**2.4 Statistics**

Pearson's correlation was used for parametric variables and Spearman's ranking coefficient for the non-parametric relationship between sharpness of the peak pressure wave and DP. 95% confidence limits are shown in **Figure 4**. For the purpose of transposing hoop stress measurements into equivalent lumenal pressures the artery was treated as a thin walled cylinder and the relationship between the tension in the wall and the corresponding internal arterial pressure was derived mathematically from the formula: Pressure equivalent (mmHg) = 47 x Hoop stress (KPa) x t/d, where t/d is the thickness to diameter ratio.
