For some patients it is essential to assess their total body water, but this is currently both expensive and time-consuming. This also makes it impossible to track day-to-day changes in their situation.

Now, a team of scientists led by physicist Professor David Smith and clinician Dr. Simon Davies has developed a powerful new method that can determine the total body water in less than two hours. Their research is published today in the Institute of Physics journal, Physiological Measurement.

Dehydration may affect our bodies in unexpected ways. Recent suggestions that dehydration can cause a range of illnesses from migraine headaches to lower back pain are dismissed by many doctors.

But there is no argument that dehydration can adversely affect the well-being of an otherwise healthy individual. For the elderly or those who are ill, the amount of water in the body may be crucial.

Patients with kidney failure, for example, have a build-up of toxins in their body water that would normally be excreted by their kidneys. Renal dialysis will remove these toxins, but an absolute knowledge of the patient's total body water is critical in assessing the required dialysis dose.

The new technique developed at Keele University in the UK and the Heyrovsky Institute of Physical Chemistry in the Czech Republic gives an oral dose of "heavy water" to the patient. Heavy water is almost identical to regular water (H2O), except that a heavier, non-radioactive, form of hydrogen called deuterium replaces the hydrogen part of the water molecule.

After the patient has been given the heavy water to drink, they breathe into a device that performs "flowing afterglow mass spectrometry." Inside this device, the breath sample reacts with charged atoms, called ions. Comparing the amounts of certain ions and molecules that go into the device with what comes out gives a measurement of the deuterium in the sample.

Samples are then taken every three to five minutes to show how the amount of deuterium present in the patient's breath varies over time.

The patients show three distinct phases of deuterium content in their breath. The first phase consists of a sharp peak reflecting the presence of deuterium still within the mouth -- this lasts for about ten minutes. The second phase, which lasts longer and has a lower peak, shows that the heavy water is being absorbed from the gastro-intestinal tract and is entering the blood stream. Finally there is a phase that shows the heavy water entering the other body compartments, notably the muscles, after which a steady value is reached that is directly related to the patient's total body water.

Determination of total body water, by "flowing afterglow mass spectrometry" has been assessed in a pilot study using volunteer subjects.

"It is clear that this method has considerable advantages over existing techniques, and can be used to study both body composition and total body water in the clinical environment. This leads to enhanced patient care in cases where too little or too much water can be a matter of life or death," said Dr. Davies.

(Reference: Rapid measurement of deuterium content of breath following oral ingestion to determine body water, Physiological Measurement, Vol. 22, Issue 4, November 2001)

[Contact: Professor David Smith]

01-Oct-2001