The VAGLAHS Institutional Review Board approved the study, and written informed consent was obtained from each subject before participation in this study.
Abbreviations: ANOVA = analysis of variance, LDI = laser Doppler imaging, NIR = near infrared, PC[O.sub.2] = partial pressure of carbon dioxide, P[O.sub.2] = partial pressure of oxygen, PVD = peripheral vascular disease, ROC = receiver operating characteristic, ROI = region of interest, SD = standard deviation, SEM = standard error of the mean, Tc = transcutaneous, TcP[O.sub.2] = Tc partial pressure of oxygen, TcPC[O.sub.2] = Tc partial pressure of carbon dioxide, VA = Department of Veterans Affairs, VAGLAHS = VA Greater Los Angeles Healthcare System.
 Physical Medicine and Rehabilitation Service, VA Greater Los Angeles Healthcare System (VAGLAHS
), West Los Angeles Healthcare Center (WLAHC), Los Angeles, CA;  Nuclear Medicine Service; Research and Development Service, VAGLAHS
;  Physical Medicine and Rehabilitation Division, David Geffen School of Medicine, UCLA;  Department of Physiology, David Geffen School of Medicine, UCLA