P. J. Klopper

The effect of mechanical stress on healing skin wounds: an experimental study in rabbits using tissue expansion

In rabbits, skin wounds were expanded by inflation of a subcutaneously implanted tissue expander in order to study the effect of mechanical stress on wound healing. Biomechanical and histomorphological properties of both expanded and non-expanded control wounds were evaluated. Expanded wounds demonstrated a significant increase in maximum load (80%) and energy absorption at maximum load (95%), when compared to non-expanded control wounds. Histomorphologically, the expanded wounds were stretched in comparison to the control wounds. The collagen in expanded wounds showed an orientation parallel to the direction of force, and displayed a more organised configuration. It is concluded that the use of tissue expanders permits the standardisation of the mechanical stress applied to experimental skin wounds. It is found that mechanical stress accelerates wound healing by producing stronger and more organised scars, however, at the expense of scar stretching.

Biomechanical and histomorphological changes in expanded rabbit skin

In 12 rabbits, biomechanical and histomorphological properties were determined in expanded, sham-operated and non-operated control skin. Results were evaluated in paired fashion. Both expanded and sham-operated skin showed a significant loss of stiffness of 60% and 35% respectively (rho less than 0.001 and rho less than 0.05). In addition, maximum stiffness in expanded skin was reached at a shorter extensibility than in sham-operated or non-operated control skin. Histomorphological examination revealed thickened dermal collagen bundles with loosened packing of collagen fibrils in both expanded and sham-operated skin. It is concluded that the surgical procedure of balloon implantation is responsible for a significant part of the reported biomechanical and histomorphological findings. Wound healing, in addition to the delay phenomenon, may therefore be a mechanism involved in skin expansion.

Hemodynamics during laparoscopy in the supine or prone position

During laparoscopy elevations in arterial pressure and a decrease in cardiac output have been reported. Laparoscopic surgery performed in the prone position may be advantageous for some surgical procedures, but the hemodynamic effects of pneumoperitoneum in this position have not been studied. We studied the effects of different levels of increased intraabdominal pressure on hemodynamics and oxygen transport in eight pigs in the prone and the supine position. Increases in intraabdominal pressure did not result in decreased cardiac output or in a reduction of oxygen transport and consumption in either position. These results suggest that laparoscopy in the prone position does not result in more severe hemodynamic depression than laparoscopy in the supine position.

Laparoscopy without pneumoperitoneum

Laparoscopic surgery with CO2 insufflation is associated with adverse effects on hemodynamics and gas exchange. The abdominal wall retractor (AWR) is an alternative for pneumoperitoneum. Hemodynamics and gas exchange during the use of an AWR were compared to those of CO2 pneumoperitoneum.In eight pigs subjected to 1 h of CO2 pneumoperitoneum or abdominal wall retraction, hemodynamics, gas exchange, and oxygen transport were studied in a randomized cross-over study design.The only change observed during abdominal wall retraction was mild respiratory alkalosis. In contrast, during CO2 pneumoperitoneum mean arterial blood pressure increased 13%, central filling pressures doubled, and a small increase in cardiac output was observed. Peak airway pressures increased 50%, end-tidal CO2 increased 20%, and respiratory acidosis was induced (arterial pH from 7.46±0.07 to 7.31±0.06 and pCO2 from 33±3 mmHg to 53±4 mmHg). Arterial PO2 decreased but mixed venous oxygen saturation and oxygen consumption were unaffected.In contrast with CO2 pneumoperitoneum, laparoscopy using abdominal wall retraction was not associated with adverse effects on hemodynamics or gas exchange.

Experimental arterial allografting under low and therapeutic dosages of cyclosporine for immunosuppression

The aim of this study was to investigate performance of preserved arterial allografts under the protection of a high-dose and a low-dose immunosuppressive regimen, with cyclosporine (CsA). Dog carotid arteries were harvested and stored for 14 days at 4 degrees C in University of Wisconsin organ preservation solution. Segments (6 cm) of carotid artery were orthotopically and bilaterally implanted in mongrel dogs (n = 18). CsA was given in two dosage regimens: 25 mg/kg/day (group I, n = 7) and 10 mg/kg/day (group II, n = 7). The control group received no CsA (group III, n=4). After 3 months of implantation, patency was assessed by angiography. The grafts were excised for investigation of vessel wall and endothelial function and morphology. For assessment of function in vitro, slices of arterial segments were connected as ring preparations to an isometric force transducer and immersed in a 5 ml organ bath (37 degrees C) containing Tyrodes solution. The contractile response was examined by adding 40 mM KCl and phenylephrine (100 microM) to the organ bath; endothelium-dependent relaxation was examined by adding methacholine (100 microM). Morphology was assessed semiquantitatively. The functional responses to KCl, phenylephrine (Phe) and methacho- line (Met) after 14 days of storage in UW, were 30.2 +/- 1.2 mN, 26.9 +/- 1.0 and 45 +/- 1.2% (means +/- SEM, n=9), respectively. Patency after three months of implantation for group I was 100% (14/14), for group II 50% (7/14), and for group III 75% (6/8). In vitro functional responses of preserved arteries, after 3 months of implantation in group I were 58.5 +/- 10.6 mN (KCl), 36.5 +/- 5.8 mN (Phe), and 57.4 +/- 9.7% (Met), respectively. Functions in group II were 1.2 +/- 0.1 mN (KCl, 0.0 mN (Phe), and 0.0% (Met). Grafts in group III showed no function. Measurement of medial thickness showed significant thinning (P <0.05) in groups II and III. Patency and function of arterial allografts under a therapeutic dose of CsA were superior to grafts implanted under low-dose CsA or no immunosuppressive treatment.

