This work was supported by R01 HL163065 and W81XWH1810518. We extend our appreciation to the dedicated staff at the Animal Research Core. We also wish to express our gratitude to Carmen Arsuaga for her invaluable expertise and vigilant care throughout the study.

The study protocol was approved by the Institutional Animal Care and Use Committee of Nationwide Children&#39;s Hospital Abigail Wexner Research Institute (AR22-0004). All animals received humane care in compliance with the Guide for the Care and Use of Laboratory Animals, published by the National Institutes of Health.
1. Animal preparation
<ol>
	<li>Have a veterinary team evaluate the sheep 1 week prior to catheterization, including a physical exam and analysis of vital si...

3D Angiography for Venous Compliance Assessment in Sheep

<ol>
	<li>Hagler, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fate+of+the+Fontan+connection:+Mechanisms+of+stenosis+and+management.">Fate of the Fontan connection: Mechanisms of stenosis and management.</a> Congenit Heart Dis. 14 (4), 571-581 (2019).</li><li>Nezerati, R. M., Eifert, M. B., Dempsey, D. K., Cosgriff-Hernandez, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrospun+vascular+grafts+with+improved+compliance+matching+to+native+vessels.">Electrospun vascular grafts with improved compliance matching to native vessels.</a> J Biomed Mater Res B Appl Biomater. 103 (2), 313-323 (2015).</li><li>Bates, O., Semple, T., Krupickova, S., Bautisa-Rodriguez, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Case+report+of+a+Gore-Tex+TCPC+conduit+dissection+causing+severe+stenosis.">Case report of a Gore-Tex TCPC conduit dissection causing severe stenosis.</a> Eur Heart J Case Rep. 5 (11), 1-6 (2021).</li><li>Sathananthan, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+importance+of+Fontan+Circuit+thrombus+in+the+adult+population:+Significant+association+with+increased+risk+of+cardiovascular+events.">Clinical importance of Fontan Circuit thrombus in the adult population: Significant association with increased risk of cardiovascular events.</a> Can J Cardiol. 35 (12), 1807-1814 (2019).</li><li>Kumar, P., Bhatia, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Computed+tomography+in+the+evaluation+of+Fontan+Circulation.">Computed tomography in the evaluation of Fontan Circulation.</a> J Cardiovasc Imaging. 29 (2), 108-122 (2021).</li><li>Abbott, W. M., Megerman, J., Hasson, J. E., L'Italien, G., Warnock, D. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+compliance+mismatch+on+graft+patency.">Effect of compliance mismatch on graft patency.</a> J Vasc Surg. 5 (2), 376-382 (1987).</li><li>Weston, M. W., Rhee, K., Tarbell, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compliance+and+diameter+mismatch+affect+the+wall+shear+rate+distribution+near+an+end-to-end+anastomosis.">Compliance and diameter mismatch affect the wall shear rate distribution near an end-to-end anastomosis.</a> J Biomech. 29 (2), 187-198 (1996).</li><li>Ballyk, P. D., Walsh, C., Butany, J., Ojha, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compliance+mismatch+may+promote+graft-artery+intimal+hyperplasia+by+altering+suture-line+stress.">Compliance mismatch may promote graft-artery intimal hyperplasia by altering suture-line stress.</a> J Biomech. 31 (3), 229-237 (1997).</li><li>Lemson, M. S., Tordoir, J. H. M., Daemen, M. J. A. P., Kitslaar, P. J. E. H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intimal+hyperplasia+in+vascular+grafts.">Intimal hyperplasia in vascular grafts.</a> Eur J Vasc Endovasc Surg. 19 (4), 336-350 (2000).</li><li>Blum, K. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+engineered+vascular+grafts+transform+into+autologous+neovessels+capable+of+native+function+and+growth.">Tissue engineered vascular grafts transform into autologous neovessels capable of native function and growth.</a> Commun Med. 2, 3 (2022).</li><li>Turner, M. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+engineered+vascular+grafts+are+resistant+to+the+formation+of+dystrophic+calcification.">Tissue engineered vascular grafts are resistant to the formation of dystrophic calcification.</a> Nat Commun. 15, 2187 (2024).</li></ol>

Compliance and distensibility are key properties for blood vessel function, serving as indicators of potential complications and interventions. Precisely quantifying and comparing changes in these parameters is important to assess graft efficacy. Our in vivo method overcomes the limitations of ex vivo analysis and maintains comparable results. Comparing our in vivo data to the ex vivo data presented by Blum et al., both methods demonstrate marked differences between the synthetic graft...

