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

Purposes: We 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. Methods: The 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). Results: Women 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. Conclusion: In 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.