The investigators propose a study for validating the test device's measurement of a parameter called 'sternal fluid index' (SFI) in patients with diagnosed medical conditions related to fluid management, e.g. end-stage renal disease (ESRD), that are undergoing dialysis. The reference device for the study measures the averaged amplitude of a thoracic bio-impedance signal (Z) and a parameter called 'thoracic fluid content' (TFC), which is equal to 1000/Z. The test device measures SFI from a localized region near the sternum, whereas the reference device measures Z and TFC from the entire thoracic cavity. This means Z (or TFC) and SFI, if measured at approximately the same time, will likely correlate but have different absolute values. Thus, the statistical analysis will investigate the ability of SFI to track fluids, as well as the agreement between fluid-dependent trends displayed by SFI and Z (or TFC), as described below.