Patients with critical cardiac anomalies require reconstructive surgery. Most reconstructive operations require the use of prosthetic materials, including vascular grafts. Potential conduits to bridge this space include synthetic or biologic materials. Initially, homografts were used as the Fontan conduit but have since been abandoned due to a high incidence of calcification and acute phase incidents1. Currently, synthetic vascular grafts derived from inorganic polymers are used. There remains a challenge that these grafts are less compliant than the native vessel into which they are implanted and have long-term complications, such as stenosis, occlusion, and calcification1,2,3,4,5.
The structure of synthetic vascular grafts lends itself to mechanical tensile strength, leading to their invariably lower compliance compared to native tissue2. Vascular compliance, which defines the vessel&#39;s change in volume over a change in pressure, serves as an indicator of a vessel&#39;s responsiveness to mechanical loads. The difference between the graft material and native vessel properties creates a compliance mismatch, which has been demonstrated to disrupt blood flow patterns, resulting in areas of recirculation and flow separation2,6,7,8,9. This phenomenon alters the shear stress on the endothelial wall and induces intimal hyperplasia2,7,8,9. Such responses can lead to graft-related complications, necessitating graft replacement or re-intervention6.
As vascular compliance assumes a key role in determining graft outcomes, the accurate measurement of this property is essential. The current gold standard for measuring vascular compliance is ex vivo tubular biaxial mechanical testing. This method involves excising a graft or vessel of interest, connecting it to latex tubes, and pressurizing it to assess circumferential stress-stretch behavior across various pressures. Compliance is determined by comparing the pressure with a measurement of the inner diameter10. However, ex vivo methods have some disadvantages. When evaluating the functionality of implanted grafts using the ex vivo method, sacrificing the animals and explanting the grafts are necessary, making it impossible to conduct prolonged examinations. Therefore, we have developed an in vivo compliance measurement protocol.
Our group focuses on developing tissue-engineered vascular grafts (TEVGs) for use in the Fontan surgery to ameliorate the congenital heart defect hypoplastic left heart syndrome (HLHS). Recent developments in the field of congenital heart surgery have improved postoperative outcomes, leading to longer life expectancies. This makes the long-term properties and success of the implanted vascular conduit increasingly crucial. Currently, no animal model of HLHS exists so we evaluate our grafts in an accelerated large animal inferior vena cava (IVC) interposition graft model. While this model does not attempt to create the flow of the Fontan circulation, it effectively recapitulates the unique hemodynamic conditions. Our recent use of this in vivo protocol demonstrated significant differences in graft compliance between our TEVG and conventional expanded polytetrafluoroethylene (PTFE) grafts11. As this previous study did not focus on methodology, we have conducted additional experiments detailing this novel in vivo method.
We implanted the synthetic graft currently serving as the standard of care, comprised of expanded polytetrafluoroethylene (PTFE), in Dorset sheep study animals and compared it to the native IVC in surgically na&#239;ve control animals. This protocol was performed on the PTFE group 5-7 years postimplantation of a PTFE conduit and unoperated control animals of varying ages. Thus, in subsequent sections describing the protocol and representative results, we will occasionally refer to the region of interest as, for example, the middle of the graft (midgraft) region of the IVC interposition graft.
This protocol allows us to analyze the in vivo compliance of the PTFE conduit, known to be non-compliant at a long-term time point, with the native vein. We chose to compare the clinical standard material, PTFE, with the native unoperated vein. We selected a long-term time point because the PTFE conduit is known to remain non-compliant and is prone to calcify, further reducing its compliance11. We opted to conduct all comparisons in vivo as systemic hemodynamic changes are accurately reflected in measurements obtained through in vivo methods. From this comparison, we found that this protocol is able to confirm the non-compliance of PTFE and obtain measurements of in vivo venous compliance in a safe and reproducible manner. This method has been successfully implemented in a published study to demonstrate statistically significant differences between PTFE conduits and tissue-engineered vascular grafts (TEVGs) in vivo11.
The overall goal of this protocol is to calculate compliance and distensibility of the thoracic IVC in an ovine large animal model using in vivo measurements from a survival procedure. To this end, we visualized and measured the changes in circumference and cross-sectional area of thoracic IVC to a fluid bolus. We simultaneously measured the intravascular change in pressure and used these measurements to calculate compliance and distensibility. Using 3D angiography imaging allows us multiple advantages, including the ability to adjust the view of the image post capture to ensure our measurements are taken from a cross-section of the vein, as well as allow us to measure multiple locations along the vessel. The three areas of interest in this study were the midgraft region, as well as the two adjacent anastomosis sites of the PTFE graft, and the comparable areas in the native IVC. By conducting experiments in vivo, there are advantages in evaluating the functionality of grafts within the actual flow of blood and surrounded by tissues and organs. The measurements obtained through this method are believed to reflect the actual functionality of the grafts in a living organism.
The protocol is divided into six main sections including preprocedure preparation of the sheep, catheterization, collection of baseline pre bolus data, collection of study data, animal recovery, and data analysis. In the animal preparation section, we discuss sedation, initiating anesthesia, and the placement of monitoring equipment used during the catheterization procedure. In the second section, we explain the process of placing the two catheter sheaths needed for data acquisition. For this protocol, both sheaths are placed in the right internal jugular vein (IJV) to allow two multitrack catheters to be introduced into the vessel. One will be positioned in the region of interest to record the change in pressure, and the other will be placed lower in the vein for contrast injection. Once the catheters are placed, a baseline pre bolus 3D angiograph is taken for comparison. Study data collection begins with preparing the saline bolus in a pressurized bag system for administration, providing the saline bolus with recording intravascular pressures, and taking the post bolus 3D angiograph. We then describe the process to facilitate the recovery of the sheep after the protocol. Lastly, we discuss the method to obtain the proper images and cross-sectional measurements for analysis and statistical comparison.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.035&#34; x 260 cm Rosen Curved Wire Guide</td>
			<td>Cook Medical</td>
			<td>G01253</td>
			<td>Guide for holding placement swapping caths (Multi-track, IVUS, etc)</td>
		</tr>
		<tr>
			<td>0.035&#34;x 150 cm Glidewire</td>
			<td>Terumo</td>
			<td>GR3507</td>
			<td>Guide for JR cath</td>
		</tr>
		<tr>
			<td>0.9% Sodium Chloride Saline</td>
			<td>Baxter Healthcare Corporation</td>
			<td>NCH pharmacy</td>
			<td>For diluting norepinpherine, pressure monitoring</td>
		</tr>
		<tr>
			<td>10.0 Endotracheal tube</td>
			<td>Coviden</td>
			<td>86117</td>
			<td>To secure airway</td>
		</tr>
		<tr>
			<td>16 G IV catheter</td>
			<td>BD</td>
			<td>382259</td>
			<td>To administer fluids and anesthetic drugs</td>
		</tr>
		<tr>
			<td>22 G IV catheter</td>
			<td>BD</td>
			<td>381423</td>
			<td>For invasive blood pressure</td>
		</tr>
		<tr>
			<td>5Fr x .35&#34; JR2.5</td>
			<td>Cook Medical&#160;</td>
			<td>G05035</td>
			<td>Guide for rosen wire</td>
		</tr>
		<tr>
			<td>70% isopropyl alcohol</td>
			<td>Aspen Vet</td>
			<td>11795782</td>
			<td>Topical cleaning solution</td>
		</tr>
		<tr>
			<td>7Fr x 100 cm Multi-track</td>
			<td>B. Braun</td>
			<td>615001</td>
			<td>Collecting pressure, Administering contrast to specific intravascular location</td>
		</tr>
		<tr>
			<td>9Fr Introducer sheath</td>
			<td>Terumo</td>
			<td>RSS901</td>
			<td>Access catheter through skin into vessel for wires to pass through</td>
		</tr>
		<tr>
			<td>ACT cartridge</td>
			<td>Abbot Diagnostics</td>
			<td>03P86-25</td>
			<td>Activated Clotting Time</td>
		</tr>
		<tr>
			<td>Angiographic syringe w/ filling spike</td>
			<td>Guerbet</td>
			<td>900103S</td>
			<td>For contrast injector</td>
		</tr>
		<tr>
			<td>Bag decanter</td>
			<td>Advance Medical Designs, LLC</td>
			<td>10-102</td>
			<td>Punctures saline bag to pour and fill sterile bowl with saline</td>
		</tr>
		<tr>
			<td>Butorphanol</td>
			<td>Zoetis</td>
			<td>NCH pharmacy</td>
			<td>Sedation drug: Concentration 10 mg/mL, Dosage 0.1 mg/kg</td>
		</tr>
		<tr>
			<td>Cath Research Pack</td>
			<td>Cardinal Health</td>
			<td>SAN33RTCH6</td>
			<td>Cath pack with misc. supplies</td>
		</tr>
		<tr>
			<td>Cetacaine</td>
			<td>Cetylite</td>
			<td>220</td>
			<td>Topical anesthetic spray</td>
		</tr>
		<tr>
			<td>Chloraprep</td>
			<td>BD</td>
			<td>930825</td>
			<td>Topical cleaning solution</td>
		</tr>
		<tr>
			<td>Chlorhexidine 2% solution</td>
			<td>Vedco INC</td>
			<td>VINV-CLOR-SOLN</td>
			<td>Topical cleaning solution</td>
		</tr>
		<tr>
			<td>Conform stretch bandage</td>
			<td>Coviden</td>
			<td>2232</td>
			<td>Neck wrap to prevent bleeding</td>
		</tr>
		<tr>
			<td>Connection tubing</td>
			<td>Deroyal</td>
			<td>77-301713</td>
			<td>Connects t-port to fluid/drug lines</td>
		</tr>
		<tr>
			<td>Diazepam</td>
			<td>Hospira Pharmaceuticals</td>
			<td>NCH pharmacy</td>
			<td>Sedation drug: Concentration 5 mg/mL, Dosage 0.5 mg/kg</td>
		</tr>
		<tr>
			<td>EKG monitoring dots</td>
			<td>3M</td>
			<td>2570</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluid administration set</td>
			<td>Alaris</td>
			<td>2420-0007</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluid warming set</td>
			<td>Carefusion</td>
			<td>50056</td>
			<td></td>
		</tr>
		<tr>
			<td>Hemcon Patch</td>
			<td>Tricol Biomedical</td>
			<td>1102</td>
			<td>Patch for hemostasis</td>
		</tr>
		<tr>
			<td>Heparin</td>
			<td>Hospira, Inc</td>
			<td>NCH pharmacy</td>
			<td>Angicoagulant: 1,000 USP units/mL</td>
		</tr>
		<tr>
			<td>Infinix-i INFX-8000C</td>
			<td>Toshiba Medical Systems</td>
			<td>2B308-124EN*E</td>
			<td>Interventional angiography system</td>
		</tr>
		<tr>
			<td>Invasive pressure transducer</td>
			<td>Medline</td>
			<td>23DBB538</td>
			<td>For invasive blood pressure</td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>Baxter Healthcare Corporation</td>
			<td>NCH pharmacy</td>
			<td>Anesthetic used in prep room</td>
		</tr>
		<tr>
			<td>Ketamine</td>
			<td>Hospira Pharmaceuticals</td>
			<td>NCH pharmacy</td>
			<td>Sedation drug: Concentration 100 mg/mL, Dosage 4 mg/kg</td>
		</tr>
		<tr>
			<td>Lubricating Jelly</td>
			<td>MedLine</td>
			<td>MDS0322273Z</td>
			<td>ET tube lubricant</td>
		</tr>
		<tr>
			<td>Micropuncture Introducer Set</td>
			<td>Cook Medical</td>
			<td>G47945</td>
			<td>Access through skin into vessel</td>
		</tr>
		<tr>
			<td>Needle &#38; syringes</td>
			<td>Cardinal Health</td>
			<td>309604</td>
			<td>For sedation</td>
		</tr>
		<tr>
			<td>Norepinpherine Bitartrate Injection, USP</td>
			<td>Baxter Healthcare Corporation</td>
			<td>NCH pharmacy</td>
			<td>1 mg/mL</td>
		</tr>
		<tr>
			<td>Optiray 320</td>
			<td>Liebel-Flarsheim Company, LLC</td>
			<td>NCH pharmacy</td>
			<td>Contrast&#160;</td>
		</tr>
		<tr>
			<td>Optixcare</td>
			<td>Aventix</td>
			<td>OPX-4252</td>
			<td>Corneal lubricant</td>
		</tr>
		<tr>
			<td>OsiriX MD</td>
			<td>Pixmeo SARL</td>
			<td>-</td>
			<td>DICOM Viewer and Analysis software</td>
		</tr>
		<tr>
			<td>Pressure infusor bag</td>
			<td>Carefusion</td>
			<td>64-10029</td>
			<td>To maintain invasive blood pressure</td>
		</tr>
		<tr>
			<td>Propofol</td>
			<td>Fresenius Kabi</td>
			<td>NCH pharmacy</td>
			<td>Anesthetic drug: Concentration 10 mg/mL, Dosage 20-45 mg&#183;kg-1&#183;h-1</td>
		</tr>
		<tr>
			<td>Silk suture 3-0</td>
			<td>Ethicon</td>
			<td>C013D</td>
			<td>To secure IV catheter&#160;</td>
		</tr>
		<tr>
			<td>SoftCarry Stretcher</td>
			<td>Four Flags Over Aspen</td>
			<td>SSTR-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Stomach tube</td>
			<td>Jorgensen Lab, INC</td>
			<td>J0348R</td>
			<td>To release gastric juices and gas and prevent bloat</td>
		</tr>
		<tr>
			<td>T-port</td>
			<td>Medline</td>
			<td>DYNDTN0001</td>
			<td>Connects to IV catheter</td>
		</tr>
		<tr>
			<td>Urine drainage bag</td>
			<td>Coviden</td>
			<td>3512</td>
			<td>Connects to stomach tube to collect gastric juices</td>
		</tr>
		<tr>
			<td>Warming blanket</td>
			<td>Jorgensen Lab, INC</td>
			<td>J1034B</td>
			<td></td>
		</tr>
	</tbody>
</table>

