Diaspirin cross-linked hemoglobin improves oxygen extraction capabilities in endotoxic shock.

We studied the effects of diaspirin cross-linked hemoglobin (DCLHb), a cell-free hemoglobin derived from human erythrocytes, on blood flow distribution and tissue oxygen extraction capabilities in endotoxic shock. Eighteen pentobarbital sodium-anesthetized, mechanically ventilated dogs received 2 mg/kg of E. coli endotoxin, followed by saline resuscitation to restore cardiac filling pressures to baseline levels. The animals were randomly divided into three groups: six served as control, six received DCLHb at a dose of 500 mg/kg (group 1) and six DCLHb at a dose of 1,000 mg/kg (group 2). Cardiac tamponade was then induced by saline injection in the pericardial sac to progressively reduce cardiac index and thereby allow study of tissue oxygen extraction capabilities. DCLHb had a dose-dependent vasopressor effect but did not significantly alter cardiac index or regional blood flow. During cardiac tamponade, critical oxygen delivery was 12.8 +/- 0.7 ml. kg(-1). min(-1) in the control group, but 8.6 +/- 0.9 and 8.2 +/- 0.7 ml. kg(-1). min(-1) in groups 1 and 2, respectively (both P < 0.05 vs. control group). The critical oxygen extraction ratio was 39.1 +/- 3.1% in the control group but 58.7 +/- 12.8% and 60.2 +/- 9.0% in groups 1 and 2, respectively. We conclude that DCLHb can improve whole body oxygen extraction capabilities during endotoxic shock in dogs.     

Subcutaneous PO2 as an index of the physiological limits for hemodilution in the rat.

This study was designed to test the hypothesis that changes in subcutaneous PO2 (PscO2) during progressive hemodilution will reliably predict a "critical point" at which tissue O2 consumption (VO2) becomes dependent on O2 delivery (QO2). Twelve pentobarbital-anesthetized male Sprague-Dawley rats (315-375 g) underwent stepwise exchange of plasma for blood (1.5 ml of plasma for each 1 ml of blood lost). The initial exchange was equal to 25% of the estimated circulatory blood volume, and each subsequent exchange was equal to 10% of the estimated circulatory blood volume. After nine exchanges, the hematocrit (Hct) fell from 42 +/- 1 to 6 +/- 1%. Cardiac output and O2 extraction rose significantly. PscO2 became significantly reduced (P < 0.05) after exchange of 45% of the blood volume (Hct = 16 +/- 1%). VO2 became delivery dependent when QO2 fell below 21 ml x min(-1) x kg body wt(-1) (mean Hct = 13 +/- 1%). Eight control rats undergoing 1:1 blood-blood exchange showed no change in PscO2, pH, HCO3(-), or hemodynamics. Measurement of PscO2 may be a useful guide to monitor the adequacy of QO2 during hemodilution.     

Effects of erythrocyte flexibility on microvascular perfusion and oxygenation during acute anemia

Responses to exchange transfusion using red blood cells (RBCs) with normal and reduced flexibility were studied in the hamster window chamber model during acute moderate isovolemic hemodilution to determine the role of RBC membrane stiffness in microvascular perfusion and tissue oxygenation. Erythrocyte stiffness was increased by 30-min incubation in 0.02% glutaraldehyde solution, and unreacted glutaraldehyde was completely removed. Filtration pressure through 5-microm pore size filters was used to quantify stiffness of the RBCs. Anemic conditions were induced by two isovolemic hemodilution steps using 6% 70-kDa dextran to a hematocrit (Hct) of 18% (moderate hemodilution). The protocol continued with an exchange transfusion to reduce native RBCs to 75% of baseline (11% Hct) with either fresh RBCs (RBC group) or reduced-flexibility RBCs (GRBC group) suspended in 5% albumin at 18% Hct; a plasma expander (6% 70-kDa dextran; Dex70 group) was used as control. Systemic parameters, microvascular perfusion, capillary perfusion [functional capillary density (FCD)], and oxygen levels across the microvascular network were measured by noninvasive methods. RBC deformability for GRBCs was significantly decreased compared with RBCs and moderate hemodilution conditions. The GRBC group had a greater mean arterial blood pressure (MAP) than the RBC and Dex70 groups. FCD was substantially higher for RBC (0.81 +/- 0.07 of baseline) vs. GRBC (0.32 +/- 0.10 of baseline) and Dex70 (0.38 +/- 0.10 of baseline) groups. Microvascular tissue Po(2) was significantly lower for Dex70 and GRBC vs. RBC groups and the moderate hemodilution condition. Results were attributed to decreased oxygen uploading in the lungs and obstruction of tissue capillaries by rigidified RBCs, indicating that the effects impairing RBC flexibility are magnified at the microvascular level, where perfusion and oxygenation may define transfusion outcome.     

