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Contribution of red blood cell aggregation to venous vascular resistance in skeletal muscle
M Cabel1, H J Meiselman, A S Popel
1Department of Physiology, University of Arizona College of Medicine, Tucson 85724, USA.
Insights
Red blood cell aggregation significantly impacts venous vascular resistance in resting muscles. Increased aggregation reduces venous conductance, highlighting its role in blood flow regulation.
Area of Science:
- Physiology
- Hemodynamics
- Vascular Biology
Background:
- Venous vascular resistance and conductance are critical determinants of blood flow regulation.
- Red blood cell (RBC) aggregation, the process by which RBCs clump together, may influence these parameters.
- Understanding factors affecting venous tone is essential for comprehending circulatory physiology.
Purpose of the Study:
- To investigate the influence of red blood cell aggregation on venous vascular resistance and conductance.
- To determine the extent to which RBC aggregation contributes to venous tone in resting skeletal muscle.
- To differentiate the effects of RBC aggregation from hematocrit and plasma viscosity.
Main Methods:
- Experiments were conducted on the cat lateral gastrocnemius muscle.
- Muscle perfusion was performed using whole blood, acellular solutions, and non-aggregating RBC suspensions.
- Venous conductance was measured under varying flow rates and conditions of altered RBC aggregation (using Dextran 40 and Dextran 250) and hematocrit.
Main Results:
- Venous conductance varied significantly with blood flow in resting muscle perfused with normal blood.
- This flow-dependent change in venous conductance was absent with acellular solutions and greatly reduced with non-aggregating RBC suspensions.
- Increased RBC aggregation (via Dextran 250) and high hematocrit (>50%) reduced the effect of flow on venous conductance, with non-aggregating RBCs showing twice the conductance of normal blood at a control flow rate.
Conclusions:
- Red blood cell aggregation plays a significant role in determining venous vascular resistance in resting muscle.
- The phenomenon of venous capacitance is heavily influenced by the degree of RBC aggregation.
- These findings underscore the importance of RBC properties beyond simple hematocrit in regulating venous return and overall circulation.
Abstract:
The effects of red blood cell aggregation on venous vascular resistance and conductance were examined in the cat lateral gastrocnemius muscle. During perfusion with blood of normal hematocrit, venous conductance fell linearly by 41% when blood flow was reduced from 5 to 1 ml x min(-1) x 100 g tissue(-1) and increased linearly by 155% when flow was increased from 5 to 20 ml x min(-1) x 100 g tissue(-1). This effect was not seen when the muscle was perfused with an acellular solution of 12% Dextran 40 in Ringer solution and was greatly reduced or absent with a nonaggregating suspension of red blood cells in Ringer solution + Dextran 40. Also, the venous vascular conductance at a control flow of 5 ml x min(-1) x 100 g tissue(-1) during perfusion with the nonaggregating red blood cell suspension was twice that with normal blood of the same hematocrit. The effect of flow on venous conductance was significantly reduced when red blood cell aggregation was increased by addition of Dextran 250 to the blood (200 mg/kg body wt) and was also reduced in animals with systemic hematocrit >50%. These findings suggest that red blood cell aggregation contributes importantly to venous vascular resistance in resting muscle.