Blood pressure and calf muscle oxygen extraction during plantar flexion exercise in peripheral artery disease

Abstract

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.

Chronic femoral artery ligation exaggerates the pressor and sympathetic nerve responses during dynamic skeletal muscle stretch in decerebrate rats

“…That investigation was designed specifically to gain translational mechanistic insights into the larger increases in blood pressure found in PAD patients versus aged-matched healthy counterparts during low-intensity rhythmic plantar flexion exercise (31,39,40), and low-intensity treadmill walking (5, 7). To investigate the mechanisms contributing to the exaggerated mechanicallysensitive component of the exercise pressor reflex in ligated rats we used a 1 Hz dynamic stretch protocol to produce repetitive mechanical stimuli that were independent of metabolites produced during dynamic skeletal muscle contraction.…”

“…This reflex is activated when mechanical and metabolic signals originating within contracting skeletal muscles stimulate thinly myelinated group III and unmyelinated group IV muscle afferents (34,36,44). The exercise pressor reflex is exaggerated in patients with atherosclerotic peripheral artery disease (PAD; 31,39,40) which contributes to the larger increase in blood pressure found during treadmill walking in this patient population compared to that found in aged-matched healthy controls (5, 7). The exercise pressor reflex is also exaggerated in a rat model of simulated PAD in which a femoral artery is ligated ~24-72 hours before the experiment (51).…”

Peripheral arterial disease: Scoping review of patient‐centred outcomes

“…Peripheral arterial disease (PAD) increases cardiovascular morbidity and mortality in 3% to 10% of the global population . It is associated with an increased hypertensive response and decreased calf muscle oxygenation during calf muscle flexion exercise . Up to 18% of those over 50 years of age with PAD experience intermittent claudication (IC), that is, pain on walking that subsides at rest …”

Esmolol acutely alters oxygen supply-demand balance in exercising muscles of healthy humans

“…) and previously described by our lab (Luck et al. ). Briefly, the NIRS device used in this study utilizes a four layer (epidermis, dermis, adipose, and muscle) Monte Carlo simulated model to trace the propagation of photons through a tissue medium.…”