Oxygen transport by low and normal oxygen affinity hemoglobin vesicles in extreme hemodilution

The oxygen transport capacity of phospholipid vesicles encapsulating purified Hb (HbV) produced with a Po(2) at which Hb is 50% saturated (P 50 ) of 8 (HbV(8)) and 29 mmHg (HbV(29)) was investigated in the hamster chamber window model by using microvascular measurements to determine oxygen delivery during extreme hemodilution. Two isovolemic hemodilution steps were performed with 5% recombinant albumin (rHSA) until Hct was 35% of baseline. Isovolemic exchange was continued using HbV suspended in rHSA solution to a total [Hb] of 5.7 g/dl in blood. P(50) was modified by coencapsulating pyridoxal 5'-phosphate. Final Hct was 11% for the HbV groups, with a plasma [Hb] of 2.1 +/- 0.1 g/dl after exchange with HbV(8) or HbV(29). A reference group was hemodiluted to Hct 11% with only rHSA. All groups showed stable blood pressure and heart rate. Arterial oxygen tensions were significantly higher than baseline for the HbV groups and the rHSA group and significantly lower for the HbV groups compared with the rHSA group. Blood pressure was significantly higher for the HbV(8) group compared with the HbV(29) group. Arteriolar and venular blood flows were significantly higher than baseline for the HbV groups. Microvascular oxygen delivery and extraction were similar for the HbV groups but lower for the rHSA group (P < 0.05). Venular and tissue Po(2) were statistically higher for the HbV(8) vs. the HbV(29) and rHSA groups (P < 0.05). Improved tissue Po(2) is obtained when red blood cells deliver oxygen in combination with a high- rather than low-affinity oxygen carrier.     

Oxygen transport during hemodilution with a perfluorocarbon-based oxygen carrier: effect of altitude and hyperoxia.

Oxygen delivery and consumption after hemodilution with a perfluorocarbon-based oxygen carrier (PFCOC) was evaluated at sea level and at 2,600 m above sea level. Fifteen anesthetized rats were subjected to a two-exchange normovolemic hemodilution of 40% of the circulating blood volume each. First exchange was performed with a colloid solution. Second exchange was with 80% PFCOC and 20% colloid. Animals were then ventilated with 100% oxygen. Experiments were performed at barometric pressure of 1.0 atm (sea-level group, n=9) or 0.74 atm (2,600-m group, n=6). Blood gases, hematocrit, fluorocrit, and hemoglobin content were measured at baseline and 15 min after each exchange. After hemodilution, total arterial content was not modified by the PFCOC in either group. In contrast, arteriovenous oxygen difference increased significantly in both groups, as did the oxygen extraction ratio. In the second exchange, although total arterial content was similar between the two groups, the perfluorocarbon and plasma phases contributed significantly more at sea level. Arteriovenous oxygen difference was significantly less at sea level with a higher contribution from the perfluorocarbon and plasma phases. In conclusion, hemodilution with a PFCOC induced changes in oxygen delivery and consumption that differ with altitude. The 2,600-m group exhibited a higher oxygen extraction ratio and arteriovenous oxygen difference, with reduced oxygen delivery and unloading from both the fluorocarbon and plasma phase. Therefore, the efficacy of PFCOCs at 2,600 m above sea level is reduced, and altitude must be taken into account when PFCOCs are used.     

