Table 1:

Pressure differences between top and bottom of the model at 4 points in time during the flow cycle for the Chiari and the normal model^a

Model	Pressure Differences (centimeters of water) Top to Bottom
	Systole		Diastole
	t = 0.00 seconds	t = 0.25 seconds	t = 0.50 seconds	t = 0.75 seconds
Normal	0.66	0.10	−0.64	−0.07
Chiari	0.75	0.13	−0.74	−0.09
Increase	14%	30%	16%	29%

a The gradient follows by dividing the difference by the distance from top to bottom. The 4 times correspond to when flow changes direction from cranial to caudal flow (t = 0.00 seconds), when caudal volume flow rate is maximal (t = 0.25 seconds), when flow changes direction from caudal to cranial flow (t = 0.50 seconds), and when cranial volume flow rate is maximal (t = 0.75 seconds). Note that the minus sign appears when pressure is highest at the caudal side of the geometry (ie, related to cranial flow). Note also that data from the times of flow reversal (ie, t = 0.00 and t = 0.50 seconds) are arbitrarily included in systole and diastole, respectively.