Before dialysis, nail-fold microcirculation will be noninvasively measured using a vediocapillaroscopic device (MC-380, Computed Microcirculation System, Kowa Optics Corp., Taiwan). The equipment and measuring procedures will be explained to the subjects. A finger to be examined will be gently placed on a microscope base plate and held still for the duration of the measurement. Computerized image processing will be used to capture and analyze data. The following morphological data will be extracted: blood velocity, capillary density, capillary width, capillary length, and the presence of abnormal capillary morphology.To identify the common microcirculation patterns of HD patients, images of nail-fold capillary will be processed use a framework that was developed by Prof. K. P. Lin and colleagues.