quantifying inferior vena cava compliance and distensibility in an in vivo ovine model using 3d angiography

Synthetic vascular grafts overcome some challenges of allografts, autografts, and xenografts but are often more rigid and less compliant than the native vessel into which they are implanted. Compliance matching with the native vessel is emerging as a key property for graft success. The current gold standard for assessing vessel compliance involves the vessel's excision and ex vivo biaxial mechanical testing. We developed an in vivo method to assess venous compliance and distensibility that better reflects natural physiology and takes into consideration the impact of a pressure change caused by flowing blood and by any morphologic changes present. 
This method is designed as a survival procedure, facilitating longitudinal studies while potentially reducing the need for animal use. Our method involves injecting a 20 mL/kg saline bolus into the venous vasculature, followed by the acquisition of pre and post bolus 3D angiograms to observe alterations induced by the bolus, concurrently with intravascular pressure measurements in target regions. We are then able to measure the circumference and the cross-sectional area of the vessel pre and post bolus. 
With these data and the intravascular pressure, we are able to calculate the compliance and distensibility with specific equations. This method was used to compare the inferior vena cava's compliance and distensibility in native unoperated sheep to the conduit of sheep implanted with a long-term expanded polytetrafluorethylene (PTFE) graft. The native vessel was found to be more compliant and distensible than the PTFE graft at all measured locations. We conclude that this method safely provides in vivo measurements of vein compliance and distensibility.

Author Spotlight: Improved Imaging for Neovascular Development in Congenital Heart Disease Research

Quantifying Inferior Vena Cava Compliance and Distensibility in an In Vivo Ovine Model Using 3D Angiography

We aim to improve long-term outcomes for congenital-heart-disease patients using a regenerative medicine approach. Our tissue-engineered vascular graft develops into a neo vessel comprised of the patient's own cells. Our goal is to make comparisons between our graft, the native vein, and the clinical standard polytetrafluoroethylene or PTFE.We have established that our neo vessel displays growth capacity and that it approaches native vessel functionality. Using this method, we've also recently demonstrated that the neo vessel retains compliance and distensibility at a long-term time point, and is resistant to the formation of dystrophic calcification. Using 3D angiography allows us to image the entire path of the thoracic inferior vena cava in our ovine large-animal model.In addition to allowing us to view the morphology of the vessel, it also allows for post-capture orientation adjustments to ensure we're obtaining measurements from a true cross-section. Our in-vivo method allows us to determine the capacity for vessel compliance and distensibility in its native context. Additionally, it allows us to take longitudinal measurements of the same study animal, which is necessary to track changes in neo-vessel development and remodeling.

We have successfully performed this procedure with over 25 sheep. Importantly, there were no instances of morbidity and mortality related to this procedure. All the sheep exhibited uncomplicated recoveries. These representative results were taken from three sheep implanted with PTFE grafts and three unoperated native sheep. Figure 5 provides the intravascular pressure measurements taken from both groups of study animals during the protocol. These values are important for the compliance and d...

Read this Scientific Article Protocol about Author Spotlight: Improved Imaging for Neovascular Development in Congenital Heart Disease Research at JoVE.com

This protocol allows for the in vivo quantification of venous compliance and distensibility using catheterization and 3D angiography as a survival procedure allowing for a variety of potential applications.

Synthetic vascular grafts overcome some challenges of allografts, autografts, and xenografts but are often more rigid and less compliant than the native ...

quantifying-inferior-vena-cava-compliance-distensibility-an-vivo