Lumenal narrowing and endothelial cell swelling in skeletal muscle capillaries during hemorrhagic shock.

Capillary lumenal narrowing in hemorrhagic shock was investigated using intravital microscopy to visualize capillaries directly in the rabbit tenuissimus muscle after a rapid single-withdrawal of 40% of the blood volume. The ensuing 1 hr shock period in the animals was marked by a protracted systemic hypotension and metabolic acidosis. Changes in capillary lumen diameter were inferred by changes in the width and length of red blood cells (RBCs) as they traversed the capillary. By the end of the shock period, RBC flux from nine experiments decreased over 60% with a -24.3 +/- 9.3% and +22.8 +/- 6.4% change in RBC width and length, respectively. The narrowed capillary lumen resulting from endothelial cell swelling elevates hydraulic resistance which may hinder resuscitation efforts to restore shock-impaired flow.