Tris-hydroxymethyl aminomethane and sodium bicarbonate to buffer metabolic acidosis in an isolated heart model

Metabolic acidosis induces a decrease in the developed force of cardiac muscle by affecting every step of the excitation--contraction coupling pathway. Due to transient worsening in intracellular acidosis, the value of administering sodium bicarbonate therapeutically during acute acidosis has been questioned. An alternative therapeutic drug, Tris-hydroxymethyl aminomethane (THAM) has the advantage of diffusing into the intracellular space. This study was designed to evaluate the effects of metabolic acidosis on myocardial performance and to determine the effects of alkalinization with sodium bicarbonate, THAM, and their combination. Using a blood-perfused isolated heart preparation, left ventricular contractility and relaxation were measured at normal pH and during metabolic acidosis (pH = 7.0). Acidosis dramatically impaired myocardial contractility and relaxation. After buffering with sodium bicarbonate, although plasma bicarbonate concentration was normalized, pH remained below normal owing to an increased PaCO2. Contractility and relation were initially worsened, then slightly improved to return to control values. THAM uncompletely buffered acidosis but significantly improved contractility and relaxation. The combination of THAM with sodium bicarbonate perfectly buffered acidosis without modifying PaCO2 and significantly improved contractility. The combination of THAM with sodium bicarbonate is based on the ability of THAM to capture the CO2 produced by the sodium bicarbonate buffer. This combination achieves a perfect correction of metabolic acidosis and improves myocardial performance.

Osteopontin is associated with bioprosthetic heart valve calcification in humans

Calcification of non-osseous tissues such as heart valves or vessels is a major concern in clinical practice. The exact mechanism is still unknown. Numerous studies have shown that mineral deposits of crystalline hydroxyapatite within these tissues were associated with increased non-collagenous protein content. More recently osteopontin was found to be associated with calcification in living tissues such as vessels and native human aortic valves. The aim of this study was to determine whether or not non-collagenous proteins can also be found in non-living tissues such as glutaraldehyde-pretreated porcine valves after implantation in humans. Thirty-eight glutaraldehyde pretreated porcine bioprostheses were studied: 16 not implanted and 22 after 11 years of implantation in the aortic and mitral valve position in humans. In areas of calcification vizualized by Von Kossa staining and microradiography, immunostaining using polyclonal antibodies against calcium-binding proteins showed osteopontin positive staining and no staining for osteocalcin, bone sialoprotein or osteonectin. In uncalcified areas and in non-implanted values, staining for osteopontin or other calcium-binding proteins was negative. Western blot analysis of macroscopically calcified and uncalcified areas showed that several proteins were adsorbed in implanted values and confirmed the presence of osteopontin in the calcified areas, while no immunolabelling was found in non-calcified areas, in uncalcified valves and in non-implanted valves. Thus the presence of osteopontin in the calcified areas of bioprosthetic heart valves implanted in human indicates that this protein is associated with bioprosthetic valvular calcification. Since these values are made of non-living connective tissue, and no cell immunostained for osteopontin was found around the calcified area, this suggests that a non-cellular mediated mechanism involving protein adsorption may play a role in bioprosthetic valvular calcification.

Hemodynamic effects of cardiomyoplasty in an experimental model of acute heart failure and atrial fibrillation

The aim of our work was to study the hemodynamic effects of dynamic cardiomyoplasty on an acute animal model of atrial fibrillated heart failure. Eight anesthetized open chest dogs suffering from atrial fibrillation and heart failure, obtained by topic acetylcholine and propranolol, were treated by a cardiomyoplasty procedure performed with an electrostimulated latissimus dorsi muscle flap (LDMF). Values considered for analysis during LDMF stimulation were selected from cardiac cycles with R-R intervals similar to those when the LDMF was not stimulated (+/- 20 ms). Atrial fibrillated heart failure showed a significant increase of systemic vascular resistance, end diastolic left ventricular pressure (EDLVP) and right atrial pressure (p < 0.05), and a significant decrease in cardiac output, systolic left ventricular pressure (SLVP), and mean aortic pressure (p < 0.05) compared with control values. LDMF stimulation in atrial fibrillated heart failure resulted in a significant increase of SLVP, cardiac output, and mean aortic pressure (p < 0.05) and a significant decrease of systemic vascular resistance, EDLVP, and right atrial pressure (p < 0.05) compared with nonstimulated values. The highest LVP values were obtained with R-R intervals long enough to allow an adequate LV filling. We conclude that dynamic cardiomyoplasty provides an appropriate recovery in this animal model of atrial fibrillated heart failure. Cardiomyoplasty is an appropriate procedure for cardiac assist when R-R intervals allow an adequate LV filling.

