Abstract 136: Near-Infrared Spectroscopy for Diagnosis and Characterization of Peripheral Artery Disease Severity

Abstract

Background: Peripheral artery disease (PAD) frequently is undertreated. ABI is the standard for diagnosis of PAD but is limited in its ability to predict functional status and risk of disease progression. Previous work with Near-Infrared Spectroscopy (NIRS) has demonstrated impaired oxygen utilization in PAD muscle and may allow for improved diagnosis and stratification of disease severity. We hypothesize that exercise produces characteristic changes in lower-extremity muscle oxygenated heme percent (StO 2 ) which differentiates PAD from control and predicts PAD severity better than ABI. Methods: We recruited 31 PAD subjects with intermittent claudication (IC) (ABI < 0.9) and 9 controls (ABI ≥ 0.9 and no IC). All subjects completed a Gardner maximal treadmill test. PAD subjects walked until IC was prohibitive (peak walking time, PWT) and controls walked for 540 seconds. StO 2 measurements were taken from the lateral gastrocnemius with the wireless MOXY NIRS monitor. StO 2 was documented at baseline, 60s, claudication onset time (COT), and PWT. For each subject, StO 2 values were expressed as percent of baseline to allow for comparison across subjects. Data were analyzed by student’s t-test and linear regression. Results: Mean baseline StO 2 values were 46±11% and 58±17%, respectively, for PAD and control subjects. Among controls, StO 2 dropped below baseline at 140±101s whereas PAD subjects dropped below baseline at 6±10s (P<0.001). PAD StO 2 s at 60s, COT, and PWT were compared to control StO 2 s at the corresponding time points. PAD patients’ StO 2 at 60s, COT, and PWT were 65.2±37.9% (n=31), 66.4±35.5% (n=31), and 73.2±26.0% (n=25) lower than controls, respectively (P < 0.001). PAD subjects were separated into tertiles of PWT. Relative to baseline, StO 2 decreased 84.2±18.4% (n=11) in the lowest tertile compared to 29.8±30.6% (n=10) in the highest tertile (P<0.05). Percent decrease in StO 2 at 60s correlated to PWT (R 2 =0.56) in contrast to ABI (R 2 =0.018). Conclusion: During exercise, PAD patients exhibited a characteristic change in StO 2 . In contrast to ABI, StO 2 predicted PAD-related exercise limitation. These data suggest NIRS in conjunction with traditional methods could be used to guide diagnostic and treatment decisions.