The role of blood flow and/or muscle hypoxia in capillary growth in chronically stimulated fast muscles

Acute Effects of Low-Intensity Electrical Stimulation on Segmental Arterial Stiffness

Electrical muscle stimulation (EMS) has traditionally been employed to improve muscle strength and glucose uptake. EMS may also reduce arterial stiffness, but little is known about whether low-intensity EMS reduces systemic and/or regional arterial stiffness. This study aimed to examine the effects of low-intensity EMS of the lower limbs on segmental arterial stiffness. Fourteen healthy subjects participated in experiments under two different protocols (control resting trial (CT) and electrical stimulation trial (ET)) in random order on separate days. The EMS was applied to the lower limbs at 4 Hz for 20 min at an intensity corresponding to an elevation of approximately 15 beats/min in pulse rate (10.7 ± 4.7% of heart rate reserve). Arterial stiffness was assessed by cardio-ankle vascular index (CAVI), CAVI₀, heart-ankle pulse wave velocity (haPWV), brachial-ankle pulse wave velocity (baPWV), heart-brachial pulse wave velocity (hbPWV), and carotid-femoral pulse wave velocity (cfPWV). In both trials, each parameter was measured at before (Pre) and 5 min (Post 1) and 30 min (Post 2) after trial. After the experiment, CT did not cause significant changes in any arterial stiffness parameters, whereas ET significantly reduced CAVI (from Pre to Post 1: −0.8 ± 0.5 unit p < 0.01), CAVI₀ (from Pre to Post 1: −1.2 ± 0.8 unit p < 0.01), haPWV (from Pre to Post 1: −47 ± 35 cm/s p < 0.01), and baPWV (from Pre to Post 1: −120 ± 63 cm/s p < 0.01), but not hbPWV or cfPWV. Arm diastolic blood pressure (BP) at Post 2 was slightly but significantly increased in the CT compared to Pre or Post 1, but not in the ET. Conversely, ankle diastolic and mean BPs at Post 1 were significantly reduced compared to Pre and Post 2 in the ET (p < 0.01). These findings suggest that low-intensity EMS of the lower limbs reduces arterial stiffness, but only in sites that received EMS.

Does a Better Perfusion of Deconditioned Muscle Tissue Release Chronic Low Back Pain?

Non-specific chronic low back pain (nsCLBP) is a multifactorial condition of unknown etiology and pathogenesis. Physical and genetic factors may influence the predisposition of individuals to CLBP, which in many instances share a musculoskeletal origin. A reduced pain level in low back pain patients that participate in exercise therapy highlights that disuse-related muscle deconditioning may predispose individuals to nsCLBP. In this context, musculoskeletal pain may be the consequence of capillary rarefaction in inactive muscle as this would lower local tissue drainage and washing out of toxic waste. Muscle activity is translated into an angio-adaptative process, which implicates angiogenic-gene expression and individual response differences due to heritable modifications of such genes (gene polymorphisms). The pathophysiologic mechanism underlying nsCLBP is still largely unaddressed. We hypothesize that capillary rarefaction due to a deconditioning of dorsal muscle groups exacerbates nsCLBP by increasing noxious sensation, reducing muscle strength and fatigue resistance by initiating a downward spiral of local deconditioning of back muscles which diminishes their load-bearing capacity. We address the idea that specific factors such as angiotensin-converting enzyme and Tenascin-C might play an important role in altering susceptibility to nsCLBP via their effects on microvascular perfusion and vascular remodeling of skeletal muscle, inflammation, and pain sensation. The genetic profile may help to explain the individual predisposition to nsCLBP, thus identifying subgroups of patients, which could benefit from ad hoc treatment types. Future therapeutic approaches aimed at relieving the pain associated with nsCLBP should be based on the verification of mechanistic processes of activity-induced angio-adaptation and muscle-perfusion.

Capillary Network Morphometry of Pig Soleus Muscle Significantly Changes in 24 Hours After Death

Capillary network characteristics are invaluable for diagnostics of muscle diseases. Biopsy material is limited in size and mostly not accessible for intensive research. Therefore, especially in human tissue, studies are performed on autopsy material. To approach the problem whether it is reliable to deduce hypotheses from autopsy material to explain physiological and pathological processes, we studied capillarity in pig soleus muscle 1 and 24 hr after death. Capillaries and muscle fibers were immunofluorescently marked, and images were acquired with a confocal microscope. Characteristics of the capillary network were estimated by image analysis methods using several plugins of the Ellipse program. Twenty-four hours after death, the measured characteristics of the capillary network differ by up to 50% when compared with samples excised 1 hr after death. Muscle fiber diameter, the measured capillary length, and tortuosity were reduced, and capillary network became more anisotropic. The main postmortem change that affects capillaries is evidently geometric deformation of muscle tissue. In conclusion, when comparing results from biopsy samples with those from autopsy samples, the effect of postmortem changes on the measured parameters must be carefully considered.

Electrical Stimulation of Denervated Rat Skeletal Muscle Retards Capillary and Muscle Loss in Early Stages of Disuse Atrophy

The purpose of the present study is to investigate the effects of low-frequency electrical muscle stimulation (ES) on the decrease in muscle mass, fiber size, capillary supply, and matrix metalloproteinase (MMP) immunoreactivity in the early stages of denervation-induced limb disuse. Direct ES was performed on the tibialis anterior muscle following denervation in seven-week-old male rats. The rats were divided into the following groups: control (CON), denervation (DN), and denervation with direct ES (DN + ES). Direct ES was performed at an intensity of 16 mA and a frequency of 10 Hz for 30 min per day, six days a week, for one week. We performed immunohistochemical staining to determine the expression of dystrophin, CD34, and MMP-2 in transverse sections of TA muscles. The weight, myofiber cross-sectional area (FCSA), and capillary-to-fiber (C/F) ratio of the tibialis anterior (TA) muscle were significantly reduced in the DN group compared to the control and DN + ES groups. The MMP-2 positive area was significantly greater in DN and DN + ES groups compared to the control group. These findings suggest beneficial effects of direct ES in reducing muscle atrophy and capillary regression without increasing MMP-2 immunoreactivity in the early stages of DN-induced muscle disuse in rat hind limbs.

An acetylation rheostat for the control of muscle energy homeostasis

In recent years, the role of acetylation has gained ground as an essential modulator of intermediary metabolism in skeletal muscle. Imbalance in energy homeostasis or chronic cellular stress, due to diet, aging, or disease, translate into alterations in the acetylation levels of key proteins which govern bioenergetics, cellular substrate use, and/or changes in mitochondrial content and function. For example, cellular stress induced by exercise or caloric restriction can alter the coordinated activity of acetyltransferases and deacetylases to increase mitochondrial biogenesis and function in order to adapt to low energetic levels. The natural duality of these enzymes, as metabolic sensors and effector proteins, has helped biologists to understand how the body can integrate seemingly distinct signaling pathways to control mitochondrial biogenesis, insulin sensitivity, glucose transport, reactive oxygen species handling, angiogenesis, and muscle satellite cell proliferation/differentiation. Our review will summarize the recent developments related to acetylation-dependent responses following metabolic stress in skeletal muscle.

Effect of magnetic stimulation in spinal cord on limb angiogenesis and implication: a pilot study

OBJECTIVE

To investigate the effect of repetitive magnetic stimulation (rMS) of the spinal cord on limb angiogenesis in healthy rats and explore its implication for the treatment of lymphedema.

METHOD

Twelve adult male Sprague-Dawley rats were divided into four groups as follows: sham rMS followed by tissue harvest 5 minutes later (group 1, n=2), 1 Hz rMS and tissue harvest 5 minutes later (group 2, n=3), 20 Hz rMS and tissue harvest 5 minutes later (group 3, n=3), 20 Hz rMS and tissue harvest 30 minutes later (group 4, n=4). Animals were treated with 20-minute rMS with 120% of the motor threshold on their left side of upper lumbar spinal cord. Expression of angiogenic factors, that is, Akt, phospho-Akt (pAkt), endothelial nitric oxide synthase (eNOS), phospho-eNOS (p-eNOS) were measured by western blot. Bilateral hindlimb muscles (quadriceps and gastrocnemius) were harvested.

