Mechanical properties of the latissimus dorsi muscle after cyclic training.

Cardiomyoplasty is a procedure developed to improve heart performance in patients suffering from congestive heart failure. The latissimus dorsi (LD) muscle is surgically wrapped around the failing ventricles and stimulated to contract in synchrony with the heart. The LD muscle is easily fatigued and as a result is unsuitable for cardiomyoplasty. For useful operation as a cardiac-assist device, the fatigue resistance of the LD muscle must be improved while retaining a high power output. The LD muscle of rabbits was subjected to a training regime in which cyclic work was performed. Training transformed the fiber-type composition from approximately equal proportions of fast oxidative glycolytic (FOG) and fast glycolytic (FG) fibers to one composed of almost entirely of FOG with no FG, which increased fatigue resistance while retaining rapid contraction kinetics. Muscle mass and cross-sectional area increased but power output decreased, relative to control muscles. This training regime represents a significant improvement in terms of preserving muscle mass and power compared with other training regimes, while enhancing fatigue resistance, although some fiber damage occurred. The power output of the trained LD muscle was calculated to be sufficient to deliver a significant level of assistance to a failing heart during cardiomyoplasty.     

Changes in canine latissimus dorsi muscle during 24 wk of continuous electrical stimulation.

To study functional, structural, and biochemical adaptations to electrical stimulation of striated muscle in a large animal, the canine latissimus dorsi (LD) muscle was conditioned continuously for 24 wk with an increasing number of pulse bursts (burst duration 250 ms, burst frequency 30 Hz). Force measurements in vivo after 12 wk showed a significant decrease in the ripple, the ratio of interstimulus to peak force amplitude, from 0.94 +/- 0.03 to 0.13 +/- 0.08 (SE; n = 8, P less than 0.05), indicating reduction in contractile speed. Also the steep part of the force-frequency relation shifted to lower frequencies. A significant change in fiber-type composition was seen with both enzyme- and immunohistochemistry, manifested by an increase of type I fibers from 29.5 +/- 2.9 to 83 +/- 8% (SE; n = 8, P less than 0.05). During this period a transient rise in the number of type IIc/Ic fibers (from 3 to 10%) was seen. In the stimulated muscle, capillary-to-fiber ratio increased from 1.9 +/- 0.4 to 2.7 +/- 0.1 (P less than 0.05). A significant increase in mitochondrial volume was also seen, especially in the peripheral part of the fiber. Both creatine kinase and lactate dehydrogenase revealed a significant decline in activity within 12 wk. At the same time a shift in lactate dehydrogenase-isozyme pattern was observed toward the cardiac composition. No additional changes occurred after 12 wk of stimulation, indicating that conversion of the canine LD muscle was complete within this period.     

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

Klabunde, Richard E., William A. Anderson, Marius Locke,Sigrid E. Ianuzzo, and C. David Ianuzzo. Regional blood flows inthe goat latissimus dorsi muscle before and after chronic stimulation. J. Appl. Physiol. 81(6):2365-2372, 1996.Latissimus dorsi muscle (LDM) regional bloodflows were determined in anesthetized goats by using coloredmicrospheres under noncontracting and contracting conditions, eitherbefore or after 8-10 wk of chronic muscle stimulation. Surgicaldissection of the LDM, leaving only the thoracodorsal artery to supplythe muscle, did not alter regional noncontracting blood flows butsignificantly reduced the normal hyperemic response to musclecontraction in muscle regions (posterior-medial) furthest from theentrance of the thoracodorsal artery. Eight to 10 wk after acute muscledissection, posterior-medial hyperemic flows were restored. Chronicstimulation of the LDM for 8-10 wk, in either dissected ornondissected muscles, did not alter regional blood flows innoncontracting muscle; however, it significantly reduced hyperemicflows in all muscle regions, although capillary density was increasedand the muscle was transformed into a predominantly type I fiber type.These results, coupled with data from previous experiments, suggestthat the muscle damage observed in the posterior-medial regions of theLDM after surgical dissection and chronic stimulation may be related toreduced hyperemic flow responses caused by surgical isolation of themuscle.

     

Effects of denervation and direct electrical stimulation upon the post-hatching differentiation of posterior latissimus dorsi muscle in chicken

The influences of denervation and of direct electrical stimulation of denervated muscle upon the post-hatching differentiation of fibre types in the fast avian muscle posterior latissimus dorsi have been investigated. Denervation inhibits the normal decrease in number of muscle fibres exhibiting acid-stable myofibrillar ATPase activity and leads to weak oxidative activity in all the fibres. Direct stimulation at a low rhythm of denervated muscle induces the normal decrease of fibres exhibiting acid-stable myofibrillar ATPase but does not allow the occurrence of normal oxidative activity pattern. The results emphasize the role of muscular activity upon the differentiation of fibre types in a developing muscle.     

