A review of water diffusion measurement by NMR in human red blood cells

Abstract

This review of water transport measurement in normal human erythrocytes attempts to harmonize discordant results obtained under diverse study conditions with two different techniques: nuclear magnetic resonance (NMR) and radioactive tracer (THO) diffusion. Natural aggregation of red cells into rouleaux appeared to cause most of the variation among results from NMR experiments. The remainder of the discrepancy was attributed to the use of inappropriate mathematical approximations of the two-site exchange equations, differences in blood storage time, and failure to adjust NMR calculations for the nonwater protons. Differences in hematocrit, frequency-magnetic field strength, or NMR pulse technique played no apparent role in the disparity among NMR reports. When these confounding factors were removed, diffusion results obtained by NMR or by influx or bulk diffusion of radioactive tracer agreed within a relatively narrow range of values. These techniques place the mean lifetime of water inside fresh normal human erythrocytes at room temperature (20-25 degrees C) between the extremes of 9.8 and 14 ms, where the uncorrected range was previously 9.8-21.7 ms. This new range of water exchange times corresponds to a range of diffusional permeability between 3.3 and 4.7 x 10(-3) cm/s.

Measurement of tissue oxygen extraction ratios from venous blood T2: Increased precision and validation of principle

“…We attribute this to the lower temperature (room temperature) used for the literature experiments. The measured was 2.5 ms, which is much shorter than previously assumed (7.1 ms) based on literature erythrocyte life times of 12 ms at physiological temperature and an Hct of 0.41 (29). In order to assess whether such a lifetime change may be due to erroneous estimation of other parameters, such as the relaxation rates and susceptibility shifts, we also fitted the data using a range of constant lifetimes between 2.5 and 7.1 ms, while varying the rates and shifts.…”

“…In order to understand better the origin of this difference, it is useful to recall the definition of this exchange lifetime as originally defined for two-compartment exchange by Luz and Meiboom, namely, Ϫ1 ϭ ery Ϫ1 ϩ plas Ϫ1 , from which it can be derived that Ϫ1 ϭ ery Ϫ1(1 Ϫ Hct). Thus, the exchange lifetime should not be confused with the erythrocyte life time ( ery ), which is about 12 Ϯ 2 ms at 37°C (29). Using an Hct of 0.41, the corresponding exchange lifetime is 7.1 ms.…”

In Vivo Determination of Absolute Cerebral Blood Volume Using Hemoglobin as a Natural Contrast Agent: An MRI Study Using Altered Arterial Carbon Dioxide Tension

“…Actually, at very short interecho spacings in a multiecho sequence, the BOLD effect becomes almost negligible. The lifetime between exchanges, Ti = (1 -Hcti) Ter y ' is determined by the measured hemoglobin level (equation 4) and the well known lifetime of water inside human erythrocytes T er y = 12 ± 2 ms (Herbst and Goldstein, 1989). This lifetime has been found to be of the same magnitude for humans, cows, sheep, and dogs (Benga, 1994;Vieira et aI., 1970), and we therefore assumed that value in cats.…”

NMR of laser-polarized xenon in human blood

“…The xenon RBC is longer than that for water molecules, which was measured to be 12 Ϯ 2 ms at room temperature (for review, see ref. 24). The regulation of such exchange processes in living organisms is under further investigation.…”