Sex differences in calf muscle hemoglobin oxygen saturation in patients with intermittent claudication

PurposesWe tested the hypotheses that women have greater impairment in calf muscle hemoglobin oxygen saturation (StO2) in response to exercise than men, and that the sex-related difference in calf muscle StO2 would partially explain the shorter claudication distances of women.MethodsThe study comprised 27 men and 24 women with peripheral arterial disease limited by intermittent claudication. Patients were characterized on calf muscle StO2 before, during, and after a graded treadmill test, as well as on demographic and cardiovascular risk factors, ankle-brachial index (ABI), ischemic window, initial claudication distance (ICD), and absolute claudication distance (ACD).ResultsWomen had a 45% lower ACD than men (296 ± 268 m vs 539 ± 288 m; P = .001) during the treadmill test. Calf muscle StO2 declined more rapidly during exercise in women than in men; the time to reach minimum StO2 occurred 54% sooner in women (226 ± 241 vs 491 ± 426 seconds; P = .010). The recovery time for calf muscle StO2 to reach the resting value after treadmill exercise was prolonged in women (383 ± 365 vs 201 ± 206 seconds; P = .036). Predictors of ACD included the time from start of exercise to minimum calf muscle StO2, the average rate of decline in StO2 from rest to minimum StO2 value, the recovery half-time of StO2, and ABI (R2 = 0.70; P < .001). The ACD of women remained lower after adjusting for ABI (mean difference, 209 m; P = .003), but was no longer significantly lower (mean difference, 72 m; P = .132) after further adjustment for the StO2 variables for the three calf muscles.ConclusionIn patients limited by intermittent claudication, women have lower ACD and greater impairment in calf muscle StO2 during and after exercise than men, the exercise-mediated changes in calf muscle StO2 are predictive of ACD, and women have similar ACD as men after adjusting for calf StO2 and ABI measures.