Oxygen delivery and consumption in the microcirculation after extreme hemodilution with perfluorocarbons

The oxygen transport capacity of fluorocarbons was investigated in the hamster chamber window model microcirculation to determine the rate at which oxygen is delivered to the tissue in conditions of extreme hemodilution [hematocrit (Hct) 11%]. Hydroxyethlyl starch (HES 200; 200 kDa molecular mass) was used as a plasma expander for two isovolemic hemodilutions performed with 10% HES 200 until a Hct of 65%. A third step reduced the Hct to 75% of baseline and was performed with either HES 200 or a 60% perfluorocarbon (PFC) emulsion. Comparisons of HES 200-only-hemodiluted animals versus 4.2 g/kg PFC emulsion-hemodiluted animals were made at 21% and 100% normobaric oxygen ventilation. It was found that systemic and microvascular oxygen delivery was 25% and 400% higher in the PFC animals compared with HES 200 animals, respectively, showing that PFCs deliver oxygen to the tissue when combined with hyperoxic ventilation in the present experiments, with no evidence of vasoconstriction or impaired microvascular function. Oxygen ventilation (100%) led to a positive base excess for the PFC group (5.5 +/- 2.5 mmol/l) versus a negative balance (-0.8 +/- 1.4 mmol/l) for the HES 200 group, suggesting that microvascular findings corresponded to systemic events.     

Stroma-free hemoglobin: its presence in plasma does not improve oxygen supply to the resting hindlimb vascular bed of hemodiluted dogs.

In hemodilution, red cell spacing in the microcirculation is increased, flow distribution may become more heterogeneous, and, as a result, oxygen supply to tissues may suffer. We tested the hypothesis that oxygen extraction from diluted blood may be enhanced by the presence of hemoglobin in the plasma phase in relatively low concentrations. In anesthetized dogs, the hindlimb vascular bed was isolated and perfused with the animal's own blood by a roller pump. One group of dogs (n = 6) was hemodiluted (hematocrit = 15.0 +/- 1.0%) with a 6% solution of dextran. A second group of dogs (n = 6) was similarly hemodiluted (hematocrit = 16.0 +/- 0.4%) with dextran containing stroma-free hemoglobin solution whereby plasma-phase hemoglobin concentration was raised to 1.1 +/- 0.1 g.dL-1. Systemic hemodynamic observations were made repeatedly over the subsequent 2.5 h, while blood flow to the hindlimb was progressively reduced in stepwise decrements. The hemoglobin-hemodiluted group showed increased systemic arterial blood pressure and total peripheral resistance when compared with the control (dextran diluted) group. The isolated hindlimb also showed evidence of increased vascular resistance in the hemoglobin-treated group. In each individual animal, critical oxygen delivery and extraction were determined by finding the intercept of the supply-independent and supply-dependent portions of the oxygen uptake/oxygen delivery relationship. Neither the critical oxygen delivery rates (5.75 +/- 0.83 vs. 6.41 +/- 0.53 mL.kg-1.min-1) nor critical oxygen extraction ratios (0.75 +/- 0.03 vs. 0.76 +/- 0.04) were found to be significantly different in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Improved oxygenation in ischemic hamster flap tissue is correlated with increasing hemodilution with Hb vesicles and their O2 affinity

The aim of this study was to test the influence of oxygen affinity of Hb vesicles (HbVs) and level of blood exchange on the oxygenation in collateralized, ischemic, and hypoxic hamster flap tissue during normovolemic hemodilution. Microhemodynamics were investigated with intravital microscopy. Tissue Po2 was measured with Clark-type microprobes. HbVs with a P50 of 15 mmHg (HbV15) and 30 mmHg (HbV30) were suspended in 6% Dextran 70 (Dx70). The Hb concentration of the solutions was 7.5 g/dl. A stepwise replacement of 15%, 30%, and 50% of total blood volume was performed, which resulted in a gradual decrease in total Hb concentration. In the ischemic tissue, hemodilution led to an increase in microvascular blood flow to maximally 141-166% of baseline in all groups (median; P < 0.01 vs. baseline, not significant between groups). Oxygen tension was transiently raised to 121 +/- 17% after the 30% blood exchange with Dx70 (P < 0.05), whereas it was increased after each step of hemodilution with HbV15-Dx70 and HbV30-Dx70, reaching 217 +/- 67% (P < 0.01) and 164 +/- 33% (P < 0.01 vs. baseline and other groups), respectively, after the 50% blood exchange. We conclude that despite a decrease in total Hb concentration, the oxygenation in the ischemic, hypoxic tissue could be improved with increasing blood exchange with HbV solutions. Furthermore, better oxygenation was obtained with the left-shifted HbVs.     

