An evaluation of the Doppler-laser system in monitoring the free skin flap in the rat.

The authors discuss their experience in monitoring the free skin flap in the rat with a newly-conceived Doppler-Laser system. The results obtained are compared with a method which is currently used as skin thermometry and the influence in the clinical field is evaluated.

Laser-Doppler versus fluorometry in the postoperative assessment of a cutaneous free flap.

To find the optimal means for monitoring the vascularity of a cutaneous free flap in the postoperative period, we have experimentally compared laser-Doppler velocimetry and fluorometry. Using the rat groin model, five groups were evaluated: 1. flap isolation without division of the pedicle vessels (island flap); 2) flap isolation, division, and repair of the pedicle artery and vein (free flap); 3) flap isolation, with ligation of the pedicle artery immediately or 1 hour later; 4) flap isolation, with ligation of the pedicle vein immediately or 1 hour later; 5) flap isolation, with ligation of the pedicle artery and vein immediately or 1 hour later. The laser-Doppler processes the signal by combination of the root mean square and differential amplification. The fluoroscan gives an index in relation to the fluorescence of a control area. The results obtained with both methods correlated well with findings in clinical situations. However, the laser-Doppler readings were more rapid and sensitive than those with fluorometry. We suggest that laser-Doppler velocimetry is a superior means of monitoring the vascular status of a free tissue transfer or digital replant.

[Progressive complications associated with polyester arterial prostheses. Study of 61 specimens following surgical excision]. / Complications évolutives associées aux prothèses artérielles en polyester. Etude de 61 spécimens après exérèse chirurgicale.

Reports of individual surgical cases tend to be anecdotal because of the unique circumstances surrounding the patient, the surgeon, the intervention and, where applicable, the prosthetic device. To overcome this limitation the authors have taken a wider collaborative approach and report the analysis of 61 explanted polyester arterial prostheses associated with delayed complications on 53 patients reoperated upon in six different French hospitals. One advantage of such an independent and centralized retrieval programme is that the impact of centre specific factors, such as patient selection and surgical techniques, is minimized. Consequently, by following a standardized protocol for the evaluation of the morphologic, pathologic and mineralogic characteristics of the tissue surrounding the excised grafts, as well as the textile structure of the prostheses themselves, it has been possible to distinguish between iatrogenic and disease related complications and to demonstrate a number of general findings associated with the clinical performance of polyester arterial prostheses. Complications such as thromboses, infections and false aneurysms appear to occur randomly after different lengths of implantation, thicker fibrous tissue capsules are associated with velour grafts with highly textured yarns, the incidence of mineralized tissue and of endothelialized luminal surfaces is rare, weft knitted textile prostheses appear less mechanically stable and more sensitive to iatrogenic trauma than warp knitted, and the incidences of lipid and cholesterol adsorption, bacterial colonization and sterile fluid loss need further investigation. These observations lead to the recommendation that for patients with longer life expectancies surgeons should consider selecting low porosity, woven or warped knitted prostheses which contain yarns that have not been highly textured.

A new laser Doppler interface for the continuous measurement of the rat gastric mucosal blood flow.

The laser Doppler system (LD) has been proposed for a tissue blood flowmetry. However, its accuracy is dependent on the pressure and direction of the laser probe. Therefore, we have devised a new interface for the measurement of the gastric mucosal blood flow in rats keeping the probe constant in pressure and direction. This interface is a small cylinder with one end fixed upon the gastric serosa and the other end fixed externally upon the skin. The laser probe adjusts exactly in direction and pressure inside this button. The LD apparatus processes two shifted beams with a differential amplification and a root mean square. It delivers an index (LDI) from 0 to 10. This interface was tested in 3 groups of rats, comparing the mucosal (open stomach) with the serosal gastric LDI and the same serosal LDI with a 133Xe washout flow. Finally, the interface was used in control and restrained rats. The gastric serosal LDI was found to be similar to the mucosal LDI. The correlation between the LDI and the 133Xe washout flow was good, with a coefficient of 0.9. Finally, the LDI of the gastric mucosal blood was significantly different in control and stressed rats. This new interface makes the LD more reliable for the monitoring of gastric mucosal flowmetry. It has the same accuracy as the xenon washout and additionally it is simpler, cheaper and may be repeated or even be used continuously.

Gastric stress ulcer of the rat: relative contribution of the pyloric sphincter, HCO3- bile reflux and mucosal blood flow.

Gastric ulceration has been induced after stress, combining 24 h of fasting and 48 h of restraint in 9 groups of 20 rats with or without a pyloroplasty or a pylorojejunostomy combined with atropine and gastric infusion of NaHCO3 or taurocholic acid. After death or sacrifice at 48 h, ulcer index and blood in the jejunum were determined. Gastric mucosal blood flow was measured semi-continuously by a laser Doppler velocimeter. There were 45% deaths after 48 h of restraint alone, and 70% in the group combining pylorojejunostomy with taurocholic acid. Mortality was lower (p less than or equal to 0.01) pylorojejunostomy alone and more significantly so (p less than or equal to 0.001) when associated with NaHCO3. There was no death when NaHCO3 and atropine were combined with restraint. The mucosal blood flow increased significantly during the first 12 h of restraint in the taurocholic acid group. Both groups with NaHCO3 had mucosal blood flows similar to the controls. Gastric acid and gastric emptying, mucosal ischemia and bile reflux are joint factors inducing gastric stress ulcer. The 100% survival and the low ulcer index after a treatment by atropine and gastric infusion of NaHCO3 suggest that these well-known drugs should be used more frequently.

