Distribution of muscle changes in experimental ischemic myopathy

A novel animal model to evaluate oxygen derived free radical damage in soft tissue

We present a novel animal model which allows the continuous intra-arterial infusion in one hindlimb of non-anaesthetized rats, without inducing ischemia. Using this model the effect of continuous infusion (1 ml/h) for 24 h with tert-butylhydroperoxide (tert-BuOOH) at a concentration of 25 mM on soft tissue of the left hind limb was studied and compared to the effect of saline infusion (control group). The tert-BuOOH-infused foot showed increased skin temperature, increased circumference, redness of the plantar skin, impaired function and increased pain sensation, while in the contralateral foot and in rats only perfused with saline these signs of inflammation were absent (p < 0.01). Histological analysis of the left gastrocnemius muscle showed edema, muscle cell degeneration with a patchy distribution pattern and vascular damage. All these features increased in severity from 4 to 24 h tert-BuOOH infusion. After 24 h of tert-BuOOH infusion infiltration of neutrophils in the interstitium was observed. Vascular permeability, expressed as left to right gastrocnemius muscle 99mTc-IgG uptake ratio, was similarly increased after 4 h (2.09 +/- 0.26) and 12 h (2.04 +/- 0.08) of tert-BuOOH infusion compared to saline (1.05 +/- 0.08) (p < 0.001), and further increased after 24 h (3.84 +/- 0.13): (p < 0.001). In this animal model free radical-related soft tissue damage was induced, by continuous infusion of tert-BuOOH, followed by increasing necrosis and vascular permeability in skeletal muscle coinciding with neutrophilic infiltration.

Perineurial hemorrhage in ischemic nerve after anticoagulation

We report a 29-year-old woman who developed severe left leg ischemia after aortic dissection and left common iliac artery occlusion. Light microscopic studies revealed severe nerve and muscle ischemic changes at the calf level. Nerves also showed extensive perineurial hemorrhage, most likely secondary to heparin administration. Perineurial hemorrhage should be considered as one of the possible complications of anticoagulant therapy.

Injury and proprioception in the lower back

No known research has attempted to quantify proprioception of the lower back or to examine the relationship between injury and proprioception in this region. The primary purpose of this study was to explore relationships between low back injury and proprioception of the lower back. Subjects were 88 working male firefighters from public emergency medical service departments. Three types of lower back proprioception (passive motion threshold, directional motion perception, and repositioning accuracy) were tested. Each type of proprioception was examined in the three primary planes of motion using a device designed by the author. Some anthropometric and personal variables were statistically controlled. All variables underwent multiple correlation analysis. The primary findings were: 1) longevity factors [age (r = .30, p < .01) and years of experience (r = .35, p < .001)] were best correlated with proprioceptive deficits in the sagittal plane; 2) injuries were correlated (p < .05) with proprioceptive deficits in the coronal (r = .22) and sagittal planes (r = .17) and with deficits in multiple planes (r = .19); 3) proprioceptive asymmetries were associated with injuries; and 4) the factor most highly correlated with the history of low back injuries was the presence of a spinal disorder (r = .40, p < .001). Impaired proprioception resulting from injury may degrade lumbar motor function, increasing workers' risk of reinjury. Restoring proprioception of the lumbar spine after injury should be a goal of treatment.

Muscle injury, cross-sectional area and fibre type distribution in mouse soleus after intermittent wheel-running

1. It was previously noticed that mouse soleus, but not extensor digitorum longus (EDL) muscles, suffer fibre damage at the onset of voluntary wheel-running without further injuries thereafter. 2. In CBA/J mice trained continuously for 5 months and rested for periods of 1, 2, 3, 4 and 5 weeks acute muscle damage was found in soleus 7 days after the resumption of wheel-running. On single cross-sections damage was present on average in 8.7 +/- 3.5% (mean +/- S.D., n = 15) of the fibres, but only in 0.47 +/- 0.21% (n = 9) and 1.3 +/- 1.1% (n = 4) in control animals rested for 0-6 weeks after continuous running or in untrained controls. 3. Repeated muscle damage occurred when mice exercised for 4 days at intervals of 21-25 days, and after thirteen running episodes within 12 months marked changes in soleus, but not EDL muscles, were present. In cross-sections the total number of muscle fibre profiles was significantly larger in soleus of intermittent runners (768 +/- 68, n = 6; P less than 0.05), compared to continuous runners (676 +/- 54, n = 3) and sedentary animals (683 +/- 33, n = 4). This is probably due to incomplete repair which results in 'split fibres'. 4. At the same time total muscle fibre cross-sectional area was significantly elevated in intermittent runners (P less than 0.05), mainly due to increase in fibre diameters. Net cross-sectional areas were 0.59 +/- 0.069 mm2 (n = 6) in intermittent, 0.53 +/- 0.076 mm2 (n = 3) in continuous runners and 0.46 +/- 0.031 mm2 (n = 3) in sedentary controls. 5. Tetanic and twitch force were also significantly elevated in soleus of intermittent runners while the ratio force/area remained the same. 6. There was an increase in the proportion of type I fibres in soleus from 75 +/- 0.9% (n = 4) in untrained controls to 90 +/- 4.4% (n = 6; P less than 0.05) in intermittent runners and 81 +/- 5.6% (n = 3; n.s.) in continuous runners. 7. Resistance to block of synaptic transmission in soleus was significantly higher in intermittent runners for two levels of curare, indicating enhanced safety margins. 8. EDL muscles in intermittent runners were not different from sedentary controls in any of the parameters studied. In particular, muscle fibres with signs of previous damage (split fibres, central nuclei) were rare (on average 0.5-0.6%) and equally frequent in all experimental groups.(ABSTRACT TRUNCATED AT 400 WORDS)

