Full disk images from SUMER/SOHO taken in the HeI, CIV and Ne VIII are used to investigate whether there exists a center-to-limb variation in the line width. Both CIV and He I show such a variation but the higher temperature NeVIII line is relatively constant. For CIV, this corresponds to ~3 km s^{-1} difference while HeI is significantly larger particularly at the limb. This work may suggest that the non-thermal motions are slightly nonisotropic in the transition region and upper chromosphere, with the horizontal unresolved motions exceeding those in the vertical plane however a more probable explanation is that the lines are broadened due to opacity effects. The more slower variation in the CIV 1548 \AA line width could be explained by increasing the opacity from zero at disk center to ~1 at the limb. For HeI the opacity is significantly grater than unity at the limb. This therefore implying all mass motions in the chromosphere, transition region and corona are isotropic.