Exercise Blood Flow Research Articles

Training-induced skeletal muscle adaptations are independent of systemic adaptations

To isolate the peripheral adaptations to training, five normal subjects exercised the nondominant (ND) wrist flexors for 41 +/- 11 days, maintaining an exercise intensity below the threshold required for cardiovascular adaptations. Before and after training, intracellular pH and the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) were measured by 31P magnetic resonance spectroscopy. Also maximal O2 consumption (VO2 max), muscle mass, and forearm blood flow were determined by graded systemic exercise, magnetic resonance imaging, and venous occlusion plethysmography, respectively. Blood flow, Pi/PCr, and pH were measured in both forearms at rest and during submaximal wrist flexion at 5, 23, and 46 J/min. Training did not affect VO2 max, exercise blood flow, or muscle mass. Resting pH, Pi/PCr, and blood flow were also unchanged. After training, the ND forearm demonstrated significantly lower Pi/PCr at 23 and 46 J/min. Endurance, measured as the number of contractions to exhaustion, also was increased significantly (63%) after training in the ND forearm. We conclude that 1) forearm training results in a lower Pi/PCr at identical submaximal work loads; 2) this improvement is independent of changes in VO2 max, muscle mass, or limb blood flow; and 3) these differences are associated with improved endurance and may reflect improved oxidative capacity of skeletal muscle.

Heterogeneous blood flow distribution within single skeletal muscles in the rabbit: role of vasomotion, sympathetic nerve activity and effect of vasodilation.

A major heterogeneous distribution of blood flow has been described on a non-microvascular level within single skeletal muscles at rest and during exercise hyperaemia both in the dog and in the rabbit. The heterogeneity in blood flow distribution could be composed of both a steady-state region-to-region variability (spatial) and a time-dependent variability (temporal) in blood flow to each region. In the present study we estimated their relative contributions to the variations in blood flow within the muscles. Furthermore, we determined whether sympathetic nerve activity contributed to and whether pharmacologically induced vasodilation affected the heterogeneous blood flow pattern. Regional blood flow measurements were based on microsphere infusions into anaesthetized rabbits. Blood flow was determined under both resting conditions and during exercise hyperaemia in regions weighing 0.25 g each within hind leg muscles. The coefficient of variation for the spatial variability was twice that of the temporal one: 0.32 and 0.16 (mean) respectively. Neither stimulation of the sympathetic nerves, sympathectomy nor vasodilation affected the heterogeneity in blood flow. When exercise hyperaemia was induced, blood flow increased in all regions so that a positive (P less than 0.05) correlation was present between resting and exercising blood flow values in the individual regions. Although regional variation in vascularization could explain the observations during exercise hyperaemia, we have at present no fully satisfying explanation for the observed regional heterogeneity in blood flow.

Venous Muscle Pump Function following Reconstructive Arterial Surgery

The changes that occur in the leg venous muscle pump function were studied before and after proximal arterial reconstruction in 25 patients with claudication but without rest pain or clinical evidence of venous disease. There was found a significant increase in the distal blood pressure index corresponding to excellent clinical results. The venous muscle pump was affected such that venous return time, RT, decreased significantly ( P < 0.02) but expelled volume, EV, was not significantly affected. It is concluded that these findings may be explained by a postoperative increase in exercise bloodflow and that alterations in RT not only can be caused by changes in venous reflux but also by alterations in arterial input to the leg. The muscle pump capability to pump blood towards the heart was unaffected (EV constant) and it can thus not be incriminated for the postreconstructive oedema often found after arterial surgery. When evaluating isolated RT changes it is necessary to consider whether the arterial input to the pump is constant.