[Pre- and intraoperative management of heparin cross hypersensitivity. Apropos of a case]

A patient with a Starr prosthetic heart valve for 13 years developed chronic idiopathic thrombocytopaenic purpura and a highly probable crossed allergy to heparin. As the valve needed to be replaced, cardiopulmonary bypass surgery was undertaken associating heparin with lioprost and Aprotinine. In this type of situation, aggregation of control platelets by the patient's plasma in the presence of unfractionated heparin and of low molecular weight heparin justifies the use of powerful antiplatelet agents such as lioprost which was associated with Aprotinine for its platelet protective effects. This original combination allowed successful cardiopulmonary bypass surgery under unfractionated heparin under excellent conditions with minimal blood loss. This case underlines the value of this approach for cardiopulmonary bypass surgery in patients with heparin-induced thrombocytopaenia.

Angiographic and electron-beam computed tomography studies of retrograde cardioplegia via the coronary sinus

Retroperfusion of the coronary sinus does not provide homogeneous distribution of cardioplegic solution. The goal of this study was to analyze the distribution of flow during retrograde cardioplegic infusion in cadaveric human hearts with two different techniques of coronary sinus cannulation: (1) internal occlusion of the coronary sinus by balloon inflation and (2) external occlusion by tightening the orifice of the coronary sinus around a simple catheter. To evaluate differences between the two techniques, angiographic and electron-beam computed tomographic studies were performed. Computed digital angiography was performed on 14 hearts. Angiographic patterns varied according to type of coronary sinus cannulation. With the balloon inflation technique, the marginal vein and the anterior descending vein were perfused first; the posterior descending vein was not perfused. This vein was opacified secondarily through a venovenous anastomosis located at the apex of the heart. Backward flow into the right atrium (steal phenomenon) was demonstrated. At completion of retroperfusion, the inferior part of the septum remained poorly opacified. Conversely, angiographic findings after external occlusion of the coronary sinus revealed simultaneous injection of all venous channels. The entire septum was well opacified at completion of retroperfusion. Electron-beam computed tomographic study was performed on eight hearts with the external occlusion technique and nine with the internal occlusion technique. The computed tomographic findings confirmed the results of digital angiography. The peak myocardial enhancement and the peak rising rate of myocardial enhancement within the interventricular septum were significantly more important (p < 0.0001) when the external coronary sinus occlusion mode was used than when the internal coronary sinus occlusion mode was used. In all hearts except one, the right ventricular wall was not opacified, regardless of the type of cannulation and the type of radiologic analysis. This study demonstrates the importance of coronary sinus cannulation technique in optimizing the protection of the interventricular septum with retrograde cardioplegic infusion.

[Effects of an anti-c-myb antisense oligonucleotide on myo-intimal proliferation. Specificity of action and consequences on vasoreactivity]

