When there is a sudden change in blood pressure in your body, the blood vessels in your brain will typically widen or narrow as necessary in order to keep your blood flow stable. This process is called “cerebral autoregulation”, and it is important, because without appropriate blood flow, your brain cannot continue to function properly. Decreases in blood flow can lead to lightheadedness, and in severe cases people can lose consciousness and parts of the brain can be damaged. While this process of “cerebral autoregulation” works fine in most healthy individuals, diseases that affect the health or function of the blood vessels supplying your brain (collectively called "cerebrovascular disease") can make it difficult for your brain to adjust to these blood pressure changes.
Cerebrovascular disease is especially common among dialysis patients. Because dialysis causes frequent drops in blood pressure and dialysis patients tend to have unhealthy brain blood vessels to begin with, there is a risk that patients may have problems keeping their brain blood supply stable during the dialysis procedure, as described above. It would therefore be useful to monitor brain blood flow in the dialysis clinic. Currently, the options for monitoring brain blood flow in real time during dialysis without using invasive equipment are very limited.
This study is focused on a new, non-invasive imaging technique called Coherent Hemodynamic Spectroscopy (CHS) designed to monitor blood flow, blood oxygenation, and “cerebral autoregulation” in your brain. Near-infrared light, when passed between optical fibers attached to your scalp, can be used to detect changes in the concentration and oxygenation of blood in your brain. This process is called Near-Infrared Spectroscopy (NIRS). Dr. Sergio Fantini at Tufts University has developed a new computational model that translates the data generated by this NIRS imaging into useful clinical markers that describe how well your brain is being supplied with blood and how efficiently your brain is adjusting to changes in blood pressure. This technique may help to diagnose and monitor brain blood flow issues in dialysis patients, and may also be helpful with patients suffering from stroke, traumatic brain injury, concussion, and other brain disorders. It may also be valuable in operating room contexts.
To test the usefulness of this technique in a clinical setting, 32 hemodialysis patients from Dialysis Clinic, Inc. (DCI) Boston and DCI Somerville will be monitored with CHS before, during, and after three of their regularly scheduled dialysis sessions, with one week between each session. In order to obtain complete, usable data for 32 patients, it may be necessary to enroll more patients in the study, with maximum enrollment estimated at 50. CHS monitoring will occur using electrodes that will be attached to optical fibers and placed on your scalp. These electrodes will be held in place with an elastic sports headband, which you will wear throughout the dialysis procedure.
- Patients receiving hemodialysis thrice weekly at Dialysis Clinic, Inc. (DCI) Boston or DCI Somerville
- Receipt of dialysis for at least one month
- Ability to provide consent
- Hospitalization for acute illness within the past month
- Severe anemia (hemoglobin <9 g/dL) on the most recent routine clinical testing (conducted twice monthly in dialysis patients)
- Frequent episodes of hypotension complicating usual dialysis (identified by hypotension being indicated on more than 5 sessions over the prior month as defined in the clinical chart by the treatment team)
- Use of thigh for dialysis access
- Severe peripheral vascular disease (identified by the presence of a non-traumatic amputation or a non-healing foot wound).
- Non-English speaking subjects will be excluded from the study, given that this is not a for-benefit study and documents will not be translated due to the small cohort size.
- Pregnant women
We will be doing several things during this study, all of which will take place during your normal dialysis sessions:
- We will perform near-infrared spectroscopy (NIRS). This involves placing several small fibers that give off infrared light onto your forehead, and holding them there with a fabric headband (like that worn by basketball players and other athletes). The device is very similar to a pulse oximeter – that is the probe that is placed on your finger when you go to the hospital in order to measure the oxygen level in your blood. The NIRS device is painless, and the only risk is if the light shines directly in your eyes; accordingly we will be very careful to cover the light source when putting it on and taking it off.
- You will be asked to perform a standard paced breathing task prior to initializing your treatment, twice during your treatment and again after dialysis has ended. This task involves you slowly inhaling for about 3 seconds and exhaling for about 3 seconds for five minutes. The breathing exercise will be timed using a stop watch, which will track the total minutes of the exercise as well as the individual seconds of each breath cycle.
- You will be asked to participate in a thigh cuff occlusion exercise lasting 10 minutes. We will place two large blood pressure cuffs around both your left and right thigh. The exercise will involve consecutive inflation and deflation of these cuffs over a period of 10 minutes. For each inflation, we will inflate the cuffs from 0 to 200mmHg, leave them inflated for a given time of no more than 60 seconds, and then they will be deflated. This 10-minute inflation/deflation cycle will occur once prior to the initiation of dialysis, every 30 minutes during your dialysis treatment, and once after your treatment has ended. A stop watch will be used to track the duration of the cycles. Each cycle will last for no more than 10 minutes at a time.
- We will use a Crit-Line to monitor the concentration of blood as it enters the dialyzer. This device is used at many dialysis units across the country, and you may have had this used before during your dialysis.
- You will be asked to wear an elastic respiratory belt around your chest for the duration of the session. This will allow us to monitor your respiratory rate.
- You will be asked to wear a small, standard-use finger blood pressure monitor, clipped onto the tip of your finger, for the duration of the session. This will allow us to monitor your blood pressure continuously during dialysis.
Importantly, we will NOT be giving you any medicines to take or changing any part of your medical care.
The following steps will take place in the study:
- We will discuss the study with you. If you decide to participate in this research study, you will provide your consent by signing and dating this form.
- First NIRS session: At a midweek dialysis session, we will have you sit at the dialysis station a few minutes early and put the NIRS device on. During this time we will conduct the first five minute paced breathing exercise. You will then have a thigh cuff placed on each leg and the 5 minute protocol as described above will be completed. We will also connect the Crit-Line to your dialyzer. We will wait about 10 minutes and then dialysis will be started according to your normal routine. The NIRS device will be working the entire time and will keep on working until the dialysis session is complete. During your treatment you will be asked to undergo a cyclic thigh occlusion exercise (as described above) every 30 minutes. Furthermore, you will be asked to undergo two more sessions of paced breathing exercises. The nurse or technician will end the dialysis session like usual. After you are disconnected, we will ask you to again undergo the cyclic thigh occlusion exercise. About 10 minutes later, we will disconnect the NIRS and the study day will be completed.
- Second NIRS Session: One week later, we will repeat the same steps as in the first NIRS Session.
- Third NIRS Session: One week after the second session, we will repeat the process a third time.