Leg Blood Flow and Muscle Metabolism in Occlusive Arterial Disease of the Leg before and after Reconstructive Surgery

Abstract

1. Leg blood flow, uptake of oxygen and glucose and release of lactate by the leg and changes in intramuscular concentrations of metabolites were studied at rest and during exercise of increasing work loads in thirteen patients with occlusive disease of the iliac or superficial femoral arteries. 2. Leg blood flow (dye-dilution technique) and oxygen uptake during exercise were low and levelled with increasing work load. Considerable increases were noted in muscle lactate concentration and in the net release of lactate from the exercising leg. Muscle content (needle-biopsy technique) of ATP and creatine phosphate decreased during exercise, with an almost complete depletion of creatine phosphate in three patients. The decrease in muscle glycogen during work did not differ significantly from that of control subjects. 3. Repeated exercise after reconstructive surgery showed a considerable improvement in physical working capacity. Leg blood flow and oxygen uptake during exercise were significantly higher than before surgery and increased linearly in relation to work intensity. The decrease in creatine phosphate and lactate concentration of the thigh muscle during exercise was less pronounced and the release of lactate was lower than before vascular reconstruction. 4. It is suggested that the onset of the severe muscle symptoms during exercise in patients with occlusive arterial disease of the leg may be related to a low concentration of ATP and creatine phosphate in the affected muscles.

Skeletal muscle metabolic changes in peripheral arterial disease contribute to exercise intolerance: a point-counterpoint discussion

“…The failure of muscle lactate to increase significantly is contrary to other evidence of the muscle lactate response to exercise in claudicants 62,64,69 or ischemic exercise in healthy individuals 81 ; but it is consistent with the findings that claudicants' calf muscle favors fat oxidation as opposed to carbohydrate oxidation during exercise 70 and this probably results in a lower-than-expected rate of lactate accumulation. 69 Such a response has been interpreted as an adaptive, not a pathological, response.…”

“…The increase in leg blood flow would, on the basis of calf perfusion measurements made during or after walking, 59,60 be no more than 40% of that seen in healthy controls; whereas the increase in a-VO 2 is the same as that observed in young, healthy subjects performing maximal calf exercise 61 or even greater than controls during cycling or walking. 62,63 These data show that calf muscle peak VO 2 in claudicants is limited by leg blood flow and not a-VO 2 .…”

“…Leg VO 2 and a-VO 2 The range of a-VO 2 data during maximal exercise in claudicants is $ 0.04 ml ml À1 blood, 63 and the standard error of the mean is usually very small (2À4% of the mean) compared with leg blood flow (15% of the mean). 57,62 At an average maximum leg blood flow of $ 400 ml min À1 , 57 a difference in a-VO 2 of 0.04 ml ml À1 would yield a range for calf muscle VO 2 of 16 ml min À1 for one leg and 32 ml min À1 for two legs. This latter value would explain no more than 3À6% of the range for peak VO 2 in claudicants.…”

The Treadmill Is a Better Functional Test Than the 6-Minute Walk Test in Therapeutic Trials of Patients With Peripheral Artery Disease

“…22,23 In contrast, revascularization results in substantial improvements in limb blood flow and oxygen delivery, but these improvements in limb flow are not well correlated with the change in exercise performance. 24 The recognition that a limitation in maximal exercise performance is a direct result of a complex pathophysiology and that both endurance and submaximal exercise performance are inherently impaired when maximal performance is limited has important implications for considering how to assess function and response to treatment in these patients.…”

Why do arms extract less oxygen than legs during exercise?

“…Compared with these values, our skiers also reached remarkably high maximal O 2 extraction values in their legs (93%). However, untrained subjects may reach rather high leg O 2 extractions after bed rest (62) or during ischemic exercise (46). Several factors may account for the observed differences in muscular O 2 extraction, which depends on the interaction of the following: 1) kinetics of O 2 off-loading from the Hb; 2) capillary muscle O 2 conductance (72); 3) blood flow, mean transit time (47), and degree of mismatch between the metabolic demand and blood flow distribution and/or degree of shunt (48); and 4) muscle maximal oxidative capacity (22) and exercise intensity.…”