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Optical coherence tomography (OCT) has the potential to be a noninvasive method for hematocrit (HCT) measurement. This study shows the effect of erythrocyte aggregation at the level seen in healthy humans and pathological states on HCT measurement based on monitoring the slope changes in OCT depth reflectivity profile using spectral-domain optical coherence tomography (SDOCT). Our measurement indicates that the HCT estimated by SDOCT depends on the erythrocyte aggregation state and the flow rate. Measured HCT in blood samples with 0.6% and 2% dextran 500 is underestimated by 4.5%-10.5% and 17.1%-19.5% for HCT from 35%-55% at a flow rate of 4.7 mm/s. Underestimation is smaller at a high flow rate as compared to a low flow rate, indicating erythrocyte aggregation is an important factor that will affect accurate HCT measurement using SDOCT. Index Terms--Erythrocyte aggregation, hematocrit (HCT), spectral-domain optical coherence tomography (SDOCT).

Hematocrit is likely to be optimized because of its influences on oxygen transport. However, optimal hematocrit must also change because shear rates and blood vessel radii within circulations change temporally. Blood vessel endothelia regulate shear stress on their walls by changing their radius. Wall shear stress is dependent on shear rate and viscosity. Because there is regulation of vessel radius by the endothelium it is hypothesized that hematocrit may be regulated near optimal by changes in plasma volume. The implication of such regulation is that changes in vascular volume (blood volume) would occur with alterations in red blood cell mass. Data are presented which indicate that regulation of optimal hematocrit normally occurs through changes in plasma volume. The regulation of optimal hematocrit has significant implications for processes that depend on oxygen transport (e.g., exercise) because of the effect of blood volume on cardiac output.

Analysis of the effect of intravenous treatment of a stable thromboxane A2 (TxA2) analogue U-46619 on extracellular fluid partition in rats shows that this analogue increases microvascular permeability in specific organs, thereby increasing hematocrit and reducing plasma volume. This shift of plasma fluid and proteins from the intravascular to the intestitial compartment, induced by TxA2 receptor activation, can be attributed to hemodynamic changes at the microvascular level and changes in microvascular permeability in target tissues.

The backscattering coefficient of saline suspensions of porcine red blood cells was measured for hematocrits up to about 90%. It was found that the coefficient peaks at approximately 15%, but then, contrary to what a simple 'gap theory' might suggest, it decays smoothly to zero, without showing another peak at high hematocrits. A one-dimensional (1-D) slab scattering model, in which the number of slabs per unit length represents the hematocrit and whose thickness and acoustical properties are similar to red cells/plasma, was also used to investigate the relation between the backscattered power and hematocrit. Monte-Carlo simulations performed for randomized boundary conditions show a similar relation to that of the 3-D system. The experimental data is compared to the Percus-Yevick theory for the packing of hard spheres, and the simulated data is compared to the Percus-Yevick theory for infinite slabs.

A study evaluated the limit to cardiac compensation, during isovolemic hemodilution (HD) in 14 anesthetized dogs. The transmural distribution (endo/epi) of myocardial blood flow (MBF) was estimated using radioactive microspheres. The tolerance of the left ventricle to HD was greatly lowered by critical coronary stenosis, which also inhibited vascular adjustment to HD. During extreme HD, subendocrinal ischemia resulted, when cardiac failure was induced by MBF becoming maldistributed. The rises in MBF were transmurally consistent and adequate to maintain myocardial oxygenation.

The effect of anemia in the mother on subsequent preterm births was studied in 35,000 pregnancies. There was no significant relationship between anemia and preterm birth except for a slight tendency for women with anemia early in the last trimester of pregnancy to give birth before term. Anemia during the last trimester could not account for the substantially higher rate of preterm birth among black women. Anemia after 30 weeks of pregnancy was not associated with premature birth. In women delivering infants weighing over 2,500 grams, the percentage of red cells in the maternal blood increased by 3 percent among black women and 2 percent among white women from the 25th week of pregnancy to term. Anemia was most likely during the 28th week of pregnancy, and became less likely as delivery approached. Anemia is not a major cause of preterm birth; comparison of women in preterm and term labor produces biased results., ABSTRACT: The effect of anemia (hematocrit

The blood level of erythropoietin, a hormone secreted by the kidneys which stimulates red blood cell production, was measured in 31 kidney-transplant patients being treated with cyclosporine, a drug which suppresses the disease-fighting immune system so that the transplanted kidney would not be rejected. Average levels of the hormone before surgery were similar to those in healthy subjects. A temporary increase just after surgery dropped to a level three times greater than normal, which lasted for an average of 280 days. The initial increase occurred before the transplanted kidney started to function, and was not accompained by an increase in red blood cell production. The second increase in erythropoietin levels occurred as the kidney started to function and as red blood cell output increased. After erythropoietin levels returned to normal, the volume of red blood cells continued to rise toward normal. In patients who have undergone a kidney transplant, small increases in levels of erythropoietin produced by the body cause an increase in red blood cell production to the same extent as large doses of erythropoietin administered to patients with an excess of urea, a compound formed by the liver, in the blood. Once started, red blood cell production in kidney-transplant patients can be sustained by normal levels of erythropoietin. The restoration of kidney function improves the response of red blood cell production to the hormone erythropoietin.

Purpose: Hematocrit effect, the influence of nonoptimal hematocrit on the accuracy of glucose analyzers, poses a safety risk to patients when tight glucose control is desired. We investigated glucometer error [...]