Collagen to Elastin Ratio in Functionally Discreet Human Cadaver Vascualture Predicts Burst Pressure of Arteries Sealed with a Bi-Polar Sealing Device

Kimberly Martin, BS, Cassandra Latimer, MS, Jaime Kean, Phd. Covidien Energy Based Devices

Introduction
The LigaSureTM technology utilizes a combination of heat generated via bi-polar radiofrequency energy and precise jaw pressure to denature the collagen and elastin in blood vessels and tissue. These proteins, along with other constituents in the vessel or tissue, re-anneal under precise pressure to form an amalgam that is in effect an autologous clip or staple. The LigaSureTM instruments are powered by the ForceTriadTM generator which uses a novel, closed loop energy delivery algorithm to achieve consistent and reliable tissue fusion.

Porcine renal arteries are often used as the tissue model for testing bi-polar vessel sealing devices due to logistics and availability. In order to assess the clinical relevance of this arterial model a pre-clinical trial was performed in conjunction with Carolinas Medical Center (Sindram et al. Surgical Endoscopy 2010) exploring the impact of collagen and elastin content on the burst pressure of sealed, functionally discreet arteries. This study suggested that the ratio of collagen to elastin was a more reliable predictor of burst pressure compared to arterial diameter or any other single variable analyzed.

To further explore the utility of porcine renal arteries as a model for human vasculature, we examined the correlation between collagen and elastin content and burst pressure in porcine arteries and functionally analogous human cadaver arteries.

Methods
One day old unfrozen cadavers were utilized for the study. The relevant vasculature was dissected and exposed, and the exposed vessels were sealed and divided in situ with LigaSure™ Atlas controlling for artery diameter. Artery diameters were measured in situ with digital calipers and subsequently sealed and divided using the LigaSureTM Atlas. Sealed artery sections were excised and the side of the seal proximal to the aorta was subjected to burst pressure testing as previously described. The seal distal to the aorta was kept intact for histological and morphologic analysis. Tissue samples from the burst portion of the vessels were used for biochemical analysis. Total collagen was determined from tissue by quantifying hydroxyproline content based upon the method previously described by Edwards and O’Brien. Total elastin content was determined using a commercially available kit (Fastin Kit,Biocolor Ltd.,Belfast, UK) as per the manufacturer’s instructions.
Sealed vessels were stained with H&E and modified trichrome. The slides were evaluated by an independent pathologist.

Results and Conclusions
There is a significant correlation between the ratio of collagen to elastin and burst pressure in human arteries. The collagen to elastin ratio and burst pressure in porcine renal arteries differ significantly from clinically relevant, commonly sealed human vessels such as the inferior mesenteric artery, however the burst pressure in cadaveric arteries remains supraphysiologic.