Biomechanical comparison of stimulated and nonstimulated skeletal muscle pulled to failure

We compared the biomechanical properties of passive and stimulated muscle rapidly lengthened to failure in an experimental animal model. The mechanical parameters compared were force to tear, change in length to tear, site of failure, and energy absorbed by the muscle-tendon unit before failure. Paired comparisons were made between 1) muscles stimulated at 64 Hz (tetanic stimulation) and passive (no stimulation) muscles, 2) muscles stimulated at 16 Hz (wave-summated stimulation) and passive muscles, and 3) muscles stimulated at 64 Hz and at 16 Hz. Both tetanically stimulated and wave-summation contracted muscles required a greater force to tear (at 64 Hz, 12.86 N more, P less than 0.0004; and at 16 Hz, 17.79 N more, P less than 0.003) than their nonstimulated controls, while there was no statistical difference in failure force between muscles stimulated at 16 Hz and 64 Hz. The energy absorbed was statistically greater for the stimulated muscles than for the passive muscles in Groups 1 and 2 (at 64 Hz, 100% more, P less than 0.0003; and 16 Hz, 88% more, P less than 0.0002). In Group 3, the tetanically contracted muscle-tendon units absorbed 18% more energy than the wave-summated stimulated muscles (P less than 0.01). All muscles tore at the distal musculotendinous junction, and there was no difference in the length increase at tear between muscles in each group. These findings may lead to enhanced understanding of the mechanism and physiology of muscle strain injuries.     

Spontaneous splenic rupture following infectious mononucleosis

Four cases of spontaneous splenic rupture after infectious mononucleosis (IM) have been treated at this institution since 1978. The condition is rare, occurring in 0.1-0.5 per cent of patients with proven infectious mononucleosis. Splenectomy is considered the treatment of choice for these patients. However, because recent trends in the management of traumatic splenic rupture are moving towards nonoperative treatment with selected patients, a similar approach has been considered for the patient with spontaneous splenic rupture following IM. The major reason for avoiding splenectomy is the increased incidence of sepsis in splenectomized patients. Yet, splenic rupture is accompanied by hemorrhage and the risks associated with blood transfusion for ongoing hemorrhage are of similar magnitude as those of sepsis following splenectomy. In addition, the grossly abnormal spleens seen at operation tend to include large, contained hematomas that may also be prone to rupture. Therefore, operative management still appears to be the preferred treatment for spontaneous splenic rupture following IM. Splenectomy is curative, safe, and obviates the need for transfusion, extended hospitalization, and activity restriction.     

Determination of elimination of pefloxacin and of its derivatives in continuous hemodiafiltration

Continuous venovenous hemofiltration with dialysis (CVVHD) is being increasingly used to treat acute renal failure. However, because of the-lack of data on the clearance of therapeutic agents during this treatment, there is a risk of using inappropriate dosages. This in vitro study was undertaken to determine the clearance of pefloxacin (P) and its two main metabolites (active N-desmethyl P and inactive N-oxide P) during CVVHD. Acitrate-dextrose (ACD) anticoagulated fresh human blood containing P and its two metabolites in the usual therapeutic levels was circulated at a rate of 100 ml min.-1 through a closed-circuit continuous venovenous hemofiltration with dialysis unit (BSM 22-Hospal hemofilter). Temperature and ionic composition of the blood were controlled. Dialysate (L2D, Hospal) was circulated on the other side of the continuous venovenous hemofiltration with dialysis membrane at three different flow rates (Qdi) (0, 500 and 1,000 ml.h-1. The dialysate/ultrafiltrate outflow was adjusted using a withdrawal pump to obtain nul ultrafiltration. Arterial blood, venous blood and ultrafiltrate were sampled simultaneously at different time points for High Performance Liquid Chromatography (HPLC) assays and determination of the clearances (Cl) and sieving coefficients (s) of each compound. Pefloxacin had a sieving coefficient of 0.42 and a clearance of 6.8 ml min-1 when Qdi was nul. With the blood flow used, clearances were found to be correlated with the dialysate flow rate; when this rate was 500 ml h-1, a pefloxacin clearance similar to that seen in healthy subjects was obtained (15.2 ml min-1). The two bacteriologically active forms of the drug (pefloxacin and N-desmethyl P) had similar elimination parameters.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the antithrombotic effects of heparin, enoxaparin and prostacycline in continuous hemofiltration

Continuous anticoagulation is required during haemofiltration to prevent the deposition of fibrin and the formation of thrombus which would lead to early clotting of the haemofilter. This study aimed to compare the efficiencies of 3 different anticoagulation protocol: 150 IU.kg-1.day-1 heparin (group HEP), 1.2 mg.kg-1.day-1 enoxaparin (group ENX), and a combination of 0.8 mg.kg-1.day-1 enoxaparin with 5 ng.kg-1.min-1 prostaglandin I2 (group ENX and PGI2). A flat ANS69S (Hospal) haemofilter was used for continuous venovenous haemofiltration. Antithrombotic efficiency was assessed with a haemofilter permeability index (HPI) including the transmembraneous pressure gradient and the rate of production of ultrafiltrate. The time required for HPI to decrease to 1/3 of its initial value (HPI1/3) was used to compare the 3 protocols. Treatment tolerance was judged by monitoring the usual haemodynamic and haemostatic parameters. No adverse effects (bleeding, thrombosis, hypotension) were observed. HPI1/3 was 15.1 +/- 2.4 h, 18.3 +/- 3.1 h and 28.2 +/- 4.2 h in groups HEP, ENX and ENX and PGI2 respectively. High dose enoxaparin reached antithrombotic efficiency without increasing the risk of haemorrhage. The use of low doses of prostaglandin I2 greatly increased HPI1/3, without any deleterious haemodynamic effects. However, the high cost of prostaglandin I2 needs to be put in the balance with the increase in duration of haemofilter life. Therefore, further investigations are required to evaluate the possible synergy between heparin and prostaglandin I2, as well as the biological parameters which need to be monitored.     

Abnormalities of retinal function (light sense) following idiopathic central serous chorioretinopathy and diffuse retinal epitheliopathy

Although central serous retinopathy is considered a "benign" condition, it is associated in healed forms with frequent and troublesome impairment of visual function. The abnormalities are even more severe after diffuse retinal pigment epitheliopathy. Since Snellen visual acuity testing is a relatively imprecise index of visual function, it does not enable the subtle visual disturbances experienced by these patients to be fully appreciated. The authors evaluated visual function disorders by static automated perimetry and contrast sensitivity in 30 patients with healed central serous retinopathy and in five patients with diffuse epitheliopathy at a cicatricial stage. The results of this study are examined and discussed.