Several reports have shown that an 18-mere antisense oligonucleotide directed against c-myb (AS 18) inhibits the proliferation of smooth muscle. The aims of this study were to confirm the specificity of a new anti-c-myb antisense and to evaluate changes in vasoreactivity following treatment with a c-myb antisense. Five groups of rats. All underwent desendothelialisation of the abdominal aorta. A solution containing pluronic gel, or one of the following oligonucleotides: AS 18, 15 mere antisense directed against c-myb, an aleatory 4G sequence containing 4 consecutive guanosines, a 15 mere antisense mismatch (n = 11), was applied around the aorta. After 21 days, the thickness and mean surface areas of the media and intima were calculated. Four groups of rats were constituted for the vasoreactivity study: control (A), desendothelialisation (B), desendothelialisation + application of AS 18 (C) and application of AS 18 alone (D). One ring per aorta was sampled at the 21st day and analysed in an organ chamber. The following results were obtained: the thickness and average surface areas of the intima were smaller (p < 0.05) in the 4G and AS 18-groups; in group B, none of the 8 segments responded to acetylcholine; in group C, 6 out of 8 segments responded. The contraction study showed no differences between groups A and D or between groups B and C. The authors conclude that the mode of action of AS 18 antisense of c-myb is non-specific but due to the presence of 4 consecutive guanosines in the oligonucleotide. Oligonucleotide with this sequence inhibits myo-intimal hyperplasia and improves endothelium-dependent relaxation in this model without affecting the contraction.

Resting energy expenditure and energy substrate utilization in children with Duchenne muscular dystrophy

The high prevalence of obesity at an early stage of Duchenne muscular dystrophy (DMD) could result not solely from reduced physical activity, but may also involve low resting energy expenditure (REE), abnormal nutrient utilization, or overfeeding. We hypothesized that the dramatic muscle mass loss in DMD should reduce the REE. REE was measured by indirect calorimetry in 13 9-13-y-old DMD boys (5 obese, 8 nonobese) and 9 male age-matched controls. Muscle mass was estimated from 3-d creatinine excretion in urine. Daily energy intake was estimated from 7-d diet records. In the nonobese DMD group (NODMD) the muscle mass was reduced by 71%, and the REE was 13% lower than in controls (47.5 versus 54.6 kcal.h-1, p < 0.05). Postabsorptive respiratory quotients appeared higher in both DMD groups than in the controls; however, the difference was significant only for the NODMD group (0.88 versus 0.83, p < 0.05). Respiratory quotients were not different between the two DMD groups. Diet records were not contributive in revealing a different dietary behavior between groups. Our results suggest that: 1) muscle mass loss in DMD is associated with a low REE, 2) low postabsorptive fat utilization might occur at an early stage of the disease, and 3) obesity is not associated with an increase in fat utilization in DMD. This study warrants further research to test low REE and low fat utilization as risk factors in developing obesity in DMD.

[Cardiomyoplasty as treatment of chronic severe cardiac failure]

INTRODUCTION AND OBJECTIVES

Cardiac assistance from skeletal muscle is now emerging as an alternative to transplant surgery. The principle of cardiomyoplasty is chronic electrostimulation of the latissimus muscle flap wrapped around the heart to obtain a phasic activity which can be integrated to ventricular kinetics. Cardiomyoplasty is appropriate for patients with cardiac insufficiency refractory to optimal medical treatment. This includes cardiac failure of ischemic and non-obstructive cardiomyopathies. Worldwide clinical experience with this technique involves more than 500 cases.

MATERIAL AND METHODS

The Broussais Hospital clinical experience involves 80 patients, operated between 1985 and 1995. All of them were closely followed in the postoperative period.

RESULTS

Recent basic and clinical data have shown that cardiomyoplasty effects on ventricular performance are due to: 1) augmentation of pump function: 2) limitation of cardiac dilatation; 3) reduction of ventricular wall stress, and 4) reverse remodeling of the left ventricular geometry. Remarkably, continuous fatigue free contraction of the latissimus dorsi muscle at the frequency of the heart has been obtained for periods exceeding 10 years in humans. Five patients underwent cardiac transplantation due to refractory heart failure.

CONCLUSIONS

Clinical experience has demonstrated that cardiomyoplasty is an efficient technique to assist patients with severe refractory cardiac failure. In the great majority of cases it reverses the heart failure and increases life expectancy. Moreover, the functional class and the quality-of-life are significantly improved. Cardiomyoplasty does not preclude the use of future orthotopic heart transplantation.

