Calf muscle adaptation in intermittent claudication. Side-differences in muscle metabolic characteristics in patients with unilateral arterial disease

Chronic changes in skeletal muscle histology and function in peripheral arterial disease

BACKGROUND

Peripheral arterial disease (PAD) is associated with an impairment in exercise performance and muscle function that is not fully explained by the reduced leg blood flow during exercise. This study characterized the effects of PAD on muscle function, histology, and metabolism.

METHODS AND RESULTS

Twenty-six patients with PAD and six age-matched control subjects were studied. Ten of the PAD patients had unilateral disease, which permitted paired comparisons between their diseased and nonsymptomatic legs. All PAD patients had a lower peak treadmill walking time and peak oxygen consumption than controls. Vascular disease (diseased leg in unilateral patients and the most severely diseased leg in bilateral patients) was associated with decreased calf muscle strength compared with control values. In patients with unilateral disease, the diseased legs had a greater percentage of angular fibers (indicating chronic denervation) and a decreased type II fiber cross-sectional area (expressed as percent of total fiber area) compared with the nonsymptomatic, or control, legs. In diseased legs, gastrocnemius muscle strength was correlated with the total calf cross-sectional area (r = 0.78, p < 0.05) and type II fiber cross-sectional area (r = 0.63, p < 0.05). Activities of citrate synthase, phosphofructokinase, and lactate dehydrogenase in all 26 PAD patients (most diseased leg) did not differ from control values. Despite a wide range in citrate synthase activity in PAD patients, activity of this enzyme was not correlated with muscle strength or treadmill exercise performance.

CONCLUSIONS

In patients with PAD, gastrocnemius muscle weakness is associated with muscle fiber denervation and a decreased type II fiber cross-sectional area. In contrast, the PAD patients displayed substantial heterogeneity in muscle enzyme activities that was not associated with exercise performance. Denervation and type II fiber atrophy may contribute to the muscle dysfunction in patients with PAD and further confirm that the pathophysiology of chronic PAD extends beyond arterial obstruction.

Effects of graded restriction of perfusion on circulation and metabolism in the working leg; quantification of a human ischaemia-model

An experimental model used with the intention of mimicking the ischaemic condition in patients with arterial obliterative disease was evaluated. The influence of reduced effective perfusion pressure by increased external pressure on leg blood flow and metabolism was determined during exercise in 10 healthy subjects. Catheters were inserted into the right femoral artery and vein and into the left femoral vein. Supine one-legged (n = 5) or two-legged (n = 5) cycle exercise was performed with the subject's legs in a pressure chamber. Zero and three different levels of local supra-atmospheric pressure were applied over the legs: 30, 50 and 60 mmHg. Three submaximal work loads were used: 24, 48 and 72 W/leg. Leg blood flow was measured by the constant-infusion dye-dilution technique. Samples were also drawn from the femoral artery and vein for oxygen saturation and lactate determinations and arterial pressure was recorded. Exercise blood flow decreased progressively with increasing chamber pressure (P less than 0.001). Exposure to 50 mmHg over the working leg led to a mean reduction of blood flow by 16% and venous oxygen saturation by 12 percentage units (P less than 0.05). Lactate release increased with increasing pressure (P less than 0.05). In summary, local application of moderate positive external pressure over the working leg reduces blood flow in a 'dose-dependent' manner, and as a consequence, femoral venous oxygen saturation decreases and lactate release increases. Thus, this method makes it possible to induce graded ischaemia in human skeletal muscle during exercise in a controlled fashion.

Lower extremity arterial disease and the aging process: a review

Atherosclerotic disease is a major health problem in the elderly population in the U.S. To date, most research has focused on the coronary and cerebral manifestations of the disease. Lower extremity arterial disease (LEAD) has received less attention. However, the use of simple objective non-invasive diagnostic techniques in recent population-based studies has allowed identification of asymptomatic LEAD and shown that the prevalence of disease is several fold higher than previously estimated. The prevalence increases sharply with age, from 3% in those under 60 years to over 20% at 75+ years. Detection of LEAD in the elderly provides a rapid, easy assessment of the level of atherosclerosis in the body and identifies those at high risk for mortality and morbidity. LEAD is associated with a relative risk of 4 to 5 for all cause mortality. In about 25% of those with LEAD, the disease progresses over time, leading to loss of mobility, gangrene or amputation. This review summarizes current knowledge regarding the etiology and natural history of LEAD from an epidemiologic viewpoint, delineating areas in which additional research is needed.

Near-infrared spectroscopy in peripheral vascular disease

Near-infrared spectroscopy has been performed on the calf muscles of 38 subjects, 21 normal controls without vascular disease and 17 patients with peripheral vascular disease. Oxygen consumption was measured in the calf by calculating the rate of conversion of oxyhaemoglobin to deoxyhaemoglobin during a period of tourniquet-induced ischaemia. Postischaemic reoxygenation was also measured. Median oxygen consumption in patients with peripheral vascular disease was 0.10 ml 100 g tissue-1 min-1, while in the control group it was 0.20 ml 100 g tissue-1 min-1 (P less than 0.03, Mann-Whitney U test). The median time taken to reach maximum oxyhaemoglobin levels after ischaemia was 40 s in patients with peripheral vascular disease and 20 s in controls (P less than 0.02). The results indicate that oxygen consumption is reduced in peripheral vascular disease. Near infrared spectroscopy is a non-invasive method for assessing metabolic improvement resulting from surgical or pharmacological treatment.

The effect of torbafylline on enzyme activities in fast and slow muscles with limited blood supply

1. Activities of a glycolytic enzyme--lactate dehydrogenase, LDH, and two oxidative enzymes--citrate synthase (CS), a marker for TCA cycle entry, and 3-hydroxyacyl-CoA dehydrogenase (HAD), which indicates the capacity for beta-oxidation of endogenous lipids, were measured in fast (tibialis anterior, TA, and extensor digitorum longus, EDL) and slow (soleus, SOL) muscles of Sprague-Dawley rats with intact and limited blood supply, and following treatment with the xanthine derivative torbafylline (Hoechst, Werk Albert, Wiesbaden). 2. Limitation of blood supply by unilateral ligation of the common iliac artery increased activity of LDH in fast muscles, and activity of CS and HAD in soleus. 3. Torbafylline treatment caused an increased LDH activity in intact fast muscles and decreased it in soleus, although the relative capacity for anaerobic and aerobic metabolism (indicated by the ratio of LDH and CS activities) remained unchanged in all cases. 4. Whilst having little effect on oxidative enzyme activity of fast muscles, torbafylline decreased the activity of CS but increased activity of HAD in soleus, suggesting a greater reliance on lipid metabolism. 5. The effect of arterial ligation on enzyme activity was ameliorated by treatment with torbafylline, possibly due to its effect on the microcirculation.

Effects of ischaemic training on force development and fibre-type composition in human skeletal muscle

Force (peak torque) of m. quadriceps femoris was measured during 60 repeated, voluntary dynamic knee extensions in 10 men before and after a 4-week training regimen of one-legged cycle exercise. Biopsies for histochemical analysis were obtained from the lateral vastus muscle after the training period. One leg was trained with the blood flow to the leg muscles reduced by local supra-atmospheric external pressure of 50 mmHg ('Ischaemic leg, I-leg'). Employing the same work-load profile the other leg was trained at normal atmospheric pressure ('Non-restricted-flow leg, N-leg'). In response to I-training, Maximum Peak Torqued (MPT; the highest torque produced in any contraction) and Initial Peak Torque (IPT; the average peak torque of the initial 12 contractions) decreased by 8% (P less than 0.01) and 9% (P less than 0.001), respectively. Final Peak Torque (FPT; the average peak torque of the final 12 contractions) increased by 13% (P less than 0.05) after I-training. No changes in MPT, IPT or FPT occurred following N-training. After training the proportion of slow-twitch fibres was higher (P less than 0.05) and the mean slow-twitch fibre area was larger (P less than 0.05) in the I-than in the N-trained leg. The results indicate that blood flow-restricted training, in contrast to non-restricted-flow training, decreases maximum voluntary dynamic force, possibly by inducing an increase in the share of the muscle cross-sectional area consisting of slow-twitch fibres. That flow-restricted training improves maintenance of force during short-term local exercise may reflect ischaemically induced changes in the metabolic characteristics of skeletal muscle.