Effect of acute normovolemic hemodilution on distribution of blood flow and tissue oxygenation in dog skeletal muscle.

Acute normovolemic hemodilution (ANH) is efficient in reducing allogenic blood transfusion needs during elective surgery. Tissue oxygenation is maintained by increased cardiac output and oxygen extraction and, presumably, a more homogeneous tissue perfusion. The aim of this study was to investigate blood flow distribution and oxygenation of skeletal muscle. ANH from hematocrit of 36 +/- 3 to 20 +/- 1% was performed in 22 splenectomized, anesthetized beagles (17 analyzed) ventilated with room air. Normovolemia was confirmed by measurement of blood volume. Distribution of perfusion within skeletal muscle was determined by using radioactive microspheres. Tissue oxygen partial pressure was assessed with a polarographic platinum surface electrode. Cardiac index (3.69 +/- 0.79 vs. 4.79 +/- 0.73 l. min-1. m-2) and muscle perfusion (4.07 +/- 0.44 vs. 5.18 +/- 0.36 ml. 100 g-1. min-1) were increased at hematocrit of 20%. Oxygen delivery to skeletal muscle was reduced to 74% of baseline values (0.64 +/- 0.06 vs. 0.48 +/- 0.03 ml O2. 100 g-1. min-1). Nevertheless, tissue PO2 was preserved (27.4 +/- 1.3 vs. 29.9 +/- 1. 4 Torr). Heterogeneity of muscle perfusion (relative dispersion) was reduced after ANH (20.0 +/- 2.2 vs. 13.9 +/- 1.5%). We conclude that a more homogeneous distribution of perfusion is one mechanism for the preservation of tissue oxygenation after moderate ANH, despite reduced oxygen delivery.     

Vasopressin vs norepinephrine in endotoxic shock: systemic, renal, and splanchnic hemodynamic and oxygen transport effects.

The effects of intravenous norepinephrine (NE, group 1) and vasopressin (AVP, group 2) infusions on systemic, splanchnic, and renal circulations were studied in anesthetized dogs under basal conditions and during endotoxic shock. Under basal conditions, AVP infusion induced a 12 +/- 7% drop in left ventricular stroke work, a 45 +/- 5% fall in portal venous blood flow, and a 31 +/- 13% decrease in intestinal mucosal blood flow (P < 0.05). AVP also decreased splanchnic oxygen delivery (Do2) and increased splanchnic and renal oxygen extraction significantly during basal conditions. Except for more pronounced brady-cardia among animals in group 2, the systemic and splanchnic changes were comparable between study groups during endotoxic shock. AVP infusion restored renal blood flow and Do2 in endotoxic shock compared with animals resuscitated with NE, which had persistently low renal blood flow and Do2. Our data demonstrate that, in contrast to NE, administration of AVP effectively restores renal blood flow and Do2 with comparable systemic and splanchnic hemodynamic and metabolic effects in endotoxin-induced circulatory shock.     

Erythrocyte-associated transients in capillary PO2: an isovolemic hemodilution study in the rat spinotrapezius muscle