Serial assessment of cardiopulmonary exercise capacity after cardiomyoplasty for either ischemic or idiopathic dilated cardiomyopathy

Cardiomyoplasty is a surgical procedure aimed at assisting the left ventricle during ejection. We describe the long-term effects of cardiomyoplasty on peak exercise capacity, with serial assessments for up to 3 years after operation. Sixteen patients (12 in New York Heart Association class III and 4 in class IV) were enrolled. The mean left ventricular ejection fraction was 18 +/- 8%. Bicycle exercise tests with respiratory gas analysis were performed preoperatively and 6, 12, 18, 24, and 36 months after operation. Mean follow-up was 12 +/- 5 months (range 6 to 24). At 6 months, peak oxygen consumption and the ventilatory threshold were unchanged (from 17.8 +/- 5.8 to 15.8 +/- 5.3 ml/min/kg, and from 12.1 +/- 2.7 to 11.4 +/- 3.4 ml/min/kg, respectively). Ventilation at 50 W, viewed as an index of polypnea at submaximal exercise, was also unchanged. Serial assessment of exercise capacity thereafter showed no changes. However, ejection fraction tended to increase from 18 +/- 8% to 21 +/- 9% (p=0.08) and 14 patients reported an improvement in their functional status, resulting in a significant change in New York Heart Association functional class (3.3 +/- 0.5 to 2.2 +/- 0.4 at 6 months and 2.4 +/- 0.4 at the last visit, p <0.005) and improvement in quality-of-life scores. Thus, cardiomyoplasty does not appear to increase peak exercise capacity in the long term, despite an improvement in the left ventricular ejection fraction. Symptoms and quality of life, however, appear to improve. This may be related in part to an insufficient number of assisted systoles during exercise, persistent deconditioning, or changes in pulmonary mechanics.

[Open heart operation under videosurgery and minithoracotomy. First case (mitral valvuloplasty) operated with success]

The development of "less invasive surgery" using small incisions and videoscopic techniques may change, in the near future, our attitude towards "traditional" surgery. This is because of specific advantages such as skin limited incisions, reduced perioperative disability and lower cost. Up to now, only abdominal, thoracic and coronary artery surgery which do not imply the opening of the heart, or closure of simple atrial septal defects, have benefitted from this new approach. This article reports the first case of open heart surgery for complex lesions of the left heart through a minithoracotomy (5 x 4 cm) with the use of videotransmission and peripheral extracorporeal circulation. The patient, a 30-year-old female, was operated upon for a combined mitral valve stenosis and insufficiency of rheumatic origin unsuccessfully treated by a previous percutaneous valve dilatation. The 2.5 h open heart procedure comprised commissurotomy, repair of torn leaflets, chordal transposition and Carpentier-Edwards prosthetic ring implantation. The patient left the hospital 12 days after the operation. Transesophageal echocardiography at discharge showed normal valve function with no residual stenosis or residual leak.

Homograft replacement of the mitral valve. Graft selection, technique of implantation, and results in forty-three patients

Because of experience gained in reconstructive mitral valve surgery, we have reevaluated the implantation of cryopreserved homografts in the mitral position. Forty-three patients, aged 11 to 69 years (mean 34 years), underwent mitral valve replacement with cryopreserved mitral homografts. The indications for the procedure were acute endocarditis (n = 14), rheumatic stenosis (n = 26), systemic lupus endocarditis (n = 2), and marasmic endocarditis (n = 1). All homografts were obtained from hearts explanted in the course of transplantation and were cryopreserved at -160 degrees C in 10% dimethyl sulfoxide solution without antibiotics. Appropriate sizing was based on morphologic study of the homografts and preoperative echocardiographic assessment of the recipient valve. In 82 homografts analyzed, the height of the anterior leaflet was 25 +/- 3 mm and the distance from the anulus to the apex of the anterior papillary muscle was 21 +/- 3 mm. The morphologic features of the papillary muscles were classified according to four types of increasing complexity. Nine valves with complex (type IV) papillary muscle abnormalities were discarded. Echocardiographic measurements of the valve were matched with those of the homograft identification cards and a slightly larger homograft was selected (measurements + 3 mm). Partial homograft replacement was done in case of a localized lesion (abscess or calcification) (n = 21). Total homograft replacement was undertaken in the presence of diffuse lesions (n = 22). Two hospital deaths occurred as a result of poor cardiac output. One patient required reoperation on the tenth postoperative day after a dehiscence on the valvular suture line. After a mean follow-up of 14 months, there has been one late death caused by a bronchial neoplasm and one reoperation for residual stenosis (partial replacement). The remaining patients were in either New York Heart Association class I (n = 25) or II (n = 13). Thirty-three patients were in sinus rhythm. Follow-up echocardiography has revealed no mitral regurgitation (n = 20), minimal mitral regurgitation (n = 13), and mild mitral regurgitation (n = 5). Surface valve area has been calculated at 2.5 +/- 0.4 cm2 in partial homograft reconstruction and 2.7 +/- 0.3 cm2 in total homograft replacement, with a transvalvular gradient of 3 +/- 4 mm Hg.

