All patients recruited who met the inclusion criteria were investigated access flow, access recirculation and cardiac function(including cardiac output,cardiac index,central blood volume,et al).Measurement time is the beginning of HD session (first 30min to 1 hr),Middle of HD session (optional),and the end of the HD session (1hr to 30 min prior to end of session). The follow-up duration is 6 months and 12 months.Repeat the assessment at the above time points.