Answer: This in vitro study arose from observations made in
the intensive therapy unit. It had been noted that
a raised mean corpuscular volume (MCV), as
measured by the Coulter Counter Model S,* could
coexist with hypernatraemia in certain states of
hyperosmolality.
The postulated underlying mechanism was that
the rate of movement of osmotically active particles,
particularly d-glucose, into the intracellular compartment exceeded their removal by normal intracellular metabolism. The result of this state would
be water shift to produce an expanded intracellular
space, a depleted extracellular space, and a rise in
plasma sodium, reflecting the overall rise in
osmolality. The observed rise in MCV would
therefore reflect this pattern, and the MCV would
function as an indicator of intracellular osmolality.
The Coulter S Counter is a widely used instrument
in haematology laboratories. The MCV is measured
by determination of the mean pulse height generated
during the period of electronic cell counting calibrated by reference to known blood specimens. The
'Coulter Principle' of one-by-one counting and
sizing of particles is now well estab
Step-by-step explanation: