The Microcirculatory Stress Response in Diabetic and Nondiabetic Feet Using Near Infrared Imaging
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Transcript
Hi, I'm Dr. Windy Cole, I'm the Director of Wound Care Research at Kent State University College of Podiatric Medicine, and I'm happy to discuss a poster that I have here at SAWC Fall, and it's on the diabetic microcirculation, the stress response in patients with diabetic autonomic neuropathy. So we hear a lot about diabetic peripheral neuropathy. We don't hear about DAN, the diabetic autonomic neuropathy, as much as we should. We aren't aware of it. And we know that patients with DAN have issues with their gastrointestinal system. Sometimes they have hypotension, but they also can have significant issues with the microcirculatory system in the lower extremity. So essentially what happens is because the microcirculatory system is so dependent on the autonomic nervous system, when patients have neuropathy, the autonomic nervous system cannot respond to different stresses and regulate the blood flow into the lower extremity.
So, with this study, we looked at two cohorts of patients. We looked at patients with diabetes and neuropathy, and we looked at patients that were relatively healthy, meaning they didn't have diabetes or neuropathy. All patients had good blood flow, so their ABI was normal. So it was, you know, at least 0 .9 or greater. So they had adequate perfusion into the lower extremity. So then we subjected them to several stresses. Elevation of the limb for 10 minutes, dependency of the limb for 10 minutes, heat via a heating pad and then ice via an ice pack for 10 minutes. We used a near-infrared spectroscopy to see what happened to the perfusion in the tissues as a surrogate for the microcirculatory response.
So near infrared spectroscopy, for those of you that aren't aware, it can tell how much oxygen is attached to the hemoglobin. So different optical spectrums of the hemoglobin can be picked up by the imaging system to tell us relatively how much perfusion or oxygenation is getting to the tissues at any time. So, we did a baseline measurement. We did a measurement after the elevation, after the dependency, after the ice, and after the heat to see what exactly changes we could detect in the perfusion. And we did it in 20 patients, so it's a pilot study to kind of just make sure that our hypothesis was on track, and we hope to extend it to a larger patient population. But the results were, as we had expected, patients that did not have diabetes and did not have neuropathy were able to keep that perfusion steady because their autonomic nervous system was intact. They were able to either close down their microvascular or open their microvascular in response to the stresses. So their StO2 levels stayed steady.
Our diabetics were a whole other story. They bounced around. So in fact, it did prove that we have a functional ischemia in the feet that typically have a normal ABI. We would think they had good perfusion. But because of the autonomic neuropathy, they have a functional ischemia and not really regulate when they have exposed stresses. So that's something that we should be more aware of because we kind of, you know, hang our hat on, oh, they have good ABI's, they have good TBI, they have good perfusion, but they do still have a higher incident of potential breakdown in the skin because of that functional ischemia.
