Identification of Peripheral Vascular Disease in Elderly Subjects Using Optical Spectroscopy

The purpose of this study was to determine the usefulness of near-infrared spectroscopy (NIRS) measurements to identify peripheral vascular disease (PVD). Usefulness was determined by the frequency of a successful test, as well as comparison with standard clinical assessments. Study subjects (N = 117, mean age = 67.8 ± 8.1 yrs) responded to a free screening for PVD. NIRS was used to measure the relative O2 saturation of hemoglobin in the soleus muscle. The time to 1/2 recovery of O2 saturation (O2Tl/2) was measured after 1 minute of repeated plantar flexions using a Cybex Eagle seated calf machine. O2Tm was used as many subjects had recovery curves that did not have an exponential line shape. The test was done on both legs and the worst leg was used for analysis. For comparative purposes, a clinical history and physical examination were performed by a physician or nurse practitioner, which included questions on intermittent claudication, examination of peripheral pulses, and questions to identify cardiovascular risk factors. NIRS signals were obtained on 105 of 117 subjects (89% success rate). Subjects with body mass index (BMI) values above 32 appeared to have NIRS 02Tm values that were less reliable than subjects with BMI values ≤ 32 (77% success rate). The O2Tm was longer in subjects with claudication and reduced pulses than in subjects without these conditions. Sensitivity comparing O2Tm to claudication and reduced pulses varied from 51–76% and specificity from 65–80%, depending on the cutoff value for O2Tm that was used (normal value plus 1 or 2 SD). A longer O2Tm was significantly associated with incidence of diabetes, smoking, hypercholesterol, and coronary bypass surgery. In summary, successful NIRS O2Tm measurements were made in 77% of the subjects, with failure primarily occurring in obese subjects. NIRS O2Tm measurements showed reasonable although not strong agreements with clinical assessments of PVD, and with some risk factors for cardiovascular disease.