A role for near infrared spectroscopy in the assessment of intermittent claudication

Near infrared spectroscopy (NIRS) can be used to monitor muscle oxyhemoglobin (HbO2), deoxyhemoglobin (Hb) and cytochrome oxidase (CytOx) oxidation. We evaluated the changes in NIRS in patients with intermittent claudication (IC) pre- and postexercise. Microalbuminuria is an index of endothelial dysfunction. Therefore, we also assessed whether the urinary excretion of albumin increased postexercise in patients with IC.

Each participant (14 patients with IC and 10 controls) underwent a treadmill test; NIRS was continuously recorded. The urinary albumin:creatinine ratio (ACR) and ankle: brachial systolic pressure index (ABPI) were measured pre- and postexercise.

The ABPI in the claudicants dropped significantly (p<0.001) postexercise. The pre-exercise ACR did not differ between claudicants and controls but postexercise, the ACR increased significantly (p<0.001) in the claudicants. There was a significant (p<0.001) difference in the degree of HbO2 deoxygenation between claudicants and controls; the rate of deoxygenation was significantly higher in claudicants than in controls (-8.4 vs. -3.4 mol/L.min, p=0.024). The period of recovery of HbO2 postexercise was also significantly slower in claudicants (192 vs 68 sec, p=0.003). There was a significant correlation between the increase in the ACR and time of recovery of HbO2 levels postexercise (r=0.86, p<0.001, n=24). A similar pattern was seen with CytOx.

NIRS may provide a simple, non-invasive assessment of the severity of IC. Furthermore, because the ACR is a marker of endothelial damage, it is possible that NIRS changes also reflect endothelial integrity. These applications of NIRS technique should be assessed in a larger study.