Collar Technique Research Articles

Temporal and spatial pattern of embolism induced by pressure collar techniques in twigs of Picea abies

The pressure collar technique enables the induction of embolism in plant xylem. This artificial cavitation is based on air seeding processes which occur when specific pressure gradients between the air and water phase of the xylem are exceeded. Standard pressure collars and a new point injection technique, which builds up a local potential gradient, were used to study the time and spatial pattern of this process. On twigs of Norway spruce (Picea abies), the cross-sectional and axial pattern, and the time-course of embolism formation were analysed via conductivity and ultrasonic measurements as well as staining experiments. Furthermore, the release of air from the twig surface was studied by immersing twig sections in water. In cross-sections, embolized areas induced by the point injection technique were smaller compared with the standard collar and restricted to a circle sector. Embolism propagated from the pressure collar towards the nearest distal and proximal nodes but not further. A release of air was also observed predominantly at the internode attached to the pressure collar. Embolism rates increased within minutes and reached approximately 80% loss of conductivity after 10 min treatment with the standard collar. The size of air entry points and embolism rates correlated significantly. Embolism formation in wood therefore depends not only on vulnerability thresholds but also on the extent of air-water interfaces within the xylem and on the time of exposure to pressure gradients. These aspects and the propagation of pressure within samples are crucial for pressure collar experiments. In addition, wood architecture influences the extent and pattern of embolism caused by air seeding processes.

A Favorable Experience With Rotational Flap Techniques for Fashioning the Firlit Preputial Collar

The Firlit collar technique for the approximation of the divergent inner leaf of the prepuce in operations to repair hypospadias and its variants are generally easily conceptualized and executed. However, in some cases the divergence is so great at the level of the corona that a simple approximation cannot be performed. Therefore, 2 techniques are described that facilitate completion of the Firlit collar in these instances. A total of 101 boys 6 to 101 months old (mean 18.9) underwent formation of a Firlit collar between July 2003 and July 2004. Among the patients 69 had coronal or glanular hypospadias, 17 had a penile or a more proximal meatus and 15 had only a hooded prepuce. In 5 patients the divergence of the inner leaf of the prepuce precluded a simple midline approximation of the 2 halves. Two techniques of forming rotational flaps of the inner leaf were used to complete construction of the Firlit preputial collar. The techniques were used as described in 5 repairs, with excellent cosmetic results. Two rotational flap techniques for the repair of the widely divergent inner leaf of the prepuce associated with hypospadias and its variants are described and recommended for their simplicity and uniformly good results.

Adenovirus-Mediated Gene Transfer of Placental Growth Factor to Perivascular Tissue Induces Angiogenesis via Upregulation of the Expression of Endogenous Vascular Endothelial Growth Factor-A

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family that binds specifically to VEGF receptor (VEGFR)-1. However, the mechanism of PlGF- and VEGFR-1-mediated angiogenesis has remained unclear and some in vitro studies suggest that VEGF-A/VEGFR-2 signaling may also play a role in PlGF-mediated angiogenesis. To clarify these issues we evaluated angiogenic responses in a well-characterized periadventitial angiogenesis model using adenovirus-mediated PlGF-2 (AdvPlGF-2) gene transfer. We also investigated the roles of VEGFR-1 and VEGFR-2 in PlGF-2-mediated angiogenesis. Using a periadventitial collar technique, AdvPlGF-2 (1 x 10(9) plaque-forming units/ml) was transferred to the adventitia of New Zealand White rabbits alone or together with adenoviruses encoding soluble VEGFR-1 (sVEGFR-1) or soluble VEGFR-2 (sVEGFR-2). Adenoviruses encoding LacZ were used as controls. All animals were killed 7 days after gene transfer. Increased neo-vessel formation, upregulation of endogenous VEGF-A expression, and a significant inflammatory response were seen in AdvPlGF-2-transduced arteries. The neo-vessels were large and well perfused. sVEGFR-1 and sVEGFR-2 suppressed the angiogenic response of PlGF-2 by 80 and 71.7%, respectively. We conclude that adenovirus-mediated PlGF-2 gene transfer to vascular tissue increases endogenous VEGF-A expression and produces significant angiogenesis. Both sVEGFR-1 and sVEGFR-2 can inhibit PlGF-2-mediated angiogenesis. PlGF-2 is a potentially useful candidate for the induction of therapeutic angiogenesis in vivo.

Periadventitial angiopoietin-1 gene transfer induces angiogenesis in rabbit carotid arteries

This study was performed to evaluate angiogenic responses of angiopoietin-1 (Ang1) in vivo after adenovirus-mediated gene transfer in the periadventitial space of the rabbit carotid arteries using a collar technique. Adenoviruses encoding LacZ and vascular endothelial growth factor (VEGF) receptor-1-Ig fusion protein (VEGF-R1-Ig) adenoviruses were used as controls. Increased neovessel formation was seen in adventitia of the Ang1 transduced arteries 7 days after the gene transfer. Neovessels in the Ang1 transduced arteries were large in size and well perfused. Ang1 binds to Tie2 (tyrosine kinase with immunoglobulin and epidermal growth factor homology domain) receptors, which were expressed in the endothelium of the neovessels. When VEGF-R1-Ig was used with Ang1, it resulted in a decrease in the number of neovessels, which implies that VEGF-A or some other VEGF-R1 ligand(s) play a crucial role in angiogenesis occurring in response to Ang1. There were no significant differences in the total number of capillaries in the adventitia of the VEGF-R1-Ig transduced arteries as compared to LacZ controls. Neointima formation was not increased in the Ang1 transduced arteries as compared to the controls. We conclude that in the periadventitial space Ang1 shows angiogenic activity and is a potentially useful factor for the induction of therapeutic vascular growth in vivo.

Validation of a GPS Collar Technique in Temperate Forests in Osaka

Validation of a GPS Collar Technique in Temperate Forests in Osaka

Carotid baroreflex control of leg vasculature in exercising and non-exercising skeletal muscle in humans.

Carotid baroreflex (CBR) function was examined in five men and three women (25 +/- 1 years) using the variable-pressure neck collar technique at rest and during dynamic, one-legged knee extension exercise at 7 W and 25 W. The CBR exhibited control of leg vascular conductance (LVC) at rest and during exercise in both an exercising leg (EL) and a non-exercising leg (NEL) across a wide range of pressures from +40 Torr neck pressure (NP) to -80 Torr neck suction (NS). Specifically, increases in LVC (% change) in response to NS were no different across -20 to -80 Torr in either EL or NEL compared to rest, P > 0.05. However, CBR-mediated decreases in percentage LVC in response to NP were attenuated in EL at both 7 W (16 +/- 1%) and 25 W (12 +/- 1%) compared to rest (40 +/- 3%; P < 0.05) as well as compared to responses in the NEL (36 +/- 6% at 7 W and 36 +/- 7% at 25 W; P < 0.05). This decrease in vascular responsiveness in EL was associated with a reduction in the gain of the percentage muscle sympathetic nerve activity (%MSNA)-%LVC relationship compared to rest (P < 0.05). Collectively, these data indicate that, despite a clear attenuation of the vascular response to MSNA in the exercising leg, CBR-mediated changes in mean arterial pressure were no different between rest and exercise.

Angiogenic responses of vascular endothelial growth factors in periadventitial tissue.

Recent discovery of new members of the vascular endothelial growth factor (VEGF) family has generated much interest as to which members may be best suited for therapeutic angiogenesis in various tissues. In this study we evaluated angiogenic responses of the different members of the VEGF family in vivo using adenoviral gene transfer. Adenoviruses (1 x 10(9) plaque-forming units [pfu]) encoding for VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-C(deltaNdeltaC) and VEGF-D(deltaNdeltaC) (deltaNdeltaC are proteolytically cleaved forms) were transferred locally to the periadventitial space of the rabbit carotid arteries using a collar technique that allows efficient local transfection of the periadventitial tissue. Expression of the transfected VEGFs was confirmed by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR). Seven days after the gene transfer maximum neovessel formation was observed in VEGF-A-, VEGF-D-, and VEGF-D(deltaNdeltaC)-transfected arteries. VEGF-C(deltaNdeltaC) also showed angiogenic activity whereas VEGF-B was not effective in inducing angiogenesis. Pericytes were detected around the neovessels, which also frequently showed the presence of intraluminal erythrocytes. Infiltration of inflammatory cells in response to VEGF-D and VEGF-D(deltaNdeltaC) was less prominent than that caused by other VEGFs. In line with the absence of lymphatics in the normal carotid arteries no significant evidence of lymphatic vessel formation was seen in response to any of the studied VEGFs in the periadventitial space. The results help to define possibilities for local angiogenic therapy around blood vessels and support the concept that angiogenic effects may be tissue-specific and depend both on the growth factor ligands and the target tissues. It is concluded that VEGF-A, VEGF-D, and VEGF-D(deltaNdeltaC) are the best candidates for therapeutic angiogenesis when delivered around large arteries.

Xylem embolization by the pressure collar in Salix viminalis L.: sites for embolization and ultrasound acoustic emission

ABSTRACT Pressurized air (3.5 MPa) produced massive embolization and loss of hydraulic conductivity in detached willow twigs (Salix viminalis L.) enclosed in a pressure collar. A state of tension in the xylem water column was not a necessary precondition for this embolization. Ultrasound acoustic emissions on the distal side and close to the collar were recorded only when air-saturated water was leaving the collar, whether moved by transpiration or by an overpressure applied to a reservoir at the base of the twig. Water released from embolized xylem elements increased the water potential of the leaves. The results show that air entry into xylem elements inside the pressure collar is the main mechanism responsible for the loss of hydraulic conductivity with the pressure collar technique, and that ultrasound signals originating within the collar are not sensed on the outside.

Operative positioning for patients undergoing repair of craniosynostosis.

A further modification of our operative positioning protocol is presented, with several novel approaches to positioning that give only slightly less exposure than that obtained with the modified prone position, but that enable the entire cranial vault remodeling to be done in one operation. The addition of two techniques has obviated both the need to use the modified prone position (except in certain difficult cases) in recent years and the need to get preoperative cervical spine film evaluation. Two new operative positioning techniques that enable a large calvarial exposure are described: one (the gel-filled collar technique) focuses on the more anterior portion of the cranial vault, and the other (the angled horseshoe technique) focuses on the posterior portion; both provide an extensive exposure of the opposite portion of the calvarium.