CONCLUSION

In a selected group of patients, the use of mitral homografts significantly extended the present limitations of reparative surgery of the mitral valve.

[Induced tissue transformation and heart surgery]

This article reports the research which led to the use of animal connective tissues in the construction of valvular prostheses and those which led to the use of electrically stimulated skeletal muscle for cardiac assistance. Although, very different at first glance these research have in common the transformation of biological tissues by physical or chemical means to adapt them to a new function. 1) Once implanted in a different species, animal connective tissues are destroyed by immunological reactions and collagen degeneration. These lesions can be prevented by both maskage of the antigenic groups and intermolecular crosslinking using Glutaraldehyde. The durability of such chemically treated tissues is based upon the stability of the biological material (concept of bioprosthesis) and not upon cell survival or tissue regeneration by host cell ingrowth (concept of graft). The valvular bioprostheses made from Glutaraldehyde treated pericardial tissue, keep after this treatment their advantage of biological tissues: they are not thrombogenic and do not require anticoagulation contrary to mechanical valves. Although they have a limited durability up to 10 to 15 years due to tissue calcification, they represent 40% of the valvular prostheses used in clinical practice today. 2) The clinical use of electrostimulated skeletal muscle has been delayed for a long time because of fatigue lesions. An original protocol of progressive sequential stimulation prior to the use of muscle prevents fatigue by the transformation of type I fatigable myosin into type II non fatigable myosin. The conditionned muscle i.e.: the latissimus dorsi, is then wrapped around the ventricles to either reinforce cardiac contraction or to replace a portion of the heart. In the past 10 years, this new operation of "dynamic cardiomyoplasty", has been performed in 84 patients suffering from the end stage heart failure in our institution and in over 500 patients throughout the world with significant functional improvement.

Proteins and bioprosthetic calcification in the rat model

BACKGROUND AND AIM OF THE STUDY

The mechanism of valvular bioprostheses calcification is still unknown, but early studies showed increased Gla-protein content in calcified valves. Using an experimental model, which reproduces the clinical process, we therefore analyzed the role of minerals and proteins in bioprosthetic valvular calcification.

METHODS

Glutaraldehyde pretreated porcine valves were studied before and after implantation in rats by X-ray, calcium (Ca) and phosphorus (P) measurement, Fourier Transform Infrared (FTIR) spectroscopy, SDS-PAGE and 45Ca ligand blotting of the extracted proteins.

RESULTS

Before implantation, there was no X-ray calcification with very little Ca and P content. After implantation, X-ray calcifications appeared on day seven with increased Ca and P up to day 35 (p < 0.05, ANOVA). FTIR revealed structural proteins alone before implantation, plus minor proportions of lipids on day two, which always preceded Ca and P appearance. Ca and P increased up to day 35, first as amorphous and changed in carbapatite over time. SDS-PAGE before implantation revealed two proteins (66-kD and 54-kD) alone, which were sustained up to day 35. The 66-kD had 45Ca affinity. On day two, many other proteins appeared on SDS-PAGE, four of which (52, 45, 14 and below 14-kD) with 45Ca affinity. Protein pattern did not change from day two to 35.