Decrease in myoglobin and enzyme contents with haemodilution in non-hypoxaemic polycythaemic patients

Quadriceps muscle biopsies from five patients with primary polycythaemia and four patients with non-primary polycythaemia, all with normal respiratory functions, were studied before and after normalization of haemoglobin and erythrocyte volume fraction by haemodilution or venaesectio. Since similar results were obtained from both groups of patients data were pooled. After normalization of the erythrocyte volume fraction myoglobin decreased by 19 +/- 16%, P less than 0.01, the activity of creatine kinase and citrate synthase by 12 +/- 8 and 14 +/- 18%, P less than 0.05, respectively. The decrease in myoglobin content was related to the decrease in haemoglobin concentration (r = 0.77, P less than 0.01). In conclusion, these data suggest that in non-hypoxaemic polycythaemia skeletal muscle shows adaptations indicative of an impaired oxygenation and a metabolic stress, adaptations that are reversed by haemodilution.

Effects of torbafylline, pentoxifylline and buflomedil on vascularisation and fibre type of rat skeletal muscles subjected to limited blood supply

1. Blood flow (measured by radio-labelled microspheres), fibre composition and capillary/fibre ratio were estimated in rat fast twitch skeletal muscles (tibialis anterior and extensor digitorum longus) five weeks after unilateral ligation of the common iliac artery in animals treated with either saline, torbafylline, pentoxifylline or buflomedil. 2. The resting blood flow was lower in muscles with limited blood supply than in their contralateral controls; this difference became statistically insignificant after treatment. Capillary/fibre ratio was similar in all muscles with either intact or limited blood supply and did not change after administration of any of the drugs. 3. The percentage of glycolytic fibres was not changed by ligation, but it decreased significantly in animals treated with torbafylline. This may improve performance in muscles with limited blood supply.

Regional distribution of citrate synthase and lactate dehydrogenase isoenzymes in the bovine heart

Gradients of oxidative and glycolytic enzyme activities in the heart were studied by comparing samples taken from 10 locations from each of six bull hearts, within 30 min after slaughter. Citrate synthase (CS) was used as a marker of the oxidative potential and the lactate dehydrogenase (LD) subunits II and M as markers of aerobic glycolytic and anaerobic glycolytic potential respectively. CS activity in the ventricular tissue was greater than that of the right atrium, and no difference was found between the right and left ventricles. The left ventricular free wall had higher CS activity at the base than at the apex of the heart. Both the H and M subunit activities of LD increased in the following order: right atrium, right ventricle, ventricular septum, left ventricle. The left ventricular free wall showed higher H and M subunit activities at the base than at the apex. Within the left ventricular wall at the base, subendocardium had higher H and M subunit activities than subepicardium. The M subunit constituted the highest fraction of LD in the subendocardium and in the papillary muscle of the left ventricle. In conclusion, this study suggests that there are metabolic differences along both the radial and the longitudinal axes of the left ventricle and across the ventricular septum. These differences indicate that the greatest cellular stress, both aerobic glycolytic and anaerobic glycolytic in nature, occurs within the subendocardium at the base of the left ventricle and in the left ventricular papillary muscle.

Fatty acid turnover in the ischaemic compared to the non-ischaemic human heart

Cardiac extraction, oxidation and release of plasma free fatty acids (FFA) was measured by coronary sinus catheterization, utilizing infusions of 3H palmitate and 14C oleate, in patients with ischaemic heart disease (IHD) at rest and during pacing induced angina pectoris and, for comparison, in healthy men of similar and younger age and men with hypertriglyceridaemia (HTG). At rest IHD patients differed from healthy men only by greater cardiac fatty acid release, which correlated with a significant glycerol release. In IHD patients, unlike in healthy men, myocardial extraction of both palmitate and oleate decreased while fractional oxidation of oleate increased during pacing. Fatty acid release was unaltered. Men with HTG had at rest higher myocardial FFA extraction than IHD patients, which did not decrease during pacing, but like in the patients oleate fractional oxidation increased on pacing. It is concluded that, in the moderately ischaemic human heart, the restricted blood flow may contribute to limit the fatty acid flux into the myocardium. The augmented cardiac fatty acid release in IHD patients is not related to ischaemia per se but may derive from an increased amount of cardiac interstitial fat.