| Popis: |
The aim of this study was to determine if photoplethysmography (PPG) could be used to analyse the foot microvascular changes caused by diabetic autonomic neuropathy. The digital PPG signals were collected from 37 healthy volunteers (Group I), 35 diabetic patients (Group II), and 38 diabetic patients with sensory neuropathy (Group III) and analysed using MAT LAB. Prominent spectral peaks with sidebands were obtained at both the high frequency (HF) and the low frequency (LF) end of the Fourier spectrum of these PPG signals. Previous studies of microcirculation have shown that both are sympathetically and parasympathetically mediated and hence are a good measure of the autonomic activity. In the HF analysis, the heart rate (HR) response from 13 participants in Group III was severely reduced and significantly different from the responses obtained from the other two groups. However the responses from remaining 25 participants had similar characteristics to those of Group II. Hence the HF analyses failed to both statistically and objectively differentiate between the diabetics with and without neuropathy. The spectral density for the frequency bandwidth of 3-20 cpm was significantly reduced in the neuropathic group, compared to the other two groups. A Statistically significant difference was observed in the spectral densities calculated from Group II and III, though no difference could be established between Groups I and III. The LF analysis of this bandwidth differentiated between Groups II and III with a sensitivity of 84% and specificity of 61%. Activities at the LF end of the spectrum mostly represent the sympathetic control as opposed to the HR variability that is mostly a measure of the parasympathetic control. These results suggest that sympathetic dysfunction possibly precedes parasympathetic dysfunction and that PPG can assess the changes in the skin microcirculation due to sympathetic damage with moderate success. |
