Deformability and Microcirculatory Flow of Red Blood Cells in Newborn Infants

摘要

Deformability of red blood cells is defined as their ability to deform (ie; to assume new shapes) in response to forces applied on the cell. This is essential for effective blood flow, particularly in the microcirculation, where red blood cells of about 8 um diameter flow through 3 to 4 um diameter vessels. Thus deformability of red blood cells is an important determinant of flow through microcirculation, of oxygen transport and release to the tissues and also of whole blood viscosity and red cell life span.;Filtration techniques are widely used as models of the microcirculation and for measurement of red cell deformability. These are based on measurements of the flow of suspensions of cells through the filter membranes. The filtration method developed by Jones et al (1984 and 1985) was used in this thesis to measure the red cell deformability. The factors other than red cell deformability, which influence the rate of filtration were eliminated so that a sensitive filtration technique for measuring red blood cell deformability was used.;This study describes the fetal red cell filterability measured in varying in vitro pH and temperature conditions which are important in newborn infants in vivo. The series of experiments performed on blood samples from newborn infants to see the effect of changing pH and temperature showed that the RBCs are sensitive to pH and temperature changes. Filterability of red blood cells is decreased at low pH and temperature when compared with normal blood temperature and pH. The effect of low pH is reversible and possibly correctable. Thus acidosis and hypothermia seen in newborn infants could affect the deformability of red cells and this might be a contributory factor in clinical complications seen in these babies.;Filterability of red cells from fetuses, newborn infants and adults was measured. It was found to be directly related to the gestational age of the infant with no significant difference between red blood cells of gestational age matched fetuses and newborn infants. However, RBCs from healthy newborn term infants showed significantly decreased filterability than those from adult RBCs. Thus the fetuses and infants who were transfused with adult blood showed considerably improved flow properties (four fold increase in filterability with adult blood transfusion) when compared to gestational age matched untransfused fetuses and infants. The filterability of red cells was negatively related to the mean cell volume (MCV) of RBC. However, multiple regression analysis showed that gestational age of the infant and MCV were independent determinants of filterability. Therefore, apart from their larger size, neonatal RBCs are inherently less filterable than those of adults.;The influence of HbF on the filterability of fetal and neonatal erythrocytes was also assessed. During filtration through 3 um pores, cells with a higher proportion of adult haemoglobin emerge from the filter sooner than the less mature cells with a higher proportion of fetal haemoglobin.;Various clinical parameters were correlated with the red cell deformability in newborn infants. Preterm babies with major complications of preterm delivery ie; respiratory distress syndrome and interventricular haemorrhage when compared with similar babies without these complications showed decreased red cell filterability but the recorded differences were not statistically significant. However red cell filterability was decreased in small for date (SFD) infants compared to gestational age matched appropriate for gestational (AGA) infants.