Remodeling of the zero-stress state of femoral arteries in response to flow overload

Abstract

The goal of this study is to quantitatively describe the remodeling of the zero-stress state of the femoral artery in flow overload. Increased blood flow, approximately as a unit step change, was imposed on the femoral artery by making an arteriovenous (a-v) fistula with the epigastric vein. The a-v fistula was created in the right leg of 36 rats, which were divided equally into six groups (2 days and 1, 2, 4, 8, and 12 wk after the fistula). The vessels in the left leg were used as controls without operative trauma. The in vivo blood pressure, flow, and femoral outer diameter and the in vitro zero-stress state geometry were measured. The in vivo shear rate at the endothelial surface increased approximately as a step function by approximately 83%, after 2 days, compared with the control artery. The arterial luminal and wall area significantly increased postsurgically from 0.15 +/- 0.02 and 0.22 +/- 0.02 mm(2) to 0.28 +/- 0.04 and 0.31 +/- 0.05 mm(2), respectively, after 12 wk. The wall thickness did not change significantly over time (P > 0.1). The opening angle decreased to 82 +/- 4.2 degrees postsurgically when compared with controls (102 +/- 4.4) after 12 wk and correlated linearly with the thickness-to-radius ratio. Histological analysis revealed vascular smooth muscle cell growth. The remodeling data are expressed mathematically in terms of indicial functions, i.e., change of a particular feature of a blood vessel in response to a unit step change of blood flow. The indicial function approach provides a quantitative description of the remodeling process in the blood vessel wall.

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“…4). These findings are in agreement with our previous longitudinal hypertension and flow-overload studies (5,39). In both models, strain reached its peak sooner and normalized faster than mean wall stress.…”

“…Consequently, the vessel sector (in the zero-stress state) shows an outward bend and hence an increase in the opening angle. Conversely, Lu et al (39) showed that flow-overload induces growth of adventitia that exceeds that of intima which is consistent with our current findings in the flow-overload model of RCA (Table 2). Hence, the vessel sector bends inward and decreases the opening angle as reported in this study.…”

“…The increase in microstructural content did not significantly affect the vessel wall thickness (Table 1), suggesting a nonuniform growth. A prevailing growth in the adventitial layer concurrently with an unchanging wall thickness is consistent with previous flow-overload studies (39). From Fig.…”

“…The remodeling of blood vessels in response to flow-overload obeys the constant WSS hypothesis (23,39). This principle implies that the volumetric flow rate is proportional to the cube of the vessel radius assuming a laminar, incompressible, Newtonian flow through a rigid cylindrical vessel (24).…”

“…Studies have demonstrated that a sudden increase in blood flow initiates an enlargement of the arterial lumen that progresses for months as the WSS tends to a homeostatic or normal level (23,25). A gradual increase in blood flow has been reported by several groups to result in outward hypertrophic remodeling of resistance (4,41,44,45,47) and conductive arteries (25,36,39). The flow-induced remodeling may be an attempt to maintain mechanical homeostasis (24,25).…”