RESULTS

Expression of Akt in left quadriceps increased in group 4 compared with group 2 and 3 (3.4 and 5.3-fold each, p=0.026). Expression of eNOS in left plus right quadriceps markedly increased in group 3 and 4 compared with group 1 and 2 (p=0.007). Expressions of eNOS, Akt and p-eNOS, pAkt in gastrocnemius were not comparable between four groups (p>0.05).

CONCLUSION

Repetitive magnetic stimulation of the spinal cord may exert an angiogenic effect closely linked to lymphangiogenesis. It has clinical implication for the possible therapy of lymphedema caused by breast, cervical or endometrial cancer operation. Future studies with the specific lymphatic endothelial cell markers are required to confirm the effect of rMS on lymphangiogenesis.

Effect of cilostazol and pentoxifylline on gait biomechanics in rats with ischemic left hindlimb

OBJECTIVE

The purpose of this study was to determine the impact of pharmacologic treatment with cilostazol and pentoxifylline on gait biomechanics of ischemic rat hindlimbs compared with nonischemic controls.

METHODS

An experimental study was designed using 30 Wistar rats divided into five groups (n = 6): control (C); ischemia (I) - animals submitted to left common iliac artery interruption without pharmacologic treatment; pentoxifylline (Pen) - rats submitted to procedure and treated with pentoxifylline 3 mg/kg twice a day for 6 weeks; cilostazol (Cil) - animals submitted to procedure and treated with cilostazol 30 mg/kg twice a day for 6 weeks; and sham (S) - animals submitted to procedure without artery interruption. Gait analysis was performed using a computed treadmill. Time, number, and duration of each hindlimb contact were obtained. The total number of contacts (TNC) and the total duration of contacts (TDC) were compared between left and right hindlimb and among groups. Left hindlimb ischemic incapacitation index (LHII) was defined by the formula: LHII = (1-TNCleft x TDCleft / TNCright x TDCright) x 100.

RESULTS

Left hindlimb TNC values were twofold lower in I, Pen, and Cil groups than in C and S groups (P < .01). In I, Pen, and Cil groups, TNC values for the left hindlimb were half of the right hindlimb ones (P < .01). Left hindlimb TDC values were lower in I and Pen groups than the other groups (P < .01). Cil group presented twofold increased values, not different from C and S groups (P = 0.16). Right hindlimb TNC values were greater for I group (P < .01). LHII was around zero in C and S groups and 82 in both I and Pen groups (P < .01). Cil group presented a LHII of 42; higher than C and S groups, but lower than I and Pen groups (P < .01).

CONCLUSIONS

Cilostazol at a dose of 30 mg/kg twice a day promoted improvement in gait performance in rats submitted to chronic hindlimb ischemia. Pentoxifylline at a dose of 3 mg/kg twice a day did not show this effect.

Morphofunctional responses to anaemia in rat skeletal muscle

Adult male Sprague-Dawley rats were randomly assigned to two groups: control and anaemic. Anaemia was induced by periodical blood withdrawal. Extensor digitorum longus and soleus muscles were excised under pentobarbital sodium total anaesthesia and processed for transmission electron microscopy, histochemical and biochemical analyses. Mitochondrial volume was determined by transmission electron microscopy in three different regions of each muscle fibre: pericapillary, sarcolemmal and sarcoplasmatic. Muscle samples sections were also stained with histochemical methods (SDH and m-ATPase) to reveal the oxidative capacity and shortening velocity of each muscle fibre. Determinations of fibre and capillary densities and fibre type composition were made from micrographs of different fixed fields selected in the equatorial region of each rat muscle. Determination of metabolites (ATP, inorganic phosphate, creatine, creatine phosphate and lactate) was done using established enzymatic methods and spectrophotometric detection. Significant differences in mitochondrial volumes were found between pericapillary, sarcolemmal and sarcoplasmic regions when data from animal groups were tested independently. Moreover, it was verified that anaemic rats had significantly lower values than control animals in all the sampled regions of both muscles. These changes were associated with a significantly higher proportion of fast fibres in anaemic rat soleus muscles (slow oxidative group = 63.8%; fast glycolytic group = 8.2%; fast oxidative glycolytic group = 27.4%) than in the controls (slow oxidative group = 79.0%; fast glycolytic group = 3.9%; fast oxidative glycolytic group = 17.1%). No significant changes were detected in the extensor digitorum longus muscle. A significant increase was found in metabolite concentration in both the extensor digitorum longus and soleus muscles of the anaemic animals as compared to the control group. In conclusion, hypoxaemic hypoxia causes a reduction in mitochondrial volumes of pericapillary, sarcolemmal, and sarcoplasmic regions. However, a common proportional pattern of the zonal distribution of mitochondria was maintained within the fibres. A significant increment was found in the concentration of some metabolites and in the proportion of fast fibres in the more oxidative soleus muscle in contrast to the predominantly anaerobic extensor digitorum longus.

Eletroestimulação muscular: alternativa de tratamento coadjuvante para pacientes com doença arterial obstrutiva periférica

A doença arterial periférica faz parte de um grupo de patologias vasculares que evolui de forma lenta e progressiva. A proposta deste artigo foi avaliar, por meio de revisão bibliográfica, os possíveis benefícios da eletroestimulação crônica como tratamento coadjuvante para pacientes arteriopatas. De acordo com a literatura analisada, concluímos que a eletroestimulação é capaz de provocar alterações importantes no perfil metabólico das fibras musculares, convertendo-as do tipo II para o tipo I, o que induz o crescimento capilar, a densidade capilar e o suprimento de oxigênio. Desta forma, este recurso terapêutico aumenta a capacidade aeróbica oxidativa e a resistência à fadiga dos músculos isquêmicos. Assim, a eletroestimulação é mais um recurso terapêutico capaz de melhorar a habilidade para caminhar destes pacientes, diminuindo gastos com cirurgias de revascularização e complicações maiores.

The role of ascorbic acid and exercise in chronic ischemia of skeletal muscle in rats

This study was designed to investigate the effects of peripheral arterial insufficiency, exercise, and vitamin C administration on muscle performance, cross-sectional area, and ultrastructural morphology in extensor digitorum longus (EDL) and soleus (Sol) muscles in rats. Adult Wistar rats were assigned to ischemia alone (isch), ischemia-exercised (exe), ischemia-vitamin C (vit C), and ischemia-exercise-vitamin C (vit C + exe) groups. Ischemia was achieved via unilateral ligation of the right common iliac artery. Contralateral muscles within the same animal served as controls. Exercise protocol consisted of 50-min intermittent level running performed every other day for 5 days. Vitamin C (100 mg/kg body wt) was administered intraperitoneally on a daily basis throughout the 14 days of the experiment. With regard to the EDL muscle, ischemia alone reduced muscle strength, which was not recovered after vitamin C administration. Exercise alone following ischemia induced the most severe structural damage and cross-sectional area decrease in the muscle, yet the reduction in tetanic tension was not significant. Exercise in conjunction with vitamin C administration preserved ischemia-induced EDL muscle tetanic tension. In the Sol muscle, a significant reduction in single twitch tension after vitamin C administration was found, whereas the tetanic force of the ischemic Sol was not significantly decreased compared with the contralateral muscles in any group. Ischemic Sol muscle cross-sectional area was reduced in all but the exe groups. In Sol, muscle strength was reduced in the vit C group, and mean cross-sectional area of ischemic Sol muscles was reduced in all groups except the exe group. These results illustrate that mild exercise, combined with a low dose of vitamin C supplementation, may have beneficial effects on ischemic EDL muscle with a smaller effect on the Sol muscle.

