Characterization of main pulmonary artery and valve annulus region of piglets using echocardiography, uniaxial tensile testing, and a novel non-destructive technique

Figures

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  FIGURE 1. Overview of testing regions of interest and applied tissue testing techniques. (A) Tissue samples were sourced from the pulmonary artery (PA) and pulmonary valve (PV) annulus region. (B) The radial testing system applied stress to the intact cardiovascular structure using a fluid-filled balloon catheter placed inside the heart. Data was collected using a pressure sensor connected to the balloon catheter system and image analysis of diameter changes. (C) The uniaxial testing system applied stress to an isolated circumferential tissue sample at a constant extension rate. Data was collected using force gauge readings and associated displacement measurements.

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  FIGURE 2. Measurements of PA and PV diameters were taken in situ using echocardiogram, and calculated ex vivo from the tissue sample circumference. (A) The in vivo measurements of the PA and PV were measured using a cross-sectional image within the echocardiogram software. A representative image is shown with PA diameter measurements. (B) PA and (C) PV diameter measurements for Yucatan (YU) and Yorkshire (YO) populations as a function of weight.

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  FIGURE 3. Compiled stress vs. strain curves for both radial and uniaxial tensile testing methods for the (A) Yucatan pulmonary artery (PA), (B) Yucatan pulmonary valve (PV) region, and (C) Yorkshire PA tissue samples.

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  FIGURE 4. Young’s Modulus for elastic and fibrous regimes. A comparison of Young’s Modulus values determined by the radial and uniaxial testing methods for (A) the pulmonary artery of both Yucatan and Yorkshire piglets, and (B) the pulmonary valve annulus region of Yucatan piglets. There was no significant difference in Young’s Modulus measurements between testing methods or breeds within a given regime. The Young’s Modulus of the fibrous regime was significantly higher compared to its corresponding elastic regime (* indicates p < 0.0005; ** indicates p < 0.0001).

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  FIGURE 5. Bland-Altman agreement analysis between the radial and uniaxial methods for determining elastic modulus. The solid middle line indicates the bias and the bounding dashed lines indicate the limits of agreement (± 1.96 SD). Data included are YU PA, YU PV, YO PA elastic modulus in the elastic and fibrous regimes (N = 30). Two outliers are noted by dashed circles. E(U) – E(R) = the difference in Young’s modulus values between the uniaxial and radial testing methods, and Avg E = the averaged Young’s modulus values for the two methods for a given stress.

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  FIGURE 6. Young’s modulus vs. stress for radial and uniaxial testing methods. Graphs are shown for (A) Yucatan piglet pulmonary artery (PA), (B) Yucatan piglet pulmonary valve (PV) region, and (C) Yorkshire pulmonary artery (PA). There is no significant difference in Young’s modulus measurements for a given stress between the two methods.

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  FIGURE 7. Juvenile porcine pulmonary artery (PA) stress response curve compared with pediatric relevant data sets. The strain averaged Yucatan PA data from the uniaxial testing method (N = 4) is presented alongside 8 month old pediatric (N = 1) and 3 year old ovine (N = 4) stress response curves previously presented by Cabrera et al. (28). Stress response data from Cabrera et al. was estimated from the reported secant modulus averages for the respective species.