Morphology and function of dog arterial grafts preserved in UW-solution*

OBJECTIVES To assess the function of arterial grafts after prolonged preservation in the University of Wisconsin solution (UW), in vitro and in vivo. METHODS Carotid arteries were harvested from dogs and stored for 1-21 days at 4 degrees C in UW (n = 10) or in PBS (0.9% NaCl, pH 7.4), (PBS) (n = 10). Slices were examined by lightmicroscopy (LM) and scanning electron microscopy (SEM). For viability testing, specimens were connected to an isometric force transducer (2 x n = 9). Contractile and relaxation responses were examined by adding phenylephrine (200 microM) and metacholine (200 microM), respectively. For in vivo studies (n = 41), 2.5cm carotid artery segments were implanted or orthotopically, as autografts and allografts, after 14 days of storage in UW or in PBS. Autologous veins were used as controls. After 28 days or 56 days, arteriography was performed and the grafts were excised for LM and SEM. RESULTS The arterial endothelial layer remained intact after up to 14 days of storage in UW. In PBS, the endothelium was lost after 3 days. The functional response after 14 days storage in UW was approximately 50% vs. 0% after 14 days in PBS. In the autografts, total patencies (28 days + 56 days) were 100% (8/8) and 63% (5/8) for UW and PBS stored grafts, respectively. In the allografts, the UW and PBS preserved grafts showed total patencies of 86% (12/14) and 83% (5/6), respectively. Microscopically, the allografts showed fibrotic degeneration. CONCLUSIONS Arteries are well preserved in UW up to 14 days of storage. Arterial autografts preserved in UW showed good patency and better integrity of the vessel wall after implantation, than grafts stored in PBS or allografts (without immunosuppressive therapy).

The prone position: using gravity for a clear view

Obtaining a clear view during laparoscopic surgery in the posterior abdominal cavity, on the abdominal backwall, or during colon surgery is time consuming and therefore one of the major objections to these procedures. In an experimental setting we positioned the animals in the prone position using the abdominal flanks to introduce the trocars. Our experience with this position is that a clear and unobstructed view of the abdominal back wall and the large intestines is obtained, facilitating laparoscopic procedures in these areas.

Effect of intracapsular hyperpressure on femoral head blood flow Laser Doppler flowmetry in dogs

Intracapsular hyperpressure in the hip joint of dogs affected femoral head blood flow, especially in the juvenile animals. Graphic recording of the laser Doppler signal curve using rapid sampling time demonstrated venous hip joint tamponade in both juvenile and adult dogs. Laser Doppler flowmetry seems to be a sensitive and reproducible method to demonstrate femoral-head blood-flow changes.

An improved model for tissue expansion and flap research in the rabbit

A pocket for tissue expander implantation in the rabbit is described at the level between the skin and the panniculus carnosus. The vascular anatomy of the undermined skin was studied with microangiography which showed a functional (sub)dermal plexus. Expanders were placed in seven rabbits and inflated daily over a period of 10 days. Blood flow in expanded skin, as measured with laser Doppler flowmetry, dropped with increasing inflation pressure. During the course of expansion, the intraluminal pressure returned to a baseline level within 24 hours after each inflation. It is concluded that an expander placed in the described layer in the rabbit causes considerable skin stretch and interferes with cutaneous blood supply and is therefore an improved model for tissue expansion in the human.

Homologous testis transplantation in dogs

Abstract There is growing interest in the possible use of homologous testis transplantation for the treatment of anorchia and male infertility. In order to test the surgical and immunological feasibility of this therapy, three series of experimental studies of homologous testis transplantation were carried out in dogs. In the first pilot study, four beagles from the same litter were transplanted using microsurgical techniques for end‐to‐end anastomosis of the testicular vessels and the vas deferens. These dogs received cyclosporin A (CyA) for 3 months after transplantation. The longest functional graft survival in this series was 163 days, strongly suggesting that long‐term survival of a homolo‐gously transplanted testis graft is possible. A second series of operations was performed on ten mongrel dogs. The same surgical technique was employed and the series was divided into three groups. Group 1 received CyA monotherapy, group 2 a combination of CyA and prednisolone, and group 3 received no immunosuppression. The average graft survival time in this series was 18 days, significantly less than the 71 days in the first series. The dogs in group 2, however, had graft survival times that were three times longer than those in the other two groups, suggesting that CyA in combination with prednisolone yields the best graft survival. In the third series, five littermates received a testis graft after castration. Immunosuppression was achieved by administration of CyA and prednisolone for 3 months. In three out of five animals, the graft survived until the immunosuppressive therapy was suspended. Histological biopsies of the graft 3 months after transplantation showed the same maturation of sperm cells as in the control testis of the same dog. The results of the last series suggest that long‐term survival of homologously transplanted testis grafts in dogs is, indeed, possible with the aid of CyA and prednisolone.