CONCLUSIONS

Valvular bioprosthesis calcification is associated with progressive increase in Ca and P content and at least five calcium-binding proteins: one intrinsic valvular protein, pre-existing to implantation, plus four other, extrinsic valvular proteins adsorbed within the tissue after implantation.

Clinical study of the effects of latissimus dorsi muscle flap stimulation after cardiomyoplasty

BACKGROUND

Beneficial hemodynamic effects after dynamic cardiomyoplasty have been inconsistently demonstrated, and the effects seen may be due to the wrap itself, to flap stimulation, or both. The aim of this study was to determine whether flap stimulation per se acts as a systolic active process after cardiomyoplasty.

METHODS AND RESULTS

Catheterizations were performed in 13 patients 14.4 +/- 7 months after cardiomyoplasty. New York Heart Association functional class decreased from 3.3 to 2.1 after the procedure (P = .0005). Hemodynamic evaluations were first performed with the stimulator on in the 2:1 mode and then after the stimulator had been off for at least 24 hours. Left ventricular (LV) ejection fraction increased from 25.1 +/- 6% before surgery to 28.2 +/- 6.7% with the stimulator on after cardiomyoplasty (P = .04). When stimulation was stopped, there was no change (P > .05) in indexes of systolic or diastolic LV function (peak systolic LV pressure, LV ejection fraction, peak positive dP/dt, peak negative dP/dt, or tau). Pulmonary capillary wedge pressure and cardiac index were unchanged when stimulated and nonstimulated settings were compared (P > .05). However, a remarkable heterogeneity of individual responses was observed. Ejection fraction and cardiac index decreased with the stimulator off in 3 patients, but peak positive dP/dt decreased in 6 patients; diastolic function deteriorated in 2 patients, but a slight improvement was noted in 3 patients. Cardiothoracic ratio, echocardiographic LV end-diastolic dimension, and fractional shortening remained unchanged between immediate (< 1 month) and long-term (36.7 +/- 25.9 months) postoperative evaluations.

CONCLUSIONS

In the majority of our patients, there was no short-term hemodynamic benefit of flap stimulation; therefore, we conclude that the efficacy of cardiomyoplasty may be a consequence of a passive "girdling effect," which limits the progression of ventricular enlargement and further deterioration of ejection fraction.

[Corynebacterium diphtheriae endocarditis complicated by septic arthritis and cerebral abscess]

The authors report a rare case of the mitis type Corynebacterium diphteriae endocarditis on a prosthetic valve complicated by septic arthritis and cerebral abscess. The authors underline the importance of regular transoesophageal echocardiographic control and underline the diagnostic value of ultrafast computed tomography for the diagnosis of aortic annular and interventricular septal abscesses in patients with mechanical prosthetic valves.

Allelic association at the D14S43 locus in early onset Alzheimer's disease. French Alzheimer's Disease Collaborative Study Group

The D14S43 marker is closely linked to the major gene for early onset autosomal dominant Alzheimer's disease on chromosome 14. Allelic frequencies at the D14S43 locus were compared in 113 familial and isolated cases of early onset Alzheimer's disease (< 60 years of age at onset) (EOAD) and 109 unaffected individuals of the same geographic origin. Allele 7 was significantly (P = 0.033) more frequent in type 1 EOAD patients (13.2%), defined by the presence of at least another first degree relative with EOAD, than in controls (4.1%). Since an autosomal dominant gene is probably responsible for type 1 patients, allelic association may reflect linkage disequilibrium at the D14S43 locus. This would mean that some patients share a common ancestral mutation. However, since multiple tests were carried out, this result must be interpreted with caution, and needs confirmation in an independent sample.