Mathematical simulations of oxygen delivery to tissue from capillaries that take into account the particulate nature of blood flow predict the existence of oxygen tension (Po(2)) gradients between erythrocytes (RBCs). As RBCs and plasma alternately pass an observation point, these gradients are manifested as rapid fluctuations in Po(2), also known as erythrocyte-associated transients (EATs). The impact of hemodilution on EATs and oxygen delivery at the capillary level of the microcirculation has yet to be elucidated. Therefore, in the present study, phosphorescence quenching microscopy was used to measure EATs and Po(2) in capillaries of the rat spinotrapezius muscle at the following systemic hematocrits (Hct(sys)): normal (39%) and after moderate (HES1; 27%) or severe (HES2; 15%) isovolemic hemodilution using a 6% hetastarch solution. A 532-nm laser, generating 10-micros pulses concentrated onto a 0.9-microm spot, was used to obtain plasma Po(2) values 100 times/s at points along surface capillaries of the muscle. Mean capillary Po(2) (Pc(O(2)); means +/- SE) significantly decreased between conditions (normal: 56 +/- 2 mmHg, n = 45; HES1: 47 +/- 2 mmHg, n = 62; HES2: 27 +/- 2 mmHg, n = 52, where n = capillary number). In addition, the magnitude of Po(2) transients (DeltaPo(2)) significantly decreased with hemodilution (normal: 19 +/- 1 mmHg, n = 45; HES1: 11 +/- 1 mmHg, n = 62; HES2: 6 +/- 1 mmHg, n = 52). Results suggest that the decrease in Pc(O(2)) and DeltaPo(2) with hemodilution is primarily dependent on Hct(sys) and subsequent microvascular compensations.     

Oxygen delivery at high blood viscosity and decreased arterial oxygen content to brains of conscious rats

We addressed the question to which extent cerebral blood flow (CBF) is maintained when, in addition to a high blood viscosity (Bvis) arterial oxygen content (CaO2) is gradually decreased. CaO2) was decreased by hemodilution to hematocrits (Hct) of 30, 22, 19, and 15% in two groups. One group received blood replacement (BR) only and served as the control. The second group received an additional high viscosity solution of polyvinylpyrrolidone (BR/PVP). Bvis was reduced in the BR group and was doubled in the BR/PVP. Despite different Bvis, CBF did not differ between BR and BR/PVP rats at Hct values of 30 and 22%, indicating a complete vascular compensation of the increased Bvis at decreased CaO2. At an Hct of 19%, local cerebral blood flow (LCBF) in some brain structures was lower in BR/PVP rats than in BR rats. At the lowest Hct of 15%, LCBF of 15 brain structures and mean CBF were reduced in BR/PVP. The resulting decrease in cerebral oxygen delivery in the BR/PVP group indicates a global loss of vascular compensation. We concluded that vasodilating mechanisms compensated for Bvis increases thereby maintaining constant cerebral oxygen delivery. Compensatory mechanisms were exhausted at a Hct of 19% and lower as indicated by the reduction of CBF and cerebral oxygen delivery.     

Severe hemodilutional anemia increases cerebral tissue injury following acute neurotrauma.

Anemia may worsen neurological outcomes following traumatic brain injury (TBI) by undefined mechanisms. We hypothesized that hemodilutional anemia accentuates hypoxic cerebral injury following TBI. Anesthetized rats underwent unilateral TBI or sham injury (n > or = 7). Target hemoglobin concentrations between 50 and 70 g/l were achieved by exchanging 40-50% of the blood volume (1:1) with pentastarch. The effect of TBI, anemia, and TBI-anemia was assessed by measuring brain tissue oxygen tension (Pbr(O(2))), regional cerebral blood flow (rCBF), jugular venous oxygen saturation (Sjv(O(2))), cerebral contusion area, and nuclear staining for programmed cell death. Baseline postinjury Pbr(O(2)) values in the TBI and TBI-anemia groups (9.3 +/- 1.3 and 11.3 +/- 4.1 Torr, respectively) were lower than the uninjured controls (18.2 +/- 5.2 Torr, P < 0.05 for both). Hemodilution caused a further reduction in Pbr(O(2)) in the TBI-anemia group relative to the TBI group without anemia (7.8 +/- 2.7 vs. 14.8 +/- 3.9 Torr, P < 0.05). The rCBF remained stable after TBI and increased comparably after hemodilution in both anemia and TBI-anemia groups. The Sjv(O(2)) was elevated after TBI (87.4 +/- 8.9%, P < 0.05) and increased further following hemodilution (95.0 +/- 1.6%, P < 0.05). Cerebral contusion area and nuclear counts for programmed cell death were increased following TBI-anemia (4.1 +/- 3.0 mm(2) and 686 +/- 192, respectively) relative to TBI alone (1.3 +/- 0.3 mm(2) and 404 +/- 133, respectively, P < 0.05 for both). Hemodilutional anemia reduced cerebral Pbr(O(2)) and oxygen extraction and increased cell death following TBI. These results support our hypothesis that acute anemia accentuated hypoxic cerebral injury after neurotrauma.     

