been done over the years with everything from piezoelectric transducers to optical and capacitative pressure sensors, but mostly they've been of use to robotics research and not prosthetics because the bigger problem of figuring out how to patch into nerves on a permanent basis was impeding progress. At Case Western Reserve University a research team successfully accessed the peripheral sensory nerves of amputees and then figured out what patterns of electrical stimulation on which nerves felt like which parts of the patients' missing hands. The inductive nervelinks were connected to patterns of sensors mounted on artificial arms developed at Case Western and the Louis Stokes Veterans Affairs Medical Center in Cleveland, Ohio. Long story short, the patients can not only sense pressure, they can tell the difference between cotton, grapes, and other materials. Even more interesting, sensory input from the prosthetic limbs relieved phantom limb pain suffered by some of the test subjects. Additionally the newly installed sense of touch has given the test subjects heretofore unparalleled dexterity in their prosthetic limbs; one test subject was able to pluck stems from grapes and cherries without crushing the fruit while blindfolded. Elsewhere in the field of limb replacement, a groundbreaking procedure carried out in Sweden in 2013 (I had no idea, one of my net.spiders discovered this by accident) combines the previous two advances. At the Chalmers University of Technology a research team headed up by Max Ortiz Catalan used ITAP techniques in conjunction with transdermal nervelinks to integrate a prosthetic limb into an unnamed patient's body. The patient has been using the limb on the job for over a year now, and can also tie shoelaces and pick up eggs without breaking them. A true cybernetic feedback loop between the brain and the prosthetic limb appears to have been achieved leading to intuitive control over the prosthetic limb. The patient has shown long term ability to maintain control over and sensory access to the prosthetic limb outside of a laboratory environment. The direct skeletal connection to the limb provides mechanical stability and ease of connectivity for the limb without any need for structural adjustment. The nervelinks mean that less effort is required on the part of the wearer to manipulate the limb, greater dexterity by exploiting the intuitive proprioceptive sense of the human brain, and no need for recalibration because the nervelinks don't really change position.

Excited about the future? I am.