Peripheral artery disease (PAD) is an atherosclerotic vascular disease that affects 200 million people worldwide. Although PAD primarily affects large arteries, it is also associated with microvascular dysfunction, an exaggerated blood pressure (BP) response to exercise, and high cardiovascular mortality. We hypothesized that fatiguing plantar flexion exercise that evokes claudication elicits a greater reduction in skeletal muscle oxygenation (SmO) and a higher rise in BP in PAD compared with age-matched healthy subjects, but low-intensity steady-state plantar flexion elicits similar responses between groups. In the first experiment, eight patients with PAD and eight healthy controls performed fatiguing plantar flexion exercise (from 0.5 to 7 kg for up to 14 min). In the second experiment, seven patients with PAD and seven healthy controls performed low-intensity plantar flexion exercise (2.0 kg for 14 min). BP, heart rate (HR), and SmO were measured continuously using near-infrared spectroscopy (NIRS). SmO is the ratio of oxygenated hemoglobin to total hemoglobin, expressed as a percent. At fatigue, patients with PAD had a greater increase in mean arterial BP (18 ± 2 vs. vs. 10 ± 2 mmHg, = 0.029) and HR (14 ± 2 vs. 6 ± 2 beats/min, = 0.033) and a greater reduction in SmO (-54 ± 10 vs. -12 ± 4%, = 0.001). However, both groups had similar physiological responses to low-intensity, nonpainful plantar flexion exercise. These data suggest that patients with PAD have altered oxygen uptake and/or utilization during fatiguing exercise coincident with an augmented BP response. In this laboratory study, patients with peripheral artery disease performed plantar flexion exercise in the supine posture until symptoms of claudication occurred. Relative to age- and sex-matched healthy subjects we found that patients had a higher blood pressure response, a higher heart rate response, and a greater reduction in skeletal muscle oxygenation as determined by near-infrared spectroscopy. Our data suggest that muscle ischemia contributes to the augmented exercise pressor reflex in peripheral artery disease.
STRUCTURED ABSTRACT
Background
Peripheral arterial disease (PAD) is an atherosclerotic vascular disease that affects over 200 million worldwide. The hallmark of PAD is ischemic leg pain and this condition is also associated with an augmented blood pressure response to exercise, impaired vascular function, and high risk of myocardial infarction and cardiovascular mortality. In this study, we tested the hypothesis that coronary exercise hyperemia is impaired in PAD.
Methods
Twelve patients with PAD and no overt coronary disease (65 ± 2 yr, 7 men) and 15 healthy control subjects (64 ± 2 yr, 9 men) performed supine plantar flexion exercise (30 contractions/min, increasing workload). A subset of subjects (N = 7 PAD, N = 8 healthy) also performed isometric handgrip exercise (40% maximum voluntary contraction to fatigue). Coronary blood velocity in the left anterior descending artery was measured by transthoracic Doppler echocardiography; blood pressure and heart rate were monitored continuously.
Results
Coronary blood velocity responses to 4 minutes of plantar flexion exercise (PAD: Δ 2.4 ± 1.2, healthy: Δ 6.0 ± 1.6 cm/s, P = 0.039) and to isometric handgrip exercise (PAD: Δ 8.3 ± 4.2, healthy: Δ 16.9 ± 3.6, P = 0.033) were attenuated in PAD patients.
Conclusions
These data indicate that coronary exercise hyperemia is impaired in PAD, which may predispose these patients to myocardial ischemia.
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