Morphological effects of electrical stimulation and intermittent muscle stretch after immobilization in soleus muscle

The objective of the present study was to assess the effectiveness of a combined protocol of muscle stretching and strengthening after immobilization of the hindlimb. Thirty female Wistar rats were divided into 6 groups: group immobilized for 14 days to cause full plantar flexion by cast (GI, n = 6); group immobilized/stretched (GIS, n = 6): submitted to the same immobilization and to 10 days of passive stretching; group immobilized/electrically stimulated (GIES, n = 6): similarly immobilized and submitted to 10 days of low frequency electrical stimulation (ES); group immobilized/stretched/electrically stimulated (GISES, n = 6): similarly immobilized, submitted to 10 days of stretching and ES application; group immobilized/free (GIF, n = 3): similarly immobilized and then left with free limbs for 10 days; control group (CG, n = 3). The middle portion of the soleus muscle was frozen and sections were stained with HE or mATPase. Morphological analysis revealed high cellular reactivity in the GISES, GIES and GIS groups. The lesser diameter and proportion of type I fibers (TIF) and type II fibers (TIIF) (at pH 9.4) and connective area (at HE stain) were measured with an image analyzer and the data obtained were analyzed statistically by the unpaired Student t-test (p < or = 0.05). The results indicated that: a) immobilization generated atrophy of both fiber types (p < 0.05); b) joint application of ES and stretching was not efficient in reestablishing the size of the two fiber types compared to CG (p < 0.05); c) the ES protocol reestablished only the size of TIIF, which showed values similar to those detected in CG (p < 0.05); d) the stretch increased the proliferation of the perimysium connective tissue (p < 0.05). Thus, we conclude that, in the model applied here to female rats, a stretching protocol may limit the volume protein gain of soleus muscle fibers and increase the connective interstitial tissue.     

Variable-frequency train stimulation of canine latissimus dorsi muscle during shortening contractions

George, David T., Stuart A. Binder-Macleod, Thomas N. Delosso, and William P. Santamore. Variable-frequency trainstimulation of canine latissimus dorsi muscle during shorteningcontractions. J. Appl. Physiol. 83(3):994-1001, 1997.In cardiomyoplasty, the latissimus dorsi muscle(LDM) is wrapped around the heart ventricles and electrically activatedwith a constant-frequency train (CFT). This study tested the hypothesesthat increased mechanical performance from the LDM could be achieved byactivating the muscle with variable-frequency trains (VFTs) of shorterduration or containing fewer stimulus pulses than the CFT now used. Themechanical performance of the canine LDM (n = 7) during shortening contractionswas measured while the muscle was stimulated with 5- and 6-pulse CFTs(of duration 132 and 165 ms, respectively) and 5- and 6-pulse VFTs (ofduration 104 and 143 ms, respectively) that were designed to takeadvantage of the catchlike property of skeletal muscle. Measurementswere made from fresh and fatigued muscles. For the fresh muscles, the VFTs elicited significantly greater peak power than did the 6-pulse CFT. When the muscles were fatigued, VFT stimulation significantly improved both the peak and mean power produced compared withstimulation by CFTs. These results show that stimulation of the LDMwith shorter duration VFTs is potentially useful for application incardiomyoplasty.

     

Effects of denervation and direct electrical stimulation upon acetylcholine receptors and acetylcholinesterase accumulation in developing latissimus dorsi muscle of the chick

The effects of denervation and of direct electrical stimulation of denervated muscle upon the acetylcholine receptor (AChR) clusters and acetylcholinesterase (AChE) spots in the fast avian muscle posterior latissimus dorsi have been investigated. Denervation at day 2 after hatching leads to a disappearance of the junctional AChR clusters and to a marked decrease of AChE spots. Direct electrical stimulation of denervated muscle allows the maintenance of AChR clusters and partly prevents the loss of AChE spots. When AChR cluster and post-synaptic AChE have disappeared in a denervated muscle, muscle activity induced by direct stimulation is unable to induce their accumulation.     

Differences in metabolic response of dog and goat latissimus dorsi muscle to chronic stimulation.

