BackgroundRecent evidence suggests that red blood cell aggregation and the ratio of hematocrit to blood viscosity (HVR), an index of the oxygen transport potential of blood, might considerably modulate blood flow dynamics in the microcirculation. It thus seems likely that these factors could play a role in sickle cell disease. Design and MethodsWe compared red blood cell aggregation characteristics, blood viscosity and HVR at different shear rates between sickle cell anemia and sickle cell hemoglobin C disease (SCC) patients, sickle cell trait carriers (AS) and control individuals (AA). ResultsBlood viscosity determined at high shear rate was lower in sickle cell anemia (n=21) than in AA (n=52), AS (n=33) or SCC (n=21), and was markedly increased in both SCC and AS. Despite differences in blood viscosity, both sickle cell anemia and SCC had similar low HVR values compared to both AA and AS. Sickle cell anemia (n=21) and SCC (n=19) subjects had a lower red blood cell aggregation index and longer time for red blood cell aggregates formation than AA (n=16) and AS (n=15), and a 2 to 3 fold greater shear rate required to disperse red blood cell aggregates. ConclusionsThe low HVR levels found in sickle cell anemia and SCC indicates a comparable low oxygen transport potential of blood in both genotypes. Red blood cell aggregation properties are likely to be involved in the pathophysiology of sickle cell disease: the increased shear forces needed to disperse red blood cell aggregates may disturb blood flow, especially at the microcirculatory level, since red blood cell are only able to pass through narrow capillaries as single cells rather than as aggregates.Key words: sickle cell disease, red blood cell aggregation, viscosity, red blood cell deformability. Citation: Tripette J, Alexy T, Hardy-Dessources M-D, Mougeneld D, Beltan E, Chalabi T, Chout

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Because of the metabolic changes induced by a physical activity, the hemorheological properties of patients with sickle cell anemia could be further impaired and increase the risks for vaso-occlusive complications. However, few studies suggest that moderate physical activity could be beneficial rather than harmful in patients with sickle cell anemia (SCA). However, the definition of what can be considered as a moderate physical activity in SCA patients is imprecise. The present study tested the effects of a short incremental cycling exercise test conducted until the first ventilatory threshold on different biomarkers. Hematological and hemorheological parameters were compared between 8 patients with SCA and 13 healthy subjects (CONT) before, immediately after the end of the exercise and at 12, 36 and 60 hours after the exercise. We observed no significant hematological or hemorheological alteration induced by the exercise in the two groups. However, the exercise resulted in a delayed improvement of the red blood cell disaggregation threshold at 36 and 60 hrs after exercise in the SCA group which was paralleled to the decrease in the platelet count in this group. The present study suggests that such an exercise might be beneficial for microcirculatory blood flow.

The present study investigated the hemorheological and endothelial alterations in sickle cell trait (SCT) carriers in response to a submaximal exercise. Eleven SCT carriers and 11 subjects with normal hemoglobin performed submaximal exercise for 15 min. Blood was sampled at rest, at the end of exercise, and at 2 and 24 h of recovery. Hemorheological alterations observed in the SCT group were as follows: 1) lower RBC deformability at high shear stress at all time-points, with no relation to oxidative stress, 2) higher disaggregation threshold at all time-points, suggesting RBC hyper-aggregation, and 3) higher blood viscosity at the end of exercise and during recovery. Exercise had a specific influence on the levels of the soluble cell adhesion molecules P and L-selectin in the SCT carriers, with higher P-selectin levels at all time-points and a greater increase in L-selectin levels during recovery. SCT carriers had slightly decreased nitrite levels at 24 h of recovery, which might be clinically insignificant. In conclusion, the hemorheological alterations in association with lower NO production found in the SCT carriers are probably not sufficient to explain the medical complications sometimes reported in SCT carriers after exercise.

Purpose: The aim of this study was to clarify whether exercising in a tropical climate induces blood rheology alterations despite ad libitum hydration.Methods: Hematological, biochemical and hemorheological changes were investigated in young healthy adults (N = 9 men, 20.7 ± 0.8 yrs) after a 10-km race in hot and humid conditions. Subjects' maximal aerobic abilities were tested using a maximal ramp exercise. Blood was sampled at rest (T R ), at the end of the race (T Ex ), and after 24 hours of recovery (T 24 ). Ad libitum hydration was allowed during the race. Blood viscosity (b), red blood cell deformability (EI), aggregation (AI) and disaggregation shear rate (␥) were measured.Results: Hematocrit, hemoglobin and plasma concentration of chlorine, sodium and potassium did not change in response to exercise. No functional consequence was observed on RBC deformability since EI remained unchanged. Percentages of echinocytes, schizocytes and stomatocytes remained in the subclinical range at all times. AI, ␥ and b did not present change.Conclusion: Running exercise in tropical climate with ad libitum hydration does not alter the main rheological properties of blood.