Aims: 

The interaction between smooth muscle and collagen largely determine the dynamic stress strain characteristics (E_dyn) of the artery wall. The purpose of this investigation was to determine the effects of increases in WSS (which causes smooth muscle relaxation) on E_dyn. Methods:

Experiments were carried out in 4 female anaesthetized pigs (24-31kg) (induction pentobarbitone 30mg/ kg i.v., maintenance 6mg/kg/h). The iliac artery and vein were connected by a shunt with a variable resistance which allowed blood flow and therefore WSS to be regulated. Stepwise increases in WSS were obtained without causing significant changes in MAP. E_dyn was calculated from diameter and pressure throughout a minimum of 5 cardiac cycles.

Results: 

Increases in WSS caused a significant increases in diameter from 3.663 ± 0.215mm to 4.488 ± 0.163mm (mean±sem. P < 0.05) and a corresponding fractional increase in diameter (fD) (range 1 – 1.5) with no significant change in MAP, 108 ± 2mmHg to 106 ± 1mmHg (mean±sem). The average value of E_dyn per cardiac cycle at baseline (fD= 1) was 2.17 ± 0.10.10³kPa and increased to a maximum of 9.23 ± 1.0.10³kPa when fD was 1.5. The relationship between E_dyn and fD is curvilinear (E_dyn = tan [3.43(fD-1.08)]+2.3) and remains relatively constant until fD exceeds 1.3.

Conclusion: 

These findings are consistent with a model of an arterial wall in which collagen is recruited both by passive stretch, in response to an increase in wall tension, and by a contraction of smooth muscle. This confirms that in a conduit artery, during WSS induced dilatation, the interaction between smooth muscle and collagen operates so as to maintain E_dyn relatively constant.