Non-Q wave versus Q wave myocardial infarction: Regional myocardial metabolism and blood flow assessed by positron emission tomography

This study compared regional myocardial blood flow at rest and during supine exercise as well as regional myocardial glucose utilization in the fasting condition in 22 patients, 11 with antecedent non-Q wave and 11 with antecedent Q wave infarction. With use of N-13 (nitrogen-13) ammonia and F-18 (fluorine-18) deoxyglucose as tracers of blood flow and exogenous glucose utilization and positron emission tomography, hypoperfused areas were noted at rest and during exercise in all 11 patients (100%) with Q wave infarction. Among the 11 patients with non-Q wave infarction such areas were noted in only 5 (45%) at rest and in 8 (73%) during exercise. Furthermore, segmentally enhanced F-18 deoxyglucose uptake corresponding to the infarcted areas (identified electrocardiographically) was seen in 10 (91%) of the 11 patients with non-Q wave infarction but in only 4 (36%) of the 11 patients with Q wave infarction (p < 0.01).In conclusion, segmental F-18 deoxyglucose uptake as a possible sign of myocardial viability was seen more frequently in non-Q wave than in Q wave infarction and, importantly, regionally enhanced F-18 deoxyglucose uptake occurred even in the absence of segmental rest or exercise blood flow abnormalities, or both, in 5 (45%) of 11 patients with non-Q wave infarction.

Systemic adenosine deaminase administration does not reduce active hyperemia in running rats

The importance of adenosine in controlling the magnitude and distribution of blood flow among and within skeletal muscles in rats during slow locomotor exercise was tested by systemic infusion of adenosine deaminase (ADA). Blood flows were measured using labeled microspheres before exercise and at 0.5, 15, and 30 min of fast treadmill walking at 15 m/min. An initial infusion of ADA (1,000 U/kg) was given 30 min before the first blood flow measurement and a second injection (1,000 U/kg) was given 5 min into exercise. These infusions maintained ADA activity above 5 U/ml blood throughout the experimental period. This plasma concentration of ADA was shown to be sufficient to result in a 64% decrease in muscle adenosine levels during ischemic contraction. Blood flows were measured in all of the muscles of the hindlimb (28 samples) and in various nonmuscular tissues in ADA-treated and control rats. Preexercise blood flows were primarily directed to slow-twitch muscles and exercise blood flows were highest in muscles with fast-twitch oxidative fibers. ADA treatment did not reduce total muscle blood flow or exercise blood flows in any of the muscles at any time. These findings do not support the hypothesis that adenosine plays an essential role in controlling muscle blood flow in skeletal muscles during normal locomotor activity.

Myocardial blood flow during exercise in dogs with left ventricular hypertrophy produced by aortic banding and perinephritic hypertension.

This study tested the hypothesis that for similar degrees of left ventricular hypertrophy, subendocardial blood flow would be facilitated by the increased diastolic coronary perfusion pressure associated with arterial hypertension, as compared with hypertrophy produced by banding the ascending aorta. Left ventricular hypertrophy was produced with perinephritic hypertension in seven adult dogs and by banding the ascending aorta in nine adult dogs. Left ventricular/body weight ratios were 6.15 +/- 0.59 g/kg in the hypertensive animals and 6.87 +/- 0.47 g/kg in dogs with aortic banding, as compared with 4.23 +/- 0.23 g/kg in seven normal dogs (p less than .01). Studies were performed at rest and during two stages of treadmill exercise to achieve heart rates of 195 and 260 beats/min. Diastolic aortic pressure was increased in animals with hypertension but not in dogs with aortic banding. Systolic ejection period was prolonged in dogs with aortic banding but not in hypertensive dogs. Mean blood flow per gram of myocardium measured with microspheres was similar at rest and during light exercise in all three groups of animals, whereas during heavy exercise blood flow was significantly greater than normal in both groups with hypertrophy. In normal dogs subendocardial/subepicardial (endo/epi) flow ratios did not change significantly during exercise. In both groups with hypertrophy, endo/epi ratios were normal at rest but decreased significantly during exercise. During heavy exercise the endo/epi ratio decreased to 0.73 +/- 0.08 in dogs with aortic banding as compared with 1.07 +/- 0.12 in hypertensive dogs (p less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of blood flow in muscles of miniature swine during exercise.

The purpose of this study was to determine how the distribution of blood flow within and among the skeletal muscles of miniature swine (22 +/- 1 kg body wt) varies as a function of treadmill speed. Radiolabeled microspheres were used to measure cardiac output (Q) and tissue blood flows in preexercise and at 3-5 min of treadmill exercise at 4.8, 8.0, 11.3, 14.5, and 17.7 km/h. All pigs (n = 8) attained maximal O2 consumption (VO2max) (60 +/- 4 ml X min-1 X kg-1) by the time they ran at 17.7 km/h. At VO2max, 87% of Q (9.9 +/- 0.5 l/min) was to skeletal muscle, which constituted 36 +/- 1% of body mass. Average total muscle blood flow at VO2max was 127 +/- 14 ml X min-1 X 100 g-1; average limb muscle flow was 135 +/- 17 ml X min-1 X 100 g-1. Within the limb muscles, blood flow was distributed so that the deep red parts of extensor muscles had flows about two times higher than the more superficial white portions of the same muscles; the highest muscle blood flows occurred in the elbow flexors (brachialis: 290 +/- 44 ml X min-1 X 100 g-1). Peak exercise blood flows in the limb muscles were proportional (P less than 0.05) to the succinate dehydrogenase activities (r = 0.84), capillary densities (r = 0.78), and populations of oxidative (slow-twitch oxidative + fast-twitch oxidative-glycolytic) fiber types (r = 0.93) in the muscles. Total muscle blood flow plotted as a function of exercise intensity did not peak until the pigs attained VO2max, although flows in some individual muscles showed a plateau in this relationship at submaximal exercise intensities. The data demonstrate that blood flow in skeletal muscles of miniature swine is distributed heterogeneously and varies in relation to fiber type composition and exercise intensity.

Myocardial blood flow and glucose metabolism in exercise induced and spontaneous ischemia

Regional myocardial perfusion and glucose uptake were assessed with rubidium 82 (Rb), F-18-deoxyglucose (FDG) and positron emission tomography (PET) in patients with coronary artery disease and stable (SA) or unstable (UA) angina pectoris and in a group of normal subjects. In SA patients at rest, myocardial perfusion and glucose uptake were comparable to those in normal subjects. However, a regionally increased FDG uptake was observed in the SA patients during recovery from an episode of exercise-induced ischaemia, in the same regions that showed abnormal perfusion during the stress test. In UA patients, regional myocardial perfusion at rest was not significantly different from that in SA patients and normal subjects. Conversely, in all UA patients myocardial glucose utilization was significantly greater than in SA patients and normal subjects. This occurred in the absence of symptoms and electrocardiographic signs of acute ischaemia at the time of the study. A significant reduction of myocardial glucose utilization — which, however, remained higher than in SA patients and normal subjects — was observed in the UA patients who were restudied during i.v. infusion of nitrates.

Exercise thallium-201 scintigraphy in dogs: effects of long-term coronary occlusion and collateral development on early and late scintigraphic images.

To examine the effects of coronary collateral development on thallium-201 (201Tl) distribution the left circumflex coronary artery was ligated in eight dogs. Three days later these animals ran on a treadmill, and 201-thallous chloride was injected into the right atrium at peak exercise. Scintigraphic scanning was begun within 10 min and continued for 3 hr. Scanning was repeated weekly for 6 weeks. In the last week radioactive microspheres were injected into the left atrium at peak exercise to measure regional myocardial blood flow. The scintigraphically determined disparity between perfusion of the ischemic and normal myocardium was most marked at 3 days after ligation. This difference gradually lessened over the first 4 weeks until there was no difference in 201Tl distribution to normally perfused myocardium and tissue distal to the ligation. Concomitant with the improvement in the scintigrams, exercise hemodynamics also improved over this 4 week period with significant increases in cardiac output and decreases in left atrial pressure. Serial coronary angiographic studies in two animals demonstrated the appearance of collaterals in the initial weeks after coronary occlusion, and by 4 weeks the left circumflex artery distal to the obstruction was completely opacified by collateral flow. The ratio of directly measured exercise blood flow to the left circumflex and normally perfused tissues was 0.89 +/- 0.08 at 6 weeks after ligation. Scintigraphic 201Tl redistribution after 3 hr also changed over the weeks after ligation. Three days after ligation washout from the ischemic area was significantly slower than that from the normal myocardium. By 6 weeks loss of 201Tl from the two regions occurred at nearly equal rates. Thus myocardial perfusion and function during exercise after coronary occlusion are dynamic events that change with time. It is likely that coronary collateral development is responsible for these phenomena. Therefore coronary collaterals do have salutary effects in the dog.

Metabolic adaptation to reduced muscle blood flow. I. Enzyme and metabolite alterations

A rat model was developed in which the adaptive effects of exposing skeletal muscle tissue to a reduced blood flow during muscle contractions could be studied. The common iliac artery was ligated in one hindlimb, using the other as control. This procedure reduced the exercise blood flow to the individual muscles of the lower limb by 76-93%, evaluated with the microsphere technique. Muscle contractions were induced by electrical stimulation of the sciatic nerves in both legs. After intermittent stimulation for 6 days, a significant increase in citrate synthase and cytochrome c oxidase activities was found in the soleus (26%) and extensor digitorum longus (EDL, 20%) muscles of the ligated legs compared with the control legs. Resting metabolite concentrations were also measured, and a reduction of the ATP level (soleus 35%, EDL 14%) and an increased glycogen content (55-71%) were found. These results demonstrate that a reduced blood flow during muscle contractions provokes an adaptive increase of the oxidative enzyme capacity as well as altered resting levels of intracellular metabolites.

Exercise and renal function.

Exercise induces profound changes in the renal haemodynamics and in electrolyte and protein excretion. Effective renal plasma flow is reduced during exercise. The reduction is related to the intensity of exercise and renal blood flow may fall to 25% of the resting value when strenuous work is performed. The combination of sympathetic nervous activity and the release of catecholamine substances is involved in this process. The reduction of renal blood flow during exercise produces a concomitant effect on the glomerular filtration rate, though the latter decreases relatively less than the former during exertion. However, the degree of hydration has an important influence on the glomerular filtration rate. An antidiuretic effect is observed during intense exercise. Changes in urine flow are dependent on the plasma antidiuretic hormone levels which are increased by intense exercise. Heavy exercise has an inhibitory effect on most electrolytes (Na, Cl, Ca, P). With potassium, however, most studies report that potassium excretion is not consistently affected by moderate to heavy exercise. Increased aldosterone production helps the body to maintain sodium by increasing its reabsorption from the filtered tubular fluid. Recent studies suggest that sympathetic stimulation may be involved during exercise. Strenuous work leads to an increased excretion of erythrocytes and leucocytes in urine. Cylindruria has been regularly found in postexercise urine in different sports. Postexercise proteinuria is a common phenomenon in humans. It seems to be directly related to the intensity of exercise, rather than to its duration. This excretion of proteins in urine is a transient state with a half-time of approximately 1 hour. Postexercise proteinuria has a pattern different from normal physiological proteinuria. Immunochemical techniques demonstrate that postexercise proteinuria is of the mixed glomerular-tubular type, the former being predominant. The increased clearance of plasma proteins suggests an increased glomerular permeability and a partial inhibition of tubular reabsorption of macromolecules. Haemoglobinuria and myoglobinuria may be observed under special exercise conditions. The degree of hydration appears to be important to reduce these abnormalities.

Exercise blood flow patterns within and among rat muscles after training.

This study was designed to determine the influence of a long-term, moderate-intensity treadmill training program on the distribution of blood flow within and among muscles of rats during exercise. One group (T) of male Sprague-Dawley rats trained for 1 h/day for 13-17 wk at 30 m/min on a motor-driven treadmill. A second group (UT) of rats was conditioned for 10 min/day for 4 wk at the same speed. Muscle succinate dehydrogenase activities were higher in T than UT rats indicating a significant training effect. Blood flows (BFs) in 32 hindlimb muscles or muscle parts and other selected organs were measured in the two groups with radiolabeled microspheres during preexercise and while the rats ran for 30 s, 5 min, or 15 min at 30 m/min on the treadmill. The data indicate 1) there were no differences in total hindlimb muscle BF between UT and T rats at any time; however, 2) T rats had higher preexercise heart rates and higher muscle BFs in the deep red extensor muscles, suggesting a greater anticipatory response to the impending exercise; 3) T rats demonstrated more rapid elevations in BF in the red extensor muscles at the commencement of exercise; 4) T rats had higher BFs in red extensor muscles during exercise, whereas UT rats had higher BFs in white muscles; and 5) T rats maintained higher BFs in the visceral organs during exercise. These findings demonstrate that exercise training results in changes in the distribution of BF within and among muscles and among organs during exercise. Specifically, data indicate the high-oxidative motor units that are primarily recruited in the muscles during the initial stages of moderate treadmill exercise receive higher blood flows in the trained rats; this presumably contributes to increased resistance to fatigue.

Blood flows within and among rat muscles as a function of time during high speed treadmill exercise.

The purpose of these experiments was to use radiolabelled microspheres to measure blood flow distribution patterns within and among rat hind-limb skeletal muscles before, during, and after high speed treadmill running at 60 min-1 to fatigue. Exercise blood flows were measured at the 0.5, 1, 2 and 3 min time points. Pre-exercise blood flow was highest in physiological extensor muscles or muscle parts with large populations of slow-twitch muscle fibres, e.g. soleus (197 ml min-1 100 g-1). Blood flows were lowest to muscles or muscle parts with high proportions of fast-twitch glycolytic fibres, e.g. white gastrocnemius (15 ml min-1 100 g-1). The most rapid increases in blood flow at the beginning of exercise and the highest peak blood flows during exercise generally occurred in physiological extensor muscles with relatively high populations of fast-twitch oxidative fibres. For example, red gastrocnemius muscle blood flow increased by 271 ml min-1 100 g-1 during the first 30 s of exercise, and attained a peak flow of 395 ml min-1 100 g-1 by the third minute of exercise. On the other hand, the slowest elevations in blood flow at the start of exercise and the lowest peak flows were observed in muscles with high populations of fast-twitch glycolytic fibres. White gastrocnemius muscle, for example, increased its blood flow by 16 ml min-1 100 g-1 during the first 30 s of running, and had a peak flow of 76 ml min-1 100 g-1 by the end of 3 min exercise. These relationships between blood flows and fibre type populations were less consistent in physiological flexor muscle groups. Following exercise, blood flows in high-oxidative muscles returned to the pre-exercise levels within 30 s. However, in low-oxidative muscles, return of blood flows to the pre-exercise levels were slower. Thus, marked differences in the absolute magnitudes of blood flows and in the rates of change in blood flows were observed within and among the hind-limb muscles before, during and after exercise. These differences were related to the fibre type compositions of the muscles.

Muscle Blood Flow in Peripheral Vascular Disease

Physiotherapists are often involved in the post-operative management and rehabilitation of the lower limb amputee. Seldom, however, does one see the usual presentation of peripheral vascular disease - ischaemia of the muscles on exercise, ie: intermittent claudication. This article discusses a technique for demonstrating limitation in exercise blood flow - the basis of this symptom. Thallium 201 scanning is extensively used in demonstrating areas of reduced blood flow to one important muscle, the heart, and this technique can be extrapolated to the muscles of the leg. Twenty-two patients being studied with Thallium-201 for suspected coronary artery disease had the muscles of the lower limb scanned with a gamma camera. The photographs obtained form the basis of this article.

Metabolic Response in Different Muscle Types to Reduced Blood Flow during Exercise in Perfused Rat Hindlimb

1. In peripheral arterial insufficiency, leg blood flow during exercise is reduced. The aim of this study was to investigate the metabolic response in different muscle types during exercise at reduced versus normal exercise blood flow. 2. A modified rat hindlimb perfusion model was used. Muscle metabolites and distribution of labelled microspheres were analysed in the soleus and the gastrocnemius muscles during exercise induced by sciatic nerve stimulation. 3. Blood flow distribution between the soleus and the gastrocnemius muscles (per unit weight) was 1.7:1 at rest, and this ratio did not change significantly during exercise at reduced flow. 4. There was a more pronounced decrease in the [phosphocreatine], the [glycogen] and the [ATP]/[ADP] ratio as well as a more pronounced increase in the [lactate] and the [lactate]/[Pyruvate] ratio in the gastrocnemius muscle during exercise at reduced blood flow as compared with values obtained at normal exercise flow. In the soleus muscle the difference between the two conditions was confined to an increased [lactate]/[pyruvate] ratio. 5. The results show that a muscle composed mainly of fast-twitch fibres with a high glycolytic and low oxidative capacity is much more susceptible to a reduced exercise flow than a muscle composed of slow-twitch, oxidative fibres. It is suggested that claudicating pain is related to these metabolic changes and it is concluded that pain most probably originates in type II fibers.

Review of energetics and blood flow in exercise.

Review of energetics and blood flow in exercise.

EXERCISE AND RENAL FUNCTION

Exercise induces profound changes in the renal haemodynamics and in electrolyte and protein excretion. Effective renal plasma flow is reduced during exercise. The reduction is related to the intensity of exercise and renal blood flow may fall to 25% of the resting value when strenuous work is performed. The combination of sympathetic nervous activity and the release of catecholamine substances is involved in this process. The reduction of renal blood flow during exercise produces a concomitant effect on the glomerular filtration rate, though the latter decreases relatively less than the former during exertion. However, the degree of hydration has an important influence on the glomerular filtration rate. An antidiuretic effect is observed during intense exercise. Changes in urine flow are dependent on the plasma antidiuretic hormone levels which are increased by intense exercise.

Tilted and non-tilted postischaemic exercise peak flow in the legs of normal human subjects

Peak flow was measured by radioactive xenon in fifteen normal subjects in the anterior tibial muscle after maximal ischaemic exercise. The postischaemic exercise peak flow was 75 +/- 13 ml/100 g muscle/min (mean +/- SD), when the test was performed while the subjects rested in the horizontal position. When the same test was performed with the subjects resting in a 45 degrees feet down tilted position, the peak flow increased very much, about 65%, and averaged 125 +/- 17 ml/100 g muscle/min. The increased peak flow in the feet tilted position is explained by passive dilatation of the vessels due to increased hydrostatic pressure. It is suggested, that measurement of maximal ischaemic exercise blood flow in the tilted position may be a more sensitive procedure for detection of minimal vascular changes due to the very high blood flow obtained.

Differences in muscle blood flow in upper and lower extremities of patients after correction of coarctation of the aorta.

Using the method 133Xe clearance we investigated blood flow and calculated vascular resistances simultaneously in the muscles of the upper and lower extremities in 58 patients following successful surgical correction of aortic coarctation carried out at age 11.5 (+/- 2.9) years. The interval from operation to investigation was 11.5 (+/- 4.5) years. Resting and maximal ischemic exercise blood flows in the upper extremity were decreased and the duration of maximal blood flow was shortened. Values recorded from the lower extremities did not differ from normal controls. The difference between upper and lower extremities was statistically significant. Vascular resistance during maximal blood flow was higher in the upper extremities than in the lower. Differences between upper and lower extremities did not change after vasodilation elicited by amyl nitrite. The degree of differences was not dependent upon the age at operation, the age of the patients at investigation, or on the time interval between operation and investigation.

Interaction of O2 and CO2 in sustained exercise hyperemia of canine skeletal muscle

The relative contribution of O2 and CO2 to the metabolic control of blood flow in long-term exercise was examined in the denervated gracilis muscle of the anesthetized dog. The data show that 1) on initiation of heavy exercise, the effluent blood PO2 and pH fall markedly and then rise slowly but remain depressed relative to control during 60 min of exercise hyperemia, while the initial increases in [K+] and osmolality rapidly approach and eventually reach preexercise levels. 2) The enhanced vasodilator activity of venous blood from exercising muscle is attenuated when effluent blood PO2 or pH is corrected to preexercise levels; it is completely abolished when both are corrected. 3) Induced reduction PO2 or pH in the arterial inflow, and thus venous outflow, of resting muscle produces a fall in resistance; simultaneous reductions of both to levels seen in heavy exercise produce a fall in resistance to near that observed during exercise. Since the enhanced vasodilator activity of venous blood from the contracting muscle was abolished by simultaneous correction of the PO2 and pH, it seems likely that these factors, acting directly or indirectly, are the principal chemicals responsible for the maintenance of the vasodilation seen in canine skeletal muscle during heavy exercise.