Redistribution of intestinal microcirculatory oxygenation during acute hemodilution in pigs.

Acute normovolemic hemodilution (ANH) compromizes intestinal microcirculatory oxygenation; however, the underlying mechanisms are incompletely understood. We hypothesized that contributors herein include redistribution of oxygen away from the intestines and shunting of oxygen within the intestines. The latter may be due to the impaired ability of erythrocytes to off-load oxygen within the microcirculation, thus yielding low tissue/plasma Po(2) but elevated microcirculatory hemoglobin oxygen (HbO(2)) saturations. Alternatively, oxygen shunting may also be due to reduced erythrocyte deformability, hindering the ability of erythrocytes to enter capillaries. Anesthetized pigs underwent ANH (20, 40, 60, and 90 ml/kg hydroxyethyl starch; ANH group: n = 10; controls: n = 5). We measured systemic and mesenteric perfusion. Microvascular intestinal oxygenation was measured independently by remission spectrophotometry [microcirculatory HbO(2) saturation (muHbO(2))] and palladium-porphyrin phosphorescence quenching [microcirculatory oxygen pressure in plasma/tissue (muPo(2))]. Microcirculatory oxygen shunting was assessed as the disparity between mucosal and mesenteric venous HbO(2) saturation (HbO(2)-gap). Erythrocyte deformability was measured as shear stress-induced cell elongation (LORCA difractometer). ANH reduced hemoglobin concentration from 8.1 to 2.2 g/dl. Relative mesenteric perfusion decreased (decreased mesenteric/systemic perfusion fraction). A paralleled reduction occurred in mucosal muHbO(2) (68 +/- 2 to 41 +/- 3%) and muPo(2) (28 +/- 1 to 17 +/- 1 Torr). Thus the proposed constellation indicative for oxygen off-load deficits (sustained muHbO(2) at decreased muPo(2)) did not develop. A twofold increase in the HbO(2)-gap indicated increasing intestinal microcirculatory oxygen shunting. Significant impairment in erythrocyte deformability developed during ANH. We conclude that reduced intestinal oxygenation during ANH is, in addition to redistribution of oxygen delivery away from the intestines, associated with oxygen shunting within the intestines. This shunting appears to be not primarily caused by oxygen off-load deficit but rather by oxygen/erythrocytes bypassing capillaries, wherein a potential contributor is impaired erythrocyte deformability.     

Effects of phentolamine on hepatic PO2 in endotoxemia

The effect of phentolamine, an alpha-adrenergic blocker, on hepatic oxygen supply, plasma glucose, and lactate, and survival in fasted male rats administered Echerichia coli endotoxin (25 mg/kg, ip) has been studied. Survival at 24 h was 8% in untreated endotoxic rats, 83% in rats receiving phentolamine (5 mg/kg, ip) and endotoxin, and 100% in phentolamine controls. Measurements during the initial 8 h postendotoxin recorded transiently lower systemic arterial pressure in the phentolamine-endotoxic rats. Arterial PO2 and increases of pH and heart rate were similar in both endotoxic groups. Lactacidemia, present by 4 h in untreated endotoxic rats, did not develop in the phentolamine group and plasma glucose was significantly higher at 8 h (98 +/- 2.5 vs. 77 +/- 5.6 mg%, mean +/- SE). Mean hepatic PO2 at 6 h in phentolamine-endotoxic rats was 9.6 mmHg with 28% of the values below 5 mmHg. By contrast, the mean in untreated endotoxic rats was 1.9 mmHg with 88% of values below 5 mmHg. Phentolamine controls were stable over 8 h; mean hepatic PO2 was 17.7 mmHg. The differences in plasma glucose and lactate suggest protection of hepatic metabolism in phentolamine-treated endotoxic rats by prevention of excessive hepatic hypoxia.     

