Haemorheological changes in chronic respiratory failure

The whole blood filtration rate (WBFR) according to Reid, the KT product using Taylor’s formula and the apparent internal viscosity (η_i) following Dintenfass’s method were determined in healthy subjects (n.26) and in patients (n.26) with chronic obstructive pulmonary disease (COPD) and chronic respiratory failure (CRF) of various degree, the latter subdivided in two groups according to the value of the hematocrit (Ht): COPD1 with Ht ⩽ 49% and COPD2 with Ht > 49%. The mean value of WBFR was significantly reduced in both COPD1 (10.37 ± 3.90 µl/s) and COPD2 (10.72 ± 4.54 µl/s) patients as compared with normals (17.84 ± 4.35 µl/s); respectively p < 0.001 and p < 0.002. In normals a slowing of WBFR was observed in relation to the increase of Ht (r= -0.52, p < 0.01), whereas in COPD1 patients the WBFR was directly correlated to Ht (r = + 0.64, p < 0.05). No difference in WBFR was observed between the two patient subgroups. An increased red cell deformability as detected by the KT value was found in COPD1 (2.69 ± 0.17) and COPD2 (2.52 ± 0.16) patients as compared with normals (2.87 ± 0.16) ; respectively p < 0.005 and p < 0.001. The impairment of WBFR in patients with CRF appeared to depend on extra-erythrocyte factors and/or increased red cell aggregation. The higher red cell deformability may be explained by the fact that the red cells altered as a consequence of the modifications of pH, Pa02 and PaC02 produced by CRF are rapidly removed from the circulation and replaced by more deformable young cells.