Fibre loss and distribution in skeletal muscle from patients with severe peripheral arterial insufficiency

Cross-sections of whole calf muscles (m soleus and m gastrocnemius) were obtained from five previously clinically health individuals who had died accidentally (controls) and from amputated legs of five patients of similar age with severe peripheral arterial insufficiency. In the controls, but not in the patients, a characteristic distribution of different fibre types over the entire cross-sections was found, with a relative increase in number of (slow twitch) type 1 fibres in the central parts of both m soleus and m gastrocnemius. A pronounced neuromuscular pathomorphology was found in the patients, especially in m gastrocnemius. The findings suggested widespread damage to the fibres. There was also a lower total number of fibres in these ischaemic muscles; about 50% of the fibres of m gastrocnemius seemed to have disappeared. The results suggested that the relative inactivity as such may be responsible for some of the structural changes, above all the dedifferentiated distribution of different fibres over the cross-section. However, repeated acute and chronic subacute ischaemia may also cause, in the long term, irreparable damage and loss of many individual fibres. This may explain why muscles of patients with peripheral arterial insufficiency are also weaker, during single contractions. The lack of corresponding muscular atrophy in these patients seems to a large extent to be explained by an increase in connective tissue.

Differential recovery of skeletal muscle and peripheral nerve function after ischemia and reperfusion

Recovery of skeletal muscle function is of prime importance in revascularization of acutely ischemic extremities. In order to study the effect of ischemia and reperfusion on peripheral nerve and skeletal muscle function, temporary unilateral hindlimb ischemia (1 or 3 hr) was induced in 12 rabbits by temporary arterial occlusion of common iliac and femoral arteries and collateral ligation. The control limb was similarly prepared without interruption of blood flow. Both anterior tibialis muscles were attached to force transducers, and the twitch and tetanic tensions were measured at the end of the ischemic interval and during reperfusion (2 hr) by either direct muscle stimulation or stimulation of the deep peroneal nerve. The ischemic limb was reperfused by removal of arterial clamps and reperfusion documented by Doppler flow over the vascular pedicle. The recovery of muscle function of the ischemic/reperfused limb relative to that of the contralateral control limb was used as the index of recovery. By the end of the ischemic interval, no contractile activity was elicited with nerve stimulation for either the 1- or the 3-hr group. After 2 hr of reperfusion, the 1-hr group regained 0.558 +/- 0.116 (mean +/- SEM) of control function with nerve stimulation, while the 3-hr group regained only 0.016 +/- 0.005 of control function (P less than 0.01). In contrast, with direct muscle stimulation, the 1-hr group produced 0.580 +/- 0.015 compared to 0.286 +/- 0.042 (P less than 0.001) after 3 hr of ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Nerve and muscle vulnerability to ischemia

Nerve and muscle vulnerability to structural damage during ischemia was examined in the hind legs of 50 cats after transient simultaneous clamping of the aorta and femoral artery for 1 to 10 h. Not until 5 h of ischemia were mild necrotic changes noted in nerves. Moderate to severe changes occurred after 8 h of ischemia. Contrariwise, mild muscle necrotic changes developed after 2-3 h, and moderate to severe changes after 5-7 h. The anterior tibialis muscle was usually more severely damaged than the gastrocnemius and soleus muscles. These studies demonstrate that: Longer periods of ischemia are required to produce nerve damage than suggested by previous tourniquet compression experiments. Longer periods of ischemia are necessary to produce necrosis in the posterior than anterior and lateral compartment muscles of the leg. Muscle is more vulnerable than nerve to ischemia.