To date murine models of treadmill exercise have been used to study general exercise physiology and angiogenesis in ischemic hind limbs. The purpose of these experiments was to develop a murine model of demand ischemia in an ischemic limb to mimic claudication in humans. The primary goal was to determine whether treadmill exercise reflected a hemodynamic picture which might be consistent with the hyperemic response observed in humans.
Aged hypercholesterolemic ApoE null mice ( ApoE−/−, n=13) were subjected to Femoral Artery Ligation (FAL), and allowed to recover from the acute ischemic response. Peripheral perfusion of the hind limbs at rest was determined by serial evaluation using laser Doppler imaging (LDI) on days 0, 7, and 14 following FAL. During the duration of the experiments, the mice were also assessed on an established 5 point clinical ischemic score which assessed the degree of digital amputation, necrosis, and cyanosis as compared to the non ischemic contralateral limb. After stabilization of the LDI ratio (ischemic limb flux/contralateral non ischemic limb flux) and clinical ischemic score, mice underwent two days of treadmill training (10 min @ 10 m/min, incline of 10°) followed by 60 minutes daily treadmill exercise (13 m/min, incline of 10°) through day 25. An evaluation of pre-exercise and post exercise perfusion using LDI was performed on two separate occasions following the onset of daily exercise. During the immediate 15 minute post exercise evaluation, LDI scanning was obtained in quadruplicate, to allow identification of peak flux ratios. Statistical analysis included unpaired t-tests and ANOVA.
After FAL, the LDI Flux ratio reached a nadir between days one and two, then stabilized by day 14 and remained stable through day 25. The clinical ischemic score stabilized at day 7, and remained stable throughout the rest of the experiment. Based on stabilization of both the clinical ischemic score and LDI ratio, exercise training began on day 15. The peak 15 minute post exercise LDI ratio increased significantly as compared to pre-exercise ratio on day 17 (0.48+0.04 vs. 0.34± 0.04, p<0.05) and day 25 (0.37±0.03 vs. 0.27±0.03, p<0.01). Within 2 hours of exercise, the LDI ratio returned to pre-exercise levels on both day 17 and 25.
Clinical and hemodynamic stabilization of limb perfusion is evident by 14 days after FAL. FAL followed by demand ischemia results in a reversible relative hyperemic response similar to those observed in exercising human claudicants. A murine model of FAL associated with demand ischemia may be a useful model to evaluate the metabolic, inflammatory and flow related changes associated with claudication in humans.