EFFECT OF LOW-VOLTAGE ELECTRICAL STIMULATION ON ANGIOGENIC GROWTH FACTORS IN ISCHAEMIC RAT SKELETAL MUSCLE

1. Low-voltage electrical stimulation (LVES) in skeletal muscle at a level far below the threshold of muscle contraction has been reported to promote local angiogenesis. However, the mechanism underlying the promotion of local angiogenesis by LVES has not been fully elucidated. In the present study, we evaluated whether angiogenic factors, such as vascular endotherial growth factor (VEGF), hepatocyte growth factor (HGF) and fibroblast growth factor (FGF), as well as other disadvantageous factors, such as inflammation (interleukin (IL)-6) and hypoxia (hypoxia-inducible factor (HIF)-1alpha), contribute to the local angiogenesis produced by LVES. 2. We completely excised bilateral femoral arteries of male Sprague-Dawley rats. After the operation, electrodes were implanted onto the centre of the fascia of the bilateral tibialis anterior (TA) muscles, tunnelled subcutaneously and exteriorized at the level of the scapulae. The right TA muscles of rats were stimulated continuously at a stimulus frequency of 50 Hz, with a 0.1 V stimulus strength and no interval, for 5 days. The left TA muscles served as controls. 3. We found that both VEGF and HGF protein were significantly increased by LVES in stimulated muscles compared with control. The VEGF level of the LVES group was 89.10 +/- 17.19 ng/g, whereas that of the control group was 65.07 +/- 12.88 ng/g, as determined by ELISA (P < 0.05). The HGF level of the LVES and control groups was 8.52 +/- 1.96 and 5.80 +/- 2.14 ng/g, respectively (P < 0.05). In contrast, there was no difference in FGF, IL-6 and HIF-1alpha between the LVES and control groups. 4. These results suggest that LVES in a hindlimb ischaemia model of rats increases not only VEGF, but also HGF, production, which may be the main mechanism responsible for the angiogenesis produced by LVES.

Low-Frequency Electrical Stimulation Increases Muscle Strength and Improves Blood Supply in Patients With Chronic Heart Failure

BACKGROUND

This study was designed to evaluate the effects of low-frequency electrical stimulation (LFES) on muscle strength and blood flow in patients with advanced chronic heart failure (CHF).

METHODS AND RESULTS

Patients with CHF (n=15; age 56.5 +/- 5.2 years; New York Heart Association III - IV; ejection fraction 18.7 +/- 3.3%) were examined before and after 6 weeks of LFES (10 Hz) of the quadriceps and calf muscles of both legs (1 h/day, 7 days/week). Dynamometry was performed weekly to determine maximal muscle strength (F(max); N) and isokinetic peak torque (PT(max); Nm); blood flow velocity (BFV) was measured at baseline and after 6 weeks of LFES using pulsed-wave Doppler velocimetry of the right femoral artery. Six weeks of LFES significantly increased F(max) (from 224.5 +/- 96.8 N to 340.0 +/- 99.4 N; p<0.001), and also PT(max) (from 94.5 +/- 41.5 Nm to 135.3 +/- 28.8 Nm; p<0.01). BFV in the femoral artery increased after 6 weeks from 35.7 +/- 15.4 cm/s to 48.2 +/- 18.1 cm/s (p<0.05); BFV values at rest before and after 6 weeks of LFES did not differ significantly.

CONCLUSIONS

LFES may improve muscle strength and blood supply, and could be recommended for the treatment of patients with severe CHF.

Nitric oxide, VEGF, and VEGFR-2: interactions in activity-induced angiogenesis in rat skeletal muscle

Vascular endothelial growth factor (VEGF) is considered to be important in promotion of capillary growth in skeletal muscles exposed to increased activity. We studied its interactions with nitric oxide (NO) by examining the expression of endothelial NO synthase (NOS), VEGF, and VEGF receptor-2 (VEGFR-2) proteins in relation to capillary growth in rat extensor digitorum longus muscles electrically stimulated for 2, 4, or 7 days with and without NOS inhibition by N(omega)-nitro-L-arginine (L-NNA, 3 mg/day). Stimulation increased all proteins from 2 days onward, concomitantly with capillary proliferation (labeling for proliferating cell nuclear antigen). Capillary-to-fiber ratio was elevated by 25% after 7 days. Concurrent oral administration of L-NNA did not affect the increase in endothelial NOS but depressed its activity, as shown by increased blood pressure and decreased arteriolar diameters in 2-day-stimulated muscles. NOS inhibition eliminated the increased expression of VEGFR-2 and VEGF proteins in muscles stimulated for 2 and 4 days but not for 7 days. However, it depressed capillary proliferation and the increase in C/F at all time points. We conclude that, in stimulated muscles, NO, generated by activation of neuronal NOS by muscle activity or endothelial NOS by increased blood flow and capillary shear stress, may increase capillary proliferation in the early stages of stimulation through upregulation of VEGFR-2 and VEGF. With longer stimulation, capillary growth appears to require NO, and high levels of VEGF and VEGFR-2 may be contributing to maintenance of the increased capillary bed.

Multicellular simulation predicts microvascular patterning and in silico tissue assembly

Remodeling of microvascular networks in mammals is critical for physiological adaptations and therapeutic revascularization. Cellular behaviors such as proliferation, differentiation, and migration are coordinated in these remodeling events via combinations of biochemical and biomechanical signals. We developed a cellular automata (CA) computational simulation that integrates epigenetic stimuli, molecular signals, and cellular behaviors to predict microvascular network patterning events. Over 50 rules obtained from published experimental data govern independent behaviors (including proliferation, differentiation, and migration) of thousands of interacting cells and diffusible growth factors in their tissue environment. From initial network patterns of in vivo blood vessel networks, the model predicts emergent patterning responses to two stimuli: 1) network-wide changes in hemodynamic mechanical stresses, and 2) exogenous focal delivery of an angiogenic growth factor. The CA model predicts comparable increases in vascular density (370+/-29 mm/mm3) 14 days after treatment with exogenous growth factor to that in vivo (480+/-41 mm/mm3) and approximately a twofold increase in contractile vessel lengths 5-10 days after 10% increase in circumferential wall strain, consistent with in vivo results. The CA simulation was thus able to identify a functional patterning module capable of quantitatively predicting vessel network remodeling in response to two important epigenetic stimuli.

Enhanced smooth muscle cell coverage of microvessels exposed to increased hemodynamic stresses in vivo

During vascular remodeling in adult organisms, new capillary growth is often coupled with the adaptation of arterioles and venules, a process that requires the recruitment and differentiation of precursor cells into smooth muscle. We studied the in vivo adaptation of microvessels in the presence of elevated pressure and circumferential wall stress using a ligation strategy for mesenteric microvascular networks. Acute pressure increases of 42.6+/-18% and 17.1+/-2.3% were respectively elicited in the 25- to 30-microm-diameter venules and arterioles supplying the networks. Wall shear rates were not significantly changed; however, diameters were increased in >10-microm-diameter venules and >20-microm-diameter arterioles. Smooth muscle cell contractile phenotype was determined in all microvessels by observing the expression of smooth muscle myosin heavy chain (SM-MHC; a marker of fully differentiated smooth muscle) and smooth muscle alpha-actin (a marker for all smooth muscle, including immature smooth muscle of fibroblast/pericyte lineage). The ratio of SM-MHC positive vessel length to smooth muscle alpha-actin-positive vessel length increased >2-fold after 5 and 10 days of the ligation treatment. Smooth muscle proliferation was studied by bromodeoxyuridine incorporation, and the increase in SM-MHC-labeled microvessel length density was accompanied by no measurable change in proliferation of SM-MHC-labeled cells 5 and 10 days after ligation. These results indicate that after a period of 5 or 10 days, mesenteric microvessels <40 microm in diameter exposed to elevated pressure and wall strain exhibit an enhanced coverage of mature, fully differentiated smooth muscle cells.

Electrical stimulation promotes angiogenesis in a rabbit hind-limb ischemia model

In previous investigations, it was shown that applying a modest regimen of electrical stimulation (ES), even in severely ischemic tissue, improves the healing process, accelerates neovascularization, and enhances angiogenesis in muscle tissue. Our objective in this current report was to further understand ES as a potential alternative treatment for severe muscle ischemia. Immediately after the left distal external iliac artery and the femoral artery were excised, ES (30 contractions per minute [cpm], 2 V, single impulses per burst) was applied to rabbit adductor muscle near the site of the excised femoralis artery for 24 hours daily over 1 month. Three other series served as controls: ES without arterial excision; arterial excision without ES or lead implantation; and arterial excision with lead implantation but no ES. Histologic study of capillary density was performed by angiography (employing a grid template) and by measuring the lower limb-calf blood pressure ratio. At the end of 30 days in the ES series, 10.5 +/-1.2 contrast-medium opacified arteries (COAs) crossed a specific grid section segment compared with 7.2 +/-1.5 in the control series without ES (p<0.05); 68.2 +/-9.3 COAs crossed a grid section compared with 43.2 +/-6.4 in controls (p<0.05); 27.3 +/-1.2 grids contained COAs compared with 29.3 +/-3.5 in controls (p<0.05); lower limb-calf blood pressure ratio was 0.81 +/-0.06 compared with 0.31 +/-0.07 in controls (p<0.05); and capillary density was 283.7 +/-24.5 mm2 compared with 91.4 +/-20.9 mm2 in controls (p<0.001). These preliminary results show that cautious ES enhances and accelerates muscle revascularization in severely ischemic tissue.

