Mechanical buckling of artery under pulsatile pressure

Abstract

Tortuosity that often occurs in carotid and other arteries has been shown to be associated with high blood pressure, atherosclerosis, and other diseases. However the mechanisms of tortuosity development are not clear. Our previous studies have suggested that arteries buckling could be a possible mechanism for the initiation of tortuous shape but artery buckling under pulsatile flow condition has not been fully studied. The objectives of this study were to determine the artery critical buckling pressure under pulsatile pressure both experimentally and theoretically, and to elucidate the relationship of critical pressures under pulsatile flow, steady flow, and static pressure. We first tested the buckling pressures of porcine carotid arteries under these loading conditions, and then proposed a nonlinear elastic artery model to examine the buckling pressures under pulsatile pressure conditions. Experimental results showed that under pulsatile pressure arteries buckled when the peak pressures were approximately equal to the critical buckling pressures under static pressure. This was also confirmed by model simulations at low pulse frequencies. Our results provide an effective tool to predict artery buckling pressure under pulsatile pressure.

Figure 1

Schematics of the experimental setups. (a) Buckling test under static pressure; (b) buckling test under steady and pulsatile flow; (c) a sample pressure waveform recorded from one experiment illustrating the mean pressure (average of the peak and minimum) and the pulse pressure (half of the difference between the peak and minimum).

Figure 1

Schematics of the experimental setups. (a) Buckling test under static pressure; (b) buckling test under steady and pulsatile flow; (c) a sample pressure waveform recorded from one experiment illustrating the mean pressure (average of the peak and minimum) and the pulse pressure (half of the difference between the peak and minimum).

Figure 2

Inflation test results of a typical artery. Changes of axial and outer wall circumferential stretch ratios plotted as functions of the lumen pressure.

Figure 3

Photographs of an artery before and after buckling. Top: at a pressure of 60 mmHg before buckling. Bottom: at a pressure of 190 mmHg after buckling. The buckling pressure of the artery was 85 mmHg.

Figure 4

Buckling behavior of an artery under pulsatile flow. The maximum and minimum deflections of the artery were plotted with respect to the pressure.

Figure 5

Comparison of the buckling behavior of an artery under different conditions. The lateral deflection plotted as functions of lumen pressure at stretch ratio (a) λ = 1.3 and (b) λ = 1.5 under static pressure (○), steady flow (□), and pulsatile flow (◆). The maximum deflection was plotted as a function of the peak pressure for pulsatile flow.

Figure 6

Model simulation results of a typical artery. The critical mean pressure p₀ and pulse pressure p_a was plotted at different frequencies and stretch ratios. (a) At excitation frequency f = 1.5 Hz. The linear regression equations for stretch ratios λ = 1.3 and 1.5 are p₀ = −1.08p_a + 56.3 and p₀ = −1.08p_a + 93.2 respectively; (b) at stretch ratio λ = 1.5. The linear regression equations are for frequencies f = 1.5 Hz, 2.5 Hz, and 3.5 Hz p₀ = −1.08p_a + 93.2, p₀ = −1.10p_a + 93.2, and p₀ = −1.17p_a + 93.2, respectively.