[Fibrinolytic inhibitors and prevention of bleeding in cardiac valve surgery. Comparison of tranexamic acid and high dose aprotinin]

In order to assess the effects of tranexamic acid in comparison to the high dose regimen of aprotinin recommended by Royston and considered to be the reference in postoperative bleeding in cardiac surgery, 35 consecutive patients were randomised to two groups according to the product prescribed. The global postoperative bleeding was comparable in the two groups (p = 0.49). One surgical reoperation for haemostasis was required in the reference group. There was one case of renal failure in the same group due to cardiac failure. No thrombotic complications were observed. Platelet function, as judged by the bleeding time and platelet aggregation to ristocetin, was the same in the two groups. The D-dimers remained low in both groups, reflecting the absence of intravascular coagulation and fibrinolysis. Tranexamic acid was as effective and as safe as high dose aprotinin. These two substances, in addition to their fibrinolytic inhibitory activity, conserved platelet protection by blocking the action of plasmin. These results seem to justify the preventive use of tranexamic acid from the moment of skin incision, especially in reoperation.

[Effect of antisense oligonucleotides on myo-intimal hyperplasia in a model of abdominal aortic injury in the rat]

Restenosis at a rate > 30% at 6 months is the major complication of both coronary and peripheral arterial angioplasty. Restenosis is mainly due to proliferation of smooth muscle cells, extracellular matrix and collagen which form a neointima. The proto-oncogene c-myb is a gene with an immediate response which has been implicated in the proliferation and alteration of the phenotype of smooth muscle cells. The antisenses are molecules of single-helix DNA the sequence of which is inverse to that of messenger RNA of the target proto-oncogene. They therefore have the possibility of forming a double helix with the messenger RNA and of preventing its translation. The antisenses of c-myb have already been successfully tested in in vitro and in vivo models of neointimal proliferation. The aim of this study was to demonstrate the efficacy of c-myb antisenses on the proliferation of smooth muscle cells in a model of abdominal aortic injury in the rat. Thirty-five male Wistar rats with an average weight of 350 grams were operated. Smooth muscle cell proliferation was obtained by desendothelialisation of the abdominal aorta from the level of the left renal vein to the aortic bifurcation. Using a randomised, double-blind protocol, 17 rats were given 500 microliters of pluronic gel (control group), 9 a sense oligonucleotide of c-myb in 500 microliters of pluronic gel (sense group) and 9 a c-myb antisense oligonucleide in 500 microliters of pluronic gel (antisense group). Two rats were given fluorescinlabelled antisenses; one was sacrificed 4 hours and the other 24 hours later.(ABSTRACT TRUNCATED AT 250 WORDS)

Technique of homograft replacement of the mitral valve

In this paper, we have reviewed previous experiences in the technique of homograft replacement of the mitral valve. Following laboratory studies, we have initiated a clinical program of partial and total homograft replacement of the mitral valve and present our early results in the first 32 patients.

Twitch analysis as an approach to motor unit activation during electrical stimulation

The mechanical twitch in response to increasing electrical stimulus intensity, delivered both over the motor point and motor nerve, was recorded in the first dorsal interosseous (FDI) and the adductor pollicis (AP), and only over the motor point in the soleus (Sol), lateral (LG), and medial (MG) gastrocnemius muscles of human subjects. The relationship between intensity of electrical stimulation (ES) and twitch torque showed a positive linear regression in all muscles. In the FDI and AP the relationship was not significantly different when ES was applied at the motor point or over the motor nerve. At small intensities of activation, ES induced larger twitch torques in the MG and LG, which contain a roughly equal proportion of slow and fast motor units (MUs) compared to the Sol, which is composed mainly of slow type fibres. Moreover, the relationship between ES intensity and twitch time-to-peak is best fitted in all muscles by a power curve that shows a greater twitch time-to-peak range in its initial part for muscles containing a larger proportion of fast MUs (LG, MG) than for muscles mainly composed of slow MUs (Sol). In conclusion, these results induced by ES at the motor point and/or over the motor nerve confirm the concept of a reversed sequence of MU activation, as compared to voluntary contractions, and document this viewpoint in muscles of different function and composition. The reversed sequence of MU activation is more clearly evident during motor point ES.