The influence of electrostimulation on the circulation of the remaining leg in patients with one-sided amputation

The aim of the authors' study was to investigate, in patients with one leg amputated, the influence of electrostimulation on the arterial circulation of the other lower limb and on the ability of a leg with deteriorated blood flow to perform work. The study encompassed 50 patients who were admitted to the rehabilitation center to obtain a leg prosthesis and learn to walk after amputation of 1 lower limb because of severe circulatory disturbance. The patients were randomly divided into 2 groups. The first group contained 25 patients treated with a standard exercise program for patients with limb amputation (control group, C). In this control group, according to the Fontaine's classification of peripheral arterial occlusive disease (PAOD), 15 patients were in stage I and 10 patients were in stage II. In the second group, the electro stimulated (ES) group, there were also 25 patients that had the same rehabilitation program, to which electrostimulation of the gastrocnemius muscle of the remaining leg was added. In this group, 14 patients were in stage I, 10 patients were in stage II, and 1 patient was in stage III of PAOD. For electrostimulation, biphasic charge-balanced asymmetrical current stimuli with a pulse duration of 0.25 ms were used. The electrostimulation program consisted of 2 hours of electrostimulation per day for 8 weeks. Each patient was examined at the start of the rehabilitation program (examination I), at the end of the 8-week program (examination II) and at the end of a 1-year follow-up period (examination III). The effects of the treatment were followed using clinical examination, determination of the ankle-brachial index (ABI), and by measuring the partial oxygen pressure (TcPO2) on the skin surface of the diseased leg at rest and during exercise. After 8 weeks of treatment, in 3 patients of the ES group, claudication disappeared, and they thus moved from clinical stage II to stage I. In the control group, there were no changes in the clinical stages of PAOD. At the end of the observation period, 6 patients in group C and 5 patients in the ES group registered a progression of PAOD. During the observation period, 3 patients in group C and 1 patient in the ES group had below-knee amputations of the remaining leg (p<0.01). Perfusion pressures and ABI of investigated legs were comparable between groups and did not change during treatment. After 1 year of observation, there was a trend to ABI decrease in both groups. The capability of the diseased leg for performing work increased significantly during treatment only in the ES group. During treatment, TcPO2 at rest on the dorsum of the foot increased nonsignificantly in the ES group but in group C a trend of decrease in its value was indicated. After 8 weeks of treatment, total and partial oxygen drop during exercise significantly decreased in the ES group; whereas, in group C, there was no significant change. During the 1-year observation period, these effects of electrostimulation disappeared; however, fewer amputations in the ES group favor the presumption that this could be a positive effect of electrostimulation. The results of the authors' study showed that electrostimulation improved oxygen delivery to a leg with disturbed arterial circulation and increased its work load capacity. The changes are probably caused by improvement of microcirculation.

Lack of flow regulation may explain the development of arteriovenous malformations

In the normal vasculature, vessels of widely different sizes maintain shear stress within a narrow range. Recently, investigators have had great success using mathematical models to explore the relationship of structure to function in normal vascular beds. When investigators first explored how vascular beds adapt to set shear stress at appropriate levels, however, some vessels tended to regress, and some tended to grow into arteriovenous shunts. Degeneration of the arterial tree is prevented when flow regulation is added to the model. The present work explores the implication of this theoretical development and illustrates how it may explain the genesis of arteriovenous malformations (AVMs). We use a simple model to illustrate how impairing local control of blood flow causes models to become structurally unstable, yielding a structure and behavior similar to AVMs. This work shows how the lack of local flow control can be the cause, not just the result, of arteriovenous malformations. With insight gained from this modeling approach, specific, focused experiments can be designed.

Low-power helium: neon laser irradiation enhances production of vascular endothelial growth factor and promotes growth of endothelial cells in vitro

BACKGROUND AND OBJECTIVE

Numerous reports suggest that low-power laser irradiation (LPLI) is capable of affecting cellular processes in the absence of significant thermal effect. The objective of the present study was to determine the effect of LPLI on secretion of vascular endothelial growth factor (VEGF) and proliferation of human endothelial cells (EC) in vitro.

STUDY DESIGN/MATERIALS AND METHODS

Cell cultures were irradiated with single different doses of LPLI (Laser irradiance from 0.10 to 6.3 J/cm(2)) by using a He:Ne continuous wave laser (632 nm). VEGF secretion by smooth muscle cells (SMC) and fibroblasts was quantified by sandwich enzyme immunoassay technique. The endothelial cell proliferation was measured by Alamar Blue assay. VEGF and transforming growth factor beta (TGF-beta) expression by cardiomyocytes was studied by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

We observed that (1) LPLI of vascular and cardiac cells results in a statistically significant increase of VEGF secretion in culture (1.6-fold for SMC and fibroblasts and 7-fold for cardiomyocytes) and is dose dependent (maximal effect was observed with LPLI irradiance of 0.5 J/cm(2) for SMC, 2.1 J/cm(2) for fibroblasts and 1.05 J/cm(2) for cardiomyocytes). (2) Significant stimulation of endothelial cell growth was obtained with LPLI-treated conditioned medium of SMC (maximal increase was observed with LPLI conditioned medium with irradiance of 1.05 J/cm(2) for SMC and 2.1 J/cm(2) for fibroblasts.

CONCLUSIONS

Our studies demonstrate that low-power laser irradiation increases production of VEGF by SMC, fibroblasts, and cardiac myocytes and stimulates EC growth in culture. These data may have significant importance leading to the establishment of new methods for endoluminal postangioplasty vascular repair and myocardial photoangiogenesis.

Peripheral vascular changes after electrically stimulated cycle training in people with spinal cord injury

OBJECTIVE

To test whether a short period of training leads to adaptations in the cross-sectional area of large conduit arteries and improved blood flow to the paralyzed legs of individuals with spinal cord injury (SCI).

DESIGN

Before-after trial.

SETTING

Rehabilitation center, academic medical center.

PARTICIPANTS

Nine men with spinal cord lesions.

INTERVENTION

Six weeks of cycling using a functional electrically stimulated leg cycle ergometer (FES-LCE).

MAIN OUTCOME MEASURES

Longitudinal images and simultaneous velocity spectra were measured in the common carotid (CA) and femoral (FA) arteries using quantitative duplex Doppler ultrasound examination. Arterial diameters, peak systolic inflow volumes (PSIVs), mean inflow volumes (MIVs), and a velocity index (VI), representing the peripheral resistance, were obtained at rest. PSIVs and VI were obtained during 3 minutes of hyperemia following 20 minutes of FA occlusion.

RESULTS

Training resulted in significant increases in diameter (p < .01), PSIVs (p < .01), and MIVs (p < .05), and reduced VI (p < .01) of the FA, whereas values in the CA remained unchanged. Postocclusive hyperemic responses were augmented, indicated by significantly higher PSIVs (p <.01) and a trend toward lower VI.

CONCLUSION

Six weeks of FES-LCE training increased the cross-sectional area of large conduit arteries and improved blood flow to the paralyzed legs of individuals with SCI.

Histochemical and ultrastructural characteristics of leg muscle fibres in patients with repairative abdominal aortic aneurysm (AAA)

Tibialis anterior (ta) muscle biopsies before and after elective abdominal aortic aneurysm (AAA) repair operation were obtained, in order to observe possible changes after the aortic declamping reperfusion. Open muscle biopsies were taken from each of eight patients (60-75 years old) which were processed for enzyme histochemistry, and for transmission electron microscopy (EM). Morphometric analysis was applied to estimate the number and the area of muscle fibres of each fibre type. Rectus abdominis muscle biopsies were served as controls. Before the operation the predominant elements found were the presence of atrophic muscle fibres, fibre size diversity, localised cellular reactions, increased extent of connective tissue, disappearance, in many cases, of the mosaic pattern, predominance of type I and oxidative fibres, and existence of fibres with core-like structures in the sarcoplasm. Type I fibres consisted of 66.95 +/- 9% of all muscle fibres, the mean cross sectional area of which was 3,372.8 +/- 1,016 microm(2) and of type II fibres was 3,786.5 +/- 6,046 microm(2). After the aortic clamping was performed mitochondrial swelling was found, as well as disorganisation of sarcomeres. After declamping of the aorta, there were also severe edema, local fibre necrosis, and adhesion of leucocytes, whereas muscle fibre areas became 3,935.18 micro 531 microm(2) for type I and 5,804 +/- 1,075 microm(2) for type II. The short ischemic period during aortic clamping and the subsequent reperfusion resulted mainly in ultrastructural changes.