Development of the blood and muscle oxygen stores in gray seals (Halichoerus grypus): implications for juvenile diving capacity and the necessity of a terrestrial postweaning fast

To successfully transition from nursing to foraging, phocid seal pups must develop adequate diving physiology within the limited time between birth and their first independent foraging trip to sea. We studied the postpartum development of oxygen stores in gray seals (Halichoerus grypus, n=40) to better understand the ontogeny of diving capacity in phocids. Hemoglobin (Hb), hematocrit (Hct), blood volume (BV), and myoglobin (Mb) levels in newborn (3 d postpartum [DPP]) and newly weaned (17+/-0.4 DPP) pups were among the lowest measured across age classes. During the pups' terrestrial postweaning fast (PWF), Hb, Hct, mass-specific BV, and Mb increased by 28%, 21%, 13%, and 29%, respectively, resulting in a 35% increase in total body mass-specific oxygen stores and a 23% increase in calculated aerobic dive limit (CADL). Although Hb and Hct levels at the end of the PWF were nearly identical to those of yearlings, total body mass-specific oxygen stores and CADL of weaned pups departing for sea were only 66%-67% and 32%-62%, respectively, of those for yearlings and adult females. The PWF represents an integral component of the physiological development of diving capacity in phocids; however, newly independent phocids still appear to have limited diving capabilities at the onset of foraging.     

Microvascular PO2 during extreme hemodilution with hemoglobin site specifically PEGylated at Cys-93(beta) in hamster window chamber

The oxygen transport capacity of nonhypertensive polyethylene glycol (PEG)-conjugated hemoglobin solutions were investigated in the hamster chamber window model. Microvascular measurements were made to determine oxygen delivery in conditions of extreme hemodilution [hematocrit (Hct) 11%]. Two isovolemic hemodilution steps were performed with a 6% Dextran 70 (70-kDa molecular mass) plasma expander until Hct was 35% of control. Isovolemic blood volume exchange was continued using two surface-modified PEGylated hemoglobins (P5K2, P(50) = 8.6, and P10K2, P(50) = 8.3; P(50) is the hemoglobin Po(2) corresponding to its 50% oxygen saturation) until Hct was 11%. P5K2 and P10K2 are PEG-conjugated hemoglobins that maintain most of the hemoglobin allosteric properties and have a cooperativity index of n = 2.2. The effects of these molecular solutions were compared with those obtained in a previous study using MP4, a PEG-modified hemoglobin whose P(50) was 5.4 and cooperativity was 1.2 (Tsai et al., Am J Physiol Heart Circ Physiol 285: H1411-H1419, 2003). Tissue oxygen levels were higher after P5K2 (7.0 +/- 2.5 mmHg) and P10K2 (6.3 +/- 2.3 mmHg) versus MP4 (1.7 +/- 0.5 mmHg) or the nonoxygen carrier Dextran 70 (1.3 +/- 1.2 mmHg). Microvascular oxygen delivery was higher after P5K2 and P10K2 (2.22 and 2.34 ml O(2)/dl blood) compared with MP4 (1.41 ml O(2)/dl blood) or Dextran 70 (0.90 ml O(2)/dl blood); however, all these values were lower than control (7.42 ml O(2)/dl blood). The total hemoglobin in blood was similar in all cases; therefore, the improvement in tissue Po(2) and oxygen delivery appears to be due to the increased cooperativity of the new molecules.     

Hemodynamic effects after partial exchange transfusion with pyridoxylated polyhemoglobin in chimpanzees.

Partial exchange transfusion with 8.5% pyridoxylated polyhemoglobin solution [PolyHb-PPa] was performed in five anesthetized spontaneously-breathing male chimpanzees weighing 22-30 kg. Mean exchange volume was 42.5 +/- 10.7 ml/kg BW (26.8-54.6 ml/kg), mean exchange rate 56.7 +/- 7.1% (48.2-67.4%). All animals survived long-term. The chimpanzee's hemodynamics remained stable for the 5 h observation period. Right and left ventricular filling pressures remained constant, mean arterial pressure and mean pulmonary arterial pressure increased by up to 40% after the exchange. Cardiac output remained unaffected by the partial exchange and stroke volume did not change substantially although oxygen capacity and oxygen transport capacity decreased by about a third. The failure of cardiac output to rise after partial exchange transfusion with PolyHb-PPa contrasts with results after isovolemic hemodilution using non-oxygen-carrying blood substitutes and is not adequately explained by the oxygen capacity of 8.5% PolyHb-PPa (9.3 ml O2/dl).     

