A hemodialysis system includes: a hemodialysis machine configured to provide hemodialysis treatment to a patient, wherein the hemodialysis treatment includes circulating extracorporeal blood of the patient through an extracorporeal blood circuit; a first oxygen saturation sensor device configured to measure oxygen saturation corresponding to the extracorporeal blood of the patient in the extracorporeal blood circuit; a second oxygen saturation sensor device configured to measure oxygen saturation corresponding to blood flowing within the patient; and at least one controller configured to determine one or more oxygen saturation phase shift (OSPS) values or one or more transcutaneous travel time values corresponding to the patient based on oxygen saturation measurements from the first oxygen saturation sensor device and the second oxygen saturation sensor device.