Changes in resistance vessels during hemorrhagic shock and resuscitation in conscious hamster model

The unanesthetized hamster dorsal skinfold preparation was used to monitor diameters and blood flow rates in resistance arteries (small arteries, Ao: diameter, 156 +/- 23 mu m) and capacitance vessels (small veins, V-0: 365 /- 64 mu m), during 45 min of hemorrhagic shock at 40 mmHg mean arterial pr essure (MAP) and resuscitation. A(0) and V-0 vessels constricted significan tly to 52 and 70% of the basal values, respectively, whereas precapillary a rterioles (A(1)-A(4), 8-60 mu m) and collecting venules (V-C-V-L, 26-80 mu m) did not change or tended to dilate. Blood flow rates in the microvessels declined to <20% of the basal values. Resuscitation with shed autologous b lood (SAB) showed incomplete recovery of A(0) and V-0 diameters even 2 h af ter resuscitation (71 +/- 14% and 81 +/- 18%, respectively, of basal value) , whereas other vessels did not change significantly. The behavior of A(0) diameter coincided with the incomplete recovery of blood flow rates in all the vessels (ca. 50%) according to Poiseuille's law, and the incomplete rec overy of functional capillary density (ca. 75%). Resuscitation with 8% huma n serum albumin in saline (HSA) tended to show higher levels of A(0) constr iction and A(4) dilation and lowered blood flow rates. Resuscitation with S AB restored tissue PO2 27 +/- 10 mmHg after 2 h, which was near control lev els (28 +/- 5 mmHg), whereas resuscitation with HSA caused tissue Po, to re main significantly depressed (6 +/- 2 mmHg), and flow rates were significan tly lower than resuscitation with SAB. These results indicate that response of the A(0) vessels is the crucial determinant of blood flow in the observ ed area. The constriction of A(0) may help sustain MAP, and constriction of V-0 may enhance blood redistribution from the skin to the vital organs und er the hypotensive condition.