Abstract Body: Background:
Walking is the most significantly impacted daily activity for patients with peripheral artery disease (PAD), as all individuals with this condition experience walking impairments, with claudication being the most common symptom. Supervised exercise therapy involving treadmill (TM) walking is the primary recommended treatment for patients with claudication. Therefore, it is crucial to understand the ischemic stress that leg muscles experience during walking in these patients.

Methods
Eighteen claudicating PAD patients participated in both a TM test and a post occlusive reactive hyperemia test (PORH), which involved blocking blood flow to the calf using a thigh cuff for 5 minutes. During these tests, near-infrared spectroscopy NIRS devices were placed on the gastrocnemius muscles of the most affected/symptomatic leg. NIRS measurements were processed with MATLAB to generate endpoints describing muscle oxygenation (StO2) dynamics during both tests (Figure 1). Statistical analysis was conducted using paired t-tests.

Results
All participants were male (average age 70 years, ABI: 0.72). Representative NIRS outputs from PORH and TM are shown in Figure 2. The overall drop in StO2 during the stress phase was similar between the two tests (p=0.21); however, the rate of oxygenation decline was much faster in TM test (time to minimum StO2, PORH 267±35s vs TM 92±54s; occlusion slope, PORH –0.3±0.2 vs TM –1.4±0.8 %/s, p<0.001). During recovery, StO2 recovered more slowly after the TM (recovery slope, PORH 1.5±0.8 vs TM 0.5±0.3 %/s, p<0.001), while reaching a higher maximum StO2 (PORH vs TM 113±8 vs 136±29%, p=0.001) and exhibiting an overall greater hyperemia response (PORH 1713±1355 vs TM 18359±15898 %*s, p<0.001).

Conclusion
In claudicating patients, walking produces profound drops in calf muscle oxygenation that are faster (within the first few steps) and produce larger oxygen deficits than those produced by acute occlusion of arterial inflow of similar duration. Furthermore, recovery of muscle oxygenation after walking is slower and more prolonged than that after PORH. These findings shed light in the rapid and profound oxygenation deficits produced by walking in the muscle of claudicating patients and may bear significantly on the need for improved revascularization strategies and modified exercise prescription for these patients.