The latissimus dorsi (LD) muscle is considered suitable to assist ventricular mechanical function in either cardiomyoplasty or extra-aortic-assist devices. Such application requires that this mixed-type skeletal muscle be transformed into a fatigue-resistant muscle, the adaptation of which can be elicited by chronic stimulation. In this study the LD muscles of dog and goat were subjected in situ to 12 wk of continuous electrical stimulation through intramuscular electrodes, and their myofibrillar and metabolic adaptations were compared. A gradual increase in the contraction rate of the muscle (in 10 wk from 30 to 80 contractions/min) caused the proportion of immunohistochemically identified type I fibers to increase in dog muscle from 30 to 74% and in goat muscle from 21 to 99%. Correspondingly, the anaerobic-glycolytic activity (fructose-6-phosphate kinase and lactate dehydrogenase activities) decreased by approximately 75% in both dog and goat muscles, whereas the oxidative capacity (fatty acid oxidation and citrate synthase activity) increased two- to threefold in goat LD muscle but remained unaltered in dog LD muscle. Muscular contents of high-energy phosphates and endogenous substrates were maintained, but the L-carnitine content decreased by 43% in both dog and goat. Our data further indicate that, for the monitoring of the metabolic adaptation of skeletal muscle, the ratio of activities of the oxidative and anaerobic-glycolytic pathways (e.g., citrate synthase to fructose-6-phosphate kinase activities) is a useful parameter in both dog and goat.(ABSTRACT TRUNCATED AT 250 WORDS)     

The reverse latissimus dorsi muscle flap for closure of meningomyelocele

Closure of the meningomyelocele wound requires stable coverage of the dural repair. In the case presented, multiple conventional attempts at reconstruction failed. A modification of the "reverse" latissimus dorsi flap is presented that successfully managed this low lumbar defect.     

Preconditioning of latissimus dorsi muscle flaps with monophosphoryl lipid a

The use of dynamic myoplasty to restore function to failing organs is an exciting new application of skeletal muscle flaps. A complication of large flap elevation that can compromise flap function is ischemia-induced necrosis; one approach to minimizing this is to pretreat tissues with ischemic preconditioning. The purpose of this study was to determine whether systemic administration of monophosphoryl lipid A, a drug known to mimic late-phase ischemic preconditioning in the heart, could reduce ischemia-induced necrosis in latissimus dorsi muscle flaps. Forty latissimus dorsi muscle flaps from 20 Sprague-Dawley rats were allocated into four groups. In group I (n = 10), flaps were not preconditioned and served as controls. In group II (n = 10), flaps received ischemic preconditioning with two 30-minute periods of ischemia interspersed by 10 minutes of reperfusion. In group III (n = 10), rats received an intravenous bolus of approximately 0.3 ml of monophosphoryl lipid A vehicle only. In group IV (n = 10), rats received an intravenous bolus of 450 microg/kg of monophosphoryl lipid A and vehicle. Twenty-four hours after treatment, all latissimus dorsi muscle flaps were elevated on a single neurovascular pedicle and subjected to 4 hours of ischemia. After 72 hours of reperfusion, latissimus dorsi muscles were harvested, weighed, stained with nitroblue tetrazolium, and assessed for percent necrosis using digitized images of muscle sections and computerized planimetry. The percent necrosis in ischemic preconditioning-treated flaps (group II) was significantly reduced by 57 percent (p < 0.05) compared with control flaps (group I). The percent necrosis in flaps treated with monophosphoryl lipid A (group IV) was significantly reduced by 58 percent (p < 0.05) compared with vehicle-control flaps (group III). There was no difference in mean percent necrosis between ischemic preconditioning (group II) and monophosphoryl lipid A-treated (group IV) flaps or between ischemic preconditioning-control (group I) and monophosphoryl lipid A vehicle-control (group III) flaps. Intravenous administration of systemic monophosphoryl lipid A mimics the late-phase protective effect of ischemic preconditioning in the authors' rat latissimus dorsi muscle flap model.     

Mechanical and electrical effects of high-frequency and high-intensity stimulation of muscle

A unique tension response can be obtained by stimulating an isometrically held skeletal muscle or a single muscle fiber by a train of high-frequency pulses (2,000 pps) at higher-than-normal intensity, or by a long DC pulse. It is called the tetanoid response, and it is composed of three well-defined stages. Initially, tension develops rapidly, and mechanical output (Po) reaches about 0.35. Subsequently, this tension is maintained at a nearly steady level for the remainder of stimulation. After stimulation, a final increase of tension takes place. Intracellular electrical recordings show that the initial development of tension is elicited by two or three action potentials generated at the beginning of the stimulation, and that no additional action potentials are generated for the remainder of stimulation. During stimulation, part of the fiber membrane (regarded in cross-section) is depolarized, which generates tension, and part of the membrane is hyperpolarized. With termination of stimulation, a single action potential is elicited via anode-break excitation (ABE) on the hyperpolarized portion of the membrane, which gives rise to the final increase of tension.