Effects of ischaemia-related suspension media and pore size on erythrocyte filterability in peripheral arterial occlusive disease

Abstract

Whether erythrocyte deformability is reduced in patients with peripheral occlusive arterial disease (POAD) is discussed controversially. Within this study erythrocyte filterability through microfilters with different pore diameters (3, 5, and 8 μm) was investigated in patients with POAD and age-matched healthy volunteers under physiological and ischaemia-related boundary conditions (lactate acidosis, hypercapnia, hypoxia, hyperosmolarity). 70 subjects were assigned to two control and three POAD groups characterized by varying combinations of risk factors (smoking, diabetes mellitus). Red blood cells (RBC) were suspended in four different media (pH/ mosmol *l⁻¹ : 7.4/ 300, 7.4/400, 6.5/300, 6.5/400) containing a physiological bicarbonate buffer adequately gased with O₂/CO₂/N₂. Mean hematocrit-corrected relative erythrocyte transit times (RCTT) and concentrations of clogging particles (CP) were measured by means of the St. George's Filtrometer. In agreement with previous reports, filtration data varied with erythrocyte volume (MCV) and mean corpuscular hemoglobin concentration (MCHC) used as estimates of surface area-to-volume ratio (SAVR) and inner viscosity (IV) of RBC, respectively. While RBC filtration rates were dominated by IV in 5 and 8 μm pores they were mainly limited by SAVR in 3 μm pores. For RCTT statistically significant differences between controls and POAD patients could not be found. CP correlated with leucocyte counts of the suspensions if filterability was not primarily limited by MCV. A quantitative agreement among these parameters, however, was only obtained in 8 μm pores and, therefore, interactions between both erythrocytes themselves and erythrocytes and leucocytes should have contributed to filter obstruction. For CP statistically significant differences were only found between controls and diabetic POAD patients in whom also higher leucocyte counts were registered. It is concluded that in clinical or pharmacological studies of RBC filterability the most important in-vitro boundary conditions (milieu, filter pore size) should be varied in order to account for the complex and partially antagonistical relationships between erythrocyte properties and pore geometry as well as blood cell interactions. Because the capillary morphology of ischaemic tissue areas is usually not known or may be subjected to dynamic alterations the meaning of the invitro filterability with respect to the in-vivo microcirculation is additionally insecured.