Linked opening angle and histological and mechanical aspects of the proximal pulmonary arteries of healthy and pulmonary hypertensive rats and calves

Abstract

Understanding how arterial remodeling changes the mechanical behavior of pulmonary arteries (PAs) is important to the evaluation of pulmonary vascular function. Early and current efforts have focused on the arteries' histological changes, their mechanical properties under in vitro mechanical testing, and their zero-stress and no-load states. However, the linkage between the histology and mechanical behavior is still not well understood. To explore this linkage, we investigated the geometry, residual stretch, and histology of proximal PAs in both adult rat and neonatal calf hypoxic models of pulmonary hypertension (PH), compared their changes due to chronic hypoxia across species, and proposed a two-layer mechanical model of artery to relate the opening angle to the stiffness ratio of the PA outer to inner layer. We found that the proximal PA remodeling in calves was quite different from that in rats. In rats, the arterial wall thickness, inner diameter, and outer layer thickness fraction all increased dramatically in PH and the opening angle decreased significantly, whereas in calves, only the arterial wall thickness increased in PH. The proposed model predicted that the stiffness ratio of the calf proximal PAs changed very little from control to hypertensive group, while the decrease of opening angle in rat proximal PAs in response to chronic hypoxia was approximately linear to the increase of the stiffness ratio. We conclude that the arterial remodeling in rat and calf proximal PAs is different and the change of opening angle can be linked to the change of the arterial histological structure and mechanics.

Stretch calculated from grip distance accurately approximates mid-specimen stretch in large elastic arteries in uniaxial tensile tests

“…Many uniaxial test studies use the grip-to-grip distance before and during loading for the stretch calculation (Bulter et al, 1984; Lammers et al, 2008; Tian et al, 2011). Conversely, some studies mark regions of the specimen with visible markers (e.g., ink) prior to testing and obtain the stretch at the mid-section of the specimen by tracking the distances between these markers during the test (Bulter et al, 1984; Holzapfel et al, 2004; Holzapfel 2006; Woo et al, 1983; Zernicke et al, 1984).…”

Pulmonary artery relative area change is inversely related to ex vivo measured arterial elastic modulus in the canine model of acute pulmonary embolization

“…However, RAC is actually a site-specific measure of proximal PAs and therefore should indicate the local properties. The proximal PAs have been shown to remodel in animal models of PH (Huang et al, 2001; Kobs et al, 2005; Lammers et al, 2008; Ooi et al, 2010; Tian et al, 2011; Wang et al, 2013), and the elastic modulus of proximal PAs have been speculated to be useful for clinical prognostics (Hunter et al, 2010). However, no studies have sought this correlation in an adult model of PH.…”

“…Next, a short ring (~3 mm long) was obtained from each PA (MPA, LPA and RPA) and its cross-section was photographed. The ring was then cut once in the radial direction to obtain the stress-free or reference state and photographed again (Tian et al, 2011). …”

Analysis of arterial wall remodeling in hypertension based on lamellar modeling

“…The most popular method to evaluate residual stresses in arterial walls is based on openingangle measurements [44,45]. In this way, a ring of arterial tissue is radially cut and the opened-angle of the resulting circular segment is a measure of residual stresses.…”