We have two kidneys.  And, these two bean-shaped organs maintain some vital functions for us every day of our lives.  Sure, we recognize that they produce the urine that we excrete- the urine that contains body wastes.  They also purify the blood as it circuits from the heart to the rest of the body.

But, the kidneys provide other vital functions.  They create the hormones that are involved in erythropoiesis- the production of red blood cells.  Two other hormones are produced by the kidneys- calcitrol and renin. Calcitrol is critical for bone health and renin regulates extracellular fluid volume and arterial vasoconstriction (blood pressure control).

Therein lies the problems.  Because dialysis only replaces some of those functions for the patient with failed kidneys.  It filters minerals  and removes waste materials from the blood- the excess is discarded as part of the “spent” dialysate (the salt water solution that traverses the dialyzer).

And, the dialysis system also manages to remove excess water from the body.  Not elegantly- basically, we suck the water out of the blood by using pressure differentials over the blood-dialysate circuit.  The goal is to bring the patient to his/her ‘dry’ weight.  (This is the hypothetical weight of the patient at which they have optimized fluid levels. It’s hypothetical since, until now, we had no scientific basis to determine the value.) The problem with that is the fluid removal is not fully regulated- and can sometimes causes a precipitous drop in the patient’s blood pressure.

Which is why researchers at MIT and Mass General have been working on a  new portable sensor that can accurately discern the patient’s hydration levels.  (Note: This device also has utility for patients with CHF- congestive heart failure [about 5 million folks] and for elderly folks (or athletes) who have a tendency to become dehydrated.)  The new sensor is based upon NMR (nuclear magnetic resonance) relaxometry.

The device uses the same technology as those MRI (magnetic resonance imaging) scanners used in the hospital.  But, since no imaging is necessary, the device can be smaller and cheaper than the conventional MRI.

The device has been described in the article written by Lina Colucci, a newly minted PhD (Health Science and Technology, MIT), Dr. Michael Cima and grad student Matthew Li (MIT), plus Drs. Kristin Corapi,  Xavier Parada, Andrew Allegretti, Dennis Ausiello, and Matthew Rosen (these are all from Mass General Hospital) that was published in Science Translational Medicine (Fluid assessment in dialysis patients by point-of-care magnetic relaxometry).

Dr. Cima began this project a decade ago, seeking a better method to measure patient hydration. He chose NMR because of his familiarity with the technique- his previous startup (T2 Biosystems) used NMR to discern bacterial infections in blood samples.  But, there’s another strong reason- the NMR signal is a function of hydrogen atoms- and most of the hydrogen atoms in the human body are associated with water (as in H₂O); one such property is T₂ relaxation time- this discerns both the quantity of hydrogen atoms (and, therefore, water) as well as the environment.

The team took its measurements before and after dialysis.  And, interestingly, they could discern healthy patients from those needing dialysis at the first measurement.  (And, as the patients underwent dialysis, the loss of water was easily monitored by the device.)  These measurement data is how the researchers discerned that dehydrated patients could be recognized.  (However, no patient testing for that condition has ensued- yet.)

While we still have no process to replace the hormones the kidneys produce, this device may help make dialysis a more useful therapy for those whose kidneys have failed.

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