Effect of indomethacin on capillary growth and microvasculature in chronically stimulated rat skeletal muscles

1. Capillary proliferation and microvessel diameters were studied in rat ankle flexors subjected to chronic electrical stimulation by implanted electrodes (10 Hz, 0.3 ms pulse width, up to 6 V, 8 h day-1) for 2 or 7 days with or without concurrent indomethacin treatment ( approximately 2 mg day-1 in drinking water) to study the role of prostaglandins in the microcirculation in relation to capillary growth. 2. Diameters of terminal arterioles, capillaries and confluent venules were measured in epi-illuminated muscles, together with capillary red cell velocity, to evaluate whether changes in capillary pressure and/or shear stress participate in capillary growth via release of prostaglandins. 3. Cell proliferation was detected following bromodeoxyuridine (BrdU) incorporation and immuno-staining of frozen sections. Labelling was assessed as the percentage of all interstitial nuclei (Haematoxylin-stained) that were BrdU positive. By comparison with serial sections stained for alkaline phosphatase, from which the capillary-to-fibre ratio (C:F) was obtained, labelling was derived for nuclei colocalised either to capillaries or to other non-capillary interstitial cells. 4. C:F increased to 1.89 +/- 0.06 from 1.47 +/- 0.04 in controls only after 7 days stimulation; indomethacin reduced this to 1.55 +/- 0.07. Capillary labelling increased from 2.9 +/- 0.5 % in controls to 11.3 +/- 2.2 % after 2 days stimulation and 10.6 +/- 0.8 % after 7 days. The increase was attenuated by indomethacin at both time points (to 5.8 +/- 1.6 % and 4.2 +/- 0.5 %, respectively). 5. Non-capillary interstitial labelling (2.0 +/- 0.4 % in controls) increased to 9.5 +/- 2.7 % after 2 days stimulation and was back to normal after 7 days (3.2 +/- 0.7 %). Indomethacin depressed the increase at 2 days to 4.0 +/- 1.3 % and had no effect at 7 days (2.9 +/- 0.13 %). Labelling in sham-operated rats with or without indomethacin or in vehicle-treated animals was no different from controls. 6. Arteriolar and venular diameters were increased by 2 days of stimulation but unchanged after 7 days. Indomethacin increased diameters of arterioles after 2 days and venules after 7 days in sham-operated animals, but had no effect on diameters of either vessel type in stimulated muscles. 7. Capillary diameters did not change during acute muscle contractions whereas red cell velocity did. Calculated shear stress in capillaries was thereby increased by 75 %. 8. Thus during chronic electrical stimulation both capillary growth and the cell proliferation that precedes it were attenuated by indomethacin. Transient stimulation-induced increases in arteriolar and venular diameters, which were unaffected by indomethacin, do not implicate increased capillary pressure as a factor in prostaglandin release and capillary growth. Estimations of increases in capillary shear stress during muscle contractions and of a 45 % higher value even at rest after chronic stimulation for 7 days suggest that shear stress is a more likely stimulus for prostaglandin release in chronically stimulated muscles.

Effects of high-intensity resistance training on untrained older men. I. Strength, cardiovascular, and metabolic responses

Most resistance training studies of older subjects have emphasized low-intensity, short-term training programs that have concentrated on strength measurements. The purpose of this study was, in addition to the determination of strength, to assess intramuscular and transport factors that may be associated with strength increments. Eighteen untrained men ages 60-75 years volunteered for the study; 9 were randomly placed in the resistance-training group (RT), and the other half served as untrained (UT) or control subjects. RT subjects performed a 16-week high-intensity (85-90% 1 repetition maximum (RT]) resistance training program (2 x/wk) consisting of 3 sets each to failure (6-8 repetitions based on 1 RM of 3 exercises): leg press (LP), half squat (HS), and leg extension (LE) with 1-2 minutes rest between sets. Pre- and post- training strength was measured for the 3 training exercises using a 1 RM protocol. Body fat was calculated using a 3-site skinfold method. Biopsies from the vastus lateralis m. were obtained for fiber type composition, cross-sectional area, and capillarization measurements. Exercise metabolism, electrocardiography, and arterial blood pressure were observed continuously during a progressive treadmill test, and resting echocardiographic data were recorded for all subjects. Pre- and post-training venous blood samples were analyzed for serum lipids. Resistance training caused significant changes in the following comparisons: % fat decreased in the RT group by almost 3%, strength improved for all exercises: LE = + 50.4%, LP = + 72.3%, HS = + 83.5%; type IIB fibers decreased and IIA fibers increased; cross-sectional areas of all fiber types (I, IIA, IIB) increased significantly, and capillary to fiber ratio increased but not significantly. No differences were noted for ECG and echocardiographic data. The RT group significantly improved treadmill performance and VO2max. Pre- and post-training serum lipids improved but not significantly. No significant changes occurred in any pre- to post-tests for the UT group. The results show that skeletal muscle in older, untrained men will respond with significant strength gains accompanied by considerable increases in fiber size and capillary density. Maximal working capacity, VO2max, and serum lipid profiles also benefited from high-intensity resistance training, but no changes were observed for HR max, or maximal responses of arterial blood pressure. Older men may not only tolerate very high intensity work loads but will exhibit intramuscular, cardiovascular, and metabolic changes similar to younger subjects.

Coupling of muscle metabolism and muscle blood flow in capillary units during contraction

Muscle blood flow is tightly coupled to the level of skeletal muscle activity: Indices of skeletal muscle metabolic rate, for example oxygen consumption or muscle work, are directly related to the magnitude of the change in muscle blood flow. Despite the large amount that is known about individual aspects of local metabolic vasodilation, the mechanisms underlying integrated aspects of the response remain largely unknown. Arteriolar dilation serves both to increase blood flow through the muscle and also to recruit capillaries and control capillary blood flow distribution. Conceptually, these two apparently separate functions of larger vs. more terminal arterioles (where larger vessels subserve conductance changes while the smaller more distal vessels have a primary role in capillary blood flow control) can be met, at least in part, by differential sensitivity of large vs. small arterioles to metabolites and agonists relevant to the metabolic response. However, longitudinal differences in sensitivity through the arteriolar network will not by themselves account for observed heterogeneities in capillary perfusion or for the close matching between blood flow and metabolism that occurs even in mixed muscles. In mixed skeletal muscles, fibres of widely different metabolic profile are dispersed throughout the muscle and even fibres of a single motor unit are not perfused by common arterioles but are matched with arterioles arising from widely disparate regions within the microvascular network. In this review we present findings that support the notion that capillaries are an integral part of the mechanism underlying this close matching between blood flow and metabolism. We review studies that indicate that capillaries are capable of responding to stimuli in their immediate environment and, importantly, are able to communicate with arterioles located remotely upstream in the arteriolar tree. Not only can skeletal muscle capillary endothelial cells induce remote arteriolar vasodilatory and vasoconstrictor responses to pharmacological stimuli such as acetylcholine or noradrenaline, but they can also initiate these remote arteriolar responses in response to skeletal muscle contraction. Capillary endothelial cells respond to skeletal muscle contraction by transmitting a dilatory signal to at least three branch orders of arterioles proximal to the capillary; these upstream dilations present a mechanism whereby capillaries can initiate their own recruitment, and whereby increased blood flow can be directed only to those exchange vessels associated with the contracting muscle fibres and where, presumably, the initiating signal is sensed. This signal involves KATP channels, although their location (on endothelial, vascular smooth muscle or skeletal muscle cells) is not yet known and has a nitric oxide-dependent component. The studies reviewed here thus indicate that capillaries have the capacity to play an active role in co-ordination of muscle blood flow responses to changed muscle metabolism. Much more remains to be learned, however, about the mechanisms underlying the signals generated by the contracting muscle and the mechanisms of transmission of the signals upstream.