Blood osmolality during in vivo changes of CO2 pressure

In 16 experiments male subjects, age 22.4 +/- 0.5 (SE) yr, inspired CO2 for 15 min (8% end-tidal CO2) or hyperventilated for 30 min (2.5% end-tidal CO2). Osmolality (Osm) and acid-base status of arterialized venous blood were determined at short intervals until 30 min after hypo- and hypercapnia, respectively. During hypocapnia [CO2 partial pressure (PCO2) -2.31 +/- 0.32 kPa (-17.4 Torr), pH + 0.19 units], Osm decreased by 3.9 +/- 0.3 mosmol/kg H2O; during hypercapnia [PCO2 + 2.10 +/- 0.28 kPa (+15.8 Torr), pH -0.12 units], Osm increased by 5.8 +/- 0.7 mosmol/kg H2O. Presentation of the data in Osm-PCO2 or Osm-pH diagrams yields hysteresis loops probably caused by exchange between blood and tissues. The dependence of Osm on PCO2 must result mainly from CO2 buffering and therefore from the formation of bicarbonate. In spite of the different buffer capacities in various body compartments, water exchange allows rapid restoration of osmotic equilibrium throughout the organism. Thus delta Osm/delta pH during a PCO2 jump largely depends on the mean buffer capacity of the whole body. The high estimated buffer value during hypercapnia (38 mmol/kg H2O) compared with hypocapnia (19 mmol/kg H2O) seems to result from very strong muscle buffering during moderate acidosis.     

Effects of anesthetic agents on systemic critical O2 delivery

The present study tested the hypothesis that anesthetic agents can alter tissue O2 extraction capabilities in a dog model of progressive hemorrhage. After administration of pentobarbital sodium (25 mg/kg iv) and endotracheal intubation, the dogs were paralyzed with pancuronium bromide, ventilated with room air, and splenectomized. A total of 60 dogs were randomized in 10 groups of 6 dogs each. The first group served as control (C). A second group (P) received a continuous infusion of pentobarbital (4 mg.kg-2.h-2), which was started immediately after the bolus dose. Three groups received enflurane (E), halothane (HL), or isoflurane (I) at the end-tidal concentration of 0.7 minimum alveolar concentration (MAC). The sixth group received halothane at the end-tidal concentration of 1 MAC (HH). Two groups received intravenous alfentanil at relatively low dose (AL) or high dose (AH). The last two groups received intravenous ketamine at either relatively low dose (KL) or high dose (KH). In each group, O2 delivery (Do2) was progressively reduced by hemorrhage. At each step, systemic Do2 and O2 consumption (VO2) were measured separately and the critical point was determined from a plot of Vo2 vs. Do2. The critical O2 extraction ratio (OER) in the control group was 65.0 +/- 7.8%. OER was lower in all anesthetized groups (P, 44.3 +/- 11.8%; E, 47.0 +/- 7.7%; HL, 45.7 +/- 11.2%; I, 44.3 +/- 7.1%; HH, 33.7 +/- 6.0%; AL, 56.5 +/- 9.6%; AH, 43.5 +/- 5.9%; KH, 57.7 +/- 7.1%), except in the KL group (78.3 +/- 10.0%). The effects of halothane and alfentanil on critical OER were dose dependent (P less than 0.05), whereas critical OER was significantly lower in the KH than in the KL group. Moreover, the effects of anesthetic agents on critical Do2 appeared related to their effects on systemic vascular resistance. Anesthetic agents therefore alter O2 extraction by their peripheral vascular effects. However, ketamine, with its unique sympathetic stimulant properties, had a lesser effect on OER than the other anesthetic agents. It could therefore be the anesthetic agent of choice in clinical situations when O2 availability is reduced.