The American journal of physiology
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Theoretical simulations of oxygen transport in skeletal muscle are used to study the role of arterioles in oxygen delivery. A three-dimensional configuration of capillaries and arterioles in a cuboidal tissue region is simulated, based on observations of hamster cheek pouch retractor muscle. Equations describing convective and diffusive oxygen transport are solved using a Green's function method. ⋯ Thus diffusive exchange between arterioles and capillaries plays an important part in distributing oxygen throughout the tissue. At higher flow and consumption rates, the relative amounts of oxygen diffusing out of arterioles and into capillaries decrease. The results are consistent with the hypothesis that oxygen content of arteriolar blood participates in metabolic regulation of blood flow.
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Mean circulatory filling pressure (MCFP) has been measured after vagally induced cardiac arrest in 11 nonpregnant and 10 near-term pregnant rabbits, anesthetized with pentobarbital sodium. MCFP was 6.1 +/- 0.4 (SD) mmHg in the nonpregnant and 7.2 +/- 0.4 mmHg in the pregnant animals. The difference of 1.1 mmHg was significant (P < 0.001). ⋯ Unstressed vascular volume and vascular compliance were derived from measurements of MCFP after increasing blood volume by 8 and 16% or reducing it by 8%. The unstressed vascular volumes, 33.9 +/- 3.9 (SD) ml/kg in the nonpregnant and 35.1 +/- 3.2 ml/kg in the pregnant group, were not significantly different, but compliance in the pregnant group (4.0 +/- 0.6 ml.kg-1.mmHg-1) was significantly greater than in the nonpregnant rabbits (3.4 +/- 0.6 ml.kg-1.mmHg-1) (P < 0.05). We conclude that there are changes in vascular capacitance in rabbit pregnancy, probably not related to alterations in vasomotor activity, but these are insufficient to fully compensate for the increase in blood volume, thus leading to the rise in MCFP.
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The effect of experimental meningitis on regional cerebral blood flow (rCBF), cerebral metabolic rate for oxygen (CMRO2), and cerebrovascular responsiveness to CO2 was determined in pentobarbital-anesthetized rabbits. The animals were inoculated intracisternally with saline (control) or log-phase Haemophilus influenzae type b (Hib). Eighteen hours later rCBF was determined with radiolabeled microspheres at normocapnia, hypocapnia, and hypercapnia. ⋯ CMRO2 in meningitis was not significantly different from control (C: 3.53 +/- 0.29, M: 3.51 +/- 0.22 ml O2.100 g-1.min-1). These findings indicate that cerebrovascular responsiveness to CO2 is preserved in experimental Hib meningitis. Furthermore, enhanced CBF together with unchanged CMRO2 indicates that "luxury" cerebral perfusion is present in this model of bacterial meningitis.
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The influence of small-volume resuscitation (hypertonic saline-10% hydroxyethyl starch, HS/HES) on liver microcirculation (intravital fluorescence microscopy) was studied in a nonheparinized hemorrhagic shock model [mean arterial pressure (MAP) 40 mmHg for 1 h] in rats. Resuscitation was performed with Ringer lactate (RL, 4-fold shed volume/20 min; n = 7), 10% hydroxyethyl starch 200/0.6 (HES, shed volume/5 min; n = 6), or 7.2% NaCl-10% hydroxyethyl starch 200/0.6 (HS/HES, 10% shed volume/2 min; n = 7). One hour after resuscitation, MAP increased in all groups, but it did not return to preshock values (P < 0.05). ⋯ Shock-induced stasis/adherence of leukocytes was further increased (P < 0.05) after resuscitation with RL (S, 38 +/- 6%; V, 55 +/- 20%) and HES (S, 31 +/- 8%; V, 23 +/- 14%). In contrast, resuscitation with HS/HES prevented increased leukocyte stasis in sinusoids (-4 +/- 4%) as well as adherence to endothelial lining of postsinusoidal venules (-5 +/- 10%). We conclude that replacement of only 10% of actual blood loss by means of small-volume resuscitation (HS/HES) can restore hepatic microvascular perfusion and prevent reperfusion-induced leukocyte stasis/adherence.
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Comparative Study
Sodium appetite, thirst, and body fluid regulation in humans during rehydration without sodium replacement.
After a 7-h H2O and Na+ depletion period (DP), produced by intermittent light exercise (8 bouts) at 35 degrees C, we examined thirst and taste palatability responses to 10 different NaCl solutions during 23 h of rehydration (RH) at 25 degrees C. During DP, net H2O and Na+ loss were 27.2 +/- 2.9 ml/kg and 3.29 +/- 0.45 meq/kg, respectively. Plasma osmolality (POsm) and plasma Na+ concentration ([Na+]p) increased significantly during DP by 3.4 +/- 1.2 mosmol/kgH2O and 3.0 +/- 1.0 meq/kgH2O, respectively. ⋯ Thus both Na+ preference and thirst in humans are influenced by body fluid and electrolyte status. The increased Na+ palatability (Na+ appetite) was preceded by osmotically induced thirst, and accompanied by nonosmotically driven thirst [extracellular fluid (ECF) thirst] and increased PAldo. The "Na+ appetite" and "ECF thirst" along with increased renal Na+ retention could contribute to ECF volume regulation after thermally induced H2O and Na+ depletion.