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Single Leg Plantar Flexion Elicits Greater Calf Muscle Oxygen Extraction in Peripheral Arterial Disease
Author(s) -
Luck J. Carter,
Muller Matthew D.,
Ross Amanda J.,
Leuenberger Urs A.,
Sinoway Lawrence I
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1288.21
Subject(s) - medicine , supine position , ankle , cardiology , peripheral , gastrocnemius muscle , intermittent claudication , heart rate , hemodynamics , oxygen saturation , blood pressure , skeletal muscle , arterial disease , anesthesia , surgery , vascular disease , oxygen , chemistry , organic chemistry
Peripheral arterial disease (PAD) is characterized by atherosclerosis in the large arteries of the lower extremity resulting in impaired oxygen delivery to the gastrocnemius muscle and exercise intolerance. However, large artery hemodynamics do not fully explain symptomology or the responses to therapy in PAD. Recent studies suggest that microvascular and/or mitochondrial dysfunction also contribute to the development of leg pain and poor walking performance. Near‐infrared spectroscopy (NIRS) is increasingly being used to noninvasively measure the oxygen hemoglobin saturation (SmO2) changes that occur within the skeletal muscle during exercise. A reduction in SmO2 during exercise is indicative of greater oxygen extraction. In this study we tested the hypothesis that single leg dynamic plantar flexion elicits enhanced oxygen extraction in PAD vs. healthy subjects. Eight patients with PAD (ankle‐brachial index: 0.64 ± 0.03) and eight age and sex‐matched healthy subjects underwent single leg dynamic plantar flexion exercise in the supine posture. Subjects exercised until fatigue or a maximum of 14 minutes at 20 contractions per minute (0.5 kg to 7.0 kg) with the most symptomatic leg. The primary outcome variable was the amount of oxygen extracted from the medial gastrocnemius during exercise. Heart rate (HR) and mean arterial pressure (MAP) were also quantified on a beat‐by‐beat basis. Changes from baseline to the last 20 seconds of exercise were calculated. Because of symptomatic leg pain, PAD patients terminated exercise at lower workloads. Gastrocnemius muscle oxygen extraction at the end of exercise was significantly greater in PAD patients (78% ± 11%; M ± SEM) than in healthy subjects (23% ± 5%, P < 0.001). Similarly, the minimum SmO2 at the end of exercise was lower in PAD compared to healthy subjects (15% ± 6% versus 60% ± 6%; p < 0.001). HR increased similarly in PAD compared to healthy subjects (15 ± 2 bpm versus 11 ± 2 bpm) whereas the increase in MAP was augmented in PAD (19 ± 2 versus 12 ± 3 mmHg; P = 0.03). The recovery phase SmO2 was blunted in PAD and full recovery was not attained within three minutes post exercise. In conclusion, a threefold increase in oxygen extraction (vs. healthy subjects) is observed in the medial gastrocnemius of PAD patients in response to plantar flexion exercise. Support or Funding Information Experiments supported by P01 HL096570 (Dr. Sinoway), UL1 TR00127 (Dr. Sinoway), KL2 TR00126 (Dr. Muller), R25 HL115473 (J. Carter Luck). The authors appreciate the technical support of their CRC research collaborators.