Hypoxemia in Maintenance Hemodialysis Patients

Following the initial recruitment, all individuals who are willing to participate and sign the informed consent document will be provided with a medical history form to complete. In addition, the investigators will ask participants to sign a HIPAA authorization form in order to look into their medical records for monthly blood work (blood chemistry), anthropometric data (height and weight), interdialytic weight gain (weight gain since last treatment) history, and current medications. Testing DURING all study protocol days: Testing will be performed on three consecutive dialysis days during a one-week period (Monday/ Wednesday/Friday or Tuesday/Thursday/Saturday). If a data collection period is missed for any reason, an alternative data collection day will be scheduled. All three study visits are identical with respect to the study procedures performed: 1. Hemodynamics: The hemodynamic response to dialysis will be obtained using the Task Force Monitor (TFM). The TFM will be connected to the subject prior the start of the HD session. The TFM is a non-invasive device that uses thoracic bioimpedance to collect a variety of data related to cardiovascular function, including: Heart Rate Variability: Beat-to-beat heart rate (HR) will be recorded using the Task Force Monitor. The ECG will be collected online at a sampling rate of 1,000 Hz, in real time, and stored on a computer (Dell, Austin, TX). Heart rate and the variability of the intervals between successive heart rates will be derived from the ECG signal. Beat-to-Beat Blood Pressure: Beat-to-beat peripheral BP will be derived via finger plethysmography (Task Force Monitor). A finger cuff will be placed around the non-dialyzing index and middle finger. These cuffs measure the change in blood pressure from successive beats continuously. Cardiac Output: Cardiac output and stroke volume will be collected by the task force monitor. An electrode will be placed around the chest to measure changes in impedance continuously. Blood Pressure: Blood pressure will be measured before the start and every 10 minutes throughout the session using an automated cuff connected to the TFM. The cuff will be placed on the non-dialyzing arm of the patient. The continuous non-invasive arterial pressure (CNAP) technology on the TFM machine will also be performed continuously during 10 minute segments every hour until the end of the HD treatment (i.e. from minute 0 to 10, 60 to 70, 120 to 130, 180 to 190). The TFM will measure these hemodynamic values continuously throughout the entire HD session. 2. Relative Blood Volume and Hematocrit: The Critline is a regular part of dialysis treatment at the Champaign Urbana clinic. The Critline non-invasively measures hematocrit, relative blood volume, and oxygen saturation in real time. A trained staff member of the Champaign Urbana Dialysis Clinic will add a disposable blood chamber to the dialysis machine. As blood travels through this chamber hematocrit and oxygen saturation are measured by the absorbance and scattering of light. The hematocrit value is then used to estimate the blood volume relative to the start of the dialysis session. 3. The Wrist0x2 will be connected prior to the HD session and measurements will be recorded continuously throughout the entire HD session. 4. Clinic Factors: The investigators will gather some information collected by the clinic including: participant weight gain since the previous treatment, the volume of fluid removed during the treatment, the composition of the dialysate used during the treatment, and the rate of flow of both the blood and dialysate through the hemodialysis machine during the treatment. 5. Lab Values: The investigators will also obtain results from monthly blood chemistries run on patient's blood samples by the clinic in the month prior to participant enrollment. These values will include but are not limited to information such as serum albumin, phosphorus, and calcium. After completion of the HD treatment, the patient will be disconnected from the TFM and Wrist0x2.