Aplicação da pinça optica para o estudo da deformabilidade das hemacias

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The deformability of erythrocytes is a critical determinant of blood flow in microcirculation. By capturing red blood cells with optical tweezers and dragging them through a viscous fluid we were able to measure their overall elasticity. Laser optical tweezers, based on photon momentum transfer, have been used successfully in a variety of biological applications. This technique is capable of measuring the whole red blood cell elasticity and viscosity. The optical trap was performed with a Nd:YAG laser strongly focused in a microscope connected to a CCD camera. A computer captured the images, where they were quantitatively and qualitatively analyzed. The elasticity measurement was obtained by dragging the RBC with the optical tweezers through the plasma fluid with a known viscosity. It should be pointed out that the laser does not exert any pressure or photo-damage on the cell. The analysis of the cell deformation vs velocity allowed us to obtain cell elasticity expressed in dyn/cm. The model we used to extract the values for the membrane elasticity and viscosity assumed that the cell is a parallelepiped with length lo, width W and negligible thickness which is located at distance Z1 trom the bottom of the Neubauer chamber and Z2 trom the cover slip. We assumed that the elastic response to an applied force is given by F=J.1(WILo)~L, where F is the force, J.1 is the elasticity and ~L is the cell length deformation. We assumed a drag force F given by F=TI(Wl.o(kq)V, where TI is the plasma viscosity, (1/Zeq)= (11Z1)+ (11Z2) and Vis the drag velocity. The equilibrium occurs when one force cancels the other. Therefore the elongation ~L as a function of drag velocity is given by ~L= (Tllo 1(J.1Zeq)] V, which can be used to extract a value for J.1 provided by the plasm viscosity TI, length lo and Zeq which are easily measured. We measured, and compared, the red blood cell deformability trom normal contrais (HbAA) , patients with: homozygous (HbSS) and heterozygous (HbAS) sickle hemoglobin, HbSS subjects on sickling crisis, hereditary spherocytosis and with iron deficiency anemia. We also studied ,the action of hydroxyurea on rheologic behavior of HbSS cells, the gamma irradiation and the heterozygosis for sickle hemoglobin on cells storage on blood donation bags. Our results showed that the red blood cell deformability was significantly lower in HbS subjects (HbSS and HbAS) , except for HbSSIHU cells, whose deformability was similar to the normal controls. Our data showed that the laser optical tweezers technique is able to detect differences in HbS red blood cells trom subjects taking hyd,roxyurea as well as to differentiate red blood cells trom normal controls and HbAS, indicating that this is a very sensitive method and can be applied for detection of drug-response in sickle cell disease. The sensitivity of the laser optical tweezers method showed that there is no significant change in elasticity over time up to 14 days of storage, regardless of whether the unit was irradiated or not. However, beyond 21 days of storage, irradiated units demonstrate decreased elasticity. RBCs elasticity trom AS units stored for 1, 14 and 21 days presented significantly lower elasticity when compared to HbAA cells stored for the same period. Mostly of RBcs trom HbAS units stored for 28 and 35 days, Hereditary spherocytosis cells and sickle crisis cells were very rigid or escaped trom the optical trapo So these cells did not stay in the trap when the velocities were increased. Hence, the accuracy of elasticity measurement was impaired.

ASSUNTO(S)

elasticidade fotons reologia anemia falciforme anemia hemolitica hematologia doadores de sangue

ACESSO AO ARTIGO

Documentos Relacionados