Changes in FGF and FGF receptor expression in low-frequency-stimulated rat muscles and rat satellite cell cultures

This study compares effects of chronic electrical stimulation on the expression levels of FGF-1, FGF-2 and their receptors (FGFRI, FGFR4) in rat tibialis anterior (TA) muscle of hypothyroid rat, as well as in satellite cell cultures derived from normal rat TA and soleus (SOL) muscles. In 5-day (5-d)-stimulated hypothyroid TA muscle, FGF-1 and FGF-2 mRNA levels were threefold elevated over control. FGFR1 and FGFR4 mRNAs were twofold and 1.5-fold elevated, respectively. In longer stimulated muscles, FGF-1 and FGFR4 mRNAs returned to basal levels, whereas FGF-2 mRNA remained elevated. FGFR1 mRNA decreased to control levels in 10-d stimulated muscles, but increased again after 20 days of stimulation. SOL- and TA-derived satellite cell cultures were stimulated for 5 days. At this time point, changes in myosin heavy chain isoforms were detectable consisting of increases in MHCI mRNA and decreases in MHCIIb and MHCIId mRNA. The comparison between 5-d-stimulated hypothyroid TA muscle and 5-d-stimulated TA- and SOL-derived satellite cell cultures revealed differences in the expression of FGF-1 and FGF-2, but similar expression levels of FGFR1 and FGFR4. Even though FGF-1 and FGF-2 mRNAs were elevated in the satellite cell cultures, their increases were less pronounced than in the stimulated hypothyroid muscle. Taking into consideration that skeletal muscle contains muscle fibres and various non-muscle tissues, e.g. blood vessels, these results suggest that the latter contribute to the observed increases in FGF-1 and FGF-2 expression in stimulated muscle.

Establishment of a simple and practical procedure applicable to therapeutic angiogenesis

BACKGROUND

Therapeutic angiogenesis is thought to be beneficial for serious ischemic diseases. This investigation was designed to establish a simple and practical procedure applicable to therapeutic angiogenesis.

METHODS AND RESULTS

When cultured skeletal muscle cells were electrically stimulated at a voltage that did not cause their contraction, vascular endothelial growth factor (VEGF) mRNA was augmented at an optimal-frequency stimulation. This increase of VEGF mRNA was derived primarily from transcriptional activation. Electrical stimulation increased the secretion of VEGF protein into the medium. This conditioned medium then augmented the growth of endothelial cells. The effect of electrical stimulation was further confirmed in a rat model of hindlimb ischemia. The tibialis anterior muscle in the ischemic limb was electrically stimulated. The frequency of stimulation was 50 Hz and strength was 0.1 V, which was far below the threshold for muscle contraction. After a 5-day stimulation, there was a significant increase in blood flow within the muscle. Immunohistochemical analysis revealed that VEGF protein was synthesized and capillary density was significantly increased in the stimulated muscle. Rats tolerated this procedure very well, and there was no muscle contraction, muscle injury, or restriction in movement.

CONCLUSIONS

We propose this procedure as a simple and practical method of therapeutic angiogenesis.

Early changes in performance, blood flow and capillary fine structure in rat fast muscles induced by electrical stimulation

1. Muscle blood flow, capillary fine structure and performance were investigated in the early stages of chronic indirect electrical stimulation of ankle flexors in the rat. 2. The fast muscles tibialis anterior (TA), extensor digitorum longus (EDL) and extensor hallucis proprius (EHP) were unilaterally stimulated via the right common peroneal nerve at 10 Hz and supramaximal voltage for 8 h a day for 2, 3 or 7 days and compared with muscles from control animals. 3. Muscle blood flow (MBF) was estimated at rest and during contractions by radioactive microspheres. It was higher at rest than in unstimulated controls only in muscles stimulated for 2 days; during contractions it was higher in some muscles stimulated for 3 days than in controls, and in all muscles by 7 days (192 +/- 17 vs. 149 +/- 12 ml (100 g)-1min-1 in controls). 4. Electron microscopical evaluation of individual capillaries in EHP fixed by superfusion in situ revealed thickening of capillary endothelium and decreased lumen volume in muscles stimulated for 7 (P < 0.005) but not 3 days. Significantly smaller capillary size indicates the presence of newly formed capillaries. 5. Isometric twitch tension, recorded from combined TA and EDL in stimulated and contralateral legs during 5 min contractions at 4 Hz, gradually declined from 175 +/- 9 to 99 +/- 4 kN m-2 after 7 days of stimulation (P < 0.05) while the fatigue index, calculated as (final twitch tension/peak twitch tension) x 100, increased from 69.8 +/- 3.4 to 90 +/- 3.0 % (P < 0. 05). No significant changes in the fatigue index occurred in muscles stimulated for 2 or 3 days. 6. Lower peak tension, but not fatigue index or MBF, was also observed in muscles contralateral to those stimulated for 3 and 7 days, which thus do not represent appropriate controls. 7. We conclude that the high resting blood flow found in muscles stimulated for 2 days may initiate the capillary growth reported previously, while the relatively modest increase in MBF during contractions in muscles that had been stimulated for 7 days may be due to increased capillary supply. Swelling of the capillary endothelium and decreased volume of the capillary lumen may result in an increased proportion of time spent by red blood cells in capillaries, which would improve oxygen extraction.

Structural autoregulation of terminal vascular beds: vascular adaptation and development of hypertension

-It is widely accepted that the early phase of primary hypertension is characterized by elevated cardiac output, whereas in later stages the increased blood pressure is due to increased peripheral resistance. To study long-term effects of increased blood flow on peripheral resistance, structural adaptation of microvascular networks in response to changes in blood flow was simulated using a previously developed theoretical model. The diameter of each vessel segment was assumed to change in response to local levels of shear stress, transmural pressure, a metabolic stimulus dependent on blood flow rate, and a conducted stimulus. Network morphologies and topologies were derived from intravital microscopy of the rat mesentery. Adaptive responses to the 4 stimuli were quantitatively balanced to yield stable and realistic distributions of vascular diameters and blood flow rates when the total flow rate was set to observed levels. To simulate effects of increased cardiac output, network flow resistance after structural adaptation was determined for a range of flow rates. Resistance increased with increasing flow, and increases in pressure were up to 3-fold greater than proportional to the increases in flow. According to the model, flow-dependent changes of network resistance result mainly from the vascular response to transmural pressure, which also causes arteriovenous asymmetry of diameters and pressure drops. Therefore, in vascular beds that exhibit arteriovenous asymmetry, increased flow may trigger increased flow resistance by a mechanism involving the tendency of vascular segments to reduce their luminal diameters in response to increased transmural pressure.

Capillary growth in relation to blood flow and performance in overloaded rat skeletal muscle

Rat extensor digitorum longus muscles were overloaded by stretch after removal of the synergist tibialis anterior muscle to determine the relationship between capillary growth, muscle blood flow, and presence of growth factors. After 2 wk, sarcomere length increased from 2.4 to 2.9 micrometers. Capillary-to-fiber ratio, estimated from alkaline phosphatase-stained frozen sections, was increased by 33% (P < 0.0001) and 60% (P < 0.01), compared with control muscles (1.44 +/- 0.06) after 2 and 8 wk, respectively. At 2 wk, the increased capillary-to-fiber ratio was not associated with any changes in mRNA for basic fibroblast growth factor (FGF-2) or its protein distribution. FGF-2 immunoreactivity was present in nerves and large blood vessels but was negative in capillaries, whereas the activity of low-molecular endothelial-cell-stimulating angiogenic factor (ESAF) was 50% higher in stretched muscles. Muscle blood flows measured by radiolabeled microspheres during contractions were not significantly different after 2 or 8 wk (132 +/- 37 and 177 +/- 22 ml. min-1. 100 g-1, respectively) from weight-matched controls (156 +/- 12 and 150 +/- 10 ml. min-1. 100 g-1, respectively). Resistance to fatigue during 5-min isometric contractions (final/peak tension x 100) was similar in 2-wk overloaded and contralateral muscles (85 vs. 80%) and enhanced after 8 wk to 92%, compared with 77% in contralateral muscles and 67% in controls. We conclude that increased blood flow cannot be responsible for initiating expansion of the capillary bed, nor does it explain the reduced fatigue within overloaded muscles. However, stretch can present a mechanical stimulus to capillary growth, acting either directly on the capillary abluminal surface or by upregulating ESAF, but not FGF-2, in the extracellular matrix.