Chemically fixed human umbilical cord vein grafts as arterial substitutes: potential and limits.

In spite of reported successes, synthetic fabric grafts and microporous and plain synthetic conduits have proven unsuitable for aorto-coronary bypasses and showed weaknesses below the knee. Readily available and uniform diameter vascular substitutes with biological and mechanical properties comparable to human vessels would be of paramount interest. Following reported successes with chemically fixed human umbilical veins (HUV), we have attempted to develop smaller diameter blood conduits and have improved the currently prevalent techniques of fixation, preparation and storage to generate more convenient surgical products. In vitro assessment of the processed HUV demonstrated that the HUV can be easily processed to make an arterial substitute that can be preserved either in a liquid medium or as a dry product. However, the in vivo implantations in dogs led to disappointing results for liquid-preserved or albuminated veins. Critical-point dried grafts gave better results, unfortunately they do not heal and they can only degrade after implantation.

A method of exocrine pancreatectomy in the rat.

The abdominal cavity of male albino rats, average weight 250 g, was opened and the duodenum approached where the ductus choledochus joins. Pancreatic ducts empty into the lower third of the choledochus. The ductus choledochus was cannulated with a Teflon catheter beneath the liver and its other end was brought out at the neck of the rat. Tissue glue was introduced into the lower part of the choledochus towards the liver. Another Teflon catheter was introduced into the duodenum, its second end brought out at the neck and connected with the first catheter by means of a metal tube, thus preserving bile flow from the liver to the duodenum. Tissue glue injection results in complete atrophy of the exocrine pancreas within 2-15 days. The islets of Langerhans remained intact.

[Glutaraldehyde - fixed human umbilical cord vein as a small diameter arterial substitute. Experimentation on the monkey]. / La veine ombilicale humaine traitée au glutaraldéhyde comme substitut artériel de petit diamètre. Expërimentation sur le singe.

Autologous saphenous veins, the preferred substitute material for aorto-coronary, femoro-popliteal and femoro-tibial by-pass, are usable in only 70% of individuals in need of such procedures. The development of small diameter substitute arteries is therefore essential to broaden the pool of patients who could benefit from this class of cardiovascular surgery. Existing substitutes, however, present major difficulties and have had limited success. In this laboratory, an attempt has been made to develop a vessel of 3 millimetres or less in diameter derived from human umbilical cord processed in glutaraldehyde. This substitute can be stored in 45% ethanol or dessicated by critical point drying. This device had been implanted as a segment of abdominal aorta in eight primates (Macaca fascicularis). Preliminary results are disappointing. The indicate that retention of a patency for more than a year post-implantation is difficultly achievable and that connective tissue hyperplasia leading to occlusion at the anastomoses is a major problem. Similar but larger diameter by-passes in the order of 6-8 millimetres should be investigated in greater detail, in order to better establish the "in-vivo" behavior of this class of tissue prosthesis. This would address the more fundamental issues pertaining to the clinical usefulness of fixed biological tissue by-pass devices.

New alternatives in the preparation of chemically fixed human umbilical veins as arterial substitutes.

Following reports of the successful use of chemically processed human umbilical veins as medium and small diameter arterial substitutes, the development of new and improved techniques for the preparation, fixation and storage of these bioprostheses has been attempted. A series of physical and "in vitro" tests was undertaken to predict the "in vivo" performance of these devices. The results indicate that the new techniques are not only technically feasible but may provide a more convenient, versatile and effective surgical product.

[Urokinase (in situ) in the case of acute ischemia of the lower limbs (author's transl)]. / L'urokinase in situ dans l'ischémie aiguë des membres inférieurs.

Eighteen patients with severe, acute ischemia of the lower limbs were treated with an arterial perfusion of the ischemic leg with Urokinase. This was associated, in thirteen patients, with a limited attempt of revascularization. The result of this treatment was an immediate improvement in twelve cases, which lasted, more than six months, in six patients. The authors insist on the interest of the arteriography performed after the fibrinolytic treatment in order to complete the revascularization.

Processes human umbilical veins as arterial substitutes--evaluation in canine models.

Human umbilical cord vein segments have been used as vessel substitutes for damaged or occluded arteries, as aorto-coronary by-passes and as arterio-venous fistulae for dialysis. The Dardik-Biograft fixed with glutaraldehyde and the Mindich-Bioflow, fixed with ethanol and dialdehyde starch, are commercially available. They were implanted in dogs as replacements for a segment of the abdominal aorta. Post-implantation status was followed by angiography. They were evaluated after removal from sacrificed animals with the aid of scanning electron microscopy and histological techniques. Attention was focused on vessel patency, dimensional stability, integrity of the anastomosis line, lumen wall microstructure, evidence of suture damage and thrombus deposition pattern. Both types of grafts gave functional by-passes for at least until 6 months post-implantation. The Dardik-Biograft appeared more prone to thrombus formation near the anastomosis. Sparse cellular development was also noted. The Mindich-Bioflow gave rise to a prosthesis of superior thromboresistance which was more subject to mechanical damage.