Structural adaptation to ischemia in skeletal muscle: effects of blockers of the renin-angiotensin system

OBJECTIVE

To investigate the effects of long-term treatment with blockers of the renin-angiotensin system on capillarization and growth of fibers in ischemic hind-limb muscles and in muscles under normal growth conditions.

METHODS

Ischemia was induced by partial ligation of the left common iliac artery.

RESULTS

Ischemia resulted in a significant increase in capillary and fiber density in the soleus muscle, a significant decrease in mean fiber size and a decrease in muscle cross-sectional area after 4 weeks compared with the contralateral nonischemic muscle. Ischemia also significantly decreased the muscle: body weight ratio of the left soleus muscle. We observed no significant effect on total number of capillaries and capillary: fiber ratio, suggesting that ischemia did not result in an increase in capillarization in this muscle. Treatments with subhypotensive and with hypotensive doses of the angiotensin converting enzyme (ACE) inhibitor benazeprilat, the angiotensin (Ang) II AT1 antagonist valsartan, or the Ang II AT2 antagonist PD 123 319 for 4 weeks did not influence any of the above-described changes in the normal and ischemic muscles and treatment effects were also independent of the degree of reduction of blood pressure.

CONCLUSION

Treatments with an ACE inhibitor and with Ang II receptor antagonists in dose ranges that moderately lower blood pressure do not influence vessel density and any of the other structural adaptations after hind-limb ischemia. Administrations of ACE inhibitors and Ang II AT1 antagonists may therefore be adequate and beneficial therapies under ischemic conditions, such as in the treatment of hypertension complicated by intermittent claudication, for which treatment must not increase ischemia.

Regional perfusion and oxygenation in the pedicled latissimus dorsi muscle flap: the effect of mobilisation and electrical stimulation

BACKGROUND

The pedicled latissimus dorsi muscle flap is dependent upon an adequate blood supply via a single nutrient artery arising at its most proximal point. It has been suggested that when the latissimus dorsi muscle is used for cardiomyoplasty there is a risk of ischaemic damage to the distal regions of the flap under the additional metabolic stress of repeated electrical stimulation.

METHODS

A rabbit model was developed in which the latissimus dorsi muscle was raised as a pedicled flap (n = 10). Needle microelectrodes were used to measure oxygenation and perfusion simultaneously in different regions of the muscle. Perfusion was measured using a gas tracer technique in which nitrous oxide was used as the marker. Muscle performance was measured by electrical stimulation of the mobilised flap.

RESULTS

The mean (standard error) perfusion of the distal muscle fell significantly from 19.5 (6.2) to 11.9 (3.8) ml.min-1 100 g-1 (P < 0.05) as a consequence of mobilisation, although tissue oxygenation was maintained. Perfusion and pO2 of the proximal regions of the flap were unchanged. During electrical stimulation perfusion increased by 72 (12)% from resting levels in the proximal region, but by only 39 (8)% in the distal muscle. Tissue pO2 decreased during stimulation by 5.7 (1.8) mmHg proximally compared to 11.7 (3.7) mmHg distally P < 0.05). During recovery the pO2 remained below baseline for 24 minutes in the proximal muscle compared to 32 minutes in the distal muscle.

CONCLUSIONS

Mobilisation results in a reduction in the perfusion of distal areas of the latissimus dorsi muscle flap. During repeated contraction the perfusion remains reduced and is unable to maintain tissue oxygen requirements. This has implications for dynamic applications of the latissimus dorsi muscle flap and supports the suggestion that ischaemia is the cause of distal muscle atrophy and fibrosis in cardiomyoplasty. Combined perfusion and pO2 data provide a new insight into muscle viability studies.

Regional blood flows in the goat latissimus dorsi muscle before and after chronic stimulation

Latissimus dorsi muscle (LDM) regional blood flows were determined in anesthetized goats by using colored microspheres under noncontracting and contracting conditions, either before or after 8-10 wk of chronic muscle stimulation. Surgical dissection of the LDM, leaving only the thoracodorsal artery to supply the muscle, did not alter regional noncontracting blood flows but significantly reduced the normal hyperemic response to muscle contraction in muscle regions (posterior-medial) furthest from the entrance of the thoracodorsal artery. Eight to 10 wk after acute muscle dissection, posterior-medial hyperemic flows were restored. Chronic stimulation of the LDM for 8-10 wk, in either dissected or nondissected muscles, did not alter regional blood flows in noncontracting muscle; however, it significantly reduced hyperemic flows in all muscle regions, although capillary density was increased and the muscle was transformed into a predominantly type I fiber type. These results, coupled with data from previous experiments, suggest that the muscle damage observed in the posterior-medial regions of the LDM after surgical dissection and chronic stimulation may be related to reduced hyperemic flow responses caused by surgical isolation of the muscle.

Cardiomyoplasty: studies on goat latissimus dorsi blood flow and muscle damage following surgical dissection and chronic electrical stimulation

BACKGROUND

Dynamic cardiomyoplasty has shown promise as a surgical treatment for congestive heart failure, however, skeletal muscle damage has been reported in the latissimus dorsi muscle flap. Possible etiologies for the muscle damage include surgical dissection of the latissimus dorsi muscle with interruption of collateral blood supply, as well as chronic electrical stimulation of the muscle.

METHODS

To investigate these possible etiologies, we conducted a series of experiments using the goat model, evaluating blood flow and muscle morphology following surgical dissection and chronic stimulation of the latissimus dorsi muscle. Four different conditions were evaluated: (1) latissimus dorsi muscle that was neither dissected nor chronically stimulated; (2) latissimus dorsi muscle that was stimulated, but not dissected; (3) latissimus dorsi muscle that was surgically dissected, but not chronically stimulated; and (4) latissimus dorsi muscle that was both surgically dissected and chronically stimulated.

CONCLUSION

We concluded that skeletal muscle damage resulted primarily from the surgical dissection, whereby the collateral blood supply to the latissimus dorsi muscle was interrupted and not primarily as a result of chronic electrical stimulation.

Heparin and basic fibroblast growth factor are associated with preservation of latissimus cardiomyoplasties in goats: a retrospective study

BACKGROUND

Chronic electrical stimulation of cardiomyoplasties often leads to atrophy and fibrosis of the skeletal muscle. In this retrospective study, we re-examined the data in our previous work, which suggested that muscle was preserved by treatment with basic fibroblast growth factor (bFGF).

METHODS

Histologic sections were reviewed for evidence of atrophy, and fibrosis from four groups of goats with latissimus dorsi cardiomyoplasty: (1) unstimulated; (2) 2-Hz stimulated x 6 weeks; (3) 2-Hz stimulated with heparin infusion (50 units/hour) x 6 weeks; and (4) 2-Hz stimulated with bFGF (80-micrograms bolus/week) x 6 weeks.

RESULTS

Muscle degeneration, as indicated by fat replacement of muscle fibers, was 56.95% +/- 9.16% (mean +/- S.E.) in the 2-Hz stimulated compared with 16.43% +/- 6.22% in unstimulated muscles. In 2-Hz = bFGF and 2 Hz-Heparin (Hep) groups, degeneration was 11.60% +/- 3.04% and 20.36% +/- 5.03%, respectively. bFGF treatment was associated with a greater latissimus blood flow than in the 2-Hz-untreated and 2 Hz-Hep groups (p < 0.05).

CONCLUSIONS

bFGF's protection against degeneration may have involved angiogenesis and myogenesis, whereas that of heparin appears to have involved only myogenesis. While the mechanism(s) of the effects of heparin and bFGF remain to be defined, we conclude that they may be a useful adjunct for cardiomyoplasty.

The effect of basic fibroblast growth factor on the blood flow and morphologic features of a latissimus dorsi cardiomyoplasty

Previous studies designed to determine whether latissimus cardiomyoplasty could be used to revascularize ischemic myocardium showed that after operation the latissimus was ischemic and had severely deteriorated. This study was undertaken to determine whether basic fibroblast growth factor, a potent angiogenic peptide, would improve the vascularity of the latissimus and enhance collateral formation between the muscle of the cardiomyoplasty and ischemic myocardium. In goats, myocardial ischemia was induced with an ameroid constrictor and cardiomyoplasty performed. The latissimus was continuously stimulated electrically at 2 Hz for 6 weeks and given four weekly bolus injections of human recombinant basic fibroblast growth factor (80 micrograms infused into the left subclavian artery). In eight animals, rates of regional blood flow were measured and both the heart and latissimus were evaluated histochemically. The latissimus blood flow rate was 0.114 +/- 0.029 ml/gm per minute, which was three times greater than that of historical controls (chronically stimulated latissimus cardiomyoplasty without basic fibroblast growth factor treatment; 0.042 +/- 0.007 ml/gm per minute, p < 0.05). Associated with the improved blood flow, there was significantly less evidence of skeletal muscle fiber dropout and muscle fibrosis in the animals treated with basic fibroblast growth factor. Latissimus-derived collateral flow to ischemic myocardium developed in five of the eight goats and averaged 0.288 +/- 0.075 ml/gm per minute. This flow was 42.8% +/- 15.7% (n = 5) of the flow required by normal myocardium (which was 0.728 +/- 0.095 ml/gm per minute). This value for latissimus-derived collateral blood flow was almost twice that of the historical controls (24.0% +/- 3.9%), but the increase did not achieve statistical significance (p = 0.08). These results hold the promise that basic fibroblast growth factor treatment might enhance the formation of extramyocardial collaterals to the heart and improve skeletal muscle function.

Basic fibroblast growth factor identified in chronically stimulated cardiomyoplasties

In the presence of myocardial ischemia, chronic electrical stimulation of a latissimus dorsi (LD) cardiomyoplasty enhances extramyocardial collateral blood flow. We postulated that basic fibroblast growth factor (bFGF) may mediate extramyocardial collateral formation. To test this hypothesis, LDs from goats with cardiomyoplasties were probed for the presence of bFGF by Western blot analysis and immunohistochemistry. Three groups were studied: static LD cardiomyoplasty (group 1); LD cardiomyoplasty stimulated at a 2-Hz frequency for 6 weeks (group 2); and LD cardiomyoplasty electrically stimulated and given human recombinant bFGF (group 3). There was no evidence of bFGF in the left LDs of group 1 by Western blot. Basic fibroblast growth factor-like immunoreactive evidence was found in the left LDs of group 2 goats by both Western blot and immunohistochemistry. In the right LDs of group 2, bFGF-like material was found by immunohistochemistry but not by Western blot, which suggests that the tissue concentrations were low (near the limits of detection). The left LDs of group 3 were positive for bFGF by Western blot and immunohistochemistry. Group 3 right LDs were positive for bFGF by immunohistochemistry. Immunohistochemical findings in group 2 indicate that bFGF is present in goat skeletal muscle. Western blot data from groups 1 and 2 suggest that bFGF may be increased in chronically stimulated cardiomyoplasties. From findings in group 3, we conclude that exogenous bFGF does not downregulate, and may upregulate, endogenous production. These results support the possibility that skeletal muscle bFGF is an important factor in extramyocardial collateral formation.

Antihypertensive therapy and adaptive mechanisms in peripheral ischemia

In the present experiments the effect of long-term peripheral ischemia on the capillary of two hind limb skeletal muscles was investigated in spontaneously hypertensive rats. Furthermore, the effect of antihypertensive therapy on changes in capillarity and on the previously observed hyperreactivity of the ischemic vascular bed to vasoconstrictors was investigated in perfused hind limbs of rats after long-term treatment with the angiotensin I converting enzyme inhibitors captopril (0.5 mg/kg.h) or zabiciprilate (0.025 mg/kg.h), the angiotensin II type 1 receptor antagonist losartan (0.625 mg/kg.h), or the calcium antagonist felodipine (0.042 or 0.42 mg/kg.h). Skeletal muscle ischemia in the left hind limb was induced by partial ligation of the left common iliac artery. Long-term (4 weeks) ischemia increased significantly the capillary-to-fiber ratio in the soleus muscle, composed predominantly of type I fibers in spontaneously hypertensive rats, of the ischemic hind limb, whereas capillarity in the contralateral muscle was not affected. Furthermore, capillarity in the gastrocnemius muscle (type II muscle fiber part) of both the ischemic and contralateral hind limb did not change. Long-term treatment with the angiotensin I converting enzyme inhibitors during ischemia abolished the increase in the capillary-to-fiber ratio in the soleus muscle, whereas a comparable antihypertensive dose of felodipine had no effect. Greater blood pressure reductions by both losartan and felodipine prevented increases in capillarization in skeletal muscle ischemia. With respect to vascular hyperreactivity during ischemia, only treatment with losartan normalized reactivity of the ischemic vascular bed to vasoconstrictors.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term follow-up (12 to 35 weeks) after dynamic cardiomyoplasty

OBJECTIVES

To obtain information on the long-term effects of dynamic cardiomyoplasty on hemodynamics and muscle histology, this surgical method was evaluated in goats.

BACKGROUND

Dynamic cardiomyoplasty has been introduced as a new method to treat patients with severe cardiac failure.

METHODS

In 24 goats, the left latissimus dorsi muscle was wrapped around the heart. The muscle was then subjected to progressive electrical stimulation. In 16 goats, invasive transesophageal Doppler echocardiographic measurements and histologic evaluation of the latissimus dorsi muscle were performed at > or = 12 weeks after the wrapping.

RESULTS

Only two goats showed an increase in aortic and left and right ventricular pressures concomitant with increased aortic flow during latissimus dorsi muscle stimulation both before and after induction of cardiac failure using imipramine. This was accompanied by a preserved latissimus dorsi muscle structure and nearly complete transformation to type I muscle fibers. The remaining 14 goats showed extensive lipomatosis in the latissimus dorsi muscle, with severe intimal hyperplasia and proliferation of smooth muscle cells in the walls of the thoracodorsal artery and its branches. An increase in endoneural and endomysial connective tissue was observed, with some goats showing destroyed nerve branches near the electrodes. These findings differed from those observed after long-term electrical stimulation of goat latissimus dorsi muscle in situ.

CONCLUSIONS

Dynamic cardiomyoplasty is of use in the treatment of severe heart failure if the histologic structure of the wrapped latissimus dorsi muscle remains intact. Long-term results in goats suggest that the current approach used in dynamic cardiomyoplasty may lead to deterioration of the wrapped muscle.

Adaptations in skeletal muscle capillarity following changes in oxygen supply and changes in oxygen demands

The effects of changes in oxygen supply and oxygen demands on fiber cross-sectional areas, capillary densities and capillary to fiber ratios were determined in three skeletal muscles of rat. The muscles examined were the vastus lateralis, soleus, and diaphragm. Reduced oxygen supply was produced by subjecting rats to ambient hypoxia, and increased oxygen demands were produced by subjecting rats to low ambient temperatures or treatment with thyroxin. Capillaries were visualized by injecting fluorescent dyes into the circulation. Muscles were quick frozen at resting lengths to preserve normal fiber geometry and were subsequently sectioned on a cryostat. All of the muscles sampled from animals in the experimental groups had elevated capillary densities. However, capillary to fiber ratios were not increased significantly in any muscle, for any experimental condition. Thus, all of the observed differences in capillarity were due to changes in the intrinsic rate of muscle fiber growth. Further, the relations of capillary density and capillary to fiber ratio to fiber area were the same as those obtained during normal maturation, suggesting that capillary growth is closely linked to the intrinsic rate of fiber growth.

Claudication induces systemic capillary endothelial swelling

An in vivo model of intermittent claudication has been developed to investigate systemic reperfusion injury associated with transient muscle ischaemia. Rats were subjected to unilateral common iliac artery ligation and two weeks of intermittent hind limb muscle stimulation. Electron microscopy demonstrated a significantly increased percentage of swollen capillary endothelial cells both locally and systemically in these "claudicant" rats, compared with controls or those undergoing muscle stimulation or artery ligation alone. These results support human data suggesting that claudication induces an inflammatory response which results in systemic